Tuberculosis Pathogenesis and Lesions
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Tuberculosis Pathogenesis and Lesions

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Questions and Answers

What characteristic best describes miliary tuberculosis lesions?

  • Abscesses that can be felt through the skin
  • Microscopic lesions resembling millet seeds (correct)
  • Large masses of necrotic tissue
  • Single large lesions with well-defined borders

    • What is the initial event in the pathogenesis of tuberculosis?

  • Entrance of MTB to macrophages (correct)
  • Replication of the microorganism inside macrophages
  • Activation of Th1 cells
  • Formation of granuloma

    • Which cytokines stimulate the Th1 response in tuberculosis pathogenesis?

  • IL-10 and IL-6
  • IFN-gamma and IL-1
  • IL-12 and IL-18 (correct)
  • TNF-alpha and IL-4

    • Which organs are most commonly involved in miliary tuberculosis?

    <p>Liver, bone marrow, spleen, and adrenals</p> Signup and view all the answers

    What is the primary histological feature of granuloma in tuberculosis?

    <p>Central caseous necrosis surrounded by activated macrophages</p> Signup and view all the answers

    Which of the following symptoms is NOT associated with the clinical features of tuberculosis?

    <p>Hair loss</p> Signup and view all the answers

    What is the most common extrapulmonary form of tuberculosis?

    <p>Spinal tuberculosis</p> Signup and view all the answers

    What type of tuberculosis occurs when there is a reactivation of dormant bacilli?

    <p>Secondary tuberculosis</p> Signup and view all the answers

    What is the typical location of lesions in primary tuberculosis?

    <p>Mid zone of the lung</p> Signup and view all the answers

    What is a common method used for diagnosing tuberculosis?

    <p>Ziehl-Neelsen staining for detecting the organism</p> Signup and view all the answers

    Which feature is NOT characteristic of secondary tuberculosis?

    <p>Primarily occurs in non-immunized individuals</p> Signup and view all the answers

    What characterizes systemic miliary tuberculosis?

    <p>Bacteria dissemination through the systemic arterial system</p> Signup and view all the answers

    Which type of cells become multinucleated giant cells in the granuloma?

    <p>Epithelioid macrophages</p> Signup and view all the answers

    What local factor is known to promote infection?

    <p>Ischemia</p> Signup and view all the answers

    Which of the following is NOT a mode of transmission for infections?

    <p>Airborne particles</p> Signup and view all the answers

    What is typically characteristic of a pyogenic bacterial infection?

    <p>Formation of pus</p> Signup and view all the answers

    What defines an infection?

    <p>The invasion of living tissue by micro-organisms or their products.</p> Signup and view all the answers

    Which type of bacteria-mediated tissue damage involves the release of lytic enzymes?

    <p>Toxin release</p> Signup and view all the answers

    Which of the following is a type of infectious microorganism that can be harmless until it causes disease?

    <p>Commensals</p> Signup and view all the answers

    Which bacterial infection type specifically affects serous cavities?

    <p>Serous</p> Signup and view all the answers

    Which host factor is considered a nonspecific defense mechanism?

    <p>Glandular secretion</p> Signup and view all the answers

    Which of the following correctly identifies a systemic factor that influences the risk of infection?

    <p>Age</p> Signup and view all the answers

    What is a common route for vertical transmission of infections?

    <p>Mother to fetus</p> Signup and view all the answers

    What is the primary function of virulence in microorganisms?

    <p>To cause disease.</p> Signup and view all the answers

    Which mechanism does NOT contribute to the spread of a microorganism within the body?

    <p>Spread through muscle tissue</p> Signup and view all the answers

    Which factor is NOT associated with the success of an infection within a host?

    <p>Host's age</p> Signup and view all the answers

    Which type of immunity is part of the specific defense mechanisms?

    <p>Humeral immunity</p> Signup and view all the answers

    Septicemia differs from bacteremia in that septicemia is typically associated with:

    <p>Systemic illness or infection.</p> Signup and view all the answers

    What role do mechanical barriers play in the host's defense?

    <p>They prevent the entry of pathogens.</p> Signup and view all the answers

    What is the primary characteristic that distinguishes septicemia from bacteremia?

    <p>Multiplication of pathogenic bacteria in the blood</p> Signup and view all the answers

    Which type of gangrene is specifically associated with the gas produced by Clostridia species?

    <p>Gas gangrene</p> Signup and view all the answers

    What symptom is typically associated with bacteremia?

    <p>Subclinical or minor symptoms</p> Signup and view all the answers

    What is a common complication of a bacterial infection leading to localized lesions in the heart?

    <p>Endocarditis</p> Signup and view all the answers

    Which statement accurately describes the nature of pus localization in bacterial infections?

    <p>Causes abscess formation</p> Signup and view all the answers

    What is one of the classic clinical presentations of septicemia?

    <p>Hypotension</p> Signup and view all the answers

    In what manner do Clostridia species contribute to gas gangrene?

    <p>By fermenting sugars and producing gas</p> Signup and view all the answers

    Diphtheria is primarily caused by which bacteria?

    <p>Corynebacterium diphtheriae</p> Signup and view all the answers

    Bacterial infections can be classified into acute and chronic types.

    <p>True</p> Signup and view all the answers

    Vertical transmission of infections typically occurs from child to parent.

    <p>False</p> Signup and view all the answers

    Infection transmission through respiratory droplets can travel more than 10 feet.

    <p>False</p> Signup and view all the answers

    Inflammatory reactions caused by bacterial infections can sometimes damage tissues carrying the same antigens.

    <p>True</p> Signup and view all the answers

    The fecal-oral route is a common transmission method for fungal infections like dermatophytes.

    <p>False</p> Signup and view all the answers

    Ischemia is a local factor that can promote infection.

    <p>True</p> Signup and view all the answers

    Pseudomembranous infections are characterized by the presence of pus.

    <p>False</p> Signup and view all the answers

    Insects can act as vectors for the transmission of diseases like malaria.

    <p>True</p> Signup and view all the answers

    Commensal microorganisms are always harmful to the human body.

    <p>False</p> Signup and view all the answers

    The virulence of a microorganism is its capacity to cause disease.

    <p>True</p> Signup and view all the answers

    Invasiveness is defined as the ability of a microorganism to spread to another suitable host.

    <p>False</p> Signup and view all the answers

    Phagocytosis is part of the specific defense mechanisms in the host.

    <p>False</p> Signup and view all the answers

    The primary complex in primary tuberculosis consists of a Ghon focus and hilar lymph nodes, both of which rarely heal by fibrosis.

    <p>False</p> Signup and view all the answers

    The presence of bacteria in the blood is referred to as bacteremia.

    <p>True</p> Signup and view all the answers

    In secondary tuberculosis, the lesion commonly occurs at the base of the lung with minimal lung parenchyma damage.

    <p>False</p> Signup and view all the answers

    Th1 cells play a crucial role in activating macrophages during the immune response against tuberculosis.

    <p>True</p> Signup and view all the answers

    Mechanisms that affect the severity of an infection are solely dependent on the specific characteristics of the host.

    <p>False</p> Signup and view all the answers

    Gas gangrene and diphtheria are both caused by viral pathogens.

    <p>False</p> Signup and view all the answers

    Miliary tuberculosis occurs when bacteria are confined within the lungs and do not disseminate through the bloodstream.

    <p>False</p> Signup and view all the answers

    The dose of microorganisms entering the body can influence the outcome of an infection.

    <p>True</p> Signup and view all the answers

    Granulomas in tuberculosis primarily consist of activated macrophages, with some fusing to form Langhans giant cells.

    <p>True</p> Signup and view all the answers

    IL-12 and IL-18 are not involved in stimulating the Th1 response during the pathogenesis of tuberculosis.

    <p>False</p> Signup and view all the answers

    Caseous necrosis is a characteristic finding in the final lesion of tuberculosis.

    <p>True</p> Signup and view all the answers

    Once formed, the lesions in primary tuberculosis can actively spread throughout the body without any dormancy.

    <p>False</p> Signup and view all the answers

    Miliary tuberculosis primarily affects the lungs and never involves the liver.

    <p>False</p> Signup and view all the answers

    Spinal tuberculosis accounts for 50% of all musculoskeletal tuberculosis cases.

    <p>True</p> Signup and view all the answers

    The term 'miliary' in miliary tuberculosis is derived from the resemblance of lesions to millet seeds.

    <p>True</p> Signup and view all the answers

    Ziehl-Neelsen staining is used to detect tuberculosis bacilli in tissue samples.

    <p>True</p> Signup and view all the answers

    Miliary lesions in tuberculosis never expand or coalesce into larger lesions.

    <p>False</p> Signup and view all the answers

    The acidic nature of the bacteria Mycobacterium tuberculosis causes them to be classified as acid-fast bacilli.

    <p>False</p> Signup and view all the answers

    Diphtheria is characterized by a necrosis-inducing exotoxin that leads to the formation of a dense, fibrino-purulent exudate.

    <p>True</p> Signup and view all the answers

    Mycobacterium bovis can be transmitted through respiratory droplets as a primary mode of infection.

    <p>False</p> Signup and view all the answers

    The major threat from diphtheria includes suffocation due to the sloughing off of its characteristic pseudomembrane.

    <p>True</p> Signup and view all the answers

    Tuberculosis infections predominantly result from the absorption of bacterial exotoxins.

    <p>False</p> Signup and view all the answers

    In TB, granulomatous inflammation is triggered by a type I hypersensitivity reaction.

    <p>False</p> Signup and view all the answers

    Diphtheria primarily affects the upper respiratory tract, leading to systemic complications through toxin dissemination.

    <p>True</p> Signup and view all the answers

    The primary causative agent of tuberculosis in humans is Mycobacterium avium.

    <p>False</p> Signup and view all the answers

    What is one systemic factor that increases the risk of infection in individuals?

    <p>Malnutrition can increase the risk of infection.</p> Signup and view all the answers

    What cells are primarily responsible for the formation of caseous necrosis in a tuberculosis granuloma?

    <p>Epithelioid macrophages and multinucleated giant cells are responsible for the formation of caseous necrosis.</p> Signup and view all the answers

    List two methods through which infectious microbes can be transmitted.

    <p>Contact and respiratory droplets are two methods of transmission.</p> Signup and view all the answers

    Describe the outcome after the initial tuberculosis infection in 95% of the cases.

    <p>In 95% of cases, the infection heals by fibrosis.</p> Signup and view all the answers

    Describe the mechanism by which bacteria cause tissue damage through inflammatory reactions.

    <p>Bacteria elicit an inflammatory reaction that can destroy both the bacteria and the infected tissue.</p> Signup and view all the answers

    What immune response is primarily activated during the pathogenesis of tuberculosis after three weeks?

    <p>The Th1 response, characterized by the stimulation of cell-mediated immunity, is activated.</p> Signup and view all the answers

    What is the anatomical location of the initial lesion (Ghon focus) in primary tuberculosis?

    <p>The Ghon focus forms a small subpleural lesion in the mid zone of the lung.</p> Signup and view all the answers

    What characterizes a catarrhal bacterial infection?

    <p>A catarrhal bacterial infection affects the mucus membranes.</p> Signup and view all the answers

    What feature differentiates secondary tuberculosis from primary tuberculosis?

    <p>Secondary tuberculosis occurs as a reinfection or reactivation of dormant bacilli.</p> Signup and view all the answers

    How can vertical transmission of infections occur during pregnancy?

    <p>Vertical transmission can occur from mother to fetus via the placenta.</p> Signup and view all the answers

    What are Langhans giant cells, and where are they typically found?

    <p>Langhans giant cells are multinucleated giant cells formed from fused macrophages, found in tuberculosis granulomas.</p> Signup and view all the answers

    What is a distinguishing feature of pseudomembranous bacterial infections?

    <p>Pseudomembranous infections are characterized by the formation of a pseudo-membrane.</p> Signup and view all the answers

    Identify a route of dissemination for microorganisms within the body.

    <p>Microorganisms can spread through lymphatic vessels.</p> Signup and view all the answers

    What occurs during the progression to systemic miliary tuberculosis?

    <p>Systemic miliary tuberculosis results from the dissemination of bacteria through the systemic arterial system.</p> Signup and view all the answers

    What role do insect vectors play in the transmission of infectious diseases?

    <p>Insect vectors, like mosquitoes, transmit diseases such as malaria.</p> Signup and view all the answers

    What causes the damage that characterizes the macroscopical appearance of secondary tuberculosis lesions?

    <p>Damage in secondary tuberculosis is caused by cavity formation and extensive lung parenchyma damage.</p> Signup and view all the answers

    What defines infection in the context of microbial invasion?

    <p>Infection is defined as the invasion of living tissue by microorganisms or their products, followed by a local reaction that may be associated with a general reaction.</p> Signup and view all the answers

    What distinguishes opportunistic infections from commensal microorganisms?

    <p>Opportunistic infections occur when normally harmless commensal microorganisms cause disease under specific conditions.</p> Signup and view all the answers

    List two factors that influence the severity and occurrence of infections.

    <p>The dose of microorganisms entering the body and the virulence of the microorganisms are two critical factors.</p> Signup and view all the answers

    What are two mechanisms of nonspecific defense in the human body?

    <p>Mechanical barriers like intact skin and glandular secretions such as gastric acidity are two nonspecific defense mechanisms.</p> Signup and view all the answers

    How does septicemia differ from bacteremia?

    <p>Septicemia is associated with systemic infection and often presents with severe clinical symptoms, while bacteremia refers to the presence of bacteria in the blood without systemic illness.</p> Signup and view all the answers

    What role does phagocytosis play in the immune response?

    <p>Phagocytosis is a nonspecific defense mechanism that involves macrophages and neutrophils engulfing and destroying pathogens.</p> Signup and view all the answers

    Describe the concept of invasiveness in the context of microbial infections.

    <p>Invasiveness refers to the ability of microorganisms to multiply and spread within the host's body.</p> Signup and view all the answers

    What is the significance of transmission in infectious diseases?

    <p>Transmission determines the ability of microorganisms to pass from one host to another, impacting the spread of infections.</p> Signup and view all the answers

    Describe the process that leads from individual miliary lesions to larger coalescent lesions in systemic miliary tuberculosis.

    <p>Individual miliary lesions can expand and coalesce to form larger lesions due to the spread of the infectious process within the involved organ parenchyma.</p> Signup and view all the answers

    What are the common clinical features associated with systemic miliary tuberculosis?

    <p>Common features include fever, night sweats, cough, hemoptysis, and weight loss, which can vary based on the organ involved.</p> Signup and view all the answers

    What role do Ziehl-Neelsen staining and PCR play in the diagnosis of tuberculosis?

    <p>Ziehl-Neelsen staining is used to detect Mycobacterium tuberculosis in specimens, while PCR amplifies the bacilli's DNA for more precise identification.</p> Signup and view all the answers

    Explain how the rising trend of tuberculosis incidence can be influenced by HIV and multidrug resistance.

    <p>Increasing HIV coinfection weakens the immune response, making individuals more susceptible to tuberculosis, while multidrug resistance complicates treatment efforts.</p> Signup and view all the answers

    Identify the most common site for spinal tuberculosis and its clinical implications.

    <p>The lower thoracic and thoracolumbar areas are the most commonly affected sites, leading to potential complications such as severe back pain and neurological deficits.</p> Signup and view all the answers

    What primarily causes the dense fibrino-purulent exudate seen in diphtheria?

    <p>The dense fibrino-purulent exudate is primarily caused by the powerful exotoxin elaborated by C. diphtheriae.</p> Signup and view all the answers

    What are the major hazards associated with diphtheria infection?

    <p>The major hazards are sloughing and aspiration of the pseudomembrane leading to suffocation, and absorption of bacterial exotoxins causing myocarditis and polyneuritis.</p> Signup and view all the answers

    How do Mycobacterium tuberculosis bacilli retain red dye during staining?

    <p>Mycobacterium tuberculosis retains the red dye due to its waxy coat, which characterizes them as acid-fast bacilli.</p> Signup and view all the answers

    What type of tissue reaction primarily results from the presence of TB bacilli in the body?

    <p>The tissue reaction primarily results in delayed hypersensitivity, leading to granulomatous inflammation with central necrosis.</p> Signup and view all the answers

    Which bacterium is responsible for the majority of tuberculosis cases worldwide?

    <p>Mycobacterium tuberculosis is responsible for the majority of tuberculosis cases worldwide.</p> Signup and view all the answers

    What form of transmission does Mycobacterium bovis typically utilize?

    <p>Mycobacterium bovis typically transmits through the alimentary tract via the consumption of milk from diseased cows.</p> Signup and view all the answers

    What is the classic clinical presentation of the pseudomembrane in diphtheria?

    <p>The classic clinical presentation is a superficial, dirty-gray pseudomembrane formed in the upper airways.</p> Signup and view all the answers

    What characterizes the lesions induced by TB bacilli in the body?

    <p>The lesions induced by TB bacilli are characterized by granulomatous inflammation that often includes necrosis at the center.</p> Signup and view all the answers

    Transmission of infections can occur via contact, respiratory droplets, fecal-oral route, and ______.

    <p>sexual transmission</p> Signup and view all the answers

    Local factors such as ______ can promote infection.

    <p>ischemia</p> Signup and view all the answers

    Bacteria can damage tissue by releasing ______ that kill cells.

    <p>toxins</p> Signup and view all the answers

    Cholera spreads through the ______ route.

    <p>fecal-oral</p> Signup and view all the answers

    Bacterial infections can be classified into ______ and chronic types.

    <p>acute</p> Signup and view all the answers

    Insects like mosquitoes can act as ______ for diseases such as malaria.

    <p>vectors</p> Signup and view all the answers

    An acute bacterial infection characterized by the formation of a pseudo-membrane is known as ______.

    <p>pseudomembranous</p> Signup and view all the answers

    The spread of microorganisms can occur through ______, which includes the circulatory system.

    <p>blood vessels</p> Signup and view all the answers

    Infection is defined as the invasion of living tissue by a micro-organism or its products followed by local reaction which may be associated with a general ______.

    <p>reaction</p> Signup and view all the answers

    Commensals microorganisms can infect the human body and be ______ to the body.

    <p>harmless</p> Signup and view all the answers

    Micro-organism factors affecting infection include dose, virulence, invasiveness, and ______.

    <p>transmission</p> Signup and view all the answers

    Nonspecific defense mechanisms include mechanical barriers like intact skin and glandular secretion such as acidity of gastric ______.

    <p>juices</p> Signup and view all the answers

    The balance between the aggressive mechanisms of the micro-organism and the defense mechanisms of the ______ determines the outcome of an infection.

    <p>host</p> Signup and view all the answers

    Opportunistic infections occur when commensal microorganisms cause ______.

    <p>disease</p> Signup and view all the answers

    The ability of a micro-organism to multiply and spread in the body is known as ______.

    <p>invasiveness</p> Signup and view all the answers

    Specific defense mechanisms in the host include cell-mediated and humoral ______.

    <p>immunity</p> Signup and view all the answers

    The presence of small numbers of bacteria in the blood without multiplication is known as ______.

    <p>Bacteraemia</p> Signup and view all the answers

    Septicemia is characterized by the ______ of highly pathogenic bacteria in the blood.

    <p>multiplication</p> Signup and view all the answers

    Gangrene involves the digestion of dead tissue by ______ bacteria in a living body.

    <p>saprophytic</p> Signup and view all the answers

    The type of gangrene associated with the presence of gas produced by Clostridia species is known as ______.

    <p>Gas gangrene</p> Signup and view all the answers

    Diphtheria is an acute, communicable disease caused by ______ diphtheriae.

    <p>Corynebacterium</p> Signup and view all the answers

    In gas gangrene, Clostridia ferments sugar producing ______ and CO2.

    <p>H2</p> Signup and view all the answers

    Clinical symptoms of septicemia may include tachycardia, hypotension, and ______.

    <p>shock</p> Signup and view all the answers

    Bacterial infection of the blood is classified into Bacteraemia and ______.

    <p>Septicemia</p> Signup and view all the answers

    The disease characterized by local growth of the bacterium in the pharynx is called ______.

    <p>diphtheria</p> Signup and view all the answers

    The bacterium causing tuberculosis is ______.

    <p>Mycobacterium tuberculosis</p> Signup and view all the answers

    TB bacilli do not produce ______ or enzymes.

    <p>exotoxin</p> Signup and view all the answers

    The classic superficial, dirty-gray pseudomembrane in diphtheria is caused by ______ of the mucosal epithelium.

    <p>necrosis</p> Signup and view all the answers

    Tuberculosis can spread through respiratory droplets and the alimentary tract from ______.

    <p>diseased cows</p> Signup and view all the answers

    Acid fast bacilli retain red dye due to their ______ coat.

    <p>waxy</p> Signup and view all the answers

    The lesions of TB are primarily due to a delayed hypersensitivity reaction, also known as ______ type.

    <p>Type IV</p> Signup and view all the answers

    Respiratory droplets are a mode of ______ for many infectious diseases.

    <p>transmission</p> Signup and view all the answers

    Miliary tuberculosis is most prominent in the liver, bone marrow, spleen, and ______

    <p>adrenals</p> Signup and view all the answers

    Spinal tuberculosis (TB) most often affects the lower thoracic and ______ area.

    <p>thoracolumbar</p> Signup and view all the answers

    Miliary lesions may expand and ______, resulting in larger lesions.

    <p>coalesce</p> Signup and view all the answers

    Fever, cough, night sweating, hemoptysis, and weight loss are clinical features according to ______ involved.

    <p>organ</p> Signup and view all the answers

    Detection of the m.o. in the specimen by using ______ staining is a method of diagnosis.

    <p>Ziehl-Neelsen</p> Signup and view all the answers

    Match the following routes of transmission with their respective examples:

    <p>Contact = S.aureus Respiratory droplets = Influenza viruses Fecal-oral route = Hepatitis A Vertical transmission = Rubella</p> Signup and view all the answers

    Match the following bacterial infection types with their characteristics:

    <p>Acute = Rapid onset Chronic = Extended duration Catarrhal = Mucus membrane affected Pseudomembranous = Formation of pseudo-membrane</p> Signup and view all the answers

    Match the following mechanisms of bacterial injury with their descriptions:

    <p>Release toxins = Kill cells directly Release lytic enzymes = Destroy tissue Elicit inflammatory reaction = Destroys infected tissue Elicit immune reaction = Causes cross reactivity</p> Signup and view all the answers

    Match the following systemic factors influencing infection with their descriptions:

    <p>Age = Risk increases in very young and very old Malnutrition = Weakens immune response Blood vessel spread = Dissemination through circulatory system Inflammatory cells = Carry M.Tb within macrophages</p> Signup and view all the answers

    Match the following types of dissemination routes with their corresponding examples:

    <p>Nervous system = Rabies Lymphatic vessels = Lymphatic spread Blood vessels = Septicemia Inflammatory cells = M.Tb</p> Signup and view all the answers

    Match the following factors that promote infection with their types:

    <p>Ischemia = Local factor Malnutrition = Systemic factor Age = Host factor Insect vectors = Biological transmission</p> Signup and view all the answers

    Match the following infectious diseases with their transmission methods:

    <p>Cholera = Fecal-oral route AIDS = Sexual transmission Malaria = Insect vector Typhoid fever = Fecal-oral route</p> Signup and view all the answers

    Match the following types of bacterial infections with their examples:

    <p>Pyogenic = Abscess Serous = Serous fluid production Catarrhal = Affected mucus membranes Pseudomembranous = Diphtheria</p> Signup and view all the answers

    Match the following diagnostic methods with their descriptions:

    <p>Ziehl-Neelsen staining = Used to detect Mycobacterium tuberculosis in specimens Biopsy of the infected tissue = Involves taking a sample for histological analysis PCR amplification = Technique to amplify DNA of bacterial pathogens X-ray = Imaging method to visualize TB-related changes in the lungs</p> Signup and view all the answers

    Match the following clinical features with their associated conditions:

    <p>Fever = Common symptom in various forms of tuberculosis Night sweating = Often indicative of systemic infection Hemoptysis = Coughing up blood, associated with lung involvement Weight loss = General symptom of chronic illnesses, including TB</p> Signup and view all the answers

    Match the following anatomical sites with their relevance in miliary tuberculosis:

    <p>Liver = Organ frequently involved in miliary TB lesions Bone marrow = Site of hematogenous spread in tuberculosis Spleen = Common location for miliary lesions Adrenals = Organ often affected by miliary tuberculosis</p> Signup and view all the answers

    Match the following types of tuberculosis with their characteristics:

    <p>Miliary tuberculosis = Characterized by small yellow-white lesions resembling millet seeds Spinal tuberculosis = Most common extrapulmonary form affecting the spine Primary tuberculosis = Involves the Ghon complex of lymph nodes and foci Drug-resistant tuberculosis = Emerging challenge causing rising TB rates globally</p> Signup and view all the answers

    Match the following features of miliary tuberculosis with their descriptions:

    <p>Miliary lesions = Macroscopic features resembling millet seeds Coalescence = Process where lesions combine to form larger ones Microscopic lesions = Initial lesion stage in the pathological process Affected organs = Includes liver, spleen, bone marrow, and adrenals</p> Signup and view all the answers

    Match the following types of tuberculosis with their characteristics:

    <p>Primary TB = Occurs after initial exposure and can form a Ghon complex Secondary TB = Reinfection or reactivation of dormant bacilli Progressive TB = Systemic dissemination of bacteria through the arterial system Miliary TB = Characterized by small lesions throughout the body</p> Signup and view all the answers

    Match the pathogenetic steps of tuberculosis with their descriptions:

    <p>Entrance of MTB to macrophages = First step in the infection process Replication inside macrophages = Leads to the microorganism's proliferation Stimulation of Th1 response = Triggered by IL-12 and IL-18 after three weeks Granuloma formation = Resulting in caseous necrosis and chronic inflammation</p> Signup and view all the answers

    Match the histological features of granuloma in tuberculosis with their descriptions:

    <p>Epithelioid macrophages = Activated macrophages that surround necrotic tissue Multinucleated giant cells = Formed by the fusion of macrophages Central caseous necrosis = Central area of dead tissue in the granuloma Chronic inflammatory cells = Surround the granuloma rim, rich in lymphocytes</p> Signup and view all the answers

    Match the type of tuberculosis lesion with its gross appearance:

    <p>Ghon focus = Small sub-pleural parenchymal lesion in the lung Apex of the lung lesion = Associated with secondary tuberculosis Miliary tuberculosis = Involves small, scattered lesions in various organs Cavitary lesions = Characterized by lung parenchyma damage in secondary TB</p> Signup and view all the answers

    Match the cytokines involved in the Th1 immune response in tuberculosis with their roles:

    <p>IL-12 = Stimulates the differentiation of T cells into Th1 IL-18 = Enhances the Th1-mediated immune response INF-Y = Activates macrophages and enhances their killing ability TNF-alpha = Promotes inflammation and reduces fungal growth</p> Signup and view all the answers

    Match the terms with their definitions concerning tuberculosis pathology:

    <p>Caseous necrosis = Cheesy-like necrotic tissue found in granulomas Fibrosis = Healing process that replaces tissue with scar tissue Th1 response = Cell-mediated immunity primarily targeting TB Granuloma = A localized inflammatory response to infection</p> Signup and view all the answers

    Match the types of immune responses with their primary functions in tuberculosis:

    <p>Cell-mediated immunity = Involves T cells activating macrophages Humoral immunity = Involves B cells producing antibodies Inflammatory response = Leads to increased blood flow and immune cell recruitment Adaptive immunity = Provides long-term protection against TB reinfection</p> Signup and view all the answers

    Match the clinical presentations of tuberculosis with their specific characteristics:

    <p>Primary tuberculosis = Typically results in a Ghon complex Secondary tuberculosis = Often presents with lung cavitation and necrosis Progressive tuberculosis = Systemic spread leading to multiorgan involvement Miliary tuberculosis = Characterized by tiny lesions disseminated throughout the body</p> Signup and view all the answers

    Match the types of infectious microorganisms with their definitions:

    <p>Pathogens = Microorganisms that cause diseases Commensals = Normally harmless microorganisms present in the body Opportunistic infections = Infections caused by commensals that become pathogenic Virulent microorganisms = Microorganisms with a high capacity to cause disease</p> Signup and view all the answers

    Match the factors influencing infection with their categories:

    <p>Dose = Micro-organism factors Mechanical barriers = Nonspecific defense mechanism Virulence = Micro-organism factors Cell-mediated immunity = Specific defense mechanism</p> Signup and view all the answers

    Match the types of transmission modes with their descriptions:

    <p>Direct contact = Transmission through physical touch Respiratory droplets = Transmission via airborne particles within close proximity Fecal-oral route = Transmission through contaminated food or water Vector-borne transmission = Transmission via insects or animals</p> Signup and view all the answers

    Match the terms related to bacterial infection with their definitions:

    <p>Bacteremia = Presence of bacteria in the blood without symptoms Septicemia = Presence of bacteria in the blood with systemic symptoms Gas gangrene = Infection caused by Clostridia species leading to gas production Diphtheria = Infection primarily caused by Corynebacterium diphtheriae</p> Signup and view all the answers

    Match the components of the immune response with their types:

    <p>Phagocytosis = Nonspecific defense mechanism Humoral immunity = Specific defense mechanism Inflammatory response = Nonspecific defense mechanism Memory cells = Specific defense mechanism</p> Signup and view all the answers

    Match the factors affecting microbial infection severity with their roles:

    <p>Invasiveness = Ability to spread in the body Resistance = Host defense against infection Virulence = Capacity to cause disease Dose = Number of microorganisms entering the body</p> Signup and view all the answers

    Match the bacterial infections with their associated pathogens:

    <p>C. botulinum = Botulism E. coli = Hemolytic uremic syndrome S. aureus = Skin infections and abscesses M. tuberculosis = Tuberculosis</p> Signup and view all the answers

    Match the components of a pathogen's characteristics with their definitions:

    <p>Invasiveness = Ability to multiply within a host Obligate pathogens = Microorganisms that always cause disease Commensal microorganisms = Organisms that can be either beneficial or harmful Viral shedding = Release of viral particles for transmission</p> Signup and view all the answers

    Match the type of bacterial infection with its description:

    <p>Bacteraemia = Presence of small numbers of bacteria in blood without multiplication Septicemia = Multiplication in the blood of highly pathogenic bacteria Diphtheria = Acute disease caused by Corynebacterium diphtheriae Gas gangrene = Infection causing black discoloration and gas production in tissues</p> Signup and view all the answers

    Match the type of gangrene with its definition:

    <p>Gas gangrene = Caused by Clostridia species, resulting in gas production Dry gangrene = Occurs with tissue necrosis without putrefaction Wet gangrene = Necrosis associated with putrefaction and bacterial infection Ischemic gangrene = Gangrene due to reduced blood flow to tissues</p> Signup and view all the answers

    Match the bacterial infection with its clinical manifestation:

    <p>Bacteraemia = Minor symptoms and sub-clinical lesions Septicemia = Profound toxemia and may result in shock Diphtheria = Hyperemic mucosal surface with membrane-like exudate Gas gangrene = Black discoloration and bad odor at the affected site</p> Signup and view all the answers

    Match the process with its corresponding effect in bacterial infections:

    <p>Tachycardia = Increased heart rate often seen in septicemia Hypotension = Low blood pressure frequently associated with septicemia Shock = Life-threatening state often resulting from severe infections Abscess formation = Localized collection of pus in infected tissue</p> Signup and view all the answers

    Match the bacterial infection mechanism with its example:

    <p>Clostridium perfringens = Causes gas gangrene by producing exotoxins Corynebacterium diphtheriae = Responsible for acute diphtheria infections S. viridans = Bacteria affecting blood after dental procedures Pseudomembranous colitis = Infection characterized by a thick yellow-green membrane</p> Signup and view all the answers

    Match the description of gangrene with its type:

    <p>Gas gangrene = Characterized by H2 and CO2 gas production Dry gangrene = Tissue necrosis without infection or moisture Wet gangrene = Necrosis accompanied by bacterial infection Frozen gangrene = Due to extreme cold exposure leading to tissue death</p> Signup and view all the answers

    Match the type of bacterial infection with its potential outcome:

    <p>Septicemia = May end in death if untreated Bacteraemia = Can lead to localized lesions such as infective endocarditis Diphtheria = Can cause serious throat obstruction Gas gangrene = Leads to severe tissue damage and systemic effects</p> Signup and view all the answers

    Match the bacterial infection with the typical setting of occurrence:

    <p>Diphtheria = Spread in crowded environments and schools Bacteraemia = Often occurs post dental procedures Septicemia = Common after severe infections and traumas Gas gangrene = Generally linked to open contaminated wounds</p> Signup and view all the answers

    Study Notes

    Tuberculosis Pathogenesis

    • Tuberculosis (TB) is caused by Mycobacterium tuberculosis (MTB)
    • MTB enters macrophages where it replicates.
    • After 3 weeks, a cell-mediated immune response (Th1 response) is stimulated by IL-12 and IL-18.
    • Th1 cells activate macrophages via release of INF-Y
    • Granulomas form with central caseous necrosis

    TB Lesions

    • TB lesions are characterized by caseous necrosis surrounded by activated macrophages.
    • Epithelioid cells and multinucleated giant cells (Langhans giant cells) are present.
    • Lymphocytes are present in a rim surrounding the necrosis, and fibrosis is present at the periphery.

    Types of TB

    • Primary TB occurs following initial exposure to TB bacilli in non-immunized individuals.

      • A small subpleural parenchymal lesion forms in the mid zone of the lung (Ghon focus) and spreads to hilar lymph nodes. This is called the primary complex.
      • 95% of primary TB cases heal by fibrosis.
      • Some primary cases may enter a dormant state, while others may progress to disseminated TB.

    • Secondary TB occurs as a reinfection or reactivation of dormant bacilli from a primary infection, often when the patient's immunity is impaired.

      • It typically occurs at the apex of the lung, causing significant damage to lung parenchyma and cavity formation.
      • Secondary TB may heal by fibrosis or progress to disseminated TB.

    • Progressive TB occurs when bacteria disseminate through the systemic arterial system.

    Systemic Miliary Tuberculosis

    • Miliary TB is a form of progressive TB characterized by small, scattered lesions resembling millet seeds.
    • The lesions can be found in the liver, bone marrow, spleen, adrenals, and other organs.

    Clinical Features of TB

    • Clinical features of TB vary based on the organ involved..
    • Common symptoms include fever, cough, night sweats, hemoptysis, and weight loss.

    Diagnosis of TB

    • History and clinical examination help identify potential cases of TB.
    • Investigations include:
      • X-ray to visualize lung lesions.
      • Detection of MTB in specimens (sputum, biopsy) using Ziehl-Neelsen staining.
      • Biopsy of infected tissue.
      • PCR amplification of TB bacilli.

    Spinal TB

    • Spinal TB (Pott's disease) is the most common extrapulmonary form of TB.
    • Spinal TB most often affects the lower thoracic and thoracolumbar areas.
    • Increasing rates of TB are due to factors such as HIV coinfection, multidrug resistance of the organism, and global migration.

    Infectious Diseases

    • Infection is the invasion of living tissue by microorganisms or their products, followed by a local reaction, which may be associated with a general reaction.

    Commensal Microorganisms

    • Commensal microorganisms are those that can inhabit the human body without causing harm.
    • Some commensal microorganisms can become opportunistic pathogens if the host's immune system is compromised.

    Factors Influencing Infection

    • Factors influencing infection include:

      • Microorganism factors:

        • Dose: number of microorganisms entering the body.
        • Virulence: capacity to cause disease.
        • Invasiveness: ability to multiply and spread in the body.
        • Transmission: ability to pass to another suitable host.

      • Host factors:

        • Non-specific defense mechanisms:
          • Mechanical barriers: e.g., intact skin.
          • Glandular secretions: e.g., acidity of gastric juices.
          • Secretion currents: e.g., flow of tears, diarrhea.
          • Phagocytosis: by macrophages and neutrophils.
        • Specific defense (immune response): by cell-mediated and humoral immunity.

      • Other factors:

        • Local factors: e.g., ischemia promotes infection.
        • Systemic factors: e.g., malnutrition.
        • Age: both very young and very old have an increased risk of infection.

    Transmission of Microbes

    • Transmission of microbes can occur through various routes:

      • Contact: e.g., Staphylococcus aureus and dermatophytes (fungi).
      • Respiratory droplets: e.g., viruses and bacteria shed in respiratory secretions during talking, coughing, and sneezing. (Most respiratory pathogens, including influenza viruses, spread in large respiratory droplets, which travel no more than 3 feet.)
      • Fecal-oral route: e.g., cholera, typhoid fever, hepatitis A.
      • Sexual transmission: e.g., AIDS, hepatitis B, syphilis.
      • Vertical transmission: from mother to fetus or newborn: e.g., rubella.
      • Insect/arthropod vectors: e.g., malaria.

    Dissemination Inside the Body

    • Routes of dissemination of microorganisms inside the body include:

      • Nervous system: e.g., rabies.
      • Within inflammatory cells: e.g., MTB within macrophages.
      • Lymphatic vessels.
      • Blood vessels.

    Mechanism of Bacterial Injury

    • Bacteria damage tissue through various mechanisms:

      • Release of toxins: e.g., toxins that kill cells.
      • Release of lytic enzymes: e.g., proteases, coagulase, and fibrinolysins that destroy tissue and facilitate bacterial spread.
      • Elicitation of an inflammatory reaction: damage to infected tissue.
      • Elicitation of an immune reaction: e.g., “cross reactivity,” damage to tissues carrying the same antigen as the bacterium.

    Types of Bacterial Infections

    • Bacterial infections are classified as:

      • Acute:

        • Catarrhal: affecting mucous membranes.
        • Serous: affecting serous cavities and producing serous fluid.
        • Pseudomembranous: characterized by the formation of a pseudo-membrane, as in diphtheria.
        • Pyogenic or suppurative (pus-producing): e.g., abscess. (M.O stimulate the secretion of IL1 & TNF, attracting neutrophils that secrete lytic enzymes, destroy tissue, and form abscesses.)

      • Chronic

    Bacterial Infection in Blood

    • Bacteremia is the presence of small numbers of bacteria in the blood without multiplication. Patients may have subclinical or minor symptoms and lesions.

      • Example: S. viridans in blood after vigorous brushing with dental sepsis. These bacteria are typically destroyed rapidly by the immune system.
      • Bacteremia can lead to localized lesions in various parts of the body, such as infective endocarditis.

    • Septicemia is the multiplication of highly pathogenic bacteria in the blood. It is a serious infection with profound toxemia in which bacteria have overwhelmed the host defenses.

      • It leads to serious consequences, including death.
      • Clinically, patients present with tachycardia, hypotension, and shock.

    Gangrene

    • Gangrene is the digestion of dead tissue by saprophytic bacteria in a living body (necrosis with putrefaction).

    • Types of gangrene include:

      • Gas gangrene: caused by infection with Clostridia species, such as Cl. perfringens.
      • Dry gangrene:
      • Wet gangrene:

    Gas Gangrene

    • Gas gangrene is caused by infection with Clostridia species, often Cl. perfringens.
    • Bacteria gain entry into tissues through open contaminated wounds.
    • Clostridia kill tissue by secreting potent exotoxins and then invade and digest dead tissue.
    • Cl. perfringens ferments sugar, producing H2 and CO2, which collect as bubbles in the dead tissue and can be palpated (gas gangrene).
    • Clinically, Gas gangrene presents with black discoloration, foul odor, and swelling at the affected site.

    Diphtheria

    • Diphtheria is an acute, communicable disease caused by Corynebacterium diphtheriae.
      • It is usually caused by the production of a powerful exotoxin that interferes with protein synthesis in the body, leading to necrosis and inflammation.

    Miliary Tuberculosis

    • Miliary tuberculosis is a disseminated form of TB where small lesions (miliary foci) are scattered throughout various organs.
    • It occurs when MTB bacilli spread through the bloodstream to multiple organs.

    Tuberculosis

    • Tuberculosis (TB) is a serious chronic pulmonary and systemic disease caused by Mycobacterium tuberculosis and Mycobacterium bovis.
    • The disease affects more than a billion individuals worldwide, with 8.7 million new cases and 1.4 million deaths each year.
    • Mycobacterium tuberculosis and Mycobacterium bovis are aerobic bacilli with a waxy coat that causes them to retain red dye when treated with acid, they are called Acid Fast Bacilli.
    • TB is diagnosed with a combination of history, clinical examination, and investigations, including X-rays, detection of the organism in specimens, and PCR amplification of Mycobacterium tuberculosis DNA.

    Pathogenesis of TB

    • Mycobacterium tuberculosis enters the body through inhalation.
    • The bacteria are phagocytosed by macrophages and replicate inside them, causing inflammation.
    • After three weeks, the immune system is stimulated (Th1 response), with the release of cytokines like IL-12 and IL-18.
    • Activated Th1 cells release INF-γ, which activates macrophages.
    • Inflammation forms granulomas with central caseous necrosis surrounded by activated macrophages (epithelioid macrophages), multinucleated giant cells (Langhans giant cells), a rim of chronic inflammatory cells rich in lymphocytes, and fibrosis at the periphery.

    Types of Tuberculosis

    • Primary TB: occurs after the initial exposure to TB bacilli in non-immunized individuals.
      • A small subpleural parenchymal lesion forms in the mid-zone of the lung (Ghon focus).
      • The lesion can spread to the hilar lymph nodes.
      • The Ghon focus and affected lymph nodes constitute a primary complex.
      • 95% of primary TB cases heal by fibrosis.
      • Some cases enter a dormant state.
      • In a small number of cases, primary TB may spread forming progressive primary TB.
    • Secondary TB: results from reinfection or reactivation of dormant bacilli from a prior primary infection.
      • Secondary TB occurs at the apex of the lung, leading to significant lung damage and cavity formation.
      • It can heal by fibrosis, or it may spread further, resulting in progressive secondary TB.
    • Progressive TB: a more severe form of TB that occurs when bacteria disseminate through the systemic arterial system.
      • Miliary tuberculosis is a type of progressive TB.

    Transmission of TB

    • The primary route of transmission is through respiratory droplets during coughing, sneezing, or talking.
    • TB can also be transmitted through the alimentary tract by consuming contaminated milk from diseased cows.
    • TB can be spread through contact with infected individuals and objects.
    • TB can affect any organ system.
    • Mycobacterium avium and Mycobacterium intracellulare can cause lung infection in people with AIDS, especially in the advanced stages.

    Treatment of TB

    • Treatment of tuberculosis typically involves a multi-drug regimen.
    • Treatment can take several months to years.
    • The goal of treatment is to eliminate the infection and prevent the development of drug-resistant strains of Mycobacterium tuberculosis.
    • Treating tuberculosis is more challenging in patients with HIV infection due to their suppressed immune system.

    Prevention of TB

    • The BCG vaccine is available to protect against tuberculosis in children.
    • Public health measures, including screening for TB infection, are crucial tools for controlling the spread of TB.
    • Early diagnosis and treatment, as well as preventative measures such as maintaining good hygiene, have an enormous impact on slowing the spread of tuberculosis.

    Tuberculosis Pathogenesis

    • Mycobacterium tuberculosis (MTB) enters macrophages and replicates inside them.
    • After approximately 3 weeks, cell-mediated immunity (Th1 response) is stimulated by IL-12 and IL-18.
    • Activated Th1 cells release IFN-γ, which further activates macrophages.
    • This process leads to the formation of granulomas with a central area of caseous necrosis.

    Tuberculosis Lesion

    • Central area of caseous necrosis.
    • Surrounded by activated macrophages (epithelioid macrophages).
    • Some macrophages fuse to form multinucleated giant cells (Langhans giant cells).
    • Rim of chronic inflammatory cells rich in lymphocytes.
    • Fibrosis at the periphery.

    Types of Tuberculosis

    • Primary TB: Occurs after initial exposure in non-immunized individuals of any age.
      • Forms a small subpleural lesion in the mid zone of the lung (Ghon focus) and spreads to the hilar lymph nodes.
      • Both lesions together are called the primary complex.
      • About 95% of cases heal by fibrosis.
      • Some cases may enter a dormant state, and a few may spread to the body forming progressive primary TB.
    • Secondary TB: Results from reactivation of dormant bacilli from primary infection or reinfection.
      • Usually occurs at the apex of the lung with significant damage to the lung parenchyma.
      • May lead to cavity formation.
      • Heals through fibrosis or may spread to form progressive secondary TB.
    • Progressive TB: Occurs when the infection spreads systemically.
      • Systemic Miliary TB: Characterized by widespread dissemination of bacteria through the systemic arterial system.

    Transmission of TB

    • Primarily through inhalation of respiratory droplets containing Mycobacterium tuberculosis.
    • Can also be transmitted through the alimentary tract by consuming milk from diseased cows (Mycobacterium bovis).
    • Mycobacterium avium and mycobacterium intracellulare can cause infection in immunocompromised individuals, especially those with AIDS.

    Tissue Reaction to TB Bacilli

    • TB bacilli don't produce exotoxins, endotoxins, or enzymes.
    • The lesion is primarily due to delayed hypersensitivity reaction (Type IV) to an antigenic protein component of the organism.
    • This leads to granulomatous inflammation with central necrosis.

    Systemic Miliary Tuberculosis

    • Characterized by small, yellow-white lesions ("millet seeds") scattered throughout the involved organ parenchyma.
    • These lesions can expand and coalesce into larger lesions.
    • Commonly affects the liver, bone marrow, spleen, and adrenals, but can involve any organ.

    Clinical Features of Tuberculosis

    • Varies depending on the organ involved.
    • Common symptoms include fever, cough, night sweats, hemoptysis (coughing up blood), and weight loss.

    Diagnosis of Tuberculosis

    • Based on clinical presentation, chest X-ray, and laboratory tests.
    • Laboratory investigations:
      • Ziehl-Neelsen staining to detect acid-fast bacilli in sputum or biopsy specimens.
      • PCR amplification of TB bacilli.
      • Biopsy of infected tissue.
      • Culture of the organism.

    Infectious Diseases

    • Infection is invasion of living tissue by a microorganism or its products, followed by localized and potentially systemic reactions.
    • Commensal microorganisms are normally present in the human body and are typically harmless.
    • Pathogens are microorganisms that cause disease. These can be bacteria, viruses, fungi, or parasites.
    • Factors Influencing Infection
      • Microorganism factors:
        • Dose: The number of microorganisms entering the body
        • Virulence: The capacity of the microorganism to cause disease
        • Invasiveness: The ability of the microorganism to multiply and spread in the body
        • Transmission: The ability of the microorganism to pass to another suitable host
      • Host Factors (Defense Mechanisms):
        • Nonspecific Defense:
          • Mechanical Barriers: Intact skin
          • Glandular Secretion: Acidity of gastric juices
          • Secretion Currents: Flow of tears, diarrhea
          • Phagocytosis: By macrophages and neutrophils
        • Specific Defense (Immune Response): Cell-mediated and humoral immunity
      • Other Factors:
        • Local Factors: Ischemia (reduced blood flow) promotes infection
        • Systemic Factors: Malnutrition
        • Age: Very young and very old individuals have an increased risk of infection
    • Transmission of Microbes:
      • Contact: e.g., Staphylococcus aureus and dermatophytes (fungi)
      • Respiratory Droplets: Viruses and bacteria can be shed in respiratory secretions (talking, coughing, sneezing)
      • Fecal-Oral Route: e.g., Cholera, Typhoid fever, Hepatitis A
      • Sexual Transmission: e.g., AIDS, Hepatitis B, Syphilis
      • Vertical Transmission (Mother to Fetus/Newborn): e.g., Rubella
      • Insect/Arthropod Vectors: e.g., Malaria
    • Dissemination Inside the Body:
      • Nervous System: e.g., Rabies
      • Inflammatory Cells: e.g., Mycobacterium tuberculosis within macrophages
      • Lymphatic Vessels
      • Blood Vessels

    Bacterial Infections

    • Mechanism of Bacterial Injury:
      • Toxin Release: Kill cells
      • Lytic Enzyme Release: Includes proteases, coagulase, and fibrinolysins that destroy tissue and facilitate bacterial spread
      • Inflammatory Reaction: May destroy both bacteria and infected tissue
      • Immune Reaction: May damage tissues with similar antigens to the bacterium ("cross-reactivity")
    • Types of Bacterial Infections:
      • Acute
      • Chronic
    • Subtypes of Acute Bacterial Infections:
      • Catarrhal: Affect mucous membranes
      • Serous: Affect serous cavities, producing serous fluid
      • Pseudomembranous: Characterized by the formation of a pseudomembrane (e.g., diphtheria)
      • Pyogenic or Suppurative (Pus Producing): e.g., abscesses. M.O. stimulate IL-1 and TNF production, attracting neutrophils that release lytic enzymes, destroying tissue and forming abscesses.
    • Bacterial Infection in Blood:
      • Bacteremia: Presence of small numbers of bacteria in the blood without multiplication. Subclinical symptoms or mild lesions are common.
      • Septicemia: Multiplication of highly pathogenic bacteria in the blood. This is a serious infection with profound toxemia, leading to potentially fatal consequences.

    Gangrene

    • Definition: Digestion of dead tissue by saprophytic bacteria in a living body (necrosis with putrefaction)
    • Types:
      • Gas Gangrene
      • Dry Gangrene
      • Wet Gangrene

    Gas Gangrene

    • Cause: Infection with Clostridium species (especially Clostridium perfringens)
    • Entry: Through open contaminated wounds
    • Mechanism: Bacteria produce potent exotoxins that kill tissue and then invade and digest the dead tissue. Fermentation of sugars produces hydrogen (H2) and carbon dioxide (CO2), which collect as bubbles in the dead tissue and can be detected by palpation ("gas gangrene").
    • Clinical Features: Black discoloration, bad odor at the affected site (skin, subcutaneous tissue, intestines, etc.).

    Diphtheria

    • Cause: Corynebacterium diphtheriae
    • Transmission: Respiratory droplets
    • Clinical Features: Local growth of bacteria in the pharynx with membrane formation. Systemic dissemination of toxin leads to lesions in distant organs.
    • Mechanism:
      • Bacteria implant on the mucosa of the upper airways.
      • They produce a powerful exotoxin that causes necrosis of the mucosal epithelium, leading to a dense fibrinopurulent exudate (the classic gray pseudomembrane of diphtheria).
    • Complications:
      • Sloughing and aspiration of pseudomembrane: Suffocation, death
      • Absorption of Bacterial Exotoxins:
        • Myocarditis and myocardial fatty change
        • Polyneuritis

    Tuberculosis

    • Cause: Mycobacterium tuberculosis (pulmonary TB) and Mycobacterium bovis (alimentary TB)
    • Characteristics: Aerobic bacilli with a waxy coat that allows them to retain red dye after acid treatment (hence the name "Acid Fast Bacilli"). Requires Ziehl Neelsen stain for identification.
    • Transmission:
      • Respiratory Tract: Inhalation (Mycobacterium tuberculosis)
      • Alimentary Tract: Through milk of diseased cows (Mycobacterium bovis)
      • Mycobacterium avium and Mycobacterium intracellulare: Cause infection in AIDS patients
    • Tissue Reaction to TB Bacilli:
      • Produce no exotoxins, endotoxins, or enzymes
      • Lesion development is primarily due to a delayed hypersensitivity reaction (Type IV) to an antigenic protein component of the organism.
      • Granulomatous inflammation with central necrosis occurs.
      • Microscopic or small, visible (2-mm) foci of yellow-white lesions are scattered through the infected organ parenchyma (these resemble millet seeds, giving rise to the term "miliary tuberculosis").
      • Miliary lesions may expand and coalesce, forming larger lesions.
      • Miliary tuberculosis is prominent in the liver, bone marrow, spleen, and adrenals but can affect any organ.
    • Clinical Features: Based on organ involvement. Common features include fever, cough, night sweats, hemoptysis, and weight loss.
    • Diagnosis:
      • History
      • Clinical Examination
      • Investigations:
        • Chest X-ray
        • Detection of M. tuberculosis in specimens (sputum, biopsy) using Ziehl Neelsen staining
        • Biopsy of infected tissue
        • Polymerase Chain Reaction (PCR) amplification of TB bacilli
    • Spinal Tuberculosis (TB): The most common extrapulmonary form of tuberculosis. It is on the rise due to factors like increasing HIV coinfection, multidrug resistance of the organism, and global migration. Spinal TB primarily affects the lower thoracic and thoracolumbar area.

    Tuberculosis Pathogenesis

    • Mycobacterium tuberculosis (MTB) enters macrophages.
    • MTB replicates inside macrophages.
    • After 3 weeks, cell-mediated immunity (Th1 response) is stimulated by IL-12 and IL-18.
    • Th1 cells activate macrophages via release of interferon-gamma (INF-Y).
    • A granuloma is formed with central caseous necrosis.

    Tuberculosis Lesions

    • The final lesion of TB consists of a central area of caseous necrosis surrounded by activated macrophages (epithelioid macrophages), some of which fuse to form multinucleated giant cells (Langhans giant cells).
    • There is a surrounding rim of chronic inflammatory cells rich in lymphocytes, and fibrosis at the periphery.

    Primary Tuberculosis

    • Occurs after initial exposure to TB bacilli in non-immunized individuals of any age.
    • Grossly, it forms a small subpleural parenchymal lesion in the mid zone of the lung (Ghon focus) and spreads to the hilar lymph nodes. Both lesions are called the primary complex.
    • 95% of cases heal by fibrosis.
    • Some may enter a dormant state, and few may spread into the body forming progressive primary TB.

    Secondary Tuberculosis

    • Occurs as a reinfection or reactivation of dormant bacilli from primary infection when immunity is impaired.
    • Macroscopically, it occurs at the apex of the lung with marked damage in the lung parenchyma and cavity formation.
    • Heals by fibrosis or may spread forming progressive secondary TB.

    Systemic Miliary Tuberculosis

    • A form of progressive tuberculosis that occurs when bacteria disseminate through the systemic arterial system.

    Factors Influencing Infection

    • Outcome of infection depends on the balance between the aggressive mechanisms of the microorganism and the defense mechanisms of the host.
    • Microorganism factors:
      • Dose: number of microorganisms entering the body.
      • Virulence: their capacity to cause disease.
      • Invasiveness: ability to multiply and spread in the body.
      • Transmission: ability to pass to another suitable host.
    • Host factors (defense mechanisms):
      • Nonspecific defense mechanisms:
        • Mechanical barriers: e.g., intact skin.
        • Glandular secretion: acidity of gastric juices.
        • Secretion currents: flow of tear, diarrhea, etc.
        • Phagocytosis: by macrophages and neutrophils.
      • Specific defense (Immune response): by cell-mediated and humoral immunity.
    • Other factors:
      • Local factors: e.g., ischemia promotes infection.
      • Systemic factors: e.g., malnutrition.
      • Age: both the very young and very old are at increased risk of infection.

    Transmission of Microbes

    • Contact: such as Staphylococcus aureus and dermatophytes (fungi).
    • Respiratory droplets: Viruses and bacteria can be shed in respiratory secretions during talking, coughing, and sneezing.
    • Fecal-oral route: as in Cholera, Typhoid fever, hepatitis A, and others.
    • Sexual transmission: As in AIDS, Hepatitis B, Syphilis.
    • Vertical transmission from mother to fetus or newborn: As in Rubella.
    • Insect/arthropod vectors: As in malaria.

    Dissemination Inside the Body

    • Through the nervous system, as in rabies.
    • Spread within inflammatory cells, as in Mycobacterium tuberculosis within macrophages.
    • Spread through lymphatic vessels.
    • Spread through blood vessels.

    Mechanism of Bacterial Injury

    • Bacteria damage tissue through several mechanisms:
      • Release toxins that kill cells.
      • Release lytic enzymes (proteases, coagulase, and fibrinolysins) that destroy tissue and facilitate spread.
      • Elicit an inflammatory reaction that may destroy both bacteria and infected tissue.
      • Elicit an immune reaction that may damage tissues carrying the same antigen as the bacterium ("cross-reactivity").

    Bacterial Infections

    • Acute:
      • Catarrhal: Affects mucus membrane.
      • Serous: Affects serous cavities and produces serous fluid.
      • Pseudomembranous: Characterized by formation of a pseudo-membrane, as in diphtheria.
      • Pyogenic or suppurative (pus producing): e.g., abscess. Microorganisms stimulate secretion of IL-1 and TNF, which stimulate complement, attract neutrophils that secrete lytic enzymes, destroy tissue, and form abscesses.
    • Chronic

    Bacterial Infections in Blood

    • Bacteremia: Presence of small numbers of bacteria in the blood without multiplication. Patients have subclinical or minor symptoms and lesions.
    • Septicemia: Multiplication in the blood of highly pathogenic bacteria. It is a serious infection with profound toxemia in which bacteria have overwhelmed the host defenses. It results in serious consequences that may end in death. Clinically, tachycardia, hypotension, and shock occur.

    Gangrene

    • Digestion of dead tissue by saprophytic bacteria in a living body (necrosis with putrefaction).
    • Types of gangrene:
      • Gas gangrene
      • Dry gangrene
      • Wet gangrene

    Gas Gangrene

    • Caused by infection with Clostridia species (e.g., Clostridium perfringes).
    • Gain entry into tissues through open contaminated wounds.
    • Kill tissue by secreting potent exotoxins and then invade and digest the dead tissue.
    • Clostridium perfringes ferments sugar producing H2 and CO2, which collect as bubbles in the dead tissue, easily detectable by palpation.
    • Clinically, black discoloration and bad odor at the affected site (like the skin and subcutaneous tissue, intestine, etc.).

    Diphtheria

    • An acute, communicable disease caused by Corynebacterium diphtheriae.
    • Individual lesions are either microscopic or small, visible (2-mm) foci of yellow-white lesion scattered through the involved organ parenchyma.
    • These foci are called "miliary" because they resemble millet seeds.
    • Miliary lesions may expand and coalesce, resulting in larger lesions.
    • Miliary tuberculosis is most prominent in the liver, bone marrow, spleen, and adrenals, but can involve any organ.

    Systemic Miliary Tuberculosis

    • Miliary TB in the spleen appears as millet seeds.

    Clinical Features of Tuberculosis

    • Vary according to the organ involved.
    • Fever, cough, night sweats, hemoptysis, and weight loss.

    Diagnosis of Tuberculosis

    • I-History
    • II- Clinical examination.
    • III- Investigation:
      • X-ray
      • Detection of the microorganism in the specimen (sputum, biopsy) by Ziehl-Neelsen staining.
      • Biopsy of the infected tissue.
      • PCR amplification of Mycobacterium tuberculosis bacilli.

    Spinal Tuberculosis

    • The most common extrapulmonary form of tuberculosis.
    • On the rise due to factors such as increasing HIV co-infection, multidrug resistance of the organism, and global migration.
    • Most often affects the lower thoracic and thoracolumbar area and accounts for 50% of all musculoskeletal tuberculosis.

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    Infectious Diseases Lecture -1- PDF

    Description

    Explore the pathogenesis, lesions, and types of tuberculosis in this comprehensive quiz. Understand how Mycobacterium tuberculosis interacts with macrophages and the immune response that follows. Learn about the characteristics of TB lesions, including caseous necrosis and the types of TB, such as primary TB.

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