Podcast
Questions and Answers
What are the primary factors contributing to the high mortality of infectious diseases in older adults and immunosuppressed individuals?
What are the primary factors contributing to the high mortality of infectious diseases in older adults and immunosuppressed individuals?
What is one way microorganisms can breach the protective barriers of healthy individuals?
What is one way microorganisms can breach the protective barriers of healthy individuals?
What role do intact keratinized epidermis play in preventing infections?
What role do intact keratinized epidermis play in preventing infections?
Which local defense mechanism of the gastrointestinal tract helps to kill certain organisms?
Which local defense mechanism of the gastrointestinal tract helps to kill certain organisms?
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What is the effect of peristalsis in the gastrointestinal tract?
What is the effect of peristalsis in the gastrointestinal tract?
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Which of the following is NOT a method by which microorganisms can enter the body?
Which of the following is NOT a method by which microorganisms can enter the body?
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What protective component is found in the gut and is crucial for preventing infections?
What protective component is found in the gut and is crucial for preventing infections?
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How does malnutrition affect the incidence of infectious diseases?
How does malnutrition affect the incidence of infectious diseases?
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Which of the following mechanisms is used by pathogens to resist antimicrobial peptides?
Which of the following mechanisms is used by pathogens to resist antimicrobial peptides?
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What is a potential effect of chronic inflammation caused by host immune responses?
What is a potential effect of chronic inflammation caused by host immune responses?
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How do pathogens evade recognition by CD4+ and CD8+ T cells?
How do pathogens evade recognition by CD4+ and CD8+ T cells?
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What does the term 'latent infection' refer to in the context of immune evasion?
What does the term 'latent infection' refer to in the context of immune evasion?
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Which condition is linked to antibody deficiencies, particularly in the case of X-linked agammaglobulinemia?
Which condition is linked to antibody deficiencies, particularly in the case of X-linked agammaglobulinemia?
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What is a consequence of immune complexes in host-pathogen interactions?
What is a consequence of immune complexes in host-pathogen interactions?
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Which of the following describes a mechanism pathogens use to resist killing by phagocytes?
Which of the following describes a mechanism pathogens use to resist killing by phagocytes?
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What type of inflammation can prevent the spread of certain pathogens but may also lead to tissue damage?
What type of inflammation can prevent the spread of certain pathogens but may also lead to tissue damage?
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What is a major determinant of tissue tropism for viruses?
What is a major determinant of tissue tropism for viruses?
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Which of the following mechanisms can lead to direct damage to host cells by viruses?
Which of the following mechanisms can lead to direct damage to host cells by viruses?
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What type of receptors do HIV viruses specifically target on T cells?
What type of receptors do HIV viruses specifically target on T cells?
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Why do enteroviruses primarily replicate in the intestine?
Why do enteroviruses primarily replicate in the intestine?
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What is one consequence of antiviral immune responses during viral infection?
What is one consequence of antiviral immune responses during viral infection?
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Rhinoviruses have a specific environmental preference for infection. What is it?
Rhinoviruses have a specific environmental preference for infection. What is it?
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Which mechanism is NOT associated with the transformation of infected cells into tumor cells?
Which mechanism is NOT associated with the transformation of infected cells into tumor cells?
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What role do physical barriers play in viral infection?
What role do physical barriers play in viral infection?
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What is the primary site of latency for HSV-1 and HSV-2 infections?
What is the primary site of latency for HSV-1 and HSV-2 infections?
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Which of the following virus types is responsible for corneal blindness in the United States?
Which of the following virus types is responsible for corneal blindness in the United States?
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What distinguishes the α-group of herpesviruses from the β-group?
What distinguishes the α-group of herpesviruses from the β-group?
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Which of the following diseases is NOT associated with herpes simplex viruses?
Which of the following diseases is NOT associated with herpes simplex viruses?
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What morphological feature is characteristic of HSV-infected cells?
What morphological feature is characteristic of HSV-infected cells?
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Which symptom is associated with herpetic whitlow?
Which symptom is associated with herpetic whitlow?
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What type of cells do β-group herpesviruses commonly infect?
What type of cells do β-group herpesviruses commonly infect?
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Which virus is known to cause exanthem subitum, also referred to as roseola infantum?
Which virus is known to cause exanthem subitum, also referred to as roseola infantum?
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Which condition is a serious complication associated with Epstein-Barr Virus (EBV) in patients with immunodeficiency?
Which condition is a serious complication associated with Epstein-Barr Virus (EBV) in patients with immunodeficiency?
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Which of the following conditions is specifically caused by Epstein-Barr Virus (EBV)?
Which of the following conditions is specifically caused by Epstein-Barr Virus (EBV)?
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Which of the following bacteria is NOT classified as a gram-positive cocci?
Which of the following bacteria is NOT classified as a gram-positive cocci?
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What type of infections are primarily caused by Staphylococcus aureus?
What type of infections are primarily caused by Staphylococcus aureus?
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Which bacterium is associated with pharyngitis and scarlet fever?
Which bacterium is associated with pharyngitis and scarlet fever?
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Which of the following clinical presentations is associated with Streptococcus pneumoniae?
Which of the following clinical presentations is associated with Streptococcus pneumoniae?
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What type of infection is primarily associated with Escherichia coli?
What type of infection is primarily associated with Escherichia coli?
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Which of the following species is a gram-negative bacterium associated with pneumonia?
Which of the following species is a gram-negative bacterium associated with pneumonia?
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What is the primary cause of Chancroid?
What is the primary cause of Chancroid?
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Which bacterium is known for utilizing a type III secretion system to inhibit phagocytosis?
Which bacterium is known for utilizing a type III secretion system to inhibit phagocytosis?
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What type of lesion is initially observed with Granuloma inguinale?
What type of lesion is initially observed with Granuloma inguinale?
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Which of the following is a characteristic of untreated Chancroid?
Which of the following is a characteristic of untreated Chancroid?
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YopJ from Yersinia pestis plays which role in the infection process?
YopJ from Yersinia pestis plays which role in the infection process?
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What is the typical time frame for the development of symptoms after the inoculation of Chancroid?
What is the typical time frame for the development of symptoms after the inoculation of Chancroid?
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What type of necrosis is observed in the histopathology of Chancroid lesions?
What type of necrosis is observed in the histopathology of Chancroid lesions?
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What is a common complication of untreated Granuloma inguinale?
What is a common complication of untreated Granuloma inguinale?
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Study Notes
Micro-Infectious Diseases
- The material is for educational purposes only
- Images and videos used in the presentation aren't owned by the lecturer
- The presentation used various sources to facilitate discussion
General Principles of Microbial Pathogenesis
- Infectious diseases remain a significant health concern worldwide, despite vaccines and antibiotics.
- Immunosuppressed individuals and those with chronic diseases are particularly vulnerable.
- Factors contributing to these issues include: inadequate access to healthcare, malnutrition
- Six of the top ten causes of death are infectious diseases
- Most deaths from infectious diseases occur in children
- Respiratory and diarrheal infections cause the greatest number of deaths
How Microorganisms Cause Disease
- Routes of entry:
- Breaching epithelial surfaces
- Inhalation
- Ingestion
- Sexual transmission
- Healthy individuals:
- Entry through respiratory tract, gastrointestinal tract, or genitourinary tract by virulent microorganisms.
- Skin (injured) is invaded by less virulent microorganisms.
General Principles of Microbial Pathogenesis (Skin)
- Protection via:
- Intact keratinized epidermis - strong mechanical barrier
- Antimicrobial fatty acids
- Defensins - small peptides toxic to bacteria
- Intact skin can be traversed by:
- Larvae of Schistosoma - release enzymes dissolving keratinocytes interconnections
- Dermatophytes
General Principles of Microbial Pathogenesis (GIT)
- Transmission through contaminated food and drinks
- Local defenses:
- Acidic gastric secretions - highly effective at killing organisms (Vibrio cholerae is reduced to 10,000 fold by stomach acid).
- Viscous layer of mucus throughout the gut.
- Pancreatic enzymes
- Bile detergents
- IgA Abs - from lymphoid tissues (Peyer's patches)
- Peristalsis - prevents organism overgrowth.
- Normal gut flora - creates a microenvironment preventing colonization of potential pathogens (e.g., Clostridium difficile)
General Principles of Microbial Pathogenesis (Examples)
- Site | Major Local Defense(s) | Basis for Failure of Local Defense | Pathogens (examples)
- Skin | Epidermal barrier | Mechanical defects (punctures, burns, ulcers) | S. aureus, Candida albicans
- GI Tract | Epithelial barrier, acidic secretions, bile and pancreatic enzymes, normal protective flora | Attachment, local proliferation, local/external invasion, acid-resistant cysts and eggs | Vibrio cholerae, Giardia, Shigella
- Respiratory Tract | Mucociliary clearance | Ciliary paralysis by toxins, viral attacks | Influenza viruses, M. pneumoniae
- Urogenital Tract | Resident alveolar macrophages, urination, normal vaginal flora, intact epidermal/epithelial | Resistance to killing, microbial attachment | E. coli, C. albicans
Gastrointestinal Tract Infections
- Local defenses are circumvented by pathogens, or when weakened, normal flora can cause disease.
- Examples:
- Norovirus - non-enveloped virus, resistant to acid, bile and pancreatic enzymes
- Cystic protozoans
- Eggs of Helminths - acid-resistant coat
- Shigella
Enteropathogenic Pathogens and Gastrointestinal Disease
- Enteropathogenic pathogens establish symptomatic disease through several distinct mechanisms:
- Adsorption and local proliferation (e.g., Vibrio cholerae, enterotoxigenic E. coli)
- Adsorption and mucosal invasion (e.g., Shigella, Salmonella enterica, Campylobacter jejuni, Entamoeba histolytica)
- "Hijacking" of host pathways of antigen uptake (e.g., Poliovirus)
Respiratory Tract
- Inhalation of dust/aerosols
- Particles inversely proportional to their size are trapped in the mucociliary blanket
- Particles < 5 microns are phagocytosized by resident alveolar macrophages or neutrophils recruited by cytokines
Urogenital Tract
- Protection from infection through regular emptying during micturition.
- Factors:
- Anatomy - Females have shorter urethras, resulting in more UTIs
- Obstruction of urinary flow
- Reflux of urine
- Antibiotic use - killing lactobacilli
- Trauma to cervical epithelium
Vertical Transmission
- Transmission from mother to fetus/newborn:
- Placental-fetal transmission (e.g., Rubella infections)
- Transmission during birth (e.g., gonococcal and chlamydial conjunctivitis)
- Postnatal transmission through maternal milk (e.g., cytomegalovirus, HIV, hepatitis B virus)
Spread and Dissemination of Microbes Within the Body
-
Disease-causing organisms can remain localized or invade tissues.
-
Spread via lymphatics, blood, or nerves
- Example: S. aureus spreads through tissues, lymphatic vessels, and regional lymph nodes to blood (bacteremia), then to distant organs such as the heart and bone
-
Exit from the body: skin shedding, coughing, sneezing, urination, defecation, sexual contact, insect vectors
Host-Pathogen Interactions
- Factors influencing the outcome of infection:
- Virulence of the microbe
- Nature of the host immune response (eliminate, exacerbate, principal cause of tissue damage)
- Immune evasion:
- Antigenic variation
- Resistance to antimicrobial peptides
- Resistance to killing by phagocytes
- Evasion of apoptosis and host cell metabolism manipulation
- Resistance to cytokine-, chemokine- and/or complement-mediated host defense
- Evasion of recognition by CD4+ helper T cells and CD8+ cytotoxic T cells
- Immunoregulatory mechanisms to downregulate anti-microbial T-cell responses
- "Lie low" by establishing a latent infection
- Genetic reassortment, high mutation rate, and diverse serotypes can contribute to the development of infectious diseases and cause varying degrees of infection.
- Mechanisms of Host Immunity Damage:
- Inflammation (granulomas- TB)
- Inflammation Due To Immune Complexes (examples: rheumatic fever, glomerulonephritis)
- Chronic Inflammation
- Cancer
- Defects in neutrophil function
- Defects in Toll-like receptor (TLR) signaling pathways (Mutations in MyD88 or IRAK4 predispose to pyogenic bacterial infections and impair TLR3 responses)
- T-cell defects (Inherited mutations can impair the generation of TH1 and TH17 cells resulting in atypical mycobacterial infections or chronic mucocutaneous candidiasis respectively).
Mechanisms of Viral Injury
-
Enter cells > replication > direct damage to the host cells
-
Tropism - preference for specific cells by viruses
- Factors include the presence of viral receptors on host cells and physical barriers
- Example: -Enteroviruses can resist degradation in the intestine by acids, bile and digestive enzymes. -Rhinoviruses only reproduce in the upper respiratory tract due to their optimal temperature requirements.
-
Mechanisms include direct cytopathic effects, anti-viral immune responses, and transformation of infected cells into malignancies
-
Viral receptors that bind to particular proteins on the surface of host cells include HIV glycoprotein gp120 interacting with CD4 on T cells, chemokine receptors CXCR4 (T cells) and CCR5 (macrophages), and EBV binding to complement receptor 2.
Mechanisms of Bacterial Injury
- Bacterial virulence depends on the microbe's ability to adhere to host cells, invade cells and tissues, and/or deliver toxins.
- Bacterial adhesins bind to host cells or the ECM
- Pili are filaments on the surface of bacteria which allow bacteria to adhere to host cells
- Mobile genetic elements (plasmids, bacteriophages) move genes between microbes that influence pathogenicity and drug resistance
- Virulence of intracellular bacteria including ways bacteria can inhibit host protein synthesis, replicate rapidly, lyse host cells within hours
- Bacteria evade the immune responses by producing toxins- bacterial proteins that cause cellular injury and disease including endotoxins and exotoxins such as proteases, hyaluronidases, coagulases, or fibrinolysins)
- Bacterial toxins that alter intracellular signaling or regulatory pathways, such as neurotoxins (e.g., Clostridium botulinum and Clostridium tetani), disrupt neurotransmitter release causing paralysis
- Superantigens, bacterial toxins that stimulate large numbers of T cells, generating a massive immune response
Sexually Transmitted Diseases
- STIs can be transmitted from the urethra, vagina, cervix, rectum, or oral pharynx.
- Infection with one STI increases the risk of additional STIs (examples N. gonorrhoeae, C. trachomatis).
- A pregnant woman can pass STIs to the fetus or child (e.g. C. trachomatis, HSV, HIV), causing serious damage.
Spectrum of Inflammatory Responses to Infection
- Suppurative (Purulent) Inflammation: Increased vascular permeability, leukocytic infiltration, and mainly neutrophils are indicative of inflammation; neutrophilic massing and tissue necrosis form pus (e.g., pneumococcal pneumonia).
- Mononuclear and Granulomatous Inflammation: Accumulation of activated macrophages ("epithelioid" cells), possible fusion to form giant cells. An area of caseous necrosis can also form (e.g., secondary syphilis).
- Cytopathic-Cytoproliferative Reaction: Characterized by cell necrosis, or cellular proliferation, usually with sparse inflammatory cells (e.g., Herpesvirus).
Tissue Necrosis
- Clostridium perfringens and other organisms cause rapid necrosis (gangrenous necrosis) from powerful toxins.
- Lesions resemble infarcts without inflammatory cells.
Chronic Inflammation and Scarring
- Many infections induce chronic inflammation that can lead to complete healing or extensive scarring (e.g., chronic HBV infection causing cirrhosis).
- Scarring involves dense fibrous septae surrounding newly generated hepatocytes.
Special Techniques for Diagnosing Infections
-
Gold standards for diagnosis:
- Culture
- Biochemical or serologic identification
- Molecular diagnosis
-
Specific techniques and corresponding infectious agents:
- Gram Stain: Most bacteria
- Acid-fast Stain: Mycobacteria, Nocardia
- Silver Stain: Fungi, Legionella, Pneumocystis
- Periodic Acid-Schiff (PAS): Fungi, Amebae
- Mucicarmine: Cryptococci, Fungi
- Giemsa: Campylobacter, Leishmania, Malaria (parasites)
- Antibody stains: All classes
- DNA probes: All Classes
- Culture: All classes
Viral Infections
- Common viral diseases and their associated organ systems are presented.
Acute (Transient) Infections
- Measles: Leading cause of vaccine-preventable death, single-stranded RNA virus. Cells are invaded, causing respiratory droplets.
- Mumps: Pain and swelling of salivary glands.
- Poliovirus: Acute systemic viral infection causing paralysis of limb and respiratory muscles. Fecal-oral route of transmission.
- Viral Hemorrhagic Fevers: Systemically caused by enveloped RNA viruses from several families (Arenaviruses, Filoviruses, Bunyaviruses, and Flaviviruses). Spread person to person.
Chronic Latent Infections (Herpesviruses)
- Latency is the persistence of viral genomes in cells.
- Herpesviruses are prevalent in humans.
- Herpes simplex viruses (HSV 1 and 2), varicella-zoster virus (VZV), and cytomegalovirus (CMV).
Chronic Productive Infections
- Hepatitis B Virus: Part of the hepadnavirus DNA virus family that can be transmitted percutaneously, perinatal, and sexually.
- Cellular injury from the host immune response to infected hepatocytes leads to the disease.
Transforming Infections
- Epstein-Barr virus (EBV): Can lead to infectious mononucleosis and malignancies such as lymphomas and nasopharyngeal carcinoma.
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Description
Explore the essential concepts related to infectious diseases and the immune system in this quiz. The questions cover aspects such as barriers to infection, local defense mechanisms, and the impact of malnutrition on disease incidence. Perfect for students studying microbiology or immunology.
