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Questions and Answers

What are the three main stages of infection?

  • Incubation, Convalescence, Exiting Host
  • Incubation, Prodromal, Convalescence (correct)
  • Invasion, Prodromal, Convalescence
  • Incubation, Prodromal, Invasion

    • The most diverse flora in the body is found in the gastrointestinal tract.

    False

    What is the definition of an endemic disease?

  • A disease that occurs only occasionally.
  • A disease that spreads rapidly and widely.
  • A disease that occurs worldwide.
  • A disease that occurs constantly in a particular population. (correct)

    • Why does the body's normal microbiota help prevent infection?

    <p>The normal microbiota competes with pathogens for nutrients and space, reducing their ability to establish themselves.</p> Signup and view all the answers

    Which of the following are considered portals of entry for pathogens?

    <p>Skin, respiratory tract, genitourinary tract.</p> Signup and view all the answers

    What is the function of a capsule in bacterial pathogenicity?

    <p>It helps the bacteria resist phagocytosis.</p> Signup and view all the answers

    Exotoxins are released from bacteria only after the cell is damaged.

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

    What is the role of a vector in disease transmission?

    <p>Vectors are living organisms, such as insects, that transmit pathogens from one host to another.</p> Signup and view all the answers

    What are some examples of zoonotic infections?

    <p>Rabies, leptospirosis, salmonellosis.</p> Signup and view all the answers

    Explain the concept of herd immunity.

    <p>Herd immunity occurs when a large proportion of the population is immune to a disease, which protects those who are not immune by reducing the spread of the disease.</p> Signup and view all the answers

    Which of the following is NOT a common example of a nosocomial infection?

    <p>Influenza.</p> Signup and view all the answers

    What is the difference between an exotoxin and an endotoxin?

    <p>Exotoxins are secreted by living bacteria, while endotoxins are released after the bacteria die and their cell walls break down.</p> Signup and view all the answers

    The primary habitat of a pathogen in the natural world is called a reservoir.

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

    What is the role of adhesins in the process of infection?

    <p>Adhesins are surface molecules on pathogens that bind to specific receptors on host cells, facilitating adherence and colonization.</p> Signup and view all the answers

    Which of the following is NOT a mechanism by which bacteria can evade phagocytosis?

    <p>Production of antibodies</p> Signup and view all the answers

    The R0 value represents the expected number of secondary cases produced by one infected person in a population that is not immune to the disease.

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

    _____ is a condition in which pathogenic microorganisms are transferred from one host to another.

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

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

    <p>Genetic inheritance</p> Signup and view all the answers

    A superantigen stimulates a very intense and specific immune response.

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

    What is the role of exotoxins in bacterial pathogenicity?

    <p>Exotoxins are toxic substances secreted by bacteria that damage host cells and tissues, contributing to the development of disease.</p> Signup and view all the answers

    The process of _____ is a crucial step in pathogenicity, as it allows bacteria to firmly attach to host cells, leading to the establishment of infection.

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

    What is the difference between a localized and a systemic infection?

    <p>A localized infection is confined to a specific area of the body, while a systemic infection spreads throughout the body via bloodstream or lymphatic system.</p> Signup and view all the answers

    Which of the following infectious diseases has the highest R number?

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

    The human body has a diverse range of microorganisms living on and within us, collectively known as microbiota.

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

    What is the difference between a commensal and a mutualistic relationship between a host and a microbe?

    <p>In a commensal relationship, one organism benefits while the other is neither harmed nor helped. In a mutualistic relationship, both organisms benefit from the interaction.</p> Signup and view all the answers

    The _____, or the basic reproduction number, indicates the average number of individuals that one infected individual will infect in a susceptible population.

    <p>R0</p> Signup and view all the answers

    Which of the following is NOT considered a major factor in the development of an infection?

    <p>Genetic inheritance</p> Signup and view all the answers

    Study Notes

    Microbe-Human Interactions

    • This lecture explored the fascinating world of microbes and their interactions with humans.
    • The lecture discussed the diverse world of microbes, their roles in maintaining health and causing disease, and the microbiome's influence on various aspects of human well-being.

    Infectious Disease Resurgence in Malaysia

    • Infectious diseases, once under control, are making a comeback in Malaysia.
    • This presentation explored the trends, causes, and challenges associated with this resurgence.

    Dengue Fever: A Persistent Threat

    • An infected Aedes mosquito bites a human, transmitting the dengue virus.
    • The virus multiplies within the body, causing symptoms like fever, headache, and muscle pain.
    • The infected person can transmit the virus to other mosquitoes, continuing the cycle.

    Common Infectious Diseases in Malaysia

    • Dengue remains the number one infectious disease in Malaysia.
    • In 2015, dengue topped the list of top five infectious diseases with 120,836 cases.
    • This was followed by tuberculosis (24,220 cases), hand-foot-and-mouth disease (HFMD - 22,578 cases), food poisoning (14,433 cases) and leptospirosis (8,291 cases).
    • As of September [year not specified], dengue cases stood at 71,641 cases, HFMD (26,030), tuberculosis (19,430), food poisoning (11,281), and measles (6,646).

    Chikungunya: The Comeback Virus

    • An infected Aedes mosquito bites a human, transmitting the virus.
    • The virus multiplies within the body, causing symptoms such as fever and joint pain.
    • The infected person can then transmit the virus to other mosquitoes.

    Malaria: Combating a Global Scourge

    • An infected female Anopheles mosquito bites a human, transmitting the malaria parasite.
    • The parasite multiplies and develops within the mosquito.
    • When the infected mosquito bites another human, the parasites are injected into the bloodstream.

    Tuberculosis: Tackling a Resurgent Disease

    • Tuberculosis (TB) is a bacterial infection primarily affecting the lungs.
    • TB spreads through the air when an infected person coughs, sneezes, or speaks.
    • Symptoms of TB include persistent cough, chest pain, fever, and weight loss.
    • Tuberculosis incidence per 100,000 people in various years are shown in a graph.

    Superbug Resistant to All Antibiotics

    • A superbug resistant to all antibiotics killed a Nevada woman.
    • Growing problem of antibiotic-resistant germs caused by overuse of these drugs.
    • Different antibiotic discovery eras are listed.

    Objectives

    • Objective 1: Relationship between normal microbiota and the host; Opportunistic microorganisms and pathogens.
    • Objective 2: Occurrence of disease, Severity of diseases, Patterns of infections.
    • Objective 3: Reservoirs of infection, Patterns of transmission and transmission of disease.
    • Objective 4: Major factors in development of an infection, Portals of entry, How bacterial pathogens penetrate host defenses, Mechanisms of exotoxin and endotoxin.

    Where Do Bacteria Live in My Body?

    • Bacteria live in various locations on and within the body, including the mouth, gums, nasal cavity, armpits, stomach, intestines, genitourinary system, joints, and toenails.

    Commensal Microbes: Coexisting with Humans

    • Skin microbes protect against pathogens and maintain skin health.
    • Gut microbes aid digestion, synthesize vitamins, and regulate immune function.
    • Respiratory microbes prevent colonization by harmful pathogens and contribute to immune system development.

    Pathogenic Microbes: Causing Disease

    • Pathogens invade host tissues and multiply, causing harm.
    • Pathogens possess toxins, enzymes, or other mechanisms to damage host cells.
    • Some pathogens evade the host's immune system.

    The Human Microbiome

    • Gut microbiome plays a key role in digestion, nutrient absorption, and immune system development.
    • Skin microbiome acts as a barrier, maintains skin integrity, and regulates immune responses.
    • Respiratory microbiome is involved in immune system development, infection protection, and lung health.
    • Vaginal microbiome maintains a healthy vaginal environment, preventing infections, and supporting reproductive health.

    Maintenance of the Normal Resident Flora

    • Normal flora (normal microbiota, commensal, residents, indigenous flora) is essential for human health.
    • Normal microflora creates an environment that may prevent infections and improve host defenses.
    • Only 10% of 500 different bacterial genera are pathogens.
    • Pathogens are infectious agents.

    Relationship between Normal Microbiota and the Host

    • Normal microbiota prevents overgrowth of pathogens through competitive exclusion or microbial antagonism.
    • Normal microbiota protect the host against colonization by competing for nutrients, producing substances that are harmful for pathogens, affecting conditions such as pH and available oxygen.
    • Eg. vaginitis: infection in the vagina is caused by an imbalance of normal microbiota.

    Maintenance of the Normal Resident Flora

    • Most areas of the body in contact with the external environment harbor resident microbes.
    • Internal organs, tissues, and fluids are typically microbe-free.
    • Transients are microbes that occupy the body for only short periods.
    • Hosts with compromised immune systems can be easily infected by these residents.

    Sterile (Microbe-Free) Anatomical Sites and Fluids

    • All internal tissues and organs, heart and circulatory system, liver, kidneys and bladder, lungs, brain and spinal cord, muscles, blood, urine in kidneys, ureters, bladder, cerebrospinal fluid, saliva, semen, and amniotic fluid are generally sterile

    Normal/resident flora in specific regions

    • Information about different anatomical sites and their common microorganisms is provided, including bacteria, fungi, and arthropods. (e.g., Skin, Gastrointestinal, Oral Cavity etc).

    Flora of the Human Skin

    • Skin is the largest and most accessible organ in the body.
    • Two populations are found on the skin: Residents (predictable and less influenced by hygiene) and Transients (influenced by hygiene).

    Flora of the Mouth

    • Mouth has the most diverse and unique flora.
    • Numerous adaptive niches exist.
    • Relatively high bacterial count in saliva (5 x 109 cells per milliliter).
    • Streptococci are the most common bacteria.

    Flora of the GIT

    • Gastrointestinal tract (GIT) has the largest amount of microbes per gram of feces (10^8–10^11).
    • The intestinal environment favors anaerobic bacteria and aerotolerant bacteria.
    • Intestinal bacteria contribute to normal intestinal odor.
    • Variations in flora distribution occur due to shifting conditions, like pH and oxygen tension.

    Initial Colonization of the Newborn

    • The uterus and its contents are normally sterile until shortly before birth.
    • Breaking of the fetal membrane exposes the infant, and subsequent handling and feeding introduce normal flora.

    Relationship between Normal Microbiota and the Host

    • Normal microbiota benefits the host by preventing pathogen overgrowth through competitive exclusion/ microbial antagonism. - The normal microbiota protect the host against colonization by competing for nutrients, producing substances harmful to pathogens. Factors affected include pH and available oxygen. - Example of vaginitis, when normal vaginal microbiota is altered.

    Relationship between Normal Microbiota and the Host: Terms

    • Microbiota and the host have a symbiotic relationship, with commensalism and mutualism as types.
    • Commensalism: One organism benefits while the other is unaffected (e.g., Staphylococcus on skin).
    • Mutualism: Both benefit (e.g., Lactobacillus producing vitamins).

    Opportunistic Microorganisms

    • Microorganisms like E. coli, typically harmless in the large intestine, can cause disease if they access other body parts.
    • Opportunistic pathogens cause disease when not in their normal habitat or in immunocompromised subjects (e.g., UTI, pulmonary infection, wounds, abscesses).

    Quick Recap of the First Objective (Overview)

    • Resident and commensal microbes (summary).
    • Transient microbes (summary).
    • Sterile internal organs and fluids (summary).
    • Common resident flora in the large intestine (summary).
    • Is E. coli resident flora of the urinary tract? (summary).
    • Relationship between resident flora and the host (summary).

    Objectives (Objective 2 & 3)

    • Occurrence of disease, Severity of Disease, Patterns of infections.
    • Reservoirs of infection, patterns of transmission, and transmission of disease.

    Occurrence of a Disease

    • Infection - pathogenic microbes penetrate host defenses, enter tissues, and multiply.
    • Infectious disease - infection damages tissue or organs. Includes incidence (new cases) and prevalence (total cases).

    Frequency of Occurrence to Classify Disease

    • Sporadic disease occurs occasionally (e.g., typhoid fever)
    • Endemic disease constantly occurs in a population (e.g., common cold)
    • Epidemic disease affects many people in a short period (e.g., initially COVID-19).
    • Pandemic disease is an epidemic affecting a large geographic area (e.g., worldwide COVID-19).

    Occurrence of a Disease

    • Common coronavirus outbreaks, including SARS-CoV, MERS-CoV, and COVID-19, and associated cases.

    R0

    • The basic reproduction number (R0) is the expected number of secondary cases generated by one infected person. It assumes a completely susceptible population, meaning most or all members haven't been vaccinated.
    • Measles has a high R0 value of 15, meaning on average, one person can spread measles to 15 others. The R0 values for different diseases and outbreaks are shown in a graph.

    R0

    • If the R-value is above 1, the number of cumulative cases will increase; but if it's below 1 the outbreak stops.

    Malaysia has successfully reduced the RO value

    • The conditional movement control order (CMCO) has reduced the infectability value (R-naught) to below 1.5.
    • Based on projection, over 1,000 Covid-19 cases would have been recorded if the RO was 1.5; but with the CMCO, the cases are down to 799.

    Patterns of Infection (Host Involvement)

    • Mixed infection: several microbes grow simultaneously at the infection site (polymicrobial)
    • Primary infection: initial infection.
    • Secondary infection: caused by an opportunistic pathogen after the primary infection.

    Patterns of Infection

    • Acute infection comes on rapidly, with severe but short-lived effects.
    • Chronic infections progress and persist over a long period.
    • Vaccination can prevent infectious diseases and develop herd immunity.

    Patterns of Infection

    • Localized infection: microbes enter and remain confined to a specific tissue (e.g., boils, abscesses).
    • Systemic infection: infection spreads to several sites (e.g., measles, influenza).
    • Focal infection: infectious agent breaks loose from a local infection and spreads to other tissues (e.g., tonsils, sinuses).

    Stages of Infection

    • Incubation period: interval between initial infection and first symptoms; agent multiplies at portal of entry. Ranges from hours to years.
    • Prodromal period: short period after incubation with early, mild symptoms.
    • Period of invasion: disease is most severe; maximum toxicity; tissue damage and symptoms.
    • Period of convalescence: body returns to pre-diseased state as immune system clears the agent.

    Objectives (Objective 3)

    • Reservoirs of infection, patterns of transmission, and transmission of disease.

    Terms (Transmission of Infectious Agents)

    • Communicable disease: when an infected host transmits an infectious agent to another, establishing infection.
    • Highly communicable disease is contagious: spreads easily.
    • Non-communicable disease: does not spread from host to host.

    Sources and transmission of microbes

    • Reservoir is the primary habitat of a pathogen.
    • Includes humans, animals, soil, water, and plants.

    Human Reservoirs

    • Carrier: individual who shelters a pathogen without showing symptoms.
    • Asymptomatic carrier: shows no symptoms.
    • Passive carrier: contaminated healthcare providers transferring pathogens.

    Animal Reservoirs

    • Zonotic diseases are infections indigenous to animals that can be transmitted to humans.
    • There are at least 150 zoonoses worldwide, and they comprise 70% of all new emerging diseases.

    Rabies outbreak in Sarawak

    • Sarawak is experiencing an increase in human and animal rabies cases.
    • The Minister of Food Industry and Regional Development urged the public to take precautions, specifically to attend to dog bites as soon as possible.

    Super-spreading Event of SARS

    • Location map of the ninth floor of the Hotel Metropole in Hong Kong showing where a super-spreading event of the severe acute respiratory syndrome (SARS) occurred.

    Patterns of Transmission (Contact Transmission)

    • Direct contact: Physical contact transmits infection without an intermediate host (e.g., sexually transmitted diseases).
    • Droplet transmission: Short-distance spread of microbes via mucous droplets; e.g., one sneeze can generate up to 20,000 droplets (e.g., Ebola, chicken pox).
    • Indirect contact: Non-living objects (fomites) transmit infectious agents (e.g., handkerchiefs, doorknobs).

    Patterns of Transmission (Vehicle Transmission)

    • Waterborne Transmission: Pathogens spread through contaminated water or sewage (e.g., Cholera by Vibrio cholerae).
    • Foodborne Transmission: incompletely cooked or contaminated foods (e.g., Salmonellosis, Salmonella typhi, Vibrio Cholerae ).
    • Airborne transmission: spread of infections via droplets, wind-borne particles containing pathogens (e.g., Tuberculosis and Measles)

    Droplet Precautions and Airborne Precautions

    • Illustrations comparing droplet size and distance and infection transmission.

    How Communicable Infectious Diseases are Acquired

    • Several modes of transmission, including contact, respiratory droplets, vertical transmission, biological vectors, and indirect transmission (vehicles).

    Common Zoonotic Infections

    • Various zoonotic diseases and their primary animal reservoirs, infection modes, and example of diseases.

    Leptospirosis

    • There have been 2,775 cases of rat urine infection and 23 deaths from leptospirosis in Malaysia.
    • The Health Ministry’s Disease Control Division director Dr. Chong noted that most sporadic cases were reported throughout the country, with rats as a reservoir and affecting humans.

    Transmission of Disease (Vectors)

    • Primarily arthropods.
    • Mechanical transmission (passive transport).
    • Biological transmission (active transmission).

    Hospital Acquired Infections

    • Nosocomial infections acquired or developed during a hospital stay.
    • Hospital environment harbors pathogens.
    • Procedures like surgeries spread drug-resistant microorganisms.

    Recap: Objectives 2 & 3

    • Disease classification (sporadic, endemic, epidemic, pandemic).
    • Basic reproduction number (R0).
    • Reservoir factors: human and animal.
    • Patterns of disease transmission (various types).
    • Examples of diseases (Influenza, Salmonellosis, TB, Typhoid, Cholera, Leptospirosis).

    Objectives (Objective 4)

    • Microbial mechanisms of pathogenicity.
    • Factors involved in the development of an infection.
    • Portals of entry, bacterial penetration of host defenses, and mechanisms of exotoxins and endotoxins.

    Major Factors in the Development of an Infection

    • Phase one: Finding a portal of entry (summary).
    • Phase two: Attaching Firmly (summary).
    • Phase three: Surviving Host Defenses (summary).
    • Phase four: Causes of damage and disease (summary).
    • Phase five: Exiting the Host (summary).

    The Different Stages

    • A summary of the different stages involved in the development of an infection.

    Recaps: Objectives 4

    • Important phases of infection (portal of entry, adhesion, virulence factors involving anti-phagocytosis, capsule, slime layer, enzymes, and toxins).

    Cell Wall Inhibitors, Ribosomes, DNA/RNA, Metabolic Pathways

    • Components of bacterial cells and processes targeted by antimicrobial drugs.

    "We rise by lifting others"

    • Inspirational quote from R. Ingersoll.

    Faecal Contamination and Typhoid Fever

    • Salmonella typhi cause typhoid fever, a serious bacterial disease transmitted through contaminated food or water, or via fecal-oral spread.
    • Bacteria colonizes the intestines causing invasive diarrhea and septicemia.

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