Microbial Pathogenicity and Epidemiology

Flashcards covering the terminology, mechanisms of pathogenicity, types of toxins, and epidemiology principles from the lecture notes.

Pathology

The scientific study of disease, concerned with its etiology, pathogenesis, and effects.

Infection

The invasion or colonization of the body by pathogenic microorganisms, or the presence of microbes in a body part where they are not normally found.

Disease

An alteration in the state of health occurring when an infection results in any change from the normal physiological condition.

Infectious disease

A disease that results specifically from the growth of microorganisms.

Communicable disease

An infectious disease that can be transmitted from one person to another, such as Rabies, gonorrhea, and measles.

Contagious disease

A type of communicable disease that is easily transmitted from person to person via direct contact, such as a cold, Influenza, and SARS.

Pathogenesis

The specific process or sequence of events by which a disease develops.

Etiology

The study of the root cause of a disease.

Koch's Postulates

A series of steps used to determine the etiology of a disease: 1. Isolate microbe from diseased animal; 2. Grow in pure culture and identify; 3. Inoculate healthy animal; 4. Reproduce disease; 5. Re-isolate and identify.

Virulence factors

Complex clinical substances produced by pathogenic microbes that determine their ability to produce disease.

$LD_{50}$ (Lethal Dose for $50\%$)

The number of microbes in a dose that will kill $50\%$ of inoculated test animals; used to express the potency of a toxin.

$ID_{50}$ (Infectious Dose for $50\%$)

The dose required to produce a demonstrable infection in $50\%$ of test animals.

Bacillus anthracis $ID_{50}$ (Skin)

$10$-$50$ endospores.

Bacillus anthracis $ID_{50}$ (Inhalation)

$10,000$-$20,000$ endospores.

Bacillus anthracis $ID_{50}$ (Ingestion)

$250,000$-$1,000,000$ endospores.

Adherence

The process by which pathogens attach to host tissues using surface molecules called adhesins or ligands that bind to receptors.

Biofilms

Microbial communities that share nutrients and help pathogens resist host defenses.

Glycocalyx

A viscous, gelatinous polymer external to the cell wall made of polysaccharide or polypeptide; includes organized capsules and unorganized slime layers.

Capsule

An organized glycocalyx firmly attached to the cell wall that contributes to virulence by preventing phagocytosis.

M protein

A cell wall component of Streptococcus pyogenes that helps the bacterium resist phagocytosis.

Opa protein

A cell wall protein of Neisseria gonorrhoeae that allows the pathogen to attach to host cells.

Mycolic acid (Waxy lipid)

A cell wall component of Mycobacterium tuberculosis that resists digestion by phagocytes.

Coagulases

Bacterial enzymes that coagulate fibrinogen in the blood.

Kinases

Bacterial enzymes that digest fibrin clots.

Hyaluronidase

An enzyme that digests polysaccharides that hold host cells together.

Collagenase

An enzyme that breaks down the protein collagen.

IgA proteases

Enzymes produced by some bacteria to destroy IgA antibodies.

Antigenic variation

The ability of some pathogens to alter their surface antigens so that they are no longer recognized by host antibodies.

Invasins

Surface proteins produced by bacteria that rearrange actin filaments of the host cytoskeleton, causing membrane ruffling.

Exotoxins

Proteins (usually A-B toxins) produced inside mostly gram-positive bacteria as part of growth and secreted during log phase; they are heat unstable and have high toxicity.

Endotoxins

Lipid portions of lipopolysaccharides (Lipid A) located in the outer membrane of gram-negative cell walls; they are released when bacteria die or divide and are heat stable.

Siderophores

Proteins secreted by pathogens that bind iron more tightly than the host's iron-binding proteins.

Incubation period

The interval between initial infection and the first appearance of any signs or symptoms.

Prodromal period

A short period following incubation characterized by early, mild, and vague symptoms of disease.

Period of illness

The phase when the disease is most severe and the person exhibits overt signs and symptoms.

Period of decline

The phase where signs and symptoms subside, but the patient may be vulnerable to secondary infections.

Convalescence

The period during which the body returns to its pre-diseased state and health is restored.

Reservoirs of infection

Natural hosts and habitats (living or non-living) that provide a pathogen with adequate conditions for survival; reservoirs are usually unaffected by the pathogen.

Vectors

Living organisms, often biting arthropods like mosquitoes or ticks, that actively transmit pathogens to other hosts.

Fomites

Non-living objects (e.g., bedding, syringes, cups) that can transmit infectious agents between hosts.

Mechanical transmission

The passive transport of pathogens on the insect's feet or other body parts.

Biological transmission

An active process where the pathogen reproduces in the vector and is transmitted via bites or feces.

Sepsis

A toxic inflammatory condition arising from the spread of microbes or their toxins from a focus of infection.

Bacteremia

The presence of bacteria in the blood.

Septicemia

Also known as blood poisoning; the systemic infection arising from the growth of bacteria in the blood.

Toxemia

The presence of toxins in the blood.

Viremia

The presence of viruses in the blood.

Primary infection

An acute infection that causes the initial illness.

Secondary infection

An opportunistic infection that occurs after a primary (predisposing) infection has weakened host defenses.

Subclinical disease

An infection that does not cause any noticeable signs or symptoms; also called an inapparent infection.

Sporadic disease

A disease that occurs only occasionally in a population.

Endemic disease

A disease constantly present in a population or region with relatively low spread.

Epidemic disease

A sudden increase in the number of cases of a disease spreading through a large population.

Pandemic disease

An epidemic disease that occurs worldwide or across several countries and continents.

Herd immunity

The protection of susceptible individuals in a population through the presence of a large number of immune individuals.

Prevalence

The total number of people in a population who develop a disease at a specified time, including both old and new cases.

Incidence

The number of people in a population who develop a disease during a specific period of time; indicates the rate of new cases.

Sensitivity formula

$$\text{Sensitivity} = \frac{TP}{TP + FN}$$

Specificity formula

$$\text{Specificity} = \frac{TN}{FP + TN}$$