Part 3 - Microbial Pathogenesis and Disease

Contamination

Microorganisms are simply present without penetrating host defenses.

Infection

A pathogen penetrates host defenses and establishes itself in tissue.

Disease

An infection that disrupts tissues/organs and produces signs and symptoms.

Acute disease

Severe but short-lived disease (e.g., influenza).

Chronic disease

Persists and progresses over a long period (e.g., tuberculosis).

Subacute disease

A disease intermediate between acute and chronic duration.

Latent disease

Involves periods of inactivity between attacks (e.g., herpes).

Local infection

Microbe is confined to a specific tissue (e.g., skin abscess).

Focal infection

Microbe breaks away from a local site and spreads via blood or lymph.

Systemic infection

Infection widely distributed in many tissues (e.g., septicemia).

Mixed infection

Several species of organisms present simultaneously.

Pathogenicity

The ability of a parasitic organism to cause disease.

Virulence

The degree or intensity of pathogenicity.

Virulence factor

A microbe characteristic or structure that contributes to its virulence.

Attenuation

The weakening of a pathogen's disease-producing ability.

Fimbriae (pili)

Adhesion structures allowing bacteria to attach and initiate colonization.

Capsules

Polysaccharide coats protecting bacteria from phagocytosis and immune recognition.

Coagulase

Enzyme that forms a fibrin clot around bacteria to protect from immune cells.

Leukocidins

Exotoxins that kill or damage white blood cells, crippling immunity.

Hemolysins

Exotoxins that lyse red blood cells to release iron and nutrients.

Normal microflora

Organisms living on or in the body that do not normally cause disease.

Resident microflora

Microbes that are always present in specific body locations.

Transient microflora

Organisms present temporarily under certain conditions.

Commensalism

A relationship where one organism benefits and the other is unaffected.

Pathogen

Any parasitic organism that causes infectious disease.

Opportunist

Harmless microflora causing disease when defenses fail or flora is disturbed.

Nosocomial infection

An infection acquired in a hospital or medical facility.

Iatrogenic disease

A condition caused directly by medical treatment.

Primary infection

The initial infection in a host.

Secondary infection

A second infection following a primary infection due to weakened defenses.

Superinfection

Secondary infection arising from antibiotic destruction of normal microflora.

Sign

Objective evidence of disease observed by an examiner.

Symptom

Evidence of disease perceived or sensed by the patient.

Syndrome

A complex of signs and symptoms that together define a disease.

Sequelae

Lasting effects that remain after recovery from an acute disease.

Septicemia

Microorganisms multiplying in the blood in large numbers.

Bacteremia

Bacteria present in the blood without necessarily multiplying.

Viremia

Viruses present in the blood without necessarily multiplying.

Toxemia

Bacterial toxins present in the blood causing symptoms.

Communicable disease

An infected host can transmit the infectious agent to another host.

Noncommunicable disease

Does not spread from host to host; acquired through special circumstances.

Horizontal transmission

Pathogen passed between individuals of the same generation.

Vertical transmission

Pathogen passed from parent to offspring.

Exogenous disease

Caused by a pathogen coming from outside the host.

Endogenous disease

Caused by the host's own microbiota when resistance drops.

Zoonosis

An infection indigenous to animals that is naturally transmissible to humans.

Mechanical vector

Transports an infectious agent on its body surface without being infected.

Biological vector

Actively participates in the pathogen's life cycle.