Infectious Diseases and Epidemiology — Key Concepts

A set of question-and-answer style flashcards covering key topics from infectious disease and epidemiology, including symbiosis, microbiota, pathogenesis, transmission, reservoirs, classification, epidemiology measures, and nosocomial infections.

What is symbiosis and what are the three types of symbiotic relationships?

Symbiosis means 'to live together'; the three types are mutualism, commensalism, and parasitism.

Define normal microbiota.

Organisms that colonize body surfaces without normally causing disease.

Differentiate resident microbiota from transient microbiota.

Resident microbiota persist for life and are usually commensal; transient microbiota remain for hours to months and cannot persist due to competition, defenses, or changes.

Which part of the respiratory tract has the most diverse resident microbiota and which part has none?

The nose has the most diverse resident microbiota; alveoli have no natural microbiota.

What is an opportunistic pathogen?

Normal microbiota or harmless microbes that can cause disease under immune suppression, disruption of normal microbiota, or unusual sites.

Contamination vs. infection: how do they differ?

Contamination is mere presence of microbes; infection occurs when microbes evade defenses, multiply, and establish in the body.

Name the four major routes of entry for pathogens.

Skin, mucous membranes, placenta, and parenteral route.

Give an example of a pathogen that can cross the placenta and its associated condition.

Toxoplasma gondii — toxoplasmosis.

Infection vs disease.

Infection is the invasion by a pathogen; disease (morbidity) occurs when the pathogen alters normal body functions.

Differentiate symptoms and signs with examples.

Symptoms are subjective (e.g., headache); signs are objective (e.g., fever, rash).

What are Koch’s postulates (briefly)?

1) The microbe must be present in every case of the disease. 2) It must be isolated in pure culture. 3) The disease must be reproduced in a healthy host by inoculation. 4) The microbe must be recovered from the experimentally infected host.

List the five stages of infectious disease.

Incubation, prodromal, illness, decline, convalescence.

Portals of entry for pathogens.

Mucous membranes (respiratory, gastrointestinal, genitourinary, conjunctiva), skin, and parenteral route.

What are virulence factors?

Factors that increase pathogenicity: adhesion, biofilms, extracellular enzymes, toxins (exotoxins and endotoxins), and antiphagocytic factors.

Differentiate exotoxins and endotoxins.

Exotoxins are proteins secreted by live bacteria (often Gram-positive); Endotoxins are lipid A of LPS released when Gram-negative bacteria die.

Which organisms secrete exotoxins vs. endotoxins?

Exotoxins: secreted by live bacteria (often Gram-positive). Endotoxins: part of the outer membrane of Gram-negative bacteria (LPS).

What are the stages of pathogenesis after entering the host?

Adherence, penetration/evasion of defenses, and damage to host tissues, with potential exit via portals of exit.

Define portals of exit.

Pathogens exit the host via routes similar to entry (e.g., respiratory secretions, saliva, feces, urine, blood, semen, vaginal secretions, tears).

What is the concept of reservoirs of infection?

Sites where pathogens are maintained and can serve as sources of infection: animal reservoirs (zoonoses), human carriers, and nonliving reservoirs (soil, water, food).

What are zoonoses?

Diseases naturally spread from animals to humans; can be acquired by direct contact or via vectors (e.g., fleas).

What is a human carrier?

An infected individual who is asymptomatic but can transmit the pathogen; some may develop illness later or never.

What are nonliving reservoirs?

Soil, water, and food can harbor microorganisms, often via contamination by feces or urine.

What are the three modes of transmission?

Contact transmission, vehicle transmission, and vector transmission.

How are infectious diseases classified?

By the body system affected, taxonomic group of the causative agent, longevity/severity, and mode of spread (local vs systemic; acute vs chronic; STDs, etc.).

Define local infection vs systemic infection.

Local infection is confined to a small region; systemic infection involves multiple systems and may spread via blood or lymph.

What is a primary infection and a secondary infection?

Primary infection is the initial infection; secondary infection follows, often due to opportunistic pathogens.

What do incidence and prevalence measure in epidemiology?

Incidence: new cases in a given area/time. Prevalence: total cases in a given area/time.

Define endemic, sporadic, epidemic, and pandemic.

Endemic: disease exists permanently in a region. Sporadic: occurs occasionally. Epidemic: new cases exceed normal expectations. Pandemic: epidemic spread worldwide.

What is a nosocomial infection?

An infection acquired in a health care facility.

What are the three types of nosocomial infections?

Exogenous (from the health care environment), endogenous (from patient’s own microbiota), and iatrogenic (caused by medical actions).

List common risk factors for nosocomial infections.

Endotracheal intubation, bladder catheter, IV catheter, hyperalimentation, immunosuppression, operative procedures.

What is the most effective method to reduce nosocomial infections?

Hand washing.

What is the germ theory of disease?

Disease is caused by infections by pathogenic microorganisms; proven by principles like Koch’s postulates.

How is normal microbiota acquired in early life?

Development in the womb is typically free of microorganisms; microbiota begin to develop during birth; most resident microbiota established in the first months of life.

Which statement best describes asymptomatic infections?

Infections with no symptoms (asymptomatic) but may have signs or be subclinical.

Give an example of a bacterium associated with placental crossing and abortion risk.

Listeria monocytogenes (Listeriosis) can cross placenta and cause abortion or fetal harm.

Give an example of a virus associated with congenital defects when crossing the placenta.

Rubivirus (rubella) can cause severe birth defects; Cytomegalovirus can cause multiple fetal issues.

Where in the body are resident microbiota found?

On surfaces and openings of the body such as nose, mouth, skin, and mucous membranes; specific sites vary by region.

What is the role of adhesion factors in pathogenesis?

Adhesion factors help microbes attach to host tissues, enabling colonization and infection.

What is an epithelium’s role in preventing infection?

Epithelial surfaces and immune defenses help prevent colonization and invasion by pathogens.