Chapter 10: Mechanisms of Infectious Disease

Vocabulary flashcards covering key concepts from the lecture notes on Mechanisms of Infectious Disease (Chapters 10, pages 1–9).

Basic objectives of organisms

All living organisms share goals of survival and reproduction and must extract essential nutrients from the environment for growth.

Normal microflora

Most organisms in the human body, especially the GI tract, with over 300 species that harmlessly inhabit exposed surfaces.

Infectious disease

A disease state resulting from interaction with another organism, harming the host when pathogens overcome defenses.

Host

Any organism capable of supporting the nutritional and physical growth requirements of another.

Colonization

Establishing a presence and multiplication of a living organism on or within the host; a necessary first step in infection.

Infection

Multiplication of an organism within a host that results in injury or pathologic damage.

Pathogen

Microorganisms so virulent that they are rarely found in the absence of disease; capable of causing disease.

Saprophyte

Free-living organisms obtaining growth from dead or decaying organic material; typically harmless but can cause opportunistic disease.

Opportunistic pathogens

Microorganisms (including saprophytes and normal flora) that can produce infectious disease when host defenses are weakened.

Virulence

The organism's inherent disease-inducing potential.

Fomite

Inanimate objects that carry an infectious agent.

Zoonoses

Infectious diseases transmitted from animal species to humans.

Nosocomial

Infections that develop in people while they are hospitalized.

Community Acquired

Infections acquired outside of health care facilities.

Commensalism

An interaction where the organism derives nutrition and shelter, but the host is not adversely affected.

Mutualism

An interaction in which both the microorganism and the host derive benefits (e.g., gut flora producing vitamin K).

Parasitism

A relationship whereby only the invasive organism benefits, while the host gains nothing or is harmed.

Prions

Protein particles that cause infectious disease and lack RNA or DNA; transmit by self-propagation.

Transmission

Mode of spread for prions: primarily by eating infected meat or receiving an infected transplant organ or cornea.

Virus

Smallest pathogens; obligate intracellular organisms with no organized cellular structure; genome is DNA or RNA ( never both ); replication requires a living cell.

Capsid

The protein coat surrounding the viral genome.

Genome type

The type of viral genome, DNA or RNA (single- or double-stranded).

Latency

Some viruses enter a latent, nonreplicating state for long periods without causing disease.

Retrovirus

Use reverse transcriptase to convert RNA genome into DNA, integrating into the host chromosome.

Oncogenic viruses

Viruses that transform normal host cells into malignant cells during replication.

Bacteria

Single-celled, prokaryotic organisms with a single circular double-stranded DNA chromosome.

Gram-positive

Bacteria with a cell wall rich in peptidoglycan; stain Gram-positive.

Gram-negative

Bacteria with an outer membrane containing lipopolysaccharide; stain Gram-negative and can induce shock.

Capsule

Extracellular layer that protects bacteria from environmental hazards and immune defenses.

Biofilm

Structured communities of bacteria that stick to and colonize surfaces.

Fungi

Free-living, eukaryotic saprophytes.

Ergosterol

Sterol in fungal cell membranes (not cholesterol); target of many antifungals; not found in bacterial cell walls.

Dermatophytes

Fungi that cause superficial infections of the skin, hair, and nails (dermatophytes).

Superficial mycoses

Infections limited to cooler cutaneous surfaces; organisms grow poorly at core body temperature.

Protozoa

Unicellular parasitic organisms causing diseases such as malaria, amebic dysentery, and giardiasis.

Helminths

Wormlike parasites (roundworms, tapeworms, and flukes). Transmission often via fertilized eggs.

Arthropods

Animal kingdom parasites and vectors (e.g., insects and arachnids) that impact infectious disease.

Epidemiology

Study of factors, agents, and circumstances that influence transmission of infectious disease among humans.

Incidence

The number of new cases of an infectious disease that occur within a defined population over a period of time.

Prevalence

The number of active cases at any given time in a population.

Endemic

A disease found in a particular geographic region with relatively stable incidence and prevalence.

Epidemic

An abrupt and unexpected increase in the incidence of disease over endemic rates.

Pandemic

The spread of disease beyond continental boundaries.

Portal of entry

The process by which a pathogen enters the body and gains access to susceptible tissues.

Penetration

Disruption in the integrity of the body's surface barriers (skin or mucous membranes) enabling entry.

Direct contact

Transmission from infected tissue or secretions to exposed, intact mucous membranes.

STIs

Sexually transmitted infections; a common mode of direct contact transmission.

Vertical transmission

From mother to child, crossing the placenta or during birth.

TORCH infections

Congenital infections: Toxoplasma, Others, Rubella, Cytomegalovirus, HSV.

Ingestion

Entry through the oral cavity and gastrointestinal tract; the agent must survive gastric acidity.

Inhalation

Entry through the respiratory tract, overcoming defenses like ciliated epithelium and phagocytes.

H. pylori urease

Enzyme that converts gastric urea to ammonia, helping neutralize stomach acid.

Exotoxins

Proteins released by bacteria that are highly specific and can cause cell death or dysfunction.

Endotoxins

Lipid-containing molecules in the outer membrane of Gram-negative bacteria that trigger inflammation and shock.

Adhesion factors

Molecules like pili or fimbriae that enable attachment to host tissues.

Intracellular survival

Bacteria surviving and replicating within phagocytic cells after ingestion.

IgA protease (N. gonorrhoeae)

Enzyme that cleaves secretory IgA, weakening mucosal immunity.

Invasive factors

Products (often enzymes) that facilitate penetration of barriers and tissues.

Phospholipases

Enzymes that destroy cellular membranes to aid invasion.

Collagenases

Enzymes that break down collagen in connective tissue to promote spread.

Hyaluronidase

Enzyme that destroys intercellular matrices to facilitate invasion.

Culture

Isolation and growth of an infectious agent outside the host for diagnosis.

Serology

Techniques that detect antibodies to identify infectious agents; IgM indicates acute infection; IgG indicates past exposure or later stages.

IgM

Antibody indicating acute or recent infection.

IgG

Antibody indicating prior exposure or later stages of infection.

PCR

Polymerase chain reaction; highly sensitive method that amplifies specific DNA segments to detect pathogens.

Immunization

Vaccination; the most efficient means of preventing infectious diseases.

IVIG

Intravenous immunoglobulin; pooled antibodies from healthy donors.

Cytokines

Substances that stimulate white cell replication, phagocytosis, and inflammation (e.g., interferons, interleukins).

Interferons

Cytokines that have antiviral and immunomodulatory effects.

Interleukins

Cytokines that regulate immune cell activity and communication.

Surgical intervention

Physical management (drainage, debridement, removal) when pathogens resist medical therapy.

Bioterrorism

Threat of deliberate use of microorganisms as weapons.

Category A

Highest-threat bioterrorism agents (e.g., anthrax, smallpox, botulism) based on risk and mortality.

Category B

Moderately presenting bioterrorism agents (e.g., Salmonella, cholera, E. coli) with moderate mortality.

Category C

Emerging pathogens with potential future risk (e.g., TB, Yellow Fever viruses).