Chapter 9: Principles of Infectious Disease and Epidemiology

Vocabulary practice flashcards covering fundamental terminology in infectious diseases, pathogen transmission, epidemiological metrics, and molecular surveillance.

Pathogenesis

The mechanism and process by which pathogens cause disease in a host.

Virulence

The degree or intensity of pathogenicity of an infectious organism.

True Pathogen

An infectious agent that can cause disease in an otherwise healthy host (such as the influenza virus).

Opportunistic Pathogen

A pathogen that typically only causes disease when the host's immune defenses are compromised or weakened (e.g., Pseudomonas aeruginosa causing hospital-acquired infections).

Emerging Pathogen

A newly identified pathogen or an agent that previously caused only sporadic disease cases.

Reemerging Pathogen

An infectious agent that was once under control but is now resurfacing, frequently due to antibiotic resistance.

Sporadic Cases

Isolated, scattered infections occurring irregularly within a particular population (e.g., Ebola cases in Africa).

Endemic Infection

An infection that is routinely and continuously detected at a baseline level in a specific population or geographic region (e.g., cold-causing rhinoviruses).

Epidemic

A widespread disease outbreak that infects significantly more individuals than expected in a particular region during a specific time frame.

Pandemic

An epidemic that has spread across numerous countries or worldwide, usually driven by novel mutations or changes in the pathogen.

Noncommunicable Disease

A disease that is not spread from person to person, such as cancer, heart disease, or diabetes.

Communicable Disease

An infectious disease caused by microbes that can be transmitted from human to human.

Contagious Disease

A communicable disease that is easily and rapidly transmitted from person to person (such as measles).

Zoonotic Disease

An infectious disease that is transmitted from non-human animals to humans.

Symptoms

Subjective evidence of disease experienced and reported by the patient that cannot be precisely measured (e.g., sore throat or pain).

Asymptomatic Infection

An infection in which the host harbors the pathogen but shows or feels no signs or symptoms of disease.

Acute Disease

A disease characterized by a rapid onset and rapid clinical progression.

Chronic Disease

A disease characterized by a slow onset and prolonged progression over time.

Reservoir

The animate or inanimate habitat (e.g., humans, animals, soil, or water) where a pathogen naturally persists and thrives.

Source

The specific object, material, or individual that actively disseminates a pathogen from the reservoir to a new susceptible host.

Direct Contact Transmission

Transmission where the host comes into direct physical contact with the source of the pathogen (e.g., kissing, sexual contact, animal bites, or swimming).

Indirect Contact Transmission

Transmission occurring when a pathogen spreads from a source to a new host without direct physical contact, typically via airborne particles, vehicles, or vectors.

Airborne Transmission

Indirect spread of pathogens within fine respiratory aerosols or dried droplet nuclei that travel distances $> 2\,\text{m}$ and remain suspended in air for extended periods.

Vehicle Transmission

Transmission of an infectious agent via contaminated inanimate materials, including fomites (objects), water (waterborne), or food (foodborne).

Biological Vector

A vector organism (typically an arthropod) in which the pathogen completes part of its biological life cycle before being transmitted, such as Anopheles mosquitoes transmitting Plasmodium.

Mechanical Vector

A vector that physically carries a pathogen from one location to another on its body without serving as an essential host in the pathogen's life cycle (e.g., flies transmitting Ascaris lumbricoides eggs).

Incubation Period

The initial stage of an infection between pathogen entry and the emergence of the earliest clinical symptoms.

Prodromal Phase

The second stage of an infectious disease where early, mild, and non-specific symptoms begin to develop.

Acute Phase

The stage of an infection representing the peak of pathogen load and the manifestation of full, classic disease symptoms.

Period of Decline

The disease stage in which pathogen replication is brought under control by host defenses or treatment, leading to resolving symptoms.

Convalescent Phase

The final stage of infection during which the host recovers and tissues heal; in some instances, the pathogen may enter a latent state.

Asymptomatic Carrier

An individual infected with a pathogen who shows no outward clinical signs or symptoms but can unknowingly transmit the agent to others (e.g., Typhoid Mary).

Epidemiology

The study of disease distribution and frequency patterns across human populations, along with methods used to prevent and control them.

Prevalence

The proportion or total number of individuals in a population who have a specific disease at a designated point in time, reflecting overall disease burden.

Incidence

The number of new cases of a disease that arise within a population at risk over a specified time period, measuring the risk of disease contraction.

Notifiable Diseases

Diseases of significant public health importance that healthcare providers and laboratories are required to report to the CDC via the NNDSS.

Reportable Diseases

Diseases that healthcare providers are legally mandated to report to local or state health authorities upon diagnosis.

Molecular Epidemiology

A discipline applying molecular biology techniques (such as PCR and DNA/RNA sequencing) to identify, track, and trace pathogen spread and mutation at the genetic level.

Phylogenetic Tree

A branching diagram based on nucleotide sequence data showing inferred evolutionary relationships and genetic ancestry among related organisms.

Influenza A Virus

An enveloped single-stranded RNA virus possessing 8 genomic segments, surrounded by a capsid and an outer lipoprotein envelope studded with hemagglutinin (H) and neuraminidase (N).