1 Disease Transmission and Pathogen Reservoirs

Vocabulary flashcards generated from lecture notes covering disease concepts, infection stages, carrier types, modes of transmission, vector dynamics, and complex persistence mechanisms.

Disease

A departure from health — a deviation from normal physiological function.

Infectious Diseases

Diseases caused by pathogens such as bacteria, viruses, fungi, or parasites.

Non-infectious Diseases

Diseases resulting from metabolic disorders, hormonal imbalances, immunological reactions, neoplasia, deficiencies, or toxicities.

Per-acute Disease

A classification of disease duration lasting hours, often causing sudden death (e.g., anthrax).

Acute Disease

A classification of disease duration lasting days to weeks (e.g., Foot and Mouth Disease, canine parvovirus).

Sub-acute Disease

A classification of disease duration lasting weeks with milder symptoms (e.g., mastitis).

Chronic Disease

A classification of disease duration lasting months to years (e.g., Johne's disease, actinomycosis).

Incubation Period

The silent phase where the pathogen establishes and multiplies in host tissues without visible clinical signs.

Prodromal Phase

The early phase of clinical disease marked by non-specific signs such as fever and lethargy.

Fastigium Phase

The phase of peak illness displaying characteristic clinical signs.

Defervescence Phase

The phase of declining clinical symptoms as host immunity develops.

Convalescent Period

The recovery phase where clinical signs resolve, but the animal may still shed pathogens.

Host–Agent Interaction Cycle

The cycle encompassing incubation (latent), clinical disease (patent), convalescent (infective), and recovery (clearance or carrier state).

Latent Infection

A dormant infection where the pathogen remains quiescent within the host and is difficult to detect.

Patent Infection

An active infection where the pathogen is actively replicating and detectable in secretions, excretions, blood, or tissues.

Carrier

An animal harboring a pathogen without showing clinical signs, acting as a silent source of infection.

Healthy Carrier

An animal that has recovered or was never symptomatic, but still harbors and can transmit the agent.

Incubatory Carrier

An animal that transmits a pathogen during the incubation period before developing clinical signs.

Convalescent Carrier

An animal that transmits a pathogen during recovery after clinical signs have resolved.

Continuous Shedder

A carrier that constantly releases pathogens into the environment (e.g., Salmonella typhi).

Intermittent Shedder

A carrier that releases pathogens unpredictably, making it particularly dangerous because it evades routine detection.

Reservoir

The natural habitat where a pathogen lives, multiplies, and persists long-term.

Source of Infection

The immediate object, individual, or substance from which an infection is acquired in a specific case.

Epidemic Focus

The location of an infection source plus the surrounding area where that source can effectively transmit the pathogen.

Epidemic Process

A chain of interconnected epidemic foci creating a broader disease outbreak.

Direct Contact Transmission

Pathogen transmission requiring intimate physical contact between infected and susceptible animals (e.g., venereal disease, bite wounds).

Indirect Contact Transmission

Pathogen transmission occurring via contaminated fomites, equipment, or handlers.

Airborne Transmission

Pathogen spread via droplet nuclei smaller than $10\,\mu\text{m}$ suspended in air that reach lung alveoli directly.

Vehicle-Borne Transmission

Pathogen transfer via non-living objects (such as milk, feed, water, soil, or equipment), typically producing explosive, point-source outbreaks.

Epidemic Curves Archetypes

Graphical outbreak patterns illustrating explosive single peak, seasonal build and decline, and rolling waves.

Mechanical Transmission

Simple physical transfer of a pathogen by a vector without multiplication or development occurring inside the vector.

Propagative Transmission

A type of biological vector transmission where the pathogen multiplies within the vector without undergoing developmental changes.

Cyclo-Propagative Transmission

A type of biological vector transmission where the pathogen both undergoes developmental changes and multiplies within the vector.

Cyclo-Developmental Transmission

A type of biological vector transmission where the pathogen undergoes developmental changes within the vector without multiplying.

Developmental-Propagative Transmission

A vector transmission process where the pathogen multiplies and migrates through developmental vector stages (e.g., Lyme disease in Ixodes ticks).

Extrinsic Incubation Period

The time required for a pathogen to develop or multiply within a vector before it can be transmitted to a host.

Transovarial Transmission

Passage of a pathogen from a female vector to her offspring through the ovary (e.g., Babesia bigemina).

Transstadial Transmission

Persistence of a pathogen in a vector as it molts from one developmental stage to the next (e.g., larva to nymph to adult).

Overwintering

Persistence mechanisms (such as adult vector hibernation or transovarial persistence) that allow pathogens to survive cold seasons.

Vertical Transmission

Direct passage of a pathogen from parent to offspring via transplacental, transmammary, transovarial, or intrapartum routes.

Horizontal Transmission

Spread of a pathogen between individual animals sharing the same environment via contact, airborne, vehicle, or vector routes.

Zig-zag Transmission

Transmission pattern alternating between vertebrate and invertebrate hosts, neither of which can maintain the pathogen independently.