Infectious Disease Transmission and Zoonosis - ANSC 625

What are pathogens?

agents, typically living organisms (except viruses and prions) that cause disease

Sometimes what three classes are separated from the larger bacteria classification?

Rickettsia, Chlamydia, Mycobacteria

Sometimes protozoa are grouped in with ____, but they are really two different groups

helminth parasites

What three factors make up the epidemiologic triad?

host factors, pathogen factors, environmental factors

Each factor of the epidemiologic triad can be altered in order to better or worse handle the other factors (T/F)

true

What are some examples of what would be considered host factors?

nutritional plane, genetics, immune competency

What are some examples of what would be considered pathogen factors?

infectious dose, mechanism of disease, life cycle, mode of transmission, virulence, resistance, pathogenicity, commensal vs pathogenic

What are some examples of what would be considered environmental factors?

sanitation, stocking density, temperature, ventilation, open/closed group, risk exposure to toxins, wildlife, humidity

What are the five types of hosts?

primary/definitive, secondary/intermediate, paratenic/transport, aberrant, reservoir

What is a primary/definitive host?

host in which pathogen undergoes sexual phase of development/replication

What is a secondary/intermediate host?

Host in which a pathogen undergoes asexual phase of development/replication

What is a paratenic or transport host?

Harbors pathogen in arrested stated of development and is not required for the life cycle. Can serve as a source to move pathogen between susceptible hosts while showing no sign of disease

What is an aberrant host?

Host that is not normally infected with the pathogen (pathogen may undergo life cycle changes and reproduction, may show no signs of disease). Can be considered a dead end if the pathogen cannot be transmitted further

What is a reservoir host?

pathogen undergoes part of the life cycle in this host, relies on it for survival. Environments can act as reservoirs. Important source of infection for other susceptible hosts, helps to maintain infections in populations (shows no signs of disease)

What are the portals of entry into the body?

GIT, blood, mucous membranes, respiratory tract, skin

What is the circle of pathogen transmission?

pathogen -> reservoir -> portal of exit -> mode of transmission -> portal of entry -> susceptible host -> repeat

What are the portals of exit?

blood, GIT, respiratory secretions, skin/mucous membrane

What are the two overarching branches of modes of disease transmission?

direct and indirect contact

What is direct contact?

directly touching body to body to transfer a pathogen

What are the versions of indirect contact?

fomites, droplet, airborne, vehicle, vector (biological and mechanical)

If an animal has no signs of disease, does that mean it has no disease?

not necessarily - it could be in the carrier state, meaning it can transmit disease without active signs. It could also be a reservoir or aberrant host

Who is the definitive host for Sarcocystis neurona?

opossum

Who is the abberant host for Sacrocystis neurona?

horse (only forms schizonts, no cysts). Causes equine protozoal myelitis

Who are the intermediate hosts for Sarcocystis neurona?

small mammals - cats, otters, skunks, racoons, etc (forms sarcocysts)

Who is the reservoir for SARS-COv-2?

bats

Who is the reservoir for EEE?

birds

How does EEE transfer from birds to the aberrant host, horses?

mosquito vector

What is the incubation period?

preclinical phase from biological onset to onset of signs

What is the prodromal phase?

whent he initial signs/symptoms develop before specific signs of disease are evident (part of clinical phase, used in human medicine)

What occurs after exposure to pathogen?

incubation period

What two things could happen after incubation?

illness or no illness

What could occur after illness?

transmission with clinical disease or carrier state (transmit disease with no active signs)

What could happen after no illness?

carrier state (transmit disease with no active signs) or infection clears (no transmission)

What are the three aspects to managing infectious disease?

prevention, surveillance, control/eradication

What can be done to prevent disease?

manipulate host genetics (selection, genetic engineering), management (biosecurity, population control), and preventative medical care

How can you survey and report disease?

monitor animals via targeted immunological testing, monitor environment, sentinel animals, isolate or cull sick animals (submit for necropsy), have contact with a network of state veterinarians and diagnostic labs

What are sentinel animals?

indicator species that can be observed for the progression of a virus

What types of infectious disease are of special concern?

zoonotic, anthroponotic, high morbidity/mortality, foreign animal diseases, reportable or notifiable disease

Up to ___ of all human infections are zoonotic in origin

75%

What is a spillover?

moment when a pathogen passes from members of one species, as host, into members of another

Why are we seeing an increase in emerging infectious disease?

anthropogenic factors (land use, hunting pressures, climate change, agriculture/invasive species, human pop density, human travel, wildlife trade)

What are fomites?

inanimate objects that can spread disease

What size are droplets?

>5 micrometers, travel up to 1 m

What are airborne pathogens?

pathogens <5 micrometers that can be transmitted via air

What is a vehicle transmitter?

inanimate pathways that move (ingestion of some sort) to carry pathogens (water, food, blood products)

What are vectors?

animals that carry pathogens from one host to another

What is a biological vector?

a vector that carries a pathogen inside its body to carry it to next host (i.e. mosquitos)

What is a mechanical vector?

a vector that does not directly ingest the pathogen to carry it to the next host (i.e. houseflies)