PID 1 Block 1: Disease reservoir and transmission

What is the chain of transmission?

1. Infectious Agent

2. Reservoir

3. Portal of Exit

4. Mode of Transmission

5. Portal of Entry

6. Susceptible Host

exposure

introduction of a new pathogen into a susceptible population

How does exposure occur between population?

1. reservoir population gets close to susceptible population

2. susceptible population gets close to reservoir population

3. or agent travels

transmission

adoption, establishment and dissemination in the susceptible population. requires a pathogen that can adapt to, and transmit between, these hosts

What is a reservoir?

-habitat or population in which an infectious agent normally lives, grows, and multiplies

-maintain pathogens over time

-different strategies to survive in reservoir

Key points about animal reservoirs

-reservoir does not mean not ill

-if asymptomatic: then we consider it a carrier

-not all sick animals are reservoirs

-an individual can be killed by the agent, but the population maintains the agent

What is the portal of exit?

-the method the pathogen uses to leave the body of the host

What are some examples of portal of exit?

saliva, vaginal secretion, feces, blood, urine

What are the two modes of transmission?

vertical or horizontal

vertical transmission types

-transplacental, fecundation and eggs

-transovarian

-perinatal

transplacental, fecundation and eggs

transplacental: in utero, through the placenta

fecundation: virus can attach to spermatozoa or oocyte

egg: transmission of the pathogen during egg development

transovarian

-only happens in ticks

-passage of pathogen from the adult female to egg through the ovaries of an arthropod

perinatal

infected during birth (at parturition) or through the colostrum/milk

What are the two types of horizontal transmission?

direct and indirect

direct transmission vs. indirect transmission

Direct:

-limited space

-with intermediary: directly from one person to the next

-short time period

indirect

-distance

-intermediary

-longer time period

What are the types of direct transmission?

contact

droplet/airborne

Examples of contact transmission

skin

mucous membranes

brutal (bite)

Examples of droplet/airborne

direct projection (droplet spread)- sneezing, coughing, or talking

airborne

waterborne- for aquatic animals only, through the gills

What are types of indirect transmission?

vehicle and vectors

Types of vehicles

common vehicle or fomite

common vehicle

water, food, soil

fomites

any substance or object that adheres to and transmits infectious material

-ex. dirty boots from farm to farm, cutting raw meat on a cutting board then cutting something else

Types of vectors

biological and mechanical

vector

arthropods who carry and transmit pathogens

mechanical vector

an animal that carries a pathogen from one host to another without being infected itself

biological vector

the pathogen undergoes changes or multiplies while in the vector

portal of entry

-the method the pathogen uses to enter the body of the susceptible person or animal

-most of the pathogens cannot go through the intact skin

-animals are well prtected

What are some portals of entry?

eyes, lungs, intestine, skin

What is the most efficient portal of entry?

eyes

susceptible host

member of a population who is at risk of becoming infected by a disease