Disease Transmission Flashcards
At a group level what do we really need and want to know about transmission?
How rapidly does the disease spread within the group
Once a disease is present the population consists of several types of individuals
Susceptibles
Infect but not yet infectious
Infected and infectious
Recovered (perhaps resistant)
Dead
For transmission what must the causative agent do?
Pass from infectious individual to susceptible individual
3 components of transmission
Exit from infectious host
Survival in external environment
Entry into new susceptible host
4 ways exit from host?
From the skin
From internal structures directly continuous with outside (secretion and excretions) - Resp, GIT, Urinary
Indirectly by movement within the body to a structure continous with outside
Directly from blood (vector)
How does “fragility” of agent affect transmission?
Fragile: close contact required i.e. rabies
Resistant: Agent can survive in external environment
4 ways agents have developed to deal with hostile environement
Resistant spore or eggs
Hide out in another animal
Utilize wind, water
Utilize a method that minimizes exposure to the external environement
Two types of horizontal transfer?
Direct
Indirect
Two types of indirect horizontal transfer
Intermediate host
vector
Two types of direc horizontal transfer
Close contact
Contaminative (distant)
5 forms of close contact direct horizontal transfer
Skin-skin
Aerosol
Secretions/excretion
Sexual
Carcasses
5 forms of Contaminative direct horizontal transfer
Air-borne
Water-borne
Fomites
Transport Host
Paratenic host
Define horizontal transfer
Transfer of infection from one host to another in the population independent of their parental relationship
Define vertical transfer
Transfer of infection from parent to offspring
ie BVD
Define direct horizontal transmission
any situation in which infection passes from one individual to another without requirng involvment of another species
2 examples of skin to skin close contact direct horizontal transmission
+ if agent is fragile
Mange
Ring worm
Explain aerosol close contact direct horizontal transmission
Very limited to distance - spray zone
I.e. bovine tuberculosis
What is the most common form of close contact direct horizontal transmission
secretion/excretions
Two examples of secretions/excretions?
Rabies
Salmonelosis
How do airborne transmissions occur?
Droplets become fixed in suspenison, water or dirt and travel long distance
Example of air-borne contaminative direct horizontal transmission
Legionnaire’s disease
What is legionnaires diease?
Fatal pneumonia
Grows in cooling towers on building and then is transfered via the ventilation in air
What are fomites?
Inatimate objects
- feed bunks
- perches
Explain transport host contaminative direct horizontal transmission
ie. mosquito host not infected, it just has dirty mouthparts
disease caued by transport host
Mosquito-borne avian pox
Explain paratenic host
Infected but not require, h/e aids in transmission
What doesnt occur in intermediate host?
Sexual reproduction. Asexual reproduction can occur, h/e sexual does not occur
Why is it important to understand how a disease is transmitted?
For disease control, elimination or eradication it is necessary to reduce or stop the occurence of new cases
Difference between eradication and elimination
Eradication: Wiped off globe
- small pox
- Renderpest
Elimination: geographic removal
- foot and mouth canada
