Infectious disease control and prevention in populations

Question 1

What is needed for infection to occur?

Answer 1

-a susceptible host
-effective contact with an infectious host

Question 2

Factors affecting probability of contact with infectious host

Answer 2

-number of contacts
-prevalence of infection in the population

Question 3

What does likelihood of transmission depend on?

Answer 3

-number of organisms to which the animal is exposed
-characteristics of the infectious agent
-route of transmission

Question 4

Endemic stability

Answer 4

**not typically due to new agent coming in, typically due to changes in disease ecology allowing for ubiquitous infectious agent to emerge that was already present

Question 5

Opportunities for control

Answer 5

1. remove agent- remove or treat of infected hosts. Includes find and cull

2.stop transmission
*direct contact, indirect contact through environ, contact with vectors

3. Enhance host resistance
   *inherent
   *acquired (active or passive)

Question 6

Methods to control disease in populations

Answer 6

-selective slaughter
-depopulation
-quarantine
-mass treatment
-mass immunization
-environmental control
-education
-applied ecology
-genetic improvement

Question 7

Selective slaughter

Answer 7

Test and slaughter= kill minority of infected animals to protect the health majority (eg. Johne’s disease, Neospora)

-need case finding (diagnostic screening test)

-works well early in disease outbreaks and in slowly spreading diseases
eg. Brucellosis eradication early, but not used now

Question 8

Mass treatment

Answer 8

Treat all animals whether sick or well
-eg. mastitis, shipping fever, parasites

-combats disease when depopulation and slaughter are not economical or viable.

-need safe, cheap, effective therapeutic agents. But be aware of treatment/disease resistance

Question 9

Mass immunization

Answer 9

Create immunity in population which limits spread and impact on disease

eg. Canine distemper, parvo virus, rabies

Question 10

Basic Reproductive Ratio (R0)

Answer 10

The avg number of susceptible individuals that are infected by each infected individual when all others are susceptible
**the ease of transmission of an infectious agent

eg. IBR: R0=7 ,FMD: R0=70

Question 11

What determines R?

Answer 11

-probability of infection on contact
-rate of contact
-duration of infectiousness

Question 12

R0<1

Answer 12

outbreak will die out

Question 13

R0>1

Answer 13

outbreak will take off

Question 14

Effective Reproductive Ratio

Answer 14

The avg number of susceptible individuals that are infected by each infected individual in the current epidemiological context

Question 15

What does effective R depend on?

Answer 15

-probability of contact
-probability of transmission given contact
-duration of infectiousness
-% of population that is susceptible

Question 16

R* (effective reproductive number) >1

Answer 16

Needed for an infectious agent to survive in a group

GOAL of control strategies is to get R* <1

Question 17

Critical fraction

Answer 17

TO achieve herd immunity or prevent an outbreak from progressing we need to create immunity in this proportion of the population

Question 18

Environmental control

Answer 18

-Use Triad (host, agent, environment) to control disease
*management, environment control, feeding, husbandry
*hygiene (ventilation, comfort, disinfect fomites, surgical sterilization)

Question 19

Environmental factors affecting disease control programs

Answer 19

1. pop density (eg. deer feeding stations)
2. Housing (eg. ventilation, sanitation, bedding, flooring, overcrowding)
3. Environmental conditions (eg. temp, humidity, wind, precipitation, climate change)

Question 20

Ontario rabies control program

Answer 20

**focus on skunk and fox strains
-vaccine bait distribution
-trap-vaccinate-release program

*raccoons
-trap, vaccinate, release
-point control= positive, would kill others within 2km… depopulation within a positive case perimeter
-aerial drops of baits

Question 21

Educations role

Answer 21

-education population about how exposure might occur

eg. Rabies in raccoons… garbage and pet food, boats and trailers

Question 22

TB in Manitoba

Answer 22

Positive cases in elk and white tailed deer in Riding Mountain National Park
-linked to historic pasture cattle in the park
-saw 7 infected cattle herds since 1997

Question 23

Management of TB in Manitoba

Answer 23

1.More than 60% of elk come outside the park to feed… need to have barrier fences to protect stored winter feed supplies

2. Prescribed burns to improve habitats
3. Increase hunting opportunities of elk
4. require hay be removed from fields to be eligible for crop insurance
5. Manitoba conservation regulations on baiting elk for hunting

6.education on elk movements/behaviours

Question 24

TB testing management

Answer 24

Put zones in place around Riding Mountain National Park and Duck mtn provincial park
-hunters were to submit samples for testing from these zones

Question 25

Manitoba TB split zone

Answer 25

Had split status for TB
-Rocky mtn= TB accredited advanced (low prevalence)
-Rest of MB= free

**Now considered TB free

Question 26

TB in MB today

Answer 26

-Mostly surveillance through hunter submissions (hunter killed surveillance)

Question 27

Chronic wasting disease transmission

Answer 27

-animal to animal or animal to environment to animal
*likely through feces and/or saliva

-pastures or feed and water equipment remain contaminated for years

Question 28

Who is most susceptible to chronic wasting disease?

Answer 28

-caribou most susceptible because they move in large herds
-rare in moose because they are normally on their own

Question 29

Chronic waste disease and TB surveillance

Answer 29

Province expanded CWD surveillance program in wildlife management zones to test for TB
-currently accept heads from deer, moose, elk
-no associated cases of bovine TB in SK wildlife to date