Population Medicine- Outbreak Investigation

Why does it matter if something is an outbreak?

• population problems (prevention, treatments)

• public health concerns

• costly for producers

An outbreak is a higher than expected number of cases

What things are necessary to know to detect a change and move forward?

• number of cases

• population at risk

• agents causing disease

• details of cases: signalment, timeline, signs/symptoms

Attack risk

attack risk= cases/population at risk

Attack risk ratio

AR exposed/AR unexposed

• >1 increased risk with exposure

• <1 decreased risk with exposure

Morbidity

morbidity= sick cases/population at risk

Mortality

proportion of dead animals out of all animals in the population at risk

Case fatality rate

Case fatality rate= dead cases/cases

Case definition

A set of criteria that an individual must meet to be counted as ill in this outbreak. Individuals that we will do something with.

• must be specific enough to exclude cases not due to this outbreak

• must be sensitive enough to include those with the disease

Population at risk

Individuals who could be (or become) cases in this outbreak

• who you want to observe for cases and target for control measures

• changes over the course of an outbreak

  • sometimes when you know the source, more are exposed than initially thought

Endemic

• variation around a constant

• seasonal (e.g WNV)

Epidemic

• point source

• propagated

• sporadic

Point Source

Propagated

Sporadic

Seasonal

World Organization for Animal Health

• reportable animal diseases

• official disease status

United State Department of Agriculture

• zoonotic disease

• organized by species and disease

Center for Disease Control and Prevention

• zoonotic disease

• food net (foodborne diseases)

Depopulation

the rapid and efficient destruction of a complete population of animals in response to urgent circumstances with as much consideration given to the welfare of the animals as practical

Conditions necessitating depopulation

• regulatory disease (Avian Influenza)

• Nonregulatory highly pathogenic diseases (PRRS, porcine epidemic virus)

• zoonotic diseases

• Intoxications and adulterations

• Radiologic exposures

• Natural disasters (forest fires)

• Market disruptions (Covid-19)

Depopulation - Authority

• SAHO or his/her designees has statutory authority

Tiers

• Tier 1: highest priority; preferred for emergency response plans whenever feasible

  • Bovine: slaughter, barbiturates, gunshot- close range, penetrating and nonpenetrating captive bolt

  • Swine: slaughter, gunshot- close range, penetrating/nonpenetrating captive bolt, carbon dioxide/monoxide, nitrogen, electrocution, water-based foam, blunt force trauma

  • Small ruminant: slaughter, barbiturates, gunshot- close range, penetrating/nonpenetrating captive bolt

• Tier 2: Secondary option, used when Tier 1 methods are unavailable or unfeasible

  • Bovine: gunshot- long range, PCB, electrocution, water based foam

  • Swine: carbon dioxide, water-based foams, gunshot- long range

• Tier 3: Last resort, Tier 1 and Tier 2 methods are precluded and doing nothing causes greater suffering

  • Bovine: Oral agents

  • Swine: sodium nitrite, ventilation shutdown

Assessment of depopulation methods

• ability to induce loss of consciousness followed by death

• time required to induce loss of consciousness

• reliability and irreversibility of the methods resulting in death

• safety of personnel

• compatibility with the safety of other humans, animals, and environment

• potential psychological or emotional impacts on personnel

• ability to manage equipment

• legal and religious requirements

• sensitivity to public sentiment regarding destruction of large numbers of animals

• availability of agents and carcass processing and disposal

Ventilation Shutdown

• total shutdown and sealing of fans, air inlets, and structural gaps

• external heaters driving up ambient temperatures

• addition of carbon dioxide induce rapid unconsciousness

• i.e. zoonotic, layered production houses, aviary, pig barns

Water based foam

loss consciousness in 1 ½ minutes

Psychological considerations: Owners and Stakeholders

owners should not be present

Disposal Methods

1. Open-air burning- not an ideal methods because of pollution, temperatures achieved can vary

2. Fixed-facility incineration- fueled by diesel, natural gas, or propane

3. Air-curtain incineration- creates a turbulent environment in which incineration is greatly accelerated, requires large quantity of dry fuel to initiate the burn, faster than open-air burning

4. Alkaline hydrolysis- uses sodium or potassium hydroxide to catalyze the hydrolysis of biological material, only solid byproducts are the bones and teeth

5. Composting- natural biological decomposition process that take place in the presence of oxygen

6. Rendering- recycling of raw animal tissue from food animals, and water cooking fats and oils into a variety of value-added products