Population Medicine Block 3: Outbreak Investigation and Control

What are the 5 phases of an outbreak investigation?

1.) describe the outbreak

2.) collect and analyze data

3.) implement control

4.) follow-up

5.) communication

an outbreak is a ______ than expected number of cases

higher

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

-number of cases

-population at risk

-agents causing disease (may not know)

-signalment

-timeline of disease

-signs/symptoms

how do you calculate attack risk?

# of affected animals/ population at risk at start of an outbreak

how do you calculate morbidity?

sick cases/population at risk

how do you calculate case fatality rate?

dead cases/cases

Define: 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

Define: population at risk

individuals who could be (or become) cases in this outbreak on current information

the population at risk is who ____________ the disease

could have gotten

How do you know you have a difference?

-statistic comparing measure to previous mean

-verifying the diagnosis with confirmatory tests

how do you know an animal has an atypical disease?

-different response to treatment

- comes up negative for the usual suspects

what is this an example of?

Equine flu affecting dogs

atypical disease

define: morbidity

proportion of sick animals out of all animals at risk of disease

define: mortality

proportion of dead animals (due to a particular disease) out of all animals in the population at risk

define: case fatality rate

proportion of dead animals out of all animals that got the disease

what two patterns are expected in epidemic curves?

-variation around a constant

-seasonal

what three patterns are seen in epidemic curves?

-point source

-propagated

-sporadic

what does a point source curve look like?

what does a propagated curve look like?

what does a sporadic curve look like?

what does a seasonal curve look like?

Case in point source outbreaks all go back to?

one source

what ratio is helpful with case in point sources?

attack risk ratio

cases in proposed epidemics may go through?

several intermediate cases to get to the original source

what is the original source also called in cases in propagated epidemics?

index case

curves help you identify ______ in the outbreak you are and _____ you are doing

where and how

for directly transmitted diseases, an individual

__________ to be a possible source

must be infected (have been infected)

what does an attack ratio over 1 signify?

increased risk with exposure

what does an attack ratio under 1 signify?

decreased risk with exposure

what does an attack ratio equal to one signify?

no effect observed

how do you get data for ARR when the source is un-known?

-case control

-cross sectional

how do you get data for ARR with a known exposure event?

cohort

the determine the source you need...

-high ARR

-pathway from source to case (plausibility based on traces)

-correct timing between exposure and disease (temporality)

the study population is _______ as the population at risk

not the same

Define 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

what conditions may depopulation may be necessary?

-regulatory diseases

-nonregulatory highly pathogenic diseases

-emerging animal production diseases

-zoonotic diseases

-intoxications and adulterations

-radiologic exposures

-natural disasters

-market disruption

the state animal health official (SAHO) has ________ to suggest depopulation

statutory authority

what is the priority and usage of a tier 1 depopulation?

highest priority; preferred for emergency response plans whenever feasible

what is the priority and usage of a tier 2 depopulation?

secondary option; used only when their 1 methods are unavailable

what is the priority and usage of a tier 3 depopulation?

last resort; used only when higher tiers are precluded and doing nothing causes greater suffering

what tier of depopulation has the highest evidence base & welfare outcomes?

tier 1

supported by multiple sources of evidence, raid loss of consciousness and optimizes animal welfare; this decreases with higher tiers

what conditions allow a tier 3 depopulation to be implemented?

applied in extreme conditions such as loss of safe animal access or severe threats to human life

What are the 10 assessments AVMA considers with depopulation methods?

- ability to induce loss of consciousness quickly before death with minimum pain or distress

- time required to induce loss of consciousness and the behavior of the animal during that time

- reliability and irreversibility of the methods resulting in death of the animal

-safety of personnel

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

- potential psychological or emotional impacts on personnel

- ability to maintain equipment in proper working order

-legal and religious requirements

- sensitivity to public sentiment regarding the destruction of large numbers of animals

- availability of agents and carcass processing and disposal venues to handle the volume

describe ventilation shutdown plus core mechanics as a depopulation method:

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

- external heathers driving up ambient temperatures rapidly

-addition of carbon dioxide to induce rapid unconsciousness via hypoxia

what was previously listed as the preferred method for floor-reared confined poultry?

water-based foam

what are tier 1 methods for bovine depopulation?

-commercial or private humane slaughter processing

-barbiturates and barbiturate derivatives

-close range gun shot

- penetrating and nonpenetrating captive bolt

what are tier 2 methods for bovine depopulation?

-long range gunshot

-PCB poll shot

-electrocution

-water based foam

what are tier 3 methods for bovine depopulation?

oral agents

what are tier 1 methods for swine depopulation?

-commercial or private humane slaughter processing

-barbiturates and barbiturate derivatives

-close range gunshot

-penetrating and non penetrating captive bolt

-carbon dioxide

-carbon monoxide

-nitrogen

-electrocution

-water-based foam

-nitrogen-filled foam

-manual blunt force trauma

what are tier 2 methods for swine depopulation?

none!

what are tier 3 methods for swine depopulation?

-sodium nitrate

-ventilation shutdown plus heat and humidity

-ventilation shutdown alone

what are tier 1 methods for small ruminant depopulation?

-commercial or private humane slaughter processing

- barbiturates and barbiturate derivatives

-close range gunshot

-penetrating and non penetrating captive bolt

what are tier 2 methods for small ruminant depopulation?

-carbon dioxide

-water based foams

-long range gunshot

what are tier 3 methods for small ruminant depopulation?

none!

what training does depopulation personnel need?

-animal handling

-approved euthanasia method to be used

-safety issues

-PPE

-biosecurity

-cleaning and disinfection procedures

what specific safety considerations might you make in relation to depopulation?

-size/weight

-temperature

-restraint methods available

-depopulation method

should the owner be present for depop?

no! if they are, brief them on the method selected, safety, and counseling services

what items might require disposal following infection or exposure?

-animals

-germplasm

-contaminated bedding

-manure v debris/compost

-contaminated feed

-PPE of workers and responders

-lagoon maintenance

what are the two burial options?

onsite and landfill

what are some burial considerations in relation to carcass disposal?

-soil properties

-slope or topography

-hydrological properties

-proximity to bodies of water, wells, public areas, roadways, residences, property lines

-accessibility

-subsequent intended use of the site

what are the three thermal methods of carcass disposal?

1.) open-air burning

2.) fixed-facility incineration

3.) air-curtain incineration

What methods are included in open-air burning?

-burning on open land

- in a dug out pit

-pyres

is open-air burning an ideal method?

no because it is polluting, temperatures achieved can vary so uncertainty exists as to whether pathogens have been inactivated

what methods are included in fixed-facility incineration?

-small on farm incinerators

-small and large incineration facilities

-crematoria

what are fixed-facility incineration typically fueled by?

-diesel, natural gas or propane

what is air-curtain incineration?

-large capacity fans driven by diesel engines

-deliver high velocity air down into either a metal refractory box or burn pit

-creates a turbulent environment in which incineration is greatly accelerated

what is alkaline hydrolysis as a disposal method?

-uses sodium or potassium hydroxide to catalyze the hydrolysis of biological material into a sterile aqueous solution

-heat (~300 F) and pressure are also applied to accelerate the process

what byproducts are left from alkaline hydrolysis?

bones and teeth which are sterile and can be crushed into powder

Any person who wants to compost deal animals must do what two things?

1.) participate in an educational course concerning composting and obtain a certificate of completion for the course

2.) use the appropriate method, technique, or practice of composting established in rules

define composting:

natural biological decomposition process that takes place in the presence of oxygen

what are the two phases of compost?

1.) temperature of the compost pile increases and the organic materials break down into relatively small compounds, soft tissue decomposes and bone soften

2.) remaining materials (mostly bones) break down fully and the compost turns to a consistent dark brown to black soil

what is rendering?

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

what information do you need for an outbreak?

-normal number of cases

-population at risk

-who was exposed to the cause

-what possible causes individuals were exposed to

-background on the disease and diagnosis

where can you find surveillance data of reportable animal diseases?

World Organization for Animal Health

what two systems does world organization for animal health have?

-world animal health information system (WAHIS)

- official disease status

where can you find surveillance data of zoonotic diseases?

-United States department of agriculture

-centers for Disease Control and prevention

where can you find surveillance data for common parasites for companion animals?

companion animal parasite council (CAPC)

where can you find surveillance data for livestock only?

USDA National Animal Health Monitoring System (NAHMS)

what are other common sources of surveillance data?

-electronic medical/health records

-voluntary health programs (DHIA and PHIP)

-Industry summaries

-diagnostic laboratories

-published studies

what might you consider with frequency?

continuous, daily, weekly, monthly, annually

what might you consider with population?

-herd/facility

-locality

-state

-region

-national

what might you consider with biases?

who is choosing to report or who are you choosing to sample

______ is how you know if your disease control worked

active surveillance

what study designs might you consider for active surveillance?

-cohort

-case-control

-cross sectional

-case series

what collection instruments might you consider for active surveillance?

-records review

-billing or credit cards

-survey or interview

-camera footage

Your dairy client thinks that there has been an increase in mastitis on their farm recently. What source(s) would you check to see if there is an increase

the farm's recent DHIA reports and farm management software

Your dairy client thinks that there has been an increase in mastitis on their farm recently. What source(s) would you check for information on likely pathogens and the signs they cause?

a published study of mastitis in Ohio dairies from 2024

What is a plus (something good about) using a prevalence from a published peer reviewed scientific study in a broad population?

Confidence it is representative with biases noted

What is a minus (something wrong) that might keep you from using data from your small animal clinic in a suspected outbreak?

It is not collected in the format you need, so you need to spend a lot of time extracting it.

what test is done for Equine Herpesvirus (EHV-1)?

veterinary nasopharyngeal swab and whole blood (EDTA) for qPCR

what is the caveat for testing for Equine Herpesvirus (EHV-1)?

shedding begins 1-2 days post-fever, do not rule out if early test is negative

what test is done to detect equine influenza (EI)?

Nasal swab for rapid PCR or stall-side antigen test

what test is done to detect botulism in equine?

clinical diagnosis is primary. test feed/forage or GI contents, not the live horse

what is the caveat for testing for botulism?

do not wait for lab confirmation to initiate antitoxin/supportive care. time=survival

what test is done for strangles (s.equi)?

active: aspirate mature node or nasopharyngeal wash for qPCR

clearance: guttural pouch, pouch lavage +qPCR

define a red zone:

-clinical

-febrile or showing clinical signs

-strict isolation (30 ft perimeter)

-dedicated staff and equipment

-no movement

define a amber zone:

-exposed

-direct/indirect contact with index

-currently afebrile

-temp check 2x daily

-no co-mingling

define a green zone:

-clean

-no contât with index

-temp check 2x daily

-staff attend this group first

during the first 0-2 hours of an outbreak what should be done?

halt movement: stop all horses entering or leaving the property, Isolate the index case immediately and contact attending veterinarian immediately

during hours 2-6 of an outbreak what should be done?

temperature sweep: take temperatures of every horse on the property and categorize