Equine Outbreaks Year 2 Pop Block 3

risk based “big four“ vaccines

• EHV-1/rhinopneumonitis (high-density events)

• equine influenza (aerosolized spread)

• streptococcus equi/strangles (endemic premises)

• clostridium botulinum (endemic soils and specific forages)

Testing for equine herpesvirus

• veterinary nasopharyngeal swab and whole blood EDTA for qPCR

• shedding begins 1-2 days post fever

• don’t rule out if early test is negative

testing for equine influenza

• nasal swab for rapid PCR or stall-side antigen test

• identifies pathogen rapidly to justify immediate perimeter expansion

testing for botulism

• clinical diagnosis is primary

• test feed/forage or GI contents, not live horse

• don’t wait for lab confirmation to initiate antitoxin/supportive care

testing for strangles

• active = aspirate mature node or nasopharyngeal wash for qPCR

• clearance = guttural pouch lavage and qPCR

• wait 24-48 hrs post-fever to swab

• use SeM serology to check for purpura risk vaccinating

Important steps to build defense against outbreaks

• risk-based vaccines

• early detection and testing

• exposure control/biosecurity

What is important in the first 24 hrs of an outbreak

stop movement, separate risk

what do you do hour 0-2 of outbreak?

• halt movement

• isolate index case immediately

• contact attending vet

what do you do hour 2-6 of outbreak?

• temperature sweep

• take temperatures of every horse on property

• categorize into red, amber, and green based on temp and contact history

what do you do hour 6-24 of outbreak?

• enforce barriers

• establish dedicated personnel, separate equipment and footbaths/PPE for each zone

• work clean to dirty

red zone

• febrile or showing clinical signs

• strict isolation (30ft perimeter)

• dedicated staff and equipment

• no movement

amber zone

• direct/indirect contact with index

• currently afebrile

• temp check 2x daily

• no co-mingling

green zone

• no contact with index

• afebrile

• temp check 2x daily

• staff attends this group first

Signs of EHV-1 and influenza outbreaks

clusters of unexplained fever or respiratory signs in a high density/mixing environment

Signs of botulism outbreaks

clusters of weakness, dysphagia, or recumbency, especially linked to shared feed source

Signs of strangles outbreak

new arrivals with fever, or resident horses developing fever followed by lymph node swelling/discharge

respiratory contact

• agent = EHV-1, EI, S equi

• core action = stop movement and event competition immediately

• separation = isolate clinical horses, cohort exposed vs clean animals

• hygiene = dedicated staff and equipment for each zone, work from clean to dirty, disinfect fomites

feedborne toxin

• agent = clostridium botulinum (preformed toxin)

• core actions = stop feeding suspect feed immediately, precent animal access areas

• preservation = retain original labels, lot codes, invoices, and unopened packages for authorities

• investigation = trace feeding dates by group, look for visual contaminants

vaccine limitations of EHV-1

• current EHV-1 vaccines labeled for reduction of respiratory disease and prevention of abortion

• no commercial vaccine is labeled to prevent equine herpesvirus myeloencephalopathy

• vaccination may mask respiratory signs (nasal discharge), leaving fever as only early indicator of viremia

• vaccinated horses can become subclinical (Trojan Horse) shedders, appearing healthy while transmitting high viral loads

clinical red flags and testing for EHV-1

• fever (102-106) typically precedes neurologic signs by several days

• neurologic progression = ataxia, hind limb weakness, urine dribbling, loss of tail tone

• testing = nasal shedding begins 1-2 days after onset of fever

immediate outbreak action of EHV-1

• do not attempt to vaccinate your way out of active EHM outbreak

• isolate febrile horse immediately

• institute twice-daily temperature monitoring for entire herd

• establish strict 30ft perimeter isolation zones and halt movement

CES Valencia Spring Tour Outbreak 2021

• forced massive reevaluation of equestrian event biosecurity

• underscored critical distinction between EHV-1 infection and EHM in dense, stressed sport-horse populations

Botulism type B

• spoiled, wet, moldy forage (anaerobic)

• endemic in Mid-Atlantic US/KY soils

• progressive flaccid paralysis, dysphagia, weak tongue tone, muscle fasciculations

• highly effective toxoid available

• vaccine recommended for endemic regions

Botulism type C

• decomposing animal carcasses baled into forage

• global risk

• rapid onset identical to type B

• high attack rate in exposed herds

• zero cross protection with type B vaccine

Botulism type A

• endemic to soils west of the Mississippi River

• similar neuromuscular blockade and profound weakness

• no commercial vaccine

transmission threat of EI

• highly contagious orthomyxovirus spreading rapidly via aerosolized droplets and fomites

• morbidity approaches 100% in naive herds, heavily targeting unvaccinated horses

vaccine role in EI outbreak

• vaccines effectively reduce both clinical severity and virus shedding

• slows transmission velocity, protect herd and prevent barn-wide shutdowns, even if individuals get mildly sick

outbreak mitigation tactic EI outbreak

• early in outbreak vet administer modified-live intranasal vaccine to unaffected at risk horses

• strict isolation of clinical horses and aggressive fomite disinfection must occur simultaneously

strangles vaccine

modified live, can cause reversion to wild type and have side effects