Controller-approved source entry - manual-review caution required Equine Infectious Disease Manual reviewBiosecurity caution

Equine Herpesvirus

Separate EHV respiratory disease, abortion storms, and neurologic EHM by timeline, fever, exposure, and biosecurity urgency.

⏱ 6-7 min read · Topic of

Practice Qs

Traps

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Study step

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Overview

EHV-1 and EHV-4 cause respiratory disease; EHV-1 is also high-yield for abortion and neurologic EHM.

Signalment / Epidemiology

Crowded barns, shows, transport, young horses, broodmares, and outbreak settings raise suspicion.

Pathophysiology

Latent herpesvirus recrudescence and viral shedding support respiratory spread; EHV-1 vasculitis drives abortion and neurologic disease.

Clinical Signs

Fever, nasal discharge, cough, abortion storms, ataxia, urine retention, and recumbency define the main exam lanes.

Diagnostics

PCR from nasal swabs and blood, plus abortion tissue testing when relevant, supports outbreak decisions.

Differential Diagnoses

Separate respiratory EHV from influenza and strangles, abortion EHV from placentitis, and EHM from EPM or trauma.

Treatment

Use isolation, biosecurity, supportive care, neurologic nursing, and outbreak management; vaccination reduces risk but is not absolute.

Prognosis

Good for uncomplicated respiratory disease; guarded with neurologic recumbency or severe outbreak spread.

NAVLE Pearls

A febrile neurologic horse is an isolation problem before it is a diagnostic puzzle.

Common NAVLE Traps

Do not assume vaccination prevents EHM or delay isolation while waiting for confirmatory testing.

Core decision

Isolate febrile or neurologic suspects quickly and treat vaccination as risk reduction, not a neurologic guarantee.

High-yield takeaways

Start with the safest next step, then narrow the case using signalment, timeline, exam findings, diagnostics, and response to treatment.
Use the traps, differentials, and practice questions to rehearse NAVLE-style reasoning instead of memorizing isolated facts.
This educational study page is not a clinical protocol; confirm patient-specific decisions with current references and clinician judgment.

30-second revision

RespiratoryEHV-1 and EHV-4 cause fever and respiratory outbreaks.

AbortionEHV-1 is a late-term abortion and abortion-storm disease.

NeurologicEHM means fever, ataxia, weakness, bladder dysfunction, isolation.

DiagnosticsPCR and abortion tissue diagnostics support decisions.

TrapVaccination does not replace biosecurity.

Exam core — read this first

NAVLE pearl → Fever often precedes neurologic EHM; temperature monitoring can identify exposed horses before signs appear.

Abortion pearl → Late-term abortion with minimal premonitory signs in a mare group is classic EHV-1 reasoning.

Biosecurity pearl → Do not wait for final confirmation before movement control when the outbreak pattern is strong.

Vaccine pearl → Available vaccines reduce respiratory disease and abortion risk but should not be presented as fully protective against EHM.

Emergency Triage Alert

Neurologic EHV Is A Biosecurity Emergency

Ataxia, urine dribbling, hindlimb weakness, recumbency, or fever in an exposed horse should trigger isolation, movement restriction, and veterinarian-directed outbreak management.

Biosecurity and Reporting Boundary

Verify official requirements

EHV-1 neurologic disease and outbreaks can involve official reporting or movement guidance depending on jurisdiction. This page is educational and not official regulatory advice.

Pattern recognition

Core pattern

fever and respiratory signs after show, transport, or new horse exposurelate-term abortion cluster or sudden abortion without many warning signsfebrile horse with ataxia, hindlimb weakness, urine dribbling, or recumbencybarn outbreak where movement control and exposed-horse monitoring are centralquestion contrasts vaccination with biosecurity expectations

Supporting clues

temperature trends in exposed horsespregnancy status and abortion timelinenasal swab and whole blood PCR contextneurologic exam and bladder functionmovement history, shows, transport, and barnmate exposure

NAVLE trigger: The key is recognizing the syndrome and protecting the premises before routine outpatient thinking.

Decision core — what NAVLE actually asks

Neurologic or febrile exposed horse

Choose isolation, movement restriction, diagnostic testing, and veterinarian-directed outbreak control.

Abortion cluster

Think EHV-1, submit fetal/placental diagnostics, isolate appropriately, and protect pregnant mares.

Respiratory outbreak

Use PCR testing, temperature monitoring, separation of affected horses, and exposure communication.

Vaccination question

Vaccination is part of risk reduction but does not replace biosecurity or guarantee prevention of EHM.

Key interpretation

Fever after exposure

Early warning

Temperature monitoring is a practical outbreak-control tool.

Ataxia plus urine dribbling

EHM anchor

Neurologic EHV shifts the case into emergency biosecurity logic.

Late abortion

EHV-1 anchor

Aborted fetus and placenta should be handled through diagnostic and biosecurity channels.

PCR result

Supportive test

Interpret with sample type, timing, and clinical signs.

Use current official guidance for reportability and movement restrictions; requirements vary by jurisdiction.

Management and treatment

Containment

Isolate suspect horses, stop risky movement, monitor temperatures, and manage exposed groups under veterinary guidance.

Containment is often the tested first action.

Supportive care

Provide supportive care for fever, respiratory disease, neurologic deficits, bladder dysfunction, and recumbency risk as directed by the veterinarian.

This page does not provide drug protocols.

Diagnostics

Use PCR testing and abortion tissue diagnostics when the syndrome fits.

Sampling strategy and timing matter.

Prognosis

Respiratory cases often recover; prognosis is guarded with recumbency, severe neurologic signs, or extensive outbreak spread.

Prevention depends on biosecurity plus vaccination strategy.

NAVLE traps — where students lose marks

Calling vaccination fully protective against EHM

Vaccines reduce some risks but should not be framed as a neurologic guarantee.

Waiting for PCR before isolation

Strong outbreak patterns require movement control while tests are pending.

Missing fever monitoring

Temperature trends can reveal exposed horses before neurologic signs.

Treating abortion as routine dystocia

Late-term abortion clusters need infectious and biosecurity reasoning.

Ignoring latency

Stress and reactivation help explain recurrence and outbreaks.

Overlooking bladder dysfunction

Urine dribbling or retention is a classic EHM clue.

Differentials — how to separate these on NAVLE

NAVLE discriminator: sort EHV from other equine neurologic, reproductive, and respiratory diseases using fever, exposure, syndrome, and outbreak context.

Differential	Key clue	Best decision bias	Trap
EHV respiratory disease	Fever, nasal discharge, cough after crowding or transport	Isolation, PCR, temperature monitoring	Routine stable cough only
EHV-1 abortion	Late-term abortion or abortion storm	Submit fetus/placenta and protect herd	Ignoring infectious abortion
EHM	Fever, ataxia, hindlimb weakness, urine dribbling	Emergency biosecurity and supportive care	Waiting for recumbency before action
EPM or trauma	Often individual neurologic disease without barn fever cluster	Neurologic localization and diagnostic workup	Missing contagious context

Practice questions

Practice EHV syndrome recognition and outbreak control

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Q1EHM triage

A horse returning from a show develops fever, hindlimb ataxia, weakness, and urine dribbling. Several barnmates are febrile. What is the best first principle?

Q2Abortion branch

Three pregnant mares abort late in gestation after a respiratory outbreak on the farm. What cause should be high on the list?

Q3Vaccine trap

An owner says EHV vaccination means neurologic disease cannot occur. What is the best correction?