Equine Outbreaks: Vaccines, Testing & Biosecurity

Four major equine outbreak diseases:

1.) Equine Herpesvirus (EHV-1)

2.) Equine Influenza

3.) Botulism

4.) Strangles

Equine herpesvirus-1 (EHV-1)

A contagious viral infection that can cause respiratory disease, abortion, and equine herpesvirus myeloencephalopathy (EHM)

Equine influenza

A highly contagious respiratory viral infection that spreads rapidly among horses, especially at shows and other large gatherings

Strangles (Streptococcus equi)

A contagious bacterial upper respiratory disease characterized by fever, lymph node enlargement, and abscess formation

Botulism (Clostridium botulinum)

A toxin-mediated disease that causes progressive flaccid paralysis, usually following ingestion of contaminated feed

How do Equine Herpesvirus (EHV-1), Equine Influenza, and Strangles spread?

through respiratory secretions, direct contact, or contaminated equipment

How does Botulism spreead?

through horses consuming the same contaminated feed rather than horse-to-horse transmission

Three layers of outbreak defense:

1.) risk based vaccines

2.) early detection and diagnostic testing

3.) exposure control (biosecurity)

Risk based vaccines

vaccines recommended according to an individual horse's exposure risk, geographic location, management practices, and likelihood of encountering a particular pathogen

Most risk based vaccines do not provide complete _______. Therefore...

immunity; vaccinated horses may still become infected and transmit pathogens

Early detection and diagnostic testing involves three things:

1.) monitoring horses for early signs of illness, especially fever

2.) perform routine temp checks during high risk events

3.) use appropriate diagnostic tests to identify the pathogen and determine what horses are shedding

Exposure control (biosecurity) involves:

-Isolating infected or potentially infected horses

-Restricting horse movement

-Establishing separate areas for infected, exposed, and unexposed horses

-Using appropriate PPE, cleaning, disinfection, and dedicated equipment

What is the first clinical sign that serves as an early warning sign for respiratory infectious diseases?

fever!

Warning signs for EHV-1 and influenza:

Clusters of unexplained fever (greater than 101.5°F) or respiratory signs, especially in densely populated facilities

Warning signs for Strangles:

Fever followed by lymph node enlargement, abscessation, or discharge, particularly in newly introduced horses

Warning signs for Botulism:

Multiple horses developing weakness, dysphagia, or recumbency, particularly after consuming a shared feed source

When an outbreak is suspected, there are three things you should do within the first 24 hours:

1.) halt movement

2.) temperature sweep/evaluating population

3.) enforce barriers

Halting movement includes...

stopping horses from entering or leaving the property and isolating the first clinically affected horse

True or false: you should NOT wait for definitive laboratory results to halt movement

true!

Temperature sweep/evaluating population

taking the temperature of every horse, and separating horses into red, amber, and green zones based on clinical signs and exposure history

Enforce barriers involves...

assigned dedicated personnel/equipment to each zone and preventing movement before groups; personnel work from "clean" to "contaminated" areas

Three zones of a premise during an outbreak:

1.) green zone

2.) amber zone

3.) red zone

green zone

aka clean zone; where unexposed and non clinical horses go

amber zone

aka exposed zone; where horses who have had contact with infected horses but not showing clinical signs go

red zone

aka clinical zone; where horses actively showing clinical signs of the disease go; require 30 ft separation perimeter from uninfected animals

When an Equine Herpesvirus (EHV-1) outbreak is suspected, what action should you take?

Isolate index cases immediately.

Implement twice-daily temperature sweeps

across all cohorts

Testing for Equine Herpesvirus (EHV-1) involves...

nasopharyngeal swab + whole blood (EDTA) for qPCR

nasopharyngeal swab for Equine Herpesvirus (EHV-1) is used to...

detect viral shedding from the respiratory tract

Nasal shedding for Equine Herpesvirus (EHV-1) begins ___-___ days after the onset of fever.

Because of this, what should you keep in mind when interpreting nasopharyngeal swab results?

1-2 days

an early negative result does not necessarily rule out infection because the horse may not yet be shedding detectable quantities of virus

whole blood (EDTA) for qPCR testing for Equine Herpesvirus (EHV-1) is used to...

detect EHV-1 viremia (determine if virus is circulating in bloodstream)

qPCR testing for Equine Herpesvirus (EHV-1) is particularly important when evaluating the risk of...

systemic disease and EHM

Equine Herpesvirus (EHV-1) vaccine

labeled for reduction of respiratory disease and prevention of abortion

Current Equine Herpesvirus (EHV-1) vaccines do NOT protect against what form of the virus?

Equine Herpesvirus

Myeloencephalopathy (EHM) (neural form)

Vaccinated Equine Herpesvirus (EHV-1) horses can become subclinical _________. Why is this dangerous?

shedders! will appear healthy while transmitting high viral loads

Clinical red flags of Equine Herpesvirus (EHV-1)

-Fever (102-106°F) typically precedes neurologic signs by several days

-Neurologic progression: ataxia, hind limb weakness, urine dribbling, loss of tail tone

Immediate outbreak action for Equine Herpesvirus (EHV-1) involves three things:

1.) isolate febrile horse immediately

2.) institute twice daily temp monitoring for the entire herd

3.) establish strict 30 ft perimeter isolation zones and halt movement

What should you NOT do at the start of an Equine Herpesvirus (EHV-1)?

try to "vaccinate your way out" of it; vaccination does not replace movement restrictions or isolation

Botulism

potentially fatal neuromuscular disease caused by botulinum neurotoxin produced by Clostridium botulinum

The toxin produced by botulism causes _______ paralysis

flaccid (muscles become weak and lose their ability to contract normally)

Equine botulism outbreaks usually involve ingestion of...

contaminated forage or feed

Three Botulism toxin types

1.) Type B

2.) Type A

3.) Type C

Type B Botulism toxin

Particularly important in Ohio and much of the eastern United States; associated with environmental contamination, including spores present in soil

Type A Botulism toxin

associated with soils west of the Mississippi River

Type C Botulism toxin

associated with decomposing animal carcasses incorporated into forage

Which Botulism toxin has an effective vaccine?

Type B

What type of vaccine is available for Botulism?

toxoid

Two scenarios that favor feed contamination with Clostridium botulinum

1.) improperly preserved forage (anaerobic, wet, poorly fermented)

2.) animal carcasses incorporated into feed

Clinical signs of Botulism

-Dysphagia

-Decreased or absent tongue tone

-Muscle fasciculations

-Progressive generalized weakness

-Flaccid paralysis

-Recumbency

When a Botulism outbreak is suspected, what action should you take?

-Immediately stop feeding suspected forage/feed

-Retain feed samples under veterinary/regulatory guidance

-Initiate supportive care

Testing for Botulism involves...

clinical diagnosis is primary; test feed/forage or GI contents, NOT the live horse

Feed traceability

the ability to identify where a feed product originated, how it was processed, and where it was distributed

Contamination of Botulism is NOT not necessarily distributed _______ throughout a shipment

evenly

Since Botulism contamination is NOT not necessarily distributed evenly throughout a shipment, this means that...

1.) One contaminated bale does not mean every bale contains the same toxin concentration

2.) One negative feed sample does not rule out contamination elsewhere in the lot

3.) Feed that appears normal may still contain toxin

Three forms of evidence supporting a common Botulism contaminated feed source:

1.) shared exposure

2.) visual contamination

3.) laboratory confirmation

shared exposure

Affected horses at different locations had consumed the same commercial feed product; the horses developed the same neurologic signs despite being on separate premises

visual contamination

animal hair and tissue may be present within feed

laboratory confirmation

tests for the specific Botulism toxin

Since Botulism is a toxin-mediated disease, severe neurologic dysfunction can occur without obvious structural _______ at necropsy

lesions

Equine Influenza

highly contagious viral respiratory disease caused by an influenza A virus in the family Orthomyxoviridae

Clinical signs of Equine Influenza

-Fever

-Coughing

-Nasal discharge

-Lethargy

-Reduced appetite

-Decreased performance

Testing for Equine Influenza involves...

Nasal swab for rapid PCR or stall side antigen test

Unlike the other diseases in this lecture, Equine Influenza vaccination is useful _______ an outbreak!

during

Effects of Equine Influenza vaccination

-Reduce clinical severity

-Decrease viral shedding

-Slow transmission between horses

-Reduce the overall impact of an outbreak

In-face vaccination of Equine Influenza

involves vaccinating unaffected, at-risk horses early during an outbreak

While the Equine Influenza vaccine can reduce additional transmission, you should still implement _______ measures to control current exposures

biosecurity

When an Equine Influenza outbreak is suspected, what action should you take?

-Isolate index cases immediately

-Implement twice-daily temperature sweeps

across all cohorts

-Quarantine new arrivals separately from resident horses

-Maintain appropriate isolation and surveillance procedures.

Strangles

a highly contagious bacterial upper respiratory disease caused by Streptococcus equi subspecies equi.

Clinical signs of Strangles

-fever

-lymphadenopathy

-lymph node abscess formation

-nasal discharge

-upper airway obstruction

Where did Strangles get its name?

because severe lymph node enlargement and abscessation can compress the upper airway, potentially interfering with breathing

Why is the guttural pouch important in Strangles?

S. equi can persist within the guttural pouches after the horse has recovered clinically, allowing them to shed the disease!

Chondroids

firm, inspissated masses of purulent material that can harbor persistent S. equi infection within the guttural pouches

When a Strangles outbreak is suspected, what action should you take?

Isolate clinical horses. Wait 24-48

hours post-fever to sample (qPCR) to avoid

false negatives

Establish clean/dirty zones.

Testing for Strangles involves...

1.) nasopharyngeal swab

2.) abscess aspirates

3.) Guttural pouch lavage + qPCR

nasopharyngeal swab and Strangles testing

May be useful during active infection, especially when mucopurulent discharge is present; samples can be submitted for PCR

abscess aspirates and Strangles testing

Material can be collected from a mature affected lymph node; useful for confirming active infection when abscessation is present

Guttural pouch lavage and Strangles testing

important for identifying persistent carriers! Samples are submitted for PCR and/or culture

Strangles vaccine

modified-live bacterial vaccine

What is the goal of the Strangles vaccine?

to reduce clinical disease severity rather than reliably prevent infection

Purpura Hemorrhagica

immune-mediated vasculitis associated with strangles, involving a type III hypersensitivity reaction

What horses should never be vaccinated with the Strangles vaccine? Why?

those with high SeM titers; increases the risk of Purpura Hemorrhagica

How can vaccination trigger Purpura Hemorrhagica?

1.) A horse becomes infected with or exposed to S. equi.

2.) The immune system produces a strong antibody response.

3.) The horse develops high SeM antibody titers.

4.) Subsequent vaccination introduces additional antigen.

5.) Immune complex formation can trigger type III hypersensitivity.

6.) Immune-mediated vasculitis develops, potentially producing severe edema and other complications.

If there is Strangles on the farm, put the vaccine ________. Instead, focus on...

away; biosecurity,

temperature screening, and isolating the clinical and exposed

Role of vaccine for EHV-1

Reduces respiratory signs & shedding; no EHM protection label!

Diagnostic priority for EHV-1

Detect early fever; Nasal/Blood qPCR

Non-negotiable action for EHV-1

Immediate isolation upon fever; do not rely on vaccines during outbreak!

Role of vaccine for Botulism

Highly effective for Type B toxin; no cross protection

Diagnostic priority for Botulism

Clinical history (forage type) + neurologic presentation

Non-negotiable action for Botulism

Halt suspect feed immediately; rapid clinical intervention

Role of vaccine for Influenza

Slows transmission velocity; protects the herd

Diagnostic priority for Influenza

Rapid PCR or stall-side antigen test

Non-negotiable action for Influenza

In-face vaccination for the unexposed + strict fomite control

Role of vaccine for Strangles

Reduces severity; risk of Purpura in high-

titer/exposed!

Diagnostic priority for Strangles

GP lavage qPCR to find subclinical carriers

Non-negotiable action for Strangles

No vaccines during outbreak; eradicate persistent guttural pouch carriers