Disease Du Jour: Equine Herpesvirus Refresher

In this episode of the Disease Du Jour podcast, we discuss equine herpesviruses types 1-5 with Nathan Slovis, DVM, DACVIM, CHT.
restricted access sign on barn door quarantine
Quarantine and isolation of a horse (or horses) that test positive for equine herpesvirus is important in preventing spread of the virus.

How do you handle an equine herpesvirus case? In this episode of Disease Du Jour, we discuss equine herpesviruses types 1-5 with Nathan Slovis, DVM, DACVIM, CHT (Certified Hyperbaric Technologist). Slovis is the Director of the McGee Center at Hagyard Equine Medical Institute in Kentucky. He walks us through the five types, with emphasis on EHV-1.

Equine Herpesvirus Type 1 (EHV-1)

“EHV-1 gets most of the publicity because in certain states it is a reportable disease,” said Slovis. “People get nervous” about dealing with authorities with reportable diseases.

Slovis said for a horse that tests positive for EHV-1, owners are worried about equine herpesvirus myeloencephalopathy (EHM). That is the neurologic form of equine herpesvirus. “That is the first thing they think about,” he said.

“We know through various studies that it’s hard to expose a horse and [spread EHV-1],” reminded Slovis. He added that “less than 10% of these horses that are affected with EHV-1 get neurologic.”

Slovis said the second thing owners think about if they have broodmares is abortion. The third thing they think about is the respiratory aspect. But the respiratory aspect is what happens in more than 90% of cases.

Testing and Dormancy of EHV-1

Slovis said equine herpesvirus type 1 respiratory disease can look like many other respiratory diseases. Horses have a fever, cough and nasal discharge.

He noted that veterinarians can’t know which disease they are dealing with unless they conduct diagnostic testing. Slovis also reminded veterinarians that equine herpesvirus can lie dormant in a horse before some sort of stress situation (physical or emotional) can cause the virus to re-activate. Then that horse can spread the virus to susceptible animals.

Slovis also noted that too many people have focused on the “neurologic” vs “non-neurologic” forms of equine herpesvirus type 1.

“I don’t care about the strain,” stressed Slovis. “The bottom line is that any strain can cause it (neurologic herpesvirus).

Treatments for Equine Herpesvirus Type 1

How can veterinarians help clients reduce the incidence of EHV-1 and how do you treat an infected horse?

Slovis discussed the use of non-steroidals (NSAIDs) and steroids in horses with equine herpesvirus. He said heparin has been used to decrease hypercoagulability. He talked about studies on heparin and even aspirin for this purpose. Slovis said there is no real “in-depth” study, “but this may decrease the chance or severity of clinical signs when you use heparin or aspirin.” He noted that European veterinarians use more aspirin and U.S. vets use more heparin.

Slovis also talked about the use of the antivirals valacyclovir and acyclovir in cases of equine herpesvirus.

Spread of Equine Herpesvirus

Slovis said if a veterinarian has a horse test positive for EHV-1 or EHV-4, those horses should be isolated.

A horse can start shedding one day after exposure, said Slovis. Horses then can shed for 7-14 days. In the Findlay outbreak, they found shedding horses up to 19 days after exposure.

He said some researchers recommend not releasing horses from and EHV-1 quarantine until 21 days after exposure with negative tests for herpesvirus in whole blood and nasal secretions. He said most states have now adopted a 14-day quarantine with negative testing before horses are released.

Equine Herpesvirus Abortion

Slovis took time to talk about EHV-1 abortion. He stressed to make sure all mares on a property are vaccinated with EHV-1 vaccines specific for abortion.

He had many other tips about on-farm management. Included in his tips was that the aborted placenta and allantoic fluids can spread the virus. Keep other mares away from those tissues and fluids.

Slovis said that farm managers also shouldn’t play “musical chairs” with mares in paddocks or fields. “You might not know for weeks that a mare has aborted,” he said. That means the tissues and fluids could expose other mares without your knowledge.

He talked about treatments if mares get ill or abort from equine herpesvirus. He also discussed shedding and quarantine.

Gamma Equine Herpesvirus

Equine herpesvirus types 1 and 4 are alpha herpesviruses. Equine herpesviruses type 2 and 5 are gamma herpesviruses.

He also mentioned that donkeys have their own alpha herpesvirus (EHV-9), which can also affect gazelles and zebras.

In the podcast, he discussed the diseases and debates about gamma herpesviruses in equids. EHV-2 can cause conjunctivitis and eye issues. EHV-5 is a vague respiratory virus potentially seen in foals and young horses. The debate is whether EHV-5 is a primary disease.

Equine Herpesvirus Type 3

EHV-3 is an equine venereal disease (equine coital exanthema virus). “You don’t see this much,” said Slovis.

He said there will be lesions on the vulva of mares and penis of stallions.

“A lot of the issue is hygiene,” he noted. Slovis said this is a disease that is more frequently seen in Europe.

About Dr. Nathan Slovis

Nathan Slovis, DVM, DACVIM, CHT, is the Director of the McGee Center at Hagyard Equine Medical Institute in Kentucky. He is a native of Annapolis, Maryland. Slovis received his Bachelor of Science from Radford University, Doctor of Veterinary Medicine from Purdue University, interned at Arizona Equine Center and completed his residency in Internal Medicine at the University of California, Davis.

Slovis has published more than 50 manuscripts in both national and international peer-reviewed veterinary journals. He is a frequent speaker at national and international veterinary conferences. Slovis is the editor of both the Atlas of Equine Endoscopy and The Atlas of Diseases/Disorders of the Foal, both distributed by Elsevier. He has also authored numerous book chapters related to equine neonatology, equine neurology, hyperbaric medicine and infectious diseases. Slovis implemented the current Infectious Disease and Equine Emergency Response Programs at Hagyard and holds the position of Infectious Disease Officer and Equine Emergency Response Co-Director.

Slovis is a Certified Hyperbaric Technologist (CHT) and a member of the Veterinary Infectious Disease Society.

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