APHIS Factsheet

Veterinary Services May 2007

Questions and 

Answers: Equine 

Herpesvirus

Q. What is equine herpesvirus type 1?

A. Equine herpesvirus type 1 (EHV-1) causes a disease of horses called equine rhinopneumonitis. It is 

found in horses worldwide but does not affect humans. 

EHV-1 usually causes respiratory symptoms with 

fever, but it can also cause abortion, nervous system 

(neurologic) disease, or death. 

Q. Are there different types of EHV-1?

A. EHV-1 has several different strains, and new 

strains can develop from natural mutations. These 

strains or mutations are thought to cause outbreaks of 

the disease. The neurologic form of the disease can 

cause a wide variety of symptoms, including incoordination, weakness or paralysis of the hind limbs and 

tail, incontinence, and loss of skin sensation. The 

horse may lie down and not be able to get up. The 

paralysis can be progressive and in some cases, the 

animal may die. 

Q. How is EHV-1 spread?

A. The virus can spread via contact with an infected 

animal, through the air, via contaminated equipment, 

or via a handler’s clothing and hands. An infected 

animal can be latently infected and sporadically shed 

the virus, or show only mild clinical signs. 

Q. Why is there a concern about EHV-1? 

A. The neurologic form of disease caused by EHV-1 

is emerging worldwide with outbreaks having a higher 

frequency than has been reported previously. Recent 

outbreaks may be related to a mutation of the EHV-1 

virus that allows it to multiply more efficiently. More 

horses are dying from this form than would normally 

be expected, and the disease also demonstrates the 

ability to affect horses of all breeds, ages, and vaccination status. This new form therefore has the potential to cause high losses in the U.S. horse population. 

Q. What is the Federal role in addressing EHV-1 

outbreaks?

A. EHV-1 is found throughout the United States and 

outbreaks are usually handled by the States involved. 

In some instances, however, shipments of horses may

be divided and shipped to multiple States. 

 During such outbreaks when animals have 

crossed State lines, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) steps in to assist with tracing animals. 

APHIS has worked closely with States and affected 

owners to help trace the movement of animals from 

their entry into the United States to their current or last 

location. 

Q. Has APHIS played a role in tracing any recent 

outbreaks of EHV-1 in the United States?

A. An outbreak of neurologic disease caused by 

EHV-1 occurred in late 2006 and involved a group 

of 15 horses shipped from Germany. After arriving in the United States, the horses were shipped to 

eight States. Five of the horses went to Florida; this 

resulted in 13 horses total identified as infected, with 

neurologic signs in 7 cases and 6 associated deaths. 

Ten Florida premises were quarantined. 

 One of the horses that arrived from Germany was 

shipped to California and died shortly after arrival 

from neurologic disease typical of EHV-1 infection. All 

horses exposed to this animal were identified.

 The remaining nine horses from Germany were 

shipped to six other States. They were quarantined 

and observed for signs of EHV-1 infection. No signs 

were seen. 

 The Florida outbreak was confirmed as due to 

EHV-1 when laboratories found neuropathogenic 

strains of EHV-1 in submitted samples. These findings, together with the observation of clinical signs 

consistent with the neurologic form of equine rhinopneumonitis, contributed to the diagnosis. Please visit 

http://www.aphis.usda.gov/vs/nahss/equine/ehv/index.

htm for updates on this recent EHV outbreak.

Q. What about EHV-1 outbreaks in other parts of 

the world?

A. Other countries have also seen an increase in the 

number and severity of reported neurologic EHV-1 

outbreaks. In 2005, significant outbreaks occurred in 

Canada, Ireland, South Africa, Switzerland, and the 

United Kingdom. 

Q. What should horseowners do to protect their 

animals from EHV-1?

A. Veterinarians and horseowners should continue to 

quarantine suspect and diagnosed cases. Using strict 

biosecurity measures in day-to-day procedures, even 

when disease is not suspected, is very important in 
United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, 

national origin, age, disability, and where applicable, sex, marital 

status, familial status, parental status, religion, sexual orientation, 

genetic information, political beliefs, reprisal, or because all or part 

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should contact USDA’s TARGET Center at (202) 720–2600 (voice 

and TDD). To file a complaint of discrimination, write to USDA, 

Director, Office of Civil Rights, 1400 Independence Avenue, S.W. , 

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(202) 720–6382 (TDD). USDA is an equal opportunity provider and 

employer. 

preventing the introduction and spread of infectious 

diseases. Information on equine biosecurity practices can be found in APHIS’ “Keeping Your Horses 

Healthy” brochure, available at http://www.aphis.

usda.gov/lpa/pubs/HorseBioSecurity_final.pdf. 

Q. Are there EHV-1 vaccine products available? 

A. There are currently 35 vaccine products licensed 

by APHIS’ Center for Veterinary Biologics (CVB) 

that contain EHV. These products are labeled as 

“Equine Rhinopneumonitis” vaccines. Some contain only EHV, and some have EHV in combination 

with other vaccines. These products all underwent 

extensive safety testing before they were licensed. 

All of them were shown to be effective in a manner that backs up the claim stated on the label. 

For example, the label may state, “as an aid in the 

control of respiratory disease due to EHV-1” or “as 

an aid in the prevention of abortion associated with 

EHV-1” or “aids in the reduction of shedding.” Currently, no licensed product has a label claim for the 

neurologic form of disease caused by EHV-1. 

Q. Have any horses gotten the neurologic form 

of EHV-1 after being vaccinated for the disease?

A. To date, CVB has not received a report of an 

adverse reaction involving the appearance of neurologic symptoms following vaccination with a licensed 

EHV vaccine. The recent outbreaks of neurological 

EHV appear to be related to a new strain of EHV1. However, APHIS remains vigilant and ready to 

respond if such an event is reported. Reporting 

adverse events is encouraged. Such events may 

be reported by telephone at (800) 752-6255; online, 

using the adverse event electronic report form available at the CVB Web site (http://www.aphis.usda.

gov/vs/cvb); or by fax or mail, using the Web site 

form and the provided CVB fax number or address. 

Q. Should owners get their horses vaccinated?

A. To date, not much is known for certain about how 

EHV-1 causes neurologic disease. As additional 

information becomes available, educational outreach 

to practitioners and horseowners will be extremely 

important. Decisions about the use of EHV vaccine in 

individual horses should be made based on your local 

situation in consultation with your veterinarian. APHIS 

will continue to work with interested groups such as 

the United States Animal Health Association, industry 

organizations, and national and State groups in making 

further recommendations and plans related to EHV-1.