Equine Herpes Virus Client Information Sheet

Equine Herpes Virus Client Information Sheet
By Laura Markey, DVM and Ada Caruthers, DVM
3/2/2007

General Information:

There are two types of herpes viruses known to cause respiratory disease (rhinopneumonitis) in horses. These are EHV-1 (equine herpes virus type 1) and EHV-4 (equine herpes virus type 4).
EHV-1 is known to cause respiratory disease, abortion, stillbirth and neurological disease. EHV-4 is usually restricted to the respiratory system and to younger horses.
EHV-1 is the agent implicated in the recent outbreak in Maryland and Virginia.

Disease Transmission:

EHV-1 is transmitted directly or indirectly from horse to horse via nasal secretions, aborted fetuses, placentas or placental fluids (afterbirth). The disease can be caused by exposure to an incoming horse or by stimulation of viral shedding by a horse that has been latently infected. The virus is found in horse populations worldwide. Most horses have been exposed to the virus at a young age, have developed respiratory disease and have recovered. However, most of these horses also remain latently infected, and shedding can be initiated by stressful events (shipping, environmental stress etc…)
Horses in a closed herd (no horses coming in or leaving) can become infected if a latently infected horse begins to shed.
Horses will become sick 3-7 days after exposure. Viral shedding from the nose will last for up to 2 weeks.

Signs and Symptoms:

Signs of respiratory disease include fever, nasal discharge, cough, anorexia, enlarged lymph nodes and lethargy. Horses with respiratory disease usually recover in 1-3 weeks.
Abortion may occur 9-120 days after exposure. Abortions usually occur in the last half of gestation. Stillbirth may also occur. Respiratory disease may or may not be seen in association with abortion or stillbirth.
The neurological form of the disease is occasionally seen. This usually begins with a high fever followed by a 6-10 day apparent recovery before onset of fever and neurological signs (usually hind limb weakness and incoordination, as well as urine leakage; front limbs can be affected but this is less common; rarely mentation is altered). Horses may or may not show respiratory disease in association with neurological disease.

Diagnostics:

Diagnostics include obtaining a nasal swab or nasal wash and blood samples for viral isolation. Other diagnostic tests are available. Placentas from aborted fetuses or stillborn foals should be sent to the laboratory for diagnostic evaluation.

Treatment and Prognosis:

There is no specific treatment for EHV. IV fluids and anti-inflammatories (banamine, DMSO, steroids) can be given to provide supportive care. Antiviral drugs may be of benefit. Quarantine for 3 weeks is essential to prevent spread.
Horses with neurological disease that remain standing have a good prognosis for recovery, and improvement generally is apparent within a few days, although a period of several weeks to more than a year may be required before horses with severe deficits show complete recovery. Some horses may be left with permanent neurological deficits. Horses that become recumbent and remain so for more than 24 hours have a poor prognosis for recovery. Recurrence or exacerbation of neurological signs in horses that have recovered completely has not been documented although the majority likely remains latently infected.
The prognosis for recovery from respiratory disease is good although horses should be allowed to rest for 4-6 weeks after recovery from infection.
Mares that abort due to EHV-1 usually do not incur any damage to the reproductive tract. Viral abortions are rarely observed in the same mare in 2 successive seasons indicating that natural infection induces immunity providing some degree of protection.

Prevention:

Affected horses should be isolated. The virus spreads via aerosol, direct contact, inanimate objects and the placenta/afterbirth. Strict disinfection of contaminated objects, clothing and environments should be implemented. Standard disinfectants will kill the virus (i.e. Bleach, chlorhexidine). Horse handlers should wear gloves, booties and protective over clothes. All sources of water should be cleaned including buckets, hoses, nozzles and water troughs. The virus can live in water for 7 days. Diseased horses should be tended to at the end of the day after healthy horses. No horses should be transported on or off the premises until 1 month after the resolution of acute signs in the last case.
The rhinopneumonitis vaccine is part of the standard vaccination protocol for most horses that travel or co-mingle with different horses. This vaccine helps to prevent the respiratory and abortion forms of the disease (protection is not 100%), however does not prevent the neurological form. Sick horses should not be vaccinated. Vaccination of uninfected horses in the face of an outbreak is controversial. Some veterinarians feel that vaccination is indicated as it will help prevent the spread of disease. Others feel that it may predispose a horse to the neurological form of the disease. This is because the neurological form may be due to the immune system’s over-reaction to the virus. The vaccine will up regulate the immune system and may exacerbate the process.

Our Recommendations:

If you notice any signs of respiratory disease, fever or neurological disease, contact us immediately.
Farms that have no current cases of EHV-1 should try to minimize travel to help contain the disease. We will vaccinate horses that are due for vaccination as scheduled. We are not recommending that anyone vaccinate any differently than we would normally recommend.

Websites for Update on Situation:

Please review these websites for a current update on the situation:

Virginia Department of Agriculture and Consumer Services
www.vdacs.virginia.gov/

Maryland Department of Agriculture
www.mda.state.md.us/

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