:: RHINOPNEUMONITIS
(EHV-1 and EHV-4)

Equine rhinopneumonitis virus, or equine herpesvirus 1 (EHV-1) and 4 (EHV-4), causes respiratory disease in horses upon their first exposure to it. In areas of high horse concentration, annual outbreaks are common, especially among weanlings. Occurrences in less populated areas are sporadic but not uncommon. EHV-4 primarily causes respiratory disease, while EHV-1 can cause respiratory disease, abortion or paralysis.

The spread of EHV-1 and EHV-4 occurs relatively slowly throughout a farm, although rapid spread is possible, especially if young horses are crowded and stressed. Like other herpesviruses, EHV-l and EHV-4 can infect previously exposed animals without causing obvious disease. Then, under stressful conditions, the virus can become active and cause disease. If the stress is due to transport, competitive events, or sale activity, there is great opportunity for infection of contact animals.

Clinical Signs

Typical signs of equine herpesvirus respiratory disease include fever, congestion, cough, loss of appetite, nasal and eye discharges, fatigue, and swollen lymph nodes. An animal's first exposure to the disease generally produces more severe signs, whereas later exposures cause mild or inapparent infections. Secondary bacterial infections can occur and should be suspected when fever persists beyond a week, the nasal discharge becomes thick and yellow instead of watery, or the cough worsens.

Diagnosis

Clinical signs of equine rhinopneumonitis are similar to other respiratory diseases in horses, so it is difficult to make a definite diagnosis from clinical signs alone. Serologic tests may help establish a diagnosis, but first exposure in foals often does not stimulate a strong or rapid antibody response, so it may be difficult to see an increased level of antibodies when comparing serum taken early in the disease to serum taken several weeks later, when most diseases would have caused a significant rise in antibody levels. Viral isolation (growing the virus in laboratory culture) can be attempted from nasal and throat swabs, but isolation can also prove difficult.

Treatment

There is no specific treatment for equine viral rhinopneumonitis. However, it is important to recognize the early stages of the disease and immediately begin rest and supportive care for affected horses. Medications to reduce fever may be given if the fever goes over 104° F. Training or work by sick horses must be discontinued. Otherwise, health and performance capability may be permanently affected. Antibiotic therapy should be instituted if secondary bacterial complications arise. Stalls should be well ventilated and as dust-free as possible.

Prevention

A vaccination program should include all horses on the premises. Scheduling of booster vaccinations and frequency of revaccinations are best determined by a local veterinarian. Vaccination will help prevent disease, and reduce the amount of viral shedding. Direct contact between sick horses and healthy horses should be avoided, as should common eating and drinking facilities. Isolation or separation of affected horses is especially important on a breeding farm because of possible abortion associated with EHV-1 infection. The general rule that new horses introduced to the farm should be isolated for up to six weeks applies, as always.

Prestige^® with Havlogen^®
                             Adjuvant
Equine Rhinopneumonitis Vaccine
   For vaccination of healthy horses against respiratory diseases caused by equine herpesvirus.

Prestige^® II with Havlogen^®
                                          Adjuvant
Equine Rhinopneumonis and Influenza Vaccine
   For vaccination of healthy horses against respiratory diseases caused by equine herpesvirus and equine influenza.

Administration and Dosage
   For primary immunization, aseptically inject 1 mL intramuscularly. Repeat the dose in 4 to 6 weeks. Foals should receive a booster dose in six months. A 1 mL dose should be administered annually and at any time epidemic conditions exist or are reported and exposure is imminent. Neomycin, Polymyxin B, Nystatin, and Thimerosal added as preservatives.

This brochure was developed by the American Association of Equine Practiitioners through a grant from Bayer Corporation.

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