Equine Herpes Virus By Dr. Joanna Bronson | http://bronsonvetservices.com/ Equine Herpes Virus (EHV) causes respiratory illness and is found worldwide in the equine population. However, it can lead to the neurologic disease EHM (myleoncephalopathy) which affects the neuromuscular system and attacks the spinal cord and brain. The majority of horses are exposed to EHV-1 early in their lives and develop a latent infection (carrying the virus their entire lives without developing signs of illness). Young and pregnant horses are especially susceptible to this airborne disease which can cause abortion and can produce neurological disease in horses of any age, sex, or breed. EHM seems to hit older horses more severely. Fortunately, most horses that do contract EHV have a fairly good prognosis, unless they develop neurologic signs then the survival rate is about 50% for this serious infection. EHV has 9 different recognized variants with number 1, 3, and 4 posing the highest risks for domestic horses. EHV-1 most commonly affects foals, yearlings, and young horses in training. Their symptoms may include elevated temperatures, watery nasal discharge, enlarged glands under the jaw with coughing. Some cases may progress to secondary pneumonia. Besides the respiratory symptoms, EHV-1 can cause abortion, neonatal death, and neurological symptoms. EHV-3 causes a venereal disease called coital exanthema which affects the external genitalia. However, it has not been shown to affect fertility. EHV-4 is a non-fatal upper respiratory tract disease that affects mares and foals and may be associated with abortion and rare cases of neurological disease. Neurologic signs appear with fever, nasal discharge, limb edema, in coordination, hindquarter weakness, recumbence (lying down), lethargy, dribbling urine, and/or diminished tail control. The virus manifests in a biphasic fever (lasting 1-2 days) which then reappears on day 6 or 7 of the infection. When the second fever spikes, neurological signs may appear in some horses; others may not have a fever but still show signs of neurological involvement. Transmission of the disease is spread between horses through contact with nasal discharge, aerosol droplets, (shedding), and through contact with contaminated sources such as stalls, water, feed, tack, and horse trailers. It can also be spread by human contact from hands and clothing. The EHV virus can live up to 7 days in the environment, but it can also remain infectious for up to a month if the environmental conditions are favorable for incubation. During show season and any other communal gathering times, the risk of exposure to the infection is much greater. Any potential exposed horse(s) should be separate and basic biosecurity guidelines should be followed to help decrease the spread of the disease. These guidelines include: · Limiting horse-to-horse contact · Limiting horse-to-human-to-horse contact · Avoiding all communal water and food sources JUNE 2022 • C & C PUBLISHING, INC. ©2022
· Avoiding or thoroughly disinfecting all shared equipment between uses · Monitoring all horses for clinical signs of EHV, taking temperatures twice daily, isolating horses with a temp above 101.5 or those showing other disease symptoms Normal disinfecting procedures are sufficient to clean with as the virus is easily killed by most disinfectants. Using a solution of 1 part chlorine to 10 parts of water is enough to disinfect. However, disinfecting surfaces that are used for cleaning is also important. Horse and human clothing should be washed in hot water with detergent and dried in a dryer for protection from transmission. It is important to clean and disinfect any surfaces prior to washing equipment on them. To diagnose an infected horse, your veterinarian will collect a nasal swab and blood sample for testing with a repeat test in 2-3 weeks to check for antibody levels specific to EHV-1. If a horse showing neurological signs tests positive for EHV-1, he is also considered positive for EHM. For any horses that may have been exposed to an infectious agent, they are at risk for the development of the disease. Even if a horse appears healthy, biosecurity procedures should be followed at home. An isolation period of at least 21-28 days is recommended. Horses that do test positive are usually treated with antiinflammatory drugs and may need IV fluids. Antibiotics are used for secondary bacterial infections although antibiotics do not have any effect on EHV itself. Some horses may be additionally treated with anti-coagulant drugs. There is no preventive vaccine. However, the Rhino/Flu vaccine protects against some forms of respiratory infection. There is always a risk of infection when horses are brought together. Keeping your horse vaccinated, healthy, and observing biosecurity protocols are the best safeguards we can offer at this time. Research is ongoing. Dr. Joanna Bronson graduated from MSU College of Veterinary Medicine at the top of her class. In 2005, she opened Bronson Veterinary Services in Coldwater, MI, a full-service equine, small animal hospital and surgical center. Bronson Veterinary Services also has a mobile unit for equine calls and after hour emergency care. (22)
WWW.SADDLEUPMAG.COM
