Treatment and Prevention
Treatment of EHV infections in horses is largely based on symptom management. Respiratory infections are usually self limiting and provided the animal is able to maintain its airway, treatment is typically not issued. Neurological cases are treated with NSAIDS (phenylbutasone, flunixin megulamate) with or without corticosteroids (dexamethasone). Some practitioners advocate the use of DMSO as it has been shown to decrease swelling in the CNS. As the prevalence of EHV-1 myeloencephalopathy (EHM) is increasing in North America, specific antiviral therapy to treat this disease is gaining in popularity. Acyclovir (9-(2-hydroxyethoxymethyl)guanine) is an acyclic nucleoside analogue which has a high activity and selectivity for herpes viruses, particularly herpes simplex viruses types 1 and 2 and varicella zoster virus. Acyclovir's selectivity is due to the initial activation of the drug by phosphorylation by a herpes virus-specified thymidine kinase. Acyclovir monophosphate is converted to a triphosphate that is a more potent inhibitor of herpes virus DNA polymerases than of cellular DNA polymerases. The relationship between the amount of acyclovir triphosphate formed and its inhibition constant (Ki) for the particular viral or cellular DNA polymerase is predictive of the inhibitory activity of acyclovir on DNA replication [18]. However recent studies of the pharmacokinetis of Acyclovir have shown that oral administration of acyclovir demonstrates poor bioavailability, and intravenous administration in horses is cost prohibitive (to treat an average sized horse can cost over $300/day) [18]. Other antiviral agents are being studied and may become available in the coming years.
EHV outbreaks are best though about from a management perspective.
Animals with clinical signs should be immediately isolated from other horses. Separate quarantine facilities are ideal, however most acreage farms are not set up to deal with infectious disease outbreaks. Because of the potential for aerosol transmission of the EHV virus, even putting a sick horse at the end of a barn may not be sufficient to halt virus spread - although if this is your only option then it is better than having the horse in the middle of the barn surrounded by other horses. Particular attention should be taken to ensure weanlings, broodmares and previously immunocomprimised horses do not come into contact with horses you suspect as having EHV as this group of horses is particularly susceptible to contracting EHV. It is important to remember that all personel, equipment, feed, water and any other objects that come into contact with horse that is shedding virus particles must be disinfected thouroughly before coming into contact with other horses. It is recommended that horses remain in quarintine for at lease 3 weeks after the resolution of clinical signs as apparently healed horses can still be infectious for quite some time.[16]