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What is Equine Herpesvirus (EHV-1)?

Equine herpesvirus (EHV-1) is a viral infection in the horse population that can cause respiratory illness, abortion in late-term mares, and EHM (equine herpesvirus myeloencephalopathy), the devastating neurologic form of EHV-1.

How is EHV-1 Spread?

EHV-1 is most commonly spread by direct horse-to-horse contact via nasal secretions from the respiratory track. The virus can also be spread indirectly from the air around a horse that is shedding the virus, as well as physical objects that have been contaminated such as, tack, grooming equipment or feed and water buckets. The virus can survive up to 7 days under normal circumstances but as long as 1 month under perfect environmental conditions.

What are Signs Your Horse has Been Infected with EHV-1?

The incubation period for EHV-1 after initial infection can be as short as 24 hours but is typically around 4-6 days or longer. EVH-1 usually causes a two-phase fever spike around day 1-2 and again at day 6-7. There is often coughing and nasal discharge that accompanies a respiratory infection as well as enlargement of the lymph nodes under the jaw. If the horse develops EHM, the neurologic form of EHV-1, there are typically minimal warning signs with mild respiratory symptoms and a fever with a rectal temperature greater than 101.5 degrees. EHM appears suddenly and progresses very quickly, reaching its peak intensity within 24-48 hours of initial neurologic signs. Neurologic signs that your horse may have EHM include:

  • Incoordination
  • Weakness from behind
  • Head tilt
  • Leaning against walls or fencing for balance
  • Lack of energy or lethargic
  • Inability to get up

Supplementing with Zinc & Lysine

Outbreaks of EHV-1 prompted clinicians to try to identify ways to help protect horses from developing EHM. During a multi-state outbreak of EHV-1, researchers found that horses supplemented with dietary zinc were less likely to develop EHM compared to non-supplemented horses.1 This decreased risk of EHM was identified in both the control group of horses, and in horses that had EHV-1 without signs of neurologic disease.1 Horses naturally infected with EHV-1 had a significantly lower concentration of serum zinc and copper compared to control horses, showing the possible significance of dietary zinc in managing EHV-1.2

Zinc is an essential trace metal that has a wide variety of cellular functions, and is important in the maintenance of B and T cell lymphocyte populations and immune system health. A deficiency of zinc can result in fewer circulating cytotoxic T-lymphocytes (CTL), which then has a direct influence on disease. Horses experimentally infected with a neuropathogenic strain of EHV-1 that had a lower concentration of EHV-1 specific CTL precursor cells prior to the EHV-1 exposure were more likely to develop neurologic disease compared to horses that had higher concentrations of EHV-1 specific CTL precursor cells.3 This finding led to the conclusion that CTL precursor cells play an important role in protective immunity against EHM.3

Lysine is an essential amino acid that has long been recognized for its role as an anti-viral nutrient. In vitro work shows that lysine stimulates the enzyme arginase, which then promotes the breakdown of arginine. Because arginine is required for the replication of certain viruses, supplementation with dietary lysine may be an effective way to help manage viral infections caused by herpes viruses.

The foundation of a strong immune system begins with a well-balanced ration that provides essential nutrients and ingredients that support immune system health. Provision of both zinc and lysine before and after horses are exposed to EHV-1 can help to prevent dietary deficiencies of these two important nutrients, and the dietary zinc may decrease the risk that a horse will develop EHM after infection with EHV-1. An equine supplement that combines zinc, lysine and blend of vitamins, minerals, antioxidants and omega-3 essential fatty acids such as Platinum Performance Equine + Additional Zinc and Lysine can be fed to optimize health and support immunity.

Literature Cited

1. Traub-Dargatz JL, Pelzel-McCluskey AM, Creekmore LH, et al. Case-Control study of a multistate equine herpesvirus myeloencephalopathy outbreak. J Vet Intern Med 2013;27:339-346.
2. Yoruk I, Deger Y, Mert H, et al. Serum concentration of copper, zinc, iron and cobalt and the copper/zinc ratio in horses with equine herpesvirus-1. Biol Trace Elem Res 2007;118:38-42.
3. Allen GP. Risk factors for development of neurologic disease after experimental exposure to equine herpesvirus-1 in horses. Am J Vet Res 2008;69:1595-1600.