My horse has been diagnosed with an eye infection called equine herpesvirus-2 (EHV-2) keratitis. I was told he is not contagious. Can you please tell me how it is spread and how best to manage it? Is lysine beneficial for this condition?

-Name withheld upon request

A: The diagnosis of EH-2 keratitis—inflammation of the cornea, the transparent membrane covering the front of the eye—is controversial and requires more research. The equine herpes-virus family is better known for EH-1 and EH-4, which cause the chronic respiratory infection known as rhino-pneumonitis that can occasionally develop into a paralyzing neurological disease, as well as EH-3, which causes a venereal disease called equine coital exanthema. 

EH-2 is a slow-growing herpesvirus that can affect all horses.We know that mares shed the virus from mucosal areas, including the eyes and the nose, and it is transmitted to foals soon after birth. But we’re not sure how EH-2 causes disease. Some have reported it to be associated with immunosuppression in foals, upper respiratory tract disease, conjunctivitis, keratitis and overall general malaise and poor performance. Still, whether EH-2 causes ocular disease in horses remains scientifically unproven. 

A relationship between the neurological, respiratory and reported ocular forms of EHV has not been established, nor has any information been published suggesting that the ocular form is directly contagious from horse to horse. Lysine is an essential amino acid that, in an oral preparation, has been used to treat herpesvirus-related keratitis in people and in cats, but whether the same treatment works for horses has not been well studied.

If you are sensing by now that we don’t know much about herpesviruses and eye disease in horses, then you are getting the right message! We need much more research before we’ll under-stand whether EHV-2 causes ocular infections, and if so, how to treat them effectively. For now, treatments for keratitis have been primarily supportive, determined on a case-by-case basis, depending on the particular signs an individual horse develops. Meanwhile, I’d recommend that you have your horse examined by a board-certified veterinary ophthalmologist.

Amber Labelle, DVM, MS, DACVO University of Illinois at Urbana–Champaign Urbana, Illinois