A 13-year-old Warmblood gelding presented to Cornell's Equine Hospital for a two-day history of inappetence, decreased manure production, and intermittent colic. The farm hosted a horseshow the week prior. A colic examination revealed a mild gas colic. The blood work showed leukopenia, neutropenia, and lymphopenia with a low-end normal platelet count. The differentials included Anaplasma phagocytophilum; gastrointestinal disorders such as coronavirus, Potomac Horse fever, salmonellosis; and viral respiratory disorders such as Equine herpesvirus-4 (EHV-4), Equine herpesvirus-1 (EHV-1), Equine Rhinitis virus A and B, and Influenza. The horse was isolated and treated supportively with low-dose flunixin meglumine, ice boots, and antibiotics. The colic resolved, however intermittent fevers continued. On day 6, the horse was depressed, with mild ventral edema and limb edema and had profound ataxia (grade 4 out of 5) in all four limbs. At this time, equine herpesvirus myeloencephalopathy (EHM) caused by EHV-1 was considered the most likely and was confirmed by a positive nasal swab and whole blood PCR test. The virus was determined to be the neuropathogenic type (ORF30 G2254). Supportive care of EHM consisted of heparin (anticoagulant), dexamethasone (anti-inflammatory), and vitamin E supplementation (antioxidant). Over the following week, the horse slowly improved and was discharged and continues to improve at home.

This horse was part of an EHV-1 outbreak on a farm of approximately 50 horses in New York State. The farm was quarantined, in-contact horses were treated with valacyclovir (anti-viral) and heparin to reduce the chances of developing EHM. Many horses had fevers and up to 10 horses developed mild to moderate neurological signs.