Topical Ganciclovir Reduces Viral Excretion in Mares With Equine Coital Exanthema

Equid alphaherpesvirus 3 (EHV-3) is the etiological agent of equine coital exanthema (ECE). Because no vaccines or antiviral therapies are available, prevention consists of clinical examination of mares and stallions before mating or semen collection and resting from breeding activities when lesions are present. However, this methodology does not identify subclinically infected animals. Ganciclovir is the most potent compound known to reduce EHV-3 replication. This study aimed to evaluate the efficacy of topical ganciclovir application to reduce EHV-3 replication in experimentally infected mares. A pilot study, after a double-blind completely randomized design, was carried out. Twenty mares were randomly divided into five groups (three treated with ganciclovir with different regimen of doses, one treated with a placebo, and one nontreated). Mares were experimentally infected with EHV-3 on day 0. Rectal temperature, clinical signs, and lesions were recorded. Daily perineal and vaginal swabs were evaluated by quantitative polymerase chain reaction for virus detection. The antibody response was assessed by a virus neutralization test in serum samples collected weekly. Mares experimentally infected with EHV-3 and treated with ganciclovir twice a day for 13 days showed reduced levels and duration of viral excretion and less severe lesions. The viral excretion period was reduced from 18 to nine days compared with the untreated groups. We concluded that ganciclovir had an antiviral effect on EHV-3 replication when topically administered in mares showing clinical signs of ECE. Further trials should be performed to optimize the dose of the antiviral for a definitive formulation.