EPIDEMIOLOGIC INVESTIGATION OF EQUID HERPESVIRUS-4 (EHV-4) EXCRETION ASSESSED BY NASAL SWABS TAKEN FROM THOROUGHBRED FOALS

Equid herpesvirus-4 (EHV-4) was detected in nasal swabs taken from foa ls using a PCR based test and this information used to study the epide miology of EHV-4 disease on three Australian Thoroughbred stud farms i n NSW in 1992. There was a very high level of agreement (kappa value o f 0.84) between the PCR results and virus isolation using cell culture techniques. There was a strong seasonal distribution of EHV-4 sheddin g. Twenty-five of 26 positive samples were collected in January and Ma rch with the remaining positive sample collected in February. Foals wi th clinical signs of upper respiratory tract infection per se were no more likely to be shedders of EHV-4 (odds ratio [OR] 1.4, 95% confiden ce limits [CL] 0.5-3.8). However, EHV-4 was more likely to be isolated from foals exhibiting copious serous or mucopurulent nasal discharge than those with no clinical signs (OR 4.6, 94% CL 1.1-19.0 and OR 2.5, 95% CL 0.8-8.0, respectively). The month of the year was more importa nt than weaning or age as a risk factor for excretion of EHV-4. Male f oals and those with a history of respiratory disease that had required veterinary treatment were more likely to shed EHV-4.