Equine adenovirus 1 infection of hospitalised and healthy foals and horses

The prevalence of equine adenovirus 1 (EAdV1) in the nasopharyngeal sections of healthy neonatal foals and horses was compared with that of hospitalized foals using an EAdV1-specific PCR assay. Nasopharyngeal swabs (NS) were obtained from 15 hospitalized foals, 12 apparently normal foals and their dams within 24 h of parturition (control) and 47 apparently healthy racehorses in training. EAdV1 was detected by PCR in the NS of 6 of the 15 (40%) hospitalized foals and 7 of the 12 (58%) control foals. There was no statistically significant difference in the prevalence of EAdV1 infection of foals in the 2 groups (P=0.34). Two of the 12 (17%) healthy mares were positive for EAdV1 as were their foals. EAdV1 was not detected in the NS of the 10 remaining mares, nor was it detected in the NS of any of the 47 racing horses. In summary, although PCR assay provides a rapid and apparently sensitive method for detection of EAdV1 in the nasal secretions of horses, the results of this study confirm that mere detection of EAdV1 by either PCR or virus isolation is not predictive of the occurrence of clinical disease. Furthermore, although mares presumably are the source of the virus that infects their progeny at the time of birth, the modes of transmission remain poorly characterized.