Abstract
The relationship between stage of reproductive tract maturity and susceptibility to the experimental establishment of persistent infection with equine arteritis virus (EAV) was investigated in 21 prepubertal and 15 peripubertal colts. Five of six prepubertal colts inoculated intranasally remained infected in the reproductive tract from post-challenge day 28 to 93 and two of six from post-challenge day 120 to 180. No virus was detected in five of these animals killed on post-challenge day 210. Each of two peripubertal colts remained infected in the reproductive tract at post-challenge day 60 and one of nine was found to be persistently infected with EAV 15 months after challenge. These findings confirm that the virus can replicate in the reproductive tract of a significant proportion of colts for a variable period of time after clinical recovery in the absence of circulating concentrations of testosterone equivalent to those found in sexually mature stallions. Long-term persistent infection with EAV does not appear to occur in colts exposed to the virus before the onset of peripubertal development. We suggest that colts should be vaccinated at approximately 6 months of age, before peripubertal development but after the disappearance of maternally acquired antibodies.