Persistence of pseudorabies virus in infected swine.

The persistence of pseudorabies virus (PRV) in pigs clinically recovered from the disease was detected by culture of tissue fragments. Weanling pigs were infected by intranasal instillation of 200,000 plaque-forming units of a strain of PRV isolated from sick pigs in Iowa, and virus was recovered from them 6 weeks to 13 months later. Tonsil, trigeminal ganglia, or pooled trigeminal ganglia and olfactory and optic nerve tissue were most consistently the source of virus. The tissue-fragment culture technique was compared with a co-culture technique for detection of virus in tissue specimens from the recovered pigs. Use of these procedures provided the means to detect PRV in pigs for periods longer than previously recognized.