Prior infection of nursery-age pigs with porcine reproductive and respiratory syndrome virus does not affect the outcome of transmissible gastroenteritis virus challenge

Virology Swine Research Unit, National Animal Disease Center, Agricultural Research Service, USDA, Ames, IA 50010, USA. Thirty-six specific-pathogen-free pigs were weaned at 2 weeks of age and separated into 4 treatment groups (A-D, 9 pigs/group). Treatment groups B and D were infected with porcine reproductive and respiratory syndrome virus (PRRSV), whereas groups A and C remained uninfected. Two weeks later, 1 pig from each group was necropsied to assess gross lung involvement, and then the remaining group D PRRSV-infected pigs and the group C uninfected pigs were challenged at 4 weeks of age with transmissible gastroenteritis virus (TGEV) to determine if prior infection with PRRSV increased the severity of TGEV disease after challenge. One hundred percent morbidity but no mortality occurred in pigs following challenge. Clinically, pigs of both groups C and D were similar in terms of onset and severity of diarrhea. The serum antibody response to TGEV and the amount and duration of TGEV shedding after challenge was similar for both groups. Only a few pigs in each group had a transient fever postchallenge, and both group C and group D pigs began to recover and to gain weight at or near the end of the first week postchallenge. It was concluded that the clinical course of TGEV disease was not markedly affected by infection of pigs with TGEV 2 weeks after they had been infected with PRRSV.