INDUCTION OF PROTECTIVE IMMUNITY AGAINST TRANSMISSIBLE GASTROENTERITIS VIRUS AFTER EXPOSURE OF NEONATAL PIGS TO PORCINE RESPIRATORY CORONAVIRUS

Objective-To test the ability of porcine respiratory coronavirus (PRCV ) to induce protective immunity to antigenically related transmissible gastroenteritis virus (TGEV) in neonatal pigs. Design-Neonatal pigs w ere exposed to PRCV when they were 2, 4, or 6 days old and challenge-e xposed to virulent TGEV at 10 days of age. Animals-34 hysterectomy-der ived, colostrum-deprived pigs. Procedure-After challenge exposure, cli nical signs were observed, body weight, antibody response, and virus s hedding were measured, and mortality was determined. Results-After exp osure to PRCV, principals had a slightly slower rate of weight gain th an did controls; with 1 exception (a PRCV-exposed pig that was dyspnei c for 1 day), principals and controls remained clinically normal until shortly after challenge exposure, when ail pigs became listless and a norectic and developed watery diarrhea. However, by day 3, most of the pigs that had been exposed to PRCV when they were either 2 or 4 days old began to recover and most (15/18) survived. Conversely, the clinic al condition of most of the other pigs worsened and most (14/16) died. Pigs exposed to PRCV when they were 2 or 4 days old also differed fro m all other pigs in that they had serum virus-neutralizing antibodies for PRCV and TGEV at the time of challenge exposure. Conclusions-The P RCV can induce protective immunity to TGEV in neonatal pigs and such i mmunity develops at or about 6 days after exposure to PRCV. Moreover, protective immunity may be coincident with the appearance of virus-neu tralizing antibody. Clinical Relevance-Exposure to PRCV should enhance a TGE herd vaccination program.