Induction of protective immunity against transmissible gastroenteritis virus after exposure of neonatal pigs to porcine respiratory coronavirus.

Wesley, R D; Woods, R D

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 were exposed to PRCV when they were 2, 4, or 6 days old and challenge-exposed to virulent TGEV at 10 days of age. ANIMALS 34 hysterectomy-derived, colostrum-deprived pigs. PROCEDURE After challenge exposure, clinical signs were observed, body weight, antibody response, and virus shedding were measured, and mortality was determined. RESULTS After exposure to PRCV, principals had a slightly slower rate of weight gain than did controls; with 1 exception (a PRCV-exposed pig that was dyspneic for 1 day), principals and controls remained clinically normal until shortly after challenge exposure, when all pigs became listless and anorectic 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 clinical 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 from all other pigs in that they had serum virus-neutralizing antibodies for PRCV and TGEV at the time of challenge exposure. CONCLUSIONS The PRCV can induce protective immunity to TGEV in neonatal pigs and such immunity develops at or about 6 days after exposure to PRCV. Moreover, protective immunity may be coincident with the appearance of virus-neutralizing antibody. CLINICAL RELEVANCE Exposure to PRCV should enhance a TGE herd vaccination program.