The postulated role of feeder swine in the perpetuation of the transmissible gastroenteritis virus.

Clinical, immunofluorescence and histopathological observations were found to be an efficient approach for the confirmation of the diagnosis of transmissible gastroenteritis in feeder swine. Two cases are reported to exemplify how feeder swine exposed to points of concentration such as holding areas, sales barns and auctions can play an important role in the epizootiology of transmissible gastroenteritis. A third field case is reported as an example of an outbreak of transmissible gastroenteritis beginning in feeder swine and then spreading to baby pigs on the farm. All baby pigs died that were born during the acute phase of the outbreak in the feeder swine. Baby pigs born shortly after the clinical signs had abated in the herd, and from sows that had been exposed orally to virulent transmissible gastroenteritis virus and vaccinated with a commercial transmissible gastroenteritis vaccine ten days before farrowing, survived. This was explained by a combination of a decrease in the amount of virus shed in the environment and the immunity induced in the sows. These observations of field outbreaks of transmissible gastroenteritis combined with recently reported experimental studies lend strong support to the hypothesis of a reservoir for transmissible gastroenteritis virus in feeder pigs. This reservoir would be based principally on the transmission of the virus on a continuous basis from the feces of recently infected pigs to susceptible pigs. Clinical signs of transmissible gastroenteritis in such pigs are difficult to recognize or absent and this contributes to the importance of the reservoir in the field.