Sites of replication of a porcine respiratory coronavirus in 5-week-old pigs with or without maternal antibodies.

On farms, where the porcine respiratory coronavirus (PRCV) is enzootic, pigs usually become infected between 5 and 10 weeks of age while losing their maternal antibodies. It was examined whether PRCV replicates in the small intestine in such pigs. This point is important since intestinal replication with PRCV might induce immunity against TGEV not only by stimulating mucosal intestinal immunity, but also by the induction of a lactogenic IgA response at later age via the gut-mammary link. Five week old pigs with and without maternal antibodies were inoculated by aerosol or directly into the intestinal lumen. In aerosol inoculated pigs, virus replication was observed to high titres in the respiratory tract. Replication occurred in epithelial cells of nasal mucosa, trachea, bronchi bronchioli and alveoli and in alveolar macrophages. Small amounts of virus produced in the respiratory tract were ingested, but no intestinal replication of PRCV was demonstrated. Differences were not observed in virus titre and sites of replication in seronegative pigs compared to those in pigs with maternal antibodies. Upon inoculation of 10(5) or 10(7) TCID50 directly into the lumen of the cranial jejunum, no intestinal replication could be demonstrated.