Virological study of two commercial pig herds with respiratory disease

A longitudinal virological and serological study was carried out in two pig herds with respiratory disease. From 598 nasal and rectal swab samples, 299 viruses were isolated which belonged to six groups, viz, adeno-, corona-, entero-, herpes-, parvo- and reovirus. Infection with porcine cytomegalovirus and enterovirus, serotype V13, was universal in both herds. In herd A, as neonatal antibody to PCMV and reovirus type 3 declined, the majority of pigs became infected with these viruses at five to eight weeks and 11 weeks respectively. The majority of pigs showed seroconversion to these viruses. Enteroviruses were excreted continuously from eight weeks and one adenovirus was isolated at 11 weeks. In herd B, a similar pattern of PCMV excretion and antibody development was found in one group of pigs but infection in the other group occurred much earlier and all pigs in this group had a poor antibody response following infection. The coronavirus of vomiting-and-wasting disease (VWD) was isolated from some three-week-old pigs which had moderate, rising antibody titres. Adenoviruses, including type 4, and enteroviruses were also recovered from pigs at an earlier age than those in herd A and in addition a parvovirus was isolated. Porcine cytomegalovirus, porcine adenovirus type 4 and the coronavirus (VWD) were considered to be the only viruses which may have been directly associated with the respiratory disease. Of the other viruses isolated only an enterovirus, serotype F34, had a tenuous link with respiratory disease.