Risk indicators for the seroprevalence of Mycoplasma hyopneumoniae, porcine influenza viruses and Aujeszky's disease virus in slaughter pigs from fattening pig herds.

Epidemiological aspects of Mycoplasma hyopneumoniae (Mh), influenza H1N1 and H3N2 viruses, and Aujeszky's disease virus (ADV) were investigated in slaughter pigs from 50 fattening pig herds. Herd factors as potential risk indicators for respiratory disease were obtained by means of a questionnaire. At slaughter, blood samples were collected from each herd, and the proportion of seropositive pigs per herd was assessed for each of these pathogens. The median herd-level seroprevalence of the agents were: Mh 88%, H1N1 100%, H3N2 60% and ADV 90%. The percentage of herds in which all investigated fattening pigs were seronegative for these agents was: Mh 0%, H1N1 0%, H3N2 12% and ADV 18%. The percentage of herds in which all investigated fattening pigs were seropositive for these agents was: Mh 8%, H1N1 71%, H3N2 22% and ADV 40%. A positive association was found between influenza H1N1 and H3N2 viruses, and a negative association between influenza H3N2 virus and ADV. There were no risk indicators for the seroprevalence of Mh. Three risk indicators were associated with the seroprevalence of influenza H1N1 virus: a fully slatted floor, an increasing number of pigs in the municipality and dry feeding. Three risk indicators were found for the seroprevalence of influenza H3N2 virus: purchase of pigs from > or = two herds, an increasing number of pigs in the municipality and natural ventilation. The seroprevalence of ADV was influenced by two risk indicators: an increasing number of pig herds in the municipality and an increasing number of pigs per pen.