Epidemiology of Haemophilus pleuropneumoniae infection in pigs: a survey of Ontario Pork Producers, 1981.

Information about factors associated with the spread and the effect of pleuropneumonia was obtained from 418 pork producers in Ontario, who returned a mailed questionnaire. The overall herd prevalence of pleuropneumonia was 23.2%. The prevalence among herds with feeder pigs only was 34.3% and 16% among sow herds. The chance of pleuropneumonia breaking out in a herd was increased with increased traffic of pigs into the herd. The source of supplementary stock had an important effect on the chance of pleuropneumonia occurring. The highest risk resulted from introducing stock from salesbarns and the lowest from stock of health status known to the purchaser and supplied by one breeder only. Mortality, primarily among feeder pigs, and unthriftiness were the major effects of Haemophilus pleuropneumoniae infection. Stress, such as crowding or inclement climatic conditions, was associated with outbreaks of pleuropneumonia. This would suggest that the infection with H. pleuropneumoniae can be subclinical until stress precipitates the disease.