Actinobacillus pleuropneumoniae. Observational study on risk factors for infection of piglets with Actinobacillus pleuropneumoniae on a conventional pig farm

Abstract

Actinobacillus pleuropneumoniae (APP) causes great economic losses in pig husbandry world-wide, due to pleuropneumonia. Direct contact is believed to be the main source of infection, but transmission via the air is demonstrated to be possible as well. This observational study was set up to gather information about the distribution of APP among sows, suckling piglets and weaned piglets on a conventional pig farm and to gain understanding in risk factors for infection with APP in the farrowing and weaner unit. Forty sows were tested three weeks pre-partum for the amount of antibodies for ApxI, ApxII, ApxIII and OMP and the amount of APP DNA present on the tonsils and their offspring was tested 3,5 weeks (all 40 litters) and 9,5 weeks (32 litters) post-partum for the presence of APP DNA on the tonsils. All sows were tested positive for antibodies and for the presence of APP DNA. At 3,5 weeks of age, 23% of the piglets, scattered over 55% of the litters, tested positive for the presence of APP DNA. No association was found between the chance of infection of a litter and the parity of the sow or the amount of present APP DNA or antibodies in the sow. Litters that were older at the moment of testing, had a higher chance of being infected than the younger litters. At 9,5 weeks of age, 42% of the piglets, scattered over 75% of the litters, tested positive for the presence of APP DNA. The infection chance was associated with the amount of antibodies for ApxI, but not with the amount of antibodies for ApxII, ApxIII and OMP. In the weaner unit, the presence of infected siblings was associated with the increase of infected piglets per pen, but the presence of infected piglets in the neighboring pens had no association with the infection of litters. This suggests that direct contact with infected piglets is the most important source of infection for piglets in the weaner unit and that entire litters may remain uninfected when direct contact with infected piglets is avoided.