Prevention and Control of Actinobacillus (Haemophilus) pleuropneumoniae Infection in Swine: A review.

Transmission of Actinobacillus pleuropneumonlae The bacterium, Actinobacillus (Haemophilus) pleuroIpneumoniae, is the causative agent of pleuropneumonia of swine (1,2). Mortality may vary but is usually high in acute outbreaks of pleuropneumonia. Survivors of acute infection often develop chronic lung lesions (sequestra, abscesses, and pleuritic adhesions) and become carriers (2). Chronically infected animals have reduced feed conversion, higher medication costs, lower weaning rates, and reduced market value. In total, it is estimated that losses due to pleuropneumonia are over 40 million dollars a year in Canada. Due to this great economic impact, prevention and control programs for pleuropneumonia should receive high priority (3). Since A. pleuropneumoniae does not persist in the environment, and only pigs are known to be susceptible to infection under natural conditions, elimination of this organism should be feasible (2). Pleuropneumonia is spread between herds by carriers. Infected pigs may carry the bacterium in the nose, tonsils, or sequestered in the lungs without demonstrating any clinical signs (4). Following the introduction of the pathogen into herds not previously exposed, morbidity and mortality may occur in all age groups. Losses are usually highest in feeder pigs, probably as the result of the stress related to rapid growth and their naive immune status. Moving and mixing pigs increases the risk of pleuropneumonia. The probability of introducing A. pleuropneumoniae into a herd increases with frequency of purchase and with the number of animals purchased at a time (5). If pigs are purchased from sales barns, the risk is significantly higher than if they are purchased directly from one breeder. Closed herds have the lowest incidence. Measures such as quarantining new stock, pest control programs, banning visitors, and purchasing health-examined stock can be correlated with reduced risk (5). Once a herd is infected, several stress factors influence the likelihood of an outbreak of the disease. Crowding, sudden climatic changes, ventilator breakdown, and intercurrent disease can all be associated with onset of clinical pleuropneumonia (2). In infected herds, measures should be taken to create optimal environmental conditions for the animals. Particular attention should be given to providing pigs with adequate space and proper ventilation and to limiting mixing of animals.