Pat Blackall, Agency for Food and Fibre Sciences
Pleuropneumonia in pigs has emerged as a major disease in the Australian pig industry. The chronic form of the disease has been estimated to cost $64/sow/year without medication costs. The disease is caused by the bacterium Actinobacillus pleuropneumoniae. This organism exists in a number of different types, with serovars 1, 7 and 15 being the most common types in Australian pigs.
The disease can be divided into three forms, peracute, acute and chronic. It can affect all age groups, but most frequently pigs between weaning and six months of age. Recent experience has highlighted that increased levels of pleurisy at slaughter checks are often an early warning sign of a pleuropneumonia problem.
In the peracute form, pigs die within 24 hours of being infected. They show a bloodstained frothy discharge from the nose and mouth with obvious breathing difficulties (panting and heaving of the chest and abdomen). Infected pigs are reluctant to move and if forced to, collapse. Their body temperature is raised and they are reluctant to eat.
In acute cases, the signs are similar but develop more slowly. Many untreated pigs, and some treated pigs, die in one to four days. Survivors may recover completely or develop into chronic cases with permanent damage to the lungs and pleura.
Chronic cases are survivors of the acute disease. Few of them die due to pleuropneumonia but they cough persistently and grow slowly.
Outbreaks of the disease can be due to the organism entering a herd for the first time. Outbreaks can also occur in herds already carrying a "silent" infection. In the latter case, there is typically some precipitating factor (overstocking, poor ventilation, entry of some other disease).
Stress conditions such as overcrowding, poor ventilation, a dusty environment and large temperature fluctuations help the disease become established in a piggery.
The condition may be suspected if pigs are dying with symptoms of pneumonia. However, either blood tests or a full autopsy with laboratory examination of samples are necessary to conclusively diagnose pleuropneumonia. Laboratory culture also allows the serovar of the A. pleuropneumoniae to be confirmed, necessary if inactivated vaccines are to be used as part of a control/prevention programme. Blood tests can detect the presence of the two major types (serovars 1 and 15) of A. pleuropneumoniae are now available. These blood tests are particularly useful for diagnosing the chronically infected herds where acutely sick or dead pigs are not seen or for screening herds being considered as a source of breeding stock.
Breeding stock should only be purchased from herds of a similar or higher health status. The use of the blood tests allows producers to confidently select sources that match the status of their herd.
In the face of an acute outbreak of the disease, antibiotics may be necessary. The most appropriate antibiotic to use and the details of the treatment programme will vary from piggery to piggery. Ask your veterinarian. While water medication is better than medication in-feed for these acute outbreaks, the use of direct injection of pigs is the best option. It is important to review management practices (stocking rate, shed environment, pig movement) to reduce the impact of stress factors.
The use of therapeutic levels of antibiotics, either in the water or in the feed, (pulse treatment) at times of high risk can be beneficial.
Vaccines are also available. The currently available vaccines (2001) provide protection only against the serovars present in the vaccine. Hence, the serovar of the strain present on a farm should be identified, by culture or serology, to ensure that the appropriate vaccine is being used.
A major control mechanism is management. Predisposing factors such as overcrowding and poor ventilation should be identified and corrected. Adoption of such practices as "all in-all out" weaner accommodation, segregated early weaning and multi-site production have been shown to be effective in controlling the disease. These practices should be supported and monitored by the use of the blood tests.
Management practices such as "all in-all out" weaner accommodation, segregated early weaning and multi-site production can be very effective in controlling the disease.
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