Pleuropneumonia in pigs
Photo of a DNA gel. The unique Australian serovar 15 isolates are in lanes 3 and 4 showing the lack of the arrowed band in lane 2. A control sample is in lane 1.
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 per sow a 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, 5, 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 affects 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 move, will 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 post-mortem 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 program.
Our microbiology research group has, with industry funding, developed a range of diagnostic tools including conventional and molecular-based serotyping and DNA fingerprinting.
Breeding stock should only be purchased from herds of a similar or higher health status.
In the face of an acute outbreak, antibiotics may be necessary. The most appropriate antibiotic to use and the details of the treatment program will vary from piggery to piggery so ask your veterinarian.
While water medication is better than in-feed medication 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.
Control and prevention programs for pleuropneumonia need to be tailored to each farm, as each farm can have a mix of different strains and have pigs with different respiratory problems.
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. Autogenous killed vaccines 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 used. Recently the Pork CRC has released the APP-Alive vaccine and vaccination procedure. The vaccine is given in a single dose to piglets before weaning.
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.
Collaboration between our researchers and two laboratories in Europe has shown that an Australian strain of pleuropneumonia in pigs is so distinct that it forms a new serovar - termed serovar 15. The name change from serovar 12 to 15 makes no difference to control and prevention programs - it simply clarifies the nature of the Australian serovar 15 isolates. Recent surveys in a range of countries have shown that serovar 15 is now one of the more important serovars associated with clinical outbreaks of pleuropneumonia.
The work showing the status of Australian pleuropneumonia strains of serovar 12 (now 15) has been reported in a formal scientific paper that has been accepted by the international scientific journal 'Veterinary microbiology'.
The above picture shows a DNA separation gel - the unique Australian serovar 15 isolates are shown in lanes 3 and 4. The controls are in lanes 1 and 2. The absence in lanes 3 and 4 of the band marked in lane 2 was part of the evidence used to confirm the nature of the Australian isolates.
- for information about serotyping and DNA fingerprinting contact Conny Turni (research scientist) at the Animal Research Institute on 07 3362 9527
- contact your local veterinarian
- contact the Customer Service Centre