Pig mortalities in Darwin region
ASF is an exotic viral disease of pigs that is currently in the national and international spotlight, and a primary focus for NT DPIR LBB disease surveillance activity. Although it does not pose a public health risk, ASF is a severe and highly contagious disease, causing 95-100 per cent mortality in pigs, with no cure or vaccine available. The virus survives in a wide range of conditions, and is resistant to cooking, freezing and thawing. Because the disease can be easily spread from pig to pig by feeding virus-contaminated foods, there is currently a huge focus on both awareness around food products that can or can’t be fed to pigs, as well as on monitoring and investigating unusual illnesses and deaths in pigs. There is no commercial pig industry in the NT, but at least 200 properties are known to keep pigs as pets or for home slaughter. The NT is also home to many millions of wild pigs, a population of particular interest when considering the risks of ASF infection in Australia.
In September 2019, a pig producer from Humpty Doo near Darwin, contacted the department regarding piglets that were dying. The herd consisted of two sows that had farrowed three to four weeks previously; one sow had two piglets and the other had eight. The owner first noted that two piglets had become very wobbly in the back legs; then, over the next three days, these animals collapsed and developed seizures. The owner euthanised the piglets on humane grounds. When another two piglets became sick with similar symptoms, the owner presented them to Berrimah Veterinary Laboratory (BVL), for examination and euthanasia.
The two piglets seen at BVL were in good body condition. The first animal examined was mildly affected; it was reluctant to move, knuckled over in the back legs, and collapsed easily. Some muscle tremors were seen, but this could have been shivering. The second piglet (from the original small litter of two piglets) was very unwell and unable to stand, but was conscious and appeared to be able to see. This piglet had thickened skin and swelling in the tissues around the neck, suggestive of oedema (fluid-swelling under the skin). Both piglets were euthanised and at the post mortem exam, a full range of body tissues was collected, for further testing.
A property visit was conducted by LBB officers to assess biosecurity measures. There was no reported access between wild and pet pigs, which would be very important to confirm in the event of an ASF outbreak. Another purpose for the visit was to investigate whether management or husbandry issues could have contributed to the disease event. The pigs were kept in a fenced enclosure within a ten acre block. The farrowing pens had concrete floors, automatic feeders, and were shaded by a tin roof. One corner of the enclosure had a concreted wallow area. Although cleaned regularly, the pigs (and piglets) were fed from the wallow, and also defecated and urinated there. Outside the farrowing pens and wallow area, the pigs had access to a dirt enclosure shaded by several large trees. The piglets were fed powdered milk, pig grower pellets, pineapples and vegetables.
Laboratory findings in the piglets included:
- Inflammation of blood vessels in the central nervous system (brain and spinal cord)
- Ulcers and erosions in the large intestine, with swollen and inflamed intestinal lymph nodes
- Inflammation of the liver
- Inflammation of the lungs
- Generalised depletion of the white blood cells.
The most likely cause of the major illnesses involving the large intestines and brains of both piglets is Oedema Disease. This is an inflammation of blood vessels called a vasculopathy, and is caused by a toxin-producing E.coli bacteria, which multiplies in the small intestine. The signs of disease seen in the large intestine were typical of Oedema Disease, and the piglets were approximately the right age for the condition. It is likely that the E. coli organism was introduced to the piglets through their recent mixing with the rest of the herd, or changes in intestinal bacteria as the piglets started eating food rather than exclusively nursing. However, signs of illness in other body tissues were also suggestive of a viral disease, Porcine Circovirus 2 (PCV2), which is common in Australian pig herds, and is seen as a concurrent infection in outbreaks of various pig diseases. Infection with PCV2 was also confirmed through laboratory testing.
Although the signs of illness in the piglets were not particularly suggestive of ASF, it is possible for ASF to cause intestinal illness and a central nervous system blood vasculopathy. Therefore, the piglet tissue samples were extensively tested for infection with ASF and other exotic diseases at the Australian Animal Health Laboratory, with no findings of any emergency or exotic animal disease.
After reaching a diagnosis, the owners were contacted and recommendations regarding husbandry and management provided to decrease the risk of disease events recurring, especially in relation to PCV2. Recommendations included creep feeding to gradually introduce piglets to new food, maintaining a clean and healthy environment (separating food from faeces, and not feeding at the wallow), and reducing the impact of stressful events such as mixing litters and animals during the vulnerable stages of life. The owners were appreciative for the support from the department, the ability to have an extensive investigation performed, and the recommendations provided.
Last updated: 28 September 2020
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