Melioidosis is a disease caused by the bacterium Burkholderia pseudomallei, which can affect animals and humans.
It is most common in tropical and subtropical regions, including northern Australia.
Melioidosis can infect a wide range of animals, including mammals, birds, reptiles and fish and can result in death if untreated. Susceptibility to infection varies.
Disease is most likely to occur following heaving rainfall and/or when soil has been disturbed, leading to exposure to the bacterium present in the subsoil.
Where does melioidosis occur?
Melioidosis results from infection by the bacterium Burkholderia pseudomallei, which is endemic in certain parts of Australia, Southeast Asia, Africa, the Middle East, India and China. The disease is mainly associated with tropical and subtropical regions, but it has occasionally been detected in temperate regions.
Melioidosis was first recognised within Australia in an outbreak in sheep in 1949 in Winton, northern Queensland. It is known to occur across northern Australia, particularly in the Northern Territory. It has been diagnosed 10 times in Western Australia since 1966, mostly in the Gidgegannup, Chittering and Toodyay area and the Kimberley region.
Which species does meliodosis affect?
Melioidosis can affect a wide range of animals including mammals, birds, reptiles and fish. Sheep, goats and pigs are commonly infected species, and there is evidence that camelids, including alpaca, are particularly susceptible to developing disease. Cases of melioidosis have also been reported in other species including cattle, buffalo, camels, horses, chickens, emus/ostriches and wildlife such as kangaroos, wallabies, koalas. Cattle are considered to be relatively resistant to melioidosis as are birds, although cases have been reported.
Melioidosis in people
Most infections in people occur through exposure to soil and water that contains the bacterium. Human infection in WA occurs primarily in the Kimberley region and in travellers from endemic countries in south-east Asia, with an average of about five cases notified per year. Risk of melioidosis in humans with environmental exposure is primarily in those with chronic underlying medical conditions, including diabetes, excess alcohol consumption, chronic lung disease, liver disease, renal disease, malignancy and steroid treatment or other non-HIV-related immune suppression.
People who are concerned about their risk of melioidisis should consult their general medical practitioner or contact their local public health unit [1].
There are no clearly documented cases of zoonotic transmission of Burkholderia pseudomallei and the risk of such transmission is considered low.
Signs of melioidosis in livestock
Melioidosis may appear as acute or chronic disease and can be mild or severe.
The signs of melioidosis in animals vary depending on species, but generally include depression, fever, weight loss, respiratory signs (heavy breathing, sneezing), lameness and swelling of the joints, and potentially death.
Signs of melioidosis in specific species can include:
| Sheep | Respiratory disease is common in sheep. Signs can include fever, severe coughing, respiratory distress and discharge from the nose and eye. Some sheep become lame and have swollen joints. Nervous signs may also occur. |
| Goats | Respiratory disease is less severe than in sheep, and coughing may not be a prominent sign. Mastitis is common and the udder may contain palpable abscesses. Wasting, lameness and hindleg weakness as well as abortion have been reported in goats. |
| Pigs | Adult pigs tend to develop few significant clinical signs, but progressive wasting, nervous signs including a lack of coordination, skin ulcers and diarrhoea have been reported. Young pigs can develop acute disease with fever, anorexia, coughing and discharge from the nose and eye. |
| Camelids (camels, llamas, alpacas): | Camelids may develop respiratory disease with coughing, nasal discharge and difficulty breathing. Hindleg weakness or lack of coordination and wasting have been reported. Acute disease resulting in sudden death has been reported in both camels and alpacas. |
| Cattle | Melioidosis has rarely been reported in cattle. Signs reported include fever, difficulty breathing and nervous signs. |
| Horses | Signs may include weakness, wasting, swelling of the limbs, mild colic, diarrhoea, coughing and nasal discharge. Skin infections can initially resemble fungal eczema, but later become papular (blister-like lumps). Acute disease with high fever, limb swelling, diarrhoea and death has also been reported. |
| Birds | Birds may be relatively resistant to melioidosis, but cases with lethargy, anorexia and diarrhoea progressing to death have been reported. |
If you see signs of disease in animals that could be melioidosis, contact your private veterinarian or your local Department of Primary Industries and Regional Development (DPIRD) Field Veterinary Officer [2].
How does melioidosis spread?
Burkholderia pseudomallei can survive in the soil for many years. The bacteria can move to the soil surface and into surface water following heavy rain or soil disturbances where it can then infect animals and people.
Animals and people can become infected by:
- exposure of wounds to contaminated soil or water
- ingesting contaminated water or soil, or
- inhaling the organism, which may become aerosolised during heavy rainfall or strong winds.
Infected animals can potentially spread bacteria by contact with their wounds, nasal secretions, milk, faeces and urine.
In order to avoid spreading the disease to other animals, including by contamination of soil, if you suspect or have an animal affected by melioidosis, you should:
- isolate affected animals
- not move affected animals off the property, and
- follow good biosecurity and decontamination procedures after contact with known or suspected affected animals.
There are no clearly documented cases of zoonotic transmission of Burkholderia pseudomallei, and the risk of such transmission is, therefore, considered to be low. However, whenever handling sick or dead animals, people should always manage their personal safety by minimising close contact with the animals, wearing protective clothing, including a face mask and eye protection, covering any skin abrasions and practising good hygiene. Veterinarians are also advised to wear personal protective equipment when carrying out postmortems.
How do I treat melioidosis in animals?
Melioidosis in animals can be treated with certain antibiotics, but is resistant to other antibiotics. Before treating animals, always ask a veterinarian to take samples for laboratory testing so that a diagnosis can be obtained and the correct antibiotics provided. Treatment may be prolonged and relapses can occur when treatment is stopped. Animals will need to be monitored after treatment ceases.
Minimising environmental contamination is an important control measure in preventing spread of disease, as Burkholderia pseudomallei can survive for months to years in the soil. Good biosecurity practices will minimise spread of the disease.
Recommendations for disposal of affected animals
The recommended method of disposal of affected dead animals is commercial incineration. Minimise the risk of disease spread during transport by wrapping the carcasses in double-thickness heavy-duty plastic, or in leakproof bins, to prevent the spilling of body fluids.
Disinfect any in-contact equipment and vehicles. One per cent sodium hypochlorite/bleach, Virkon and peracetic acid are all thought to be suitable disinfectants. Equipment and vehicles should be disinfected, cleaned, and then disinfected a second time. Follow the manufacturer’s directions and take into account all human safety and environmental recommendations.
If commercial incineration cannot be undertaken, ensure that any other form of off-farm or on-farm disposal inactivates the bacterium by heating carcasses to a minimum of 74 degrees Celsius for 20 minutes.
If on-farm disposal is undertaken, ensure that the potential for environmental contamination and persistence of Burkholderia pseudomallei is managed. Decontaminate the disposal site to inactivate the bacteria and manage the site to prevent access by other animals. Consider environmental requirements when using chemicals or disinfectants and contact the local government authority environmental health officer as required.
Take appropriate personal precautions when handling carcasses and decontaminating equipment, or working in the same environment where animals may have been infected. Note that aerosolisation of Burkholderia pseudomallei may still be possible even after disinfection, so it is advisable to wear correctly fitted personal protection equipment to prevent inhalation of the bacterium when handling contaminated equipment.
More information on melioidosis in people can be found on the WA Department of Health website [3].