Melioidosis in Dogs

What is melioidosis?

Melioidosis is a bacterial infection that is typically associated with tropical regions. Melioidosis most commonly occurs in Southeastern Asia and Northern Australia. Transmission occurs more commonly in the rainy season.

Although melioidosis is primarily a tropical disease, numerous cases of canine melioidosis have been diagnosed in North America in recent years. With increases in international travel and international dog rescue operations, it is expected that this trend will continue and that we may begin to see even more cases of melioidosis in future years.

While most North American cases of melioidosis have been associated with a history of travel to (or importation from) affected areas, there have been several reported cases in animals and humans without a known travel history. This suggests that these individuals may have been exposed to undiagnosed imported cases of the disease.

What causes melioidosis?

The bacteria that causes melioidosis, Burkholderia pseudomallei, is typically found in soil and water. It is introduced to these areas when it is shed in the milk, feces, urine, or wound drainage of infected animals. B. pseudomallei can survive in soil or water for months or even years. While B. pseudomallei is most common in moist soils, it can survive even in intermittently moist soils (such as garden soil).

"Animals can acquire melioidosis in a number of ways."

Animals can acquire melioidosis in a number of ways. The soil can serve as a source of infection if it is ingested, or if contaminated soil comes in contact with skin wounds. Animals can also be infected after feeding on the carcasses of infected animals. In some cases, animals are infected after inhaling the organism. Inhalation is especially common in periods of high wind, especially after heavy rainfall. There have been indications to suggest venereal transmission is possible, though this has not been proven. 

Experimentally, it has been shown that B. pseudomallei can be transmitted by some flea and mosquito species. This is not thought to play a role in natural transmission, but it remains a possibility.

What are the clinical signs of melioidosis?

In dogs, melioidosis can cause a variety of clinical signs. It mimics a number of other diseases; therefore, it is sometimes referred to as ’the great imitator.’

Some infected dogs may not show any signs of illness but will shed the bacteria. Other dogs show observable signs of illness, which may develop anywhere from days to years after infection.

Clinically-affected dogs often develop a fever, along with abscesses (pus-filled bumps) under the skin. Severe diarrhea, muscle pain, lethargy, and signs of pneumonia (shortness of breath, coughing, labored breathing) may also occur. Abscesses often develop within the internal organs, including the liver, lungs, and testicles. Affected dogs may also develop lameness (limping).

How is melioidosis diagnosed?

Melioidosis is not a common infection; therefore, it will rarely be one of the first considerations when your dog presents to the veterinarian for vague signs of illness. If your pet presents to the veterinarian with signs of illness without a known cause, your veterinarian will perform a number of tests in an attempt to determine the cause of clinical signs.

Blood tests, including a complete blood cell count and serum biochemistry profile, will be used to assess your dog’s overall internal health and organ function. Radiographs (X-rays) may also be performed to look for causes of respiratory or abdominal disease, depending on your pet’s clinical signs of illness.

Diagnosis requires laboratory testing that can identify B. pseudomallei in the dog’s tissues or in discharge that is found from the skin lesions. Blood tests may also be used to identify the organism.

How is melioidosis treated?

Treatment of melioidosis requires prolonged courses of antibiotics. The organism is resistant to many antibiotics, meaning that specific, expensive antibiotics may be required.

There is little information regarding the treatment of melioidosis in animals. Therefore, treatment protocols are typically designed based on human treatments. A combination of intravenous and oral antibiotics is often used, in order to maximize the odds of clearing the infection.

In some cases, the infection returns after treatment is stopped. Animals often require repeated courses of antibiotics in order to fully eliminate the infection or, at a minimum, control clinical signs.

In some states, melioidosis is a reportable disease and treatment may only be undertaken with the permission and supervision of government officials.

Can melioidosis affect people?

Yes. The bacteria that causes melioidosis is zoonotic, meaning that it can affect humans. Signs of infection in humans vary, but can include skin infections, sepsis, pneumonia, and abscesses within the organs.

In most cases, affected humans are thought to be infected by contaminated soil or water. However, cases of direct transmission from animals to humans have been reported.

Infected dogs should be handled with care. It is safest to assume that any fluids (e.g., feces, urine, and nasal secretions) are potentially infectious. Use gloves when cleaning up after your pet and clean contaminated areas carefully. Numerous disinfectants are effective against B. pseudomallei, including dilute bleach.

Does melioidosis affect additional animal species?

B. pseudomallei has been shown to affect a wide variety of animal species. In addition to dogs and humans, the organism can also infect cats, rodents, cattle, sheep, goats, horses, pigs, reptiles, birds, and fish.

Numerous outbreaks have been noted in zoos, given the bacteria’s ability to affect a wide variety of species.

In Australia, the disease is most commonly observed in goats, sheep, and pigs.