What is melioidosis?
Melioidosis is also called Whitmore’s disease. It’s a deadly condition that can affect both humans and animals. The cause of this infection is the bacterium Burkholderia pseudomallei, which can be spread through contact with contaminated water and soil.
The disease is rare in the United States, but it’s a public health problem in Southeast Asia, northern Australia, and other places with a tropical climate. Melioidosis has the potential to spread to areas where it’s not typically found. For that reason, B. pseudomallei, the cause of melioidosis, has been identified as a potential biological weapon.
Symptoms of melioidosis
The symptoms of melioidosis vary depending on the type of infection. Types of melioidosis include pulmonary (lung), bloodstream, local, and disseminated infections.
In general, it takes two to four weeks for symptoms to appear after exposure to the bacterium. However, symptoms may take hours or years to appear, and some people have the disease without having symptoms.
The most common way melioidosis shows up in people is through a lung infection. A lung problem can arise independently, or it can result from a blood infection. Lung symptoms can be mild, like bronchitis, or severe, including pneumonia and leading to septic shock. Septic shock is a serious blood infection that can rapidly lead to death.
Symptoms of pulmonary infection may include:
- cough with normal sputum (the mixture of saliva and mucus that can rise into the throat from coughing) or no sputum, called a nonproductive cough
- chest pain during breathing
- high fever
- headache and general muscle soreness
- weight loss
Pulmonary melioidosis infection can mimic tuberculosis because they both can lead to pneumonia, high fever, night sweats, weight loss, bloody sputum, and pus or blood in the lung tissues. X-rays of lungs with melioidosis may or may not show empty spaces, called cavitations, which are a signature of tuberculosis.
Without fast, appropriate treatment, a pulmonary infection can progress to septicemia, which is an infection of the bloodstream. Septicemia is also known as septic shock and is the most serious form of melioidosis. It’s common and life-threatening.
Septic shock usually occurs quickly, though it may develop more gradually in some. Its symptoms include:
- fever, especially with shivers and sweating (rigors)
- sore throat
- breathing problems, including shortness of breath
- upper abdominal pain
- joint pain and muscle tenderness
- sores with pus on the skin or internally in the liver, spleen, muscle, or prostate
People with these specific conditions have a higher risk of developing a melioidosis bloodstream infection:
- kidney disease
- alcohol abuse
- liver disease
- chronic lung infections, including cystic fibrosis, chronic obstructive pulmonary disease (COPD), and bronchiectasis
- cancer or another condition that affects immune system function but isn’t related to HIV
People older than age 40 may also have a higher risk of contracting a melioidosis blood infection and developing more serious symptoms than younger people.
This type of melioidosis affects the skin and organs just under the skin. Local infections can spread to the bloodstream, and bloodstream infections can cause local infections. Symptoms may include:
- pain or swelling in a contained (localized) area, such as the parotid glands, which are most commonly associated with mumps and are located below and in front of the ear
- ulcerations or abscesses on, or just below, the skin — these may start as firm, gray or white nodules that become soft and inflamed, and then look like wounds caused by flesh-eating bacteria
In this type of melioidosis, sores form in more than one organ and may or may not be related to septic shock. Symptoms may include:
- weight loss
- stomach or chest pain
- muscle or joint pain
Infected sores are most commonly located in the liver, lung, spleen, and prostate. Less commonly, infections occur in the joints, bones, lymph nodes, or brain.
Causes of melioidosis
People and animals who have direct contact with soil or water that’s contaminated with the bacterium B. pseudomallei can develop melioidosis. The most common ways of direct contact include:
- breathing in contaminated dust or water droplets
- drinking contaminated water that hasn’t been chlorinated
- touching contaminated soil with the hands or feet, especially if there are small cuts in the skin
It’s very rare for one person to spread the infection to another, and insects aren’t thought to play a significant role in transmission.
The bacteria can live for years in contaminated soil and water.
Incidence of melioidosis
Where melioidosis occurs
Experts believe cases of melioidosis are greatly unreported in many tropical and subtropical areas. The areas with the most reported cases of melioidosis are:
- northern Australia
It’s also common in Vietnam, Papua New Guinea, Hong Kong, Taiwan, and much of India, Pakistan, and Bangladesh. It’s been less commonly reported in Central America, Brazil, Peru, Mexico, and Puerto Rico.
Weather’s role in transmission
Outbreaks of melioidosis are most common after a heavy rainfall, typhoon, monsoon, or flooding — even in arid regions. Pneumonia is a common first symptom during these periods. There may be other ways the bacterium is spread environmentally that haven’t been discovered.
People with the highest risk
People most likely to come in contact with B. pseudomallei in water or soil include:
- military personnel
- workers in construction, farming, fishing, and forestry
- adventure travelers and ecotourists, including those who’ve spent less than a week in an area where the disease is prevalent
Animals most affected
Many animals are susceptible to melioidosis. In addition to contact with contaminated water and soil, animals can pick up the bacterium from infected animals’ milk, urine, feces, nasal secretions, and wounds. The most commonly affect affected animals are:
Cases have also been reported in horses, cats, dogs, cattle, chickens, marsupials, tropical fish, iguanas, and other animals. It has killed some zoo populations.
How melioidosis is diagnosed
Melioidosis can affect almost any organ and can mimic many other diseases. That’s why it’s sometimes called “the great imitator.” But a misdiagnosis can be fatal.
Culturing the bacterium B. pseudomallei is considered the gold standard diagnostic test. To do this, doctors get small samples of a person’s blood, sputum, pus, urine, synovial fluid (found between joints), peritoneal fluid (found in the abdominal cavity), or pericardial fluid (found around the heart). The sample is put on a growing medium, such as agar, to see if the bacteria grows. However, culturing isn’t always successful in all cases of melioidosis.
Sometimes during outbreaks, experts get samples from the soil or water. The Centers for Disease Control and Prevention offers diagnostic help.
Treatment may vary depending on the type of melioidosis.
The first stage of treatment for melioidosis is a minimum of 10 to 14 days of an antibiotic given by intravenous (IV) line. Treatment with this antibiotic may last as long as eight weeks. Doctors may prescribe either:
- ceftazidime (Fortaz, Tazicef), given every six to eight hours
- meropenem (Merrem), given every eight hours
The second stage of treatment is three to six months of one of these two oral antibiotics:
- sulfamethoxazole-trimethoprim (Bactrim, Septra, Sulfatrim), taken every 12 hours
- doxycycline (Adoxa, Alodox, Avidoxy, Doryx, Monodox), taken every 12 hours
Relapses don’t occur as often as they once did. They occur mostly in people who don’t complete the full course of antibiotics.
How to prevent melioidosis
There are no vaccines for humans to prevent melioidosis, though they are being studied.
People who live in or are visiting areas where melioidosis is common should take these actions to prevent infection:
- When working in soil or water, wear waterproof boots and gloves.
- Avoid contact with soil and standing water if you have open wounds, diabetes, or chronic kidney disease.
- Be vigilant about avoiding exposure by inhalation during severe weather events.
- Healthcare workers should wear masks, gloves, and gowns.
- Meat cutters and processors should wear gloves and regularly disinfect knives.
- If drinking dairy products, be sure they are pasteurized.
- Get screened for melioidosis if you’re about to start immunosuppressive therapy.
Outlook for melioidosis
Even with newer IV antibiotic treatments, a significant number of people still die from melioidosis each year, particularly from sepsis and its complications. Death rates are higher in areas with limited access to medical care. People traveling to at-risk areas should be aware of melioidosis and take steps to limit their potential exposure. If travelers develop pneumonia or septic shock upon returning from tropical or subtropical areas, their doctors need to consider melioidosis as a possible diagnosis.