A new study finds that melioidosis, a difficult to diagnose deadly bacterial disease endemic in Southeast Asia and Northern Australia, is likely to be present in many more countries than previously thought. DW examines.
The study, published in the science journal Nature Microbiology, warns that millions of people worldwide may be at risk of contracting melioidosis, a bacterial disease present in 79 countries, including 34 that have never reported the disease.
The authors of the paper released on January 11 recommend that health workers and policy-makers give the infectious disease a higher priority, as they expect the number of melioidosis cases to climb given diabetes increases across the tropics, especially among the poor, and the rise in international travel which increases the risk of introducing the pathogen to new areas.
Contracted through the skin, inhalation or by drinking contaminated water, melioidosis can be difficult to diagnose as it mimics other diseases. The lack of early diagnosis and treatment, resistance of the bacteria to a wide range of antibiotics, the need for extended treatment (up to 20 weeks) and the possibility of relapse, even after appropriate treatment, make the mortality rate significant. Inadequate treatment may result in case fatality rates exceeding 70 percent, say experts.
The study, led by researchers at Oxford University, the Thailand-based Mahidol Oxford Tropical Medicine Research Unit (MORU), the University of Washington in Seattle, and Mahidol University, estimates that melioidosis killed 89,000 of the 165,000 people infected in 2015 - nearly as many as the annual global mortality from measles (95,000 deaths per year) and greater than deaths from leptospirosis (50,000 per year) or dengue (12,500 per year), two current health priorities for many international health organizations.
This suggests that melioidosis is severely underreported in the 45 countries in which it is known to be endemic and that it is probably endemic in a further 34 countries that have never reported it. "The large numbers of estimated cases and fatalities emphasize that the disease warrants renewed attention from public health officials and policymakers," WHO spokesperson Tarik Jasarevic told DW.
Who's most at risk?
High-risk melioidosis groups include not only people whose immune systems are not working properly - especially diabetics - but also those with chronic kidney, liver and lung diseases, blood and bone marrow problems, and people who use steroids or have an excessive alcohol intake.
The risk is also highest in people who are regularly exposed to soil and water contact like rice farmers, as Oxford researcher Dr. David Dance, one of the contributors to the report, told DW. Also at risk are aboriginal populations in northern Australia where the bacterium is believed to have originated.
However, as Dance indicates, even healthy people may get the disease if they are unlucky enough to be exposed to a high dose of the bacterium, for example, by near-drowning in a contaminated pond or flooded rice-field, or during really heavy storms.
'The great mimicker'
Researchers say the disease can manifest itself in many ways. In fact, it is sometimes called the "great mimicker," which is why it is so difficult to diagnose without the support of a modern laboratory.
"The main symptoms are non-specific, such as fever, shortness of breath, confusion, and sometimes skin pustules or abscesses. The bacterium causes septicaemia (blood poisoning), pneumonia and/or abscesses, especially in the liver and spleen, the prostate gland in men, and the salivary glands and lymph nodes in children, but potentially any part of the body can be infected," said Dr. Dance, who studies infectious diseases including melioidosis at the Laos-Oxford-Mahosot-Wellcome Research Unit (LOMWRU) in Vientiane, Lao PDR.
And the tricky part is that the organism can sometimes remain latent in the body for years, as Professor Peter Hotez, Dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston, Texas, told DW.
Lack of awareness
The disease was first identified among morphine addicts in Burma in 1911, and since then it has been found extensively in Southeast Asia, especially in Thailand, Singapore, Malaysia, Myanmar, Lao PDR, Cambodia and Vietnam, and northern Australia. During the independence wars in Vietnam, many cases were reported among French and US military personnel.
But although melioidosis has been recognized for more than 100 years, awareness of it is still low even among medical and laboratory staff in confirmed endemic areas, said study co-author Dr. Direk Limmathurotsakul, head of Microbiology at MORU and assistant professor at Mahidol University. "It especially affects the rural poor in the tropics, who often do not have access to microbiology labs," he added.
The researchers also indicate that many doctors and microbiologists in these areas are simply not familiar with the disease and the organism. And even when they are, there are very few places where it is compulsory to notify cases of melioidosis to public health authorities, so surveillance systems tend to grossly underestimate the number of cases that are occurring.
"The only places where surveillance is probably relatively complete, and where the number of cases comes close to our estimates, are Australia, Brunei Darussalam, and Singapore," said Oxford researcher Dance. These are countries in which the actual numbers of cases are quite small (for example, 550 cases in Singapore over the last 10 years, and between 30 and 100 cases occurring annually in the Northern Territory of Australia, according to the reports).
Thailand is the country where the greatest number of cases are diagnosed (approximately 2,000 per year), but even this is only one quarter of the number of cases predicted by our modeling.
"Mortality from melioidosis in affluent countries with modern microbiology laboratory facilities as well as state-of-the-art intensive care facilities can now be as low as 10 percent," Professor Bart Currie, an Infectious Diseases Physician from the Menzies School of Health Research and Royal Darwin Hospital in northern Australian city of Darwin, told DW.
Health experts say it is very difficult to diagnose the disease without the support of modern laboratory facilities
The role of soil and water
The latest study, which was funded by the UK-based Wellcome Trust, claims to be the first to provide an evidence-based estimate of the global extent of melioidosis, which is caused by Burkholderia pseudomallei, a highly pathogenic bacterium commonly found in soil and water in South and Southeast Asia and Northern Australia.
According to the World Health Organization (WHO), a person or animal can become infected by inhaling contaminated dust or water droplets, ingesting contaminated water, or coming into contact with contaminated soil, e.g. through a cut.
The soil, water and climate are clearly suitable for the organism to survive in the environment in many parts of Asia, but particularly those tropical countries that have heavy annual monsoons. This is likely the reason why the disease has been reported in 20 countries in Southeast Asia, the Indian sub-continent, and the Pacific region.
In fact, the study predicts high infection rates in countries like India and Vietnam, where the disease is gradually being recognized more frequently.
"We know that infected humans and animals can shed the bacterium into the environment, and if the soil and water are suitable that might help establish a new focus of the disease, and of course there is increasing international travel every year," Oxford researcher Dance explains. Fortunately, he added, the bacterium doesn't seem to be able to spread directly from people or animals to other people.
Burkholderia pseudomallei is commonly found in soil and water in South and Southeast Asia and Northern Australia
Global risk zones
Scientists say that over the past 25 years, the number of cases reported from parts of the world where the disease was not known previously to exist has been increasing.
According to the researchers, the highest melioidosis risk zones at the moment are in South Asia, East Asia and the Pacific, including all countries in Southeast Asia and tropical Australia, sub-Saharan Africa and South America, with risk zones of varying sizes in Central America, southern Africa and the Middle East.
"What we have done is to take all this information, combine it with information about the sort of environments where the bacterium can survive and the numbers of susceptible people who live in those regions and, with the assistance of very sophisticated spatial modeling techniques, used this to predict the true numbers of cases that are likely to have occurred around the world last year, and how many of those are likely to have died," said Dr. Dance.
How to limit the risk
And as Professor Currie indicates, the more recent spread may be occurring as a result of increasing human, animal, plant and soil movements around the world - which may explain the cases in the Americas - including a small number of cases in the US where the person acquiring melioidosis has not travelled to a known melioidosis region overseas. "Contaminated medical products exported from Asia have been hypothesized as one area of concern," said Currie.
Given this development, Professor Currie advises people with the above-mentioned risk factors living in melioidosis-endemic regions to avoid, whenever possible, exposure to wet season soils.