Melioidosis is so unknown and underfunded that to call it a “neglected tropical disease” would be an euphemism. In most of the world melioidosis is seen as an “imported disease” and correct diagnosis often depends on analyzing the patient’s last vacation destination. However, a recently published Nature Microbiology study suggests that the global distribution of melioidosis’ causative agent Burkholderia pseudomallei is significantly vaster and the number of cases much higher than expected.
B. pseudomallei is a saprophytic bacteria, which means it lives off dead or decomposing matter and is therefore perfectly happy living in the soil or water. When an animal or a human accidentally becomes infected with B. pseudomallei, the bacteria causes melioidosis and a number of genes that allow B. pseudomallei to live successfully in the soil become virulence factors in animals, thus contributing to the high case fatality rate (CFR) of B. pseudomallei. The symptoms of melioidosis are shared amongst many diseases, thus making it hard to correctly diagnose, particularly outside of northern Australia and Southeast Asia, where melioidosis is endemic.
By calculating the environmental suitability of the world’s regions for B. pseudomallei, the paper greatly expands the probable global distribution of the bacteria to most tropical areas and, by then comparing the burden of melioidosis in its known endemic region to this extended area, predicts the global yearly burden of melioidosis as 165,000 cases resulting in 89,000 deaths. While these numbers may seem high, particularly for a disease most people have never heard of, according to Dr. Danny Milner, this “potential number of cases is probably a really good estimate.” He does, however, caution that their “case fatality rate is a little more problematic, because you’re comparing very different populations, some which may have co-evolved with the disease.”
For Dr. Milner, the Nature Microbiology paper is “from a statistical point of view a really beautiful paper […] and it’s meant to be a wake up call”. But while the paper highlights the need for something to be done, it glosses over what exactly should to be done. Diagnosis of melioidosis requires culturing the bacteria in a lab and because inhalation is one of the routes of infection this work must be done in Biosafety Level 3 (BSL3) facilities, which not all countries have and which are necessary to keep people both inside and outside the lab from getting infected. “And,” Dr. Milner cautions, “I think this is an issue because how we go about [understanding melioidosis] is actually more important than anything else, because it could be quite dangerous.”
Special thanks to Dr. Danny Milner, Associate Professor in the Department of Immunology and Infectious Disease at the Harvard T. H. Chan School of Public Health, for his time, expertise, commentary and reading suggestions.
This Germ Can Live Decades In Distilled Water, Kill Humans In 48 Hours , Angus Chen for NPR’s Goats and Soda: Stories of Life in a Changing World