“It’s always concerning when you have a new organism that should be in another part of the world than yours.”
- Sarah Park, M.D., Assistant Clinical Professor, Department of Pediatrics, John A. Burns School of Medicine, Honolulu, Hawaii
“Once an invasive species arrives, it’s almost impossible to get rid of it.”
- Sean Hann, American politician, New York State Assembly
According to the U.S. Department of Agriculture, an invasive species is one that is “non-native or alien to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.” Most people are aware of invasive plant species. (In Minnesota, for example, glossy buckthorn, a native to Europe and Asia, is an incredibly tenacious plant flourishing in many of our parks and fields, and Eurasian watermilfoil, also native to Europe and Asia, clogs up many of our ponds and lakes.) But few people know that some microbes are also invasive species.
Recently, the Centers for Disease Control and Prevention (CDC) warned that the bacterium Burkholderia pseudomallei has gained a foothold along the U.S. Golf Coast. (See USA Today Network June 21, 2023, “CDC warns of potentially deadly invasive bacteria found in southern Gulf States: What to Know.”). In this week’s Germ Gems post, I feature B. pseudomallei— an invasive microbial species.
Where did B. pseudomallei come from? B. pseuodomallei is native to Southeast Asia and northern Australia, where it’s found in soil and fresh water. This bacterium causes melioidosis— a deadly disease that kills about 90,000 people every year, most in that area of the world.
Neither B. pseudomallei nor melioidosis are, however, new subjects for these Germ Gems posts. In my September 1, 2021 post, “CDC Health Alert: Burkholderia pseudomallei Infections in Four States,” I related the story of four cases of melioidosis that cropped up in 2021 in Kansas, Minnesota, Texas, and Georgia. (Two of the cases were fatal.)
As I pointed out in that earlier post, at that time, the CDC had failed to find the source for the cases of melioidosis. But not long after, to the great credit of epidemiologists at the CDC, the source was discovered—an aromatherapy spray made in India and sold at Walmart. (Walmart ultimately removed the product from its stores.)
Subsequently, the CDC investigated three cases of melioidosis in Mississippi. The CDC researchers found B. pseudomallei in the environment (soil and water). The CDC now considers the bacterium endemic to the U.S. Gulf Coast. How prevalent B. pseudomallei is in the environment (soil and fresh water) is not yet clear. Nonetheless, the CDC’s finding does mean that we must now consider this bacterium an invasive species. (Over the course of my four-plus decades career as an infectious diseases specialist this is the first time that a bacterium was found to have invaded the U.S. environment.)
What does B. pseudomallei do to humans? As I stated above, B. pseudomallei causes the potentially life-threatening disease melioidosis. While melioidosis is fatal in 10% to 50% of cases (immunocompromised patients are at highest risk of dying), the risk of healthy people contracting melioidosis is very low. (Details of the disease melioidosis can be found in my September 1, 2021Germ Gems post.)
What is important to know for those who live along the Gulf Coast, or for those planning to visit the area, is that the CDC has alerted healthcare providers that this invasive species is now among us. Because melioidosis is infamously known as “the great mimicker,” the healthcare providers’ index of suspicion of possible B. pseudomallei infection should be raised when caring for patients in that area with diseases looking like tuberculosis, the flu, pneumonia, encephalomyelitis, septic arthritis, or osteomyelitis. Unlike the management of many invasive plant species, most of which seem almost impossible to get rid of, highly effective antibiotics are readily available to treat patients infected with B. pseudomallei.
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