“Geography is destiny.” - Abraham Verghese, American physician, author, and professor of medicine
“By recognizing that infectious disease is not some faraway exotic issue but a global problem, and by sharing the responsibility for its prevention, diagnosis and control, the whole world will be a lot safer.”
- Seth Berkley, CEO of GAVIAlliance
Recently, the Center for Disease Control and Prevention (CDC) reported that it’s investigating four cases (two fatal) of Burkholderia pseudomallei infection in the U.S. For the general public, the response, if any, was probably “What the *%$! is Burkholderia pseudomallei?” My reaction, however, was “Wow, that’s really interesting and scary!”
B. psueodomallei causes a disease called melioidosis –a disease that is virtually unheard of in the U.S. Yet, melioidosis kills about 89,000 people a year in Southeast Asia and northern Australia. As four cases in total recently were been reported in the states of Kansas, Minnesota, Texas and Georgia, we should all be aware of this disease. Therefore, this week’s Germ Gems post is on melioidosis—a very interesting, albeit vicious, bacterial infection.
Where does Burkholderia psuedomallei hang out? B. psuedomallei is a gram-negative bacterium that is named after its discoverer Walter Burkholder, a Cornell University plant pathologist. (He determined it causes “onion rot”). It is found in soils, ponds, streams, pools, stagnant water, and rice fields in many countries in Southeast Asia and northern Australia. The only places it occurs naturally in the U.S., however, are in Puerto Rico and the U.S. Virgin Islands.
How is B. psuedomallei transmitted to humans? People, and many other animals, get infected through direct contact with contaminated soil or water. Also, inhalation of contaminated dust or water droplets, drinking contaminated water, ingesting contaminated food, or other contact with contaminated soil, especially through skin abrasions, are other ways to acquire the bacterium. Person-to-person spread is very rare.
Around a dozen cases of melioidosis are reported each year in the U.S. Most are in travelers or immigrants from places where the disease is widespread. Surprisingly, none of the four Americans who contracted the disease in the recent report from the CDC had been out of the country. Also, hundreds of samples of soil, water, and products from the properties in and around these patients’ homes tested negative for B. psuedomallei. Nonetheless, genome testing showed that the four bacterial strains that sickened the patients are closely related to each other, suggesting there is a common source for these cases. As none has yet been found, the CDC has a real mystery on its hands.
What are the clinical features of melioidosis? Alfred Whitmore first described melioidosis in 1912 in present day Myanmar. (It’s also called Whitmore’s disease.) Most B. pseudomallei infections are asymptomatic. For those who become ill, a majority experience symptoms associated with sepsis (predominantly fever) with or without pneumonia or localized abscesses in various organs, such as, the liver, spleen, lungs, prostate, and kidneys. The diagnosis is usually established by isolating B. psuedomallei in cultures of the blood or pus obtained from an internal organ. (Great care must be taken when culturing B. psuedomallei, because of its significant risk of aerosolization.)
Approximately 165,000 people contract melioidosis per year worldwide and about 89,000 (54%) die. Risk factors for fatal infection include diabetes mellitus, chronic liver, kidney, or lung disease, and conditions that compromise immunity. Most children with fatal melioidosis, however, have none of these risk factors. This was the case with the two fatal pediatric cases recently reported by the CDC.
Melioidosis has been given the nickname “the great mimicker” because of the presence of nonspecific signs and symptoms. Like Mycobacterium tuberculosis, the cause of tuberculosis which is also a great mimicker, B. pseudomallei can become latent (dormant) and reactivate years later if immune defenses become compromised.
Treatment. Antibiotics are the mainstay of treatment of melioidosis. B. psuedomallei is frequently resistant to multiple antibiotics, and antibiotic selection is based on antibiotic susceptibility testing. Treatment generally starts with an intravenous antibiotic (ceftazidime or imipenem) for 2 weeks, followed by 3-6 months of an oral antibiotic (trimethoprim/sulfamethoxazole or amoxicillin/clavulanic acid).
Prevention. There is no vaccine for melioidosis. In areas where melioidosis is widespread, avoiding contact with contaminated soil or water is crucial. For example, people working in rice paddies and other kinds of agricultural work should wear boots.
Nefarious transmission? Because B. psuedomallei is highly virulent and transmitted by an aerosol, melioidosis has been on the radar screen of bioterrorists as a biological weapon. In fact, B. pseudomallei and the closely related B. mallei, a cause of infections primarily in horses, are considered by the CDC as “Category B Bioterrorism Agents.” This is due to the history of confirmed use of B. mallei in biological warfare, including the U.S. Civil War, World War I, World War II,, and purportedly by the Russians in Afghanistan in the 1980s.
While many details of the four cases of melioidosis reported by the CDC aren’t yet published, fortunately, there’s no reason to suspect a treacherous means of transmission. Public health officials and clinicians are now alerted to these cases. This may well be the end of the outbreak in the U.S., but if there are additional cases, effective antibiotic therapy is thankfully available.