Mellioidosis: A Category B Bioterrorism Disease That Gets ‘No Respect’


Burkholderia pseudomallei bacteria growing on a medium of sheep blood agar after 72 hours growth at 37 C. 

By COL (ret.) Dr. Zygmunt Dembek, Associate Professor in the Department of Military and Emergency Medicine at the Uniformed Services University of the Health Sciences

This piece examines the little-publicized Category B bioterrorism agent Burkholderia pseudomallei and the disease of melioidosis. Of particular concern are the recent 21st century melioidosis outbreaks that have occurred in the United Sates where only imported melioidosis cases had previously been reported, and endemic melioidosis was unknown. Further, the accidental contamination of an aromatherapy spray that sickened four people and caused two deaths brings to light the bioterrorism potential of this disease. 

What is Mellioidosis?

Melioidosis is a disease of concern caused by the bacteria Burkholderia pseudomallei. Melioidosis and its causative agent are considered Category B bioterrorism diseases by the US Centers for Disease Control and Prevention (CDC). These are among the second highest priority agents and diseases having bioterrorism potential. The CDC considers Category B pathogens and diseases to be moderately easy to disseminate, resulting in moderate morbidity and low mortality, and requiring specific enhancements of the CDC’s diagnostic capacity and enhanced disease surveillance for detection and diagnosis.   

B. pseudomallei is also on the US Health and Human Services (HHS) and US Department of Agriculture (USDA) Select Agents and Toxins List. Yet many working in public health would likely have difficulty describing the disease and its causative agent. 

How Burkhoderia pseudomallei Causes Illness

B. pseudomallei commonly spreads to humans by inoculation of nasal, oral, and conjunctival mucous membranes, abraded or lacerated skin, or by inhalation. Melioidosis is often contracted by direct contact with B. pseudomallei-contaminated soil and water. Having breaks in the skin when coming into direct contact with B. pseudomallei contaminated soil or water can cause infection. Some cases of melioidosis are understood to have been caused by inhaling contaminated dust and water mists or ingesting contaminated food and water. Aerosols containing B. pseudomallei are highly infectious for laboratory workers. As a consequence, clinical chemistries, hematology and other laboratory tests are done under laboratory Biosafety Level 2 (BSL-2) conditions, while any work performed with cultures of B. pseudomallei must be conducted under the more stringent biosecurity requirements of BSL-3 laboratory conditions. It is also possible for healthcare workers and others to contract melioidosis from contaminated infectious material. 

Melioidosis Symptoms 

In areas of the world where it is endemic, most exposed individuals do not develop symptomatic illness.  Most of the individuals who develop symptomatic illness also have predisposing medical conditions (e.g., diabetes, cirrhosis, impaired immunity). Clinical case presentations therefore vary from mild illness to septicemia with up to 90% case fatality rate (CFR) with 24-48 hours after illness onset. Confirmed melioidosis is often treated with two weeks of intravenous antibiotics, followed by three to six months of oral antibiotics. There are no human vaccines available for melioidosis. 

Mellioidosis Geolocation

Melioidosis is most often a disease found in the tropics and is widespread in Southeast Asia (it can be isolated in 50% of the rice paddies in Thailand) and in northern Australia.  As such, this pathogen has not been especially high on most health officials concerns for bioterrorism in temperate climates. That changed in 2022, when B. pseudomallei was found in the environment along the Gulf Coast of Mississippi. There is an intensive investigation currently underway by public health authorities to determine how widespread this organism is in the continental United States. 

Texas and Mississippi

In the Texas County of Atacosa, two human cases with B. pseudomallei infection had been discovered in 2004 and 2018 that were not clearly linked to prior exposure in Southeast Asia and northern Australia.  While neither of these two melioidosis cases was related to one another other than arising in the same Texas County, the B. pseudomallei isolates from them both appear to be quite close genetically.  Environmental investigations could not find any source of exposure for these Texas cases. 

An initial human melioidosis case was discovered in southern Mississippi in 2020. The epidemiologic investigation conducted at that time did not determine the source of this infection. In May of 2022 a second case of B. psuedomallei in Mississippi provided genetic evidence that it was similar to the 2020 case.  Renewed environmental sampling around the house of the 2020 melioidosis case led to the discovery of B. pseudomallei in three environmental samples taken near that initial patient’s home. Genetic analysis of B. pseudomallei bacterial samples from the Mississippi cases showed that they are closely related to a Western hemisphere strain found in tropical portions of the Americas.   

As a result of the Texas and Mississippi melioidosis cases, the CDC has recently conducted disease modeling that found the Gulf Coast states of Alabama, Florida, Louisiana, Mississippi, and Texas all contain environmental conditions that are favorable to the growth of B. pseudomallei

B. pseudomallei – An Agent of Biowarfare

The use of B. pseudomallei as a biological warfare (BW) agent was studied by the US in the 1950’s and 1960’s, but it was never weaponized.  It has been reported that the Soviet BW program had also evaluated B. pseudomallei as a BW agent.  Recent events have brought attention to the potential of B. pseudomallei to be used as an agent of bioterrorism (BT). 

From March through July of 2021, four cases of B. pseudomallei occurred, with 2 deaths. These cases were spread among the states of Georgia, Kansas, Texas, and Minnesota. An intensive investigation by the respective state health agencies and the CDC discovered that a bottle of aromatherapy spray from the house of one of the fatal cases contained B. pseudomallei. The contaminated “Better Homes & Gardens Lavender & Chamomile Essential Oil Infused Aromatherapy Room Spray with Gemstones” spray was sold at about 55 Walmart stores and also online. This aromatherapy spray was made in India, and the genetic testing of the B. pseudomallei from the 4 case-patients matched it to a strain found in South Asia. 

Upon discovery that it contained the suspect pathogen, the spray was immediately pulled from store shelves and the internet, and the US Consumer Product and Safety Commission (CPSC) issued an immediate recall of this item, along with five other scents in this same product line. There were continuing investigations conducted as to whether any other scents or brands posed a similar health risk. 

B. pseudomallei – An Agent of Bioterrorism

This event with contaminated aromatherapy spray highlights the potential for B. pseudomallei to cause illness from unsuspected sources. Regarding bioterrorism potential, it would not be out of the realm of possibility for someone to isolate a source of B. pseudomallei (whether in Asia, Australia, or the Americas), and to grow that isolate in culture for use in an aerosol spray such as in the contaminated aromatherapy spray bottles. While some pathogens such as Bacillus anthracis, the causative agent of anthrax disease, have much greater ‘name brand recognition’, health authorities must also have disease detection system capacity in place that allow detection of not as well-known diseases such as melioidosis. 

What Have We Learned?

In summary, the lessons learned from these novel outbreaks of B. pseudomallei occurring in the US in the 21st century include the fact that we can no longer assume that B. pseudomallei and subsequent infections of melioidosis are all imported, and the potential instances of endemic melioidosis need to be thoroughly investigated by health authorities. The ability of melioidosis to be spread either from natural or deliberate means dictates that this knowledge be incorporated into public health surveillance systems. 

About the Author

COL, USAR (Ret) Zygmunt F Dembek, PhD, MS, MPH, LHD (Hon) is an Associate Professor in the Department of Military and Emergency Medicine at the Uniformed Services University of the Health Sciences and a Senior Scientist at Battelle Memorial Institute. He is an internationally recognized thought leader in biodefense and epidemiology, former Chief of Biodefense Epidemiology and Education and Training Programs at the US Army Medical Research Institute of Infectious Disease (USAMRIID), and has conducted clinical, epidemiology and infectious disease training in Africa, Asia, Europe, the Caucasus, and North and Latin America. He was the Senior Editor for the peer-reviewed Textbook of Military Medicine, Medical Aspects of Biological Warfare, and Lead Editor for USAMRIID’s Medical Management of Biological Casualties Handbook (Blue Book), 7th Edition. 

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