Meliodosis: A Tropical Disease Warning

The Centre for Disease Control (CDC) in the NT has reported that 97 people have contracted the soil-borne disease since last wet season (2012), and nine of them have died.
Most of the reports of melioidosis in Australia originate in the Northern Territory, however, the disease is also endemic in Queensland. The disease usually occurs during the rainy season and may be accentuated by extreme flooding from rain, and from tsunamis, as occurred in Thailand in 2005.
Burkholderia pseudomallei exists as an environmental saprophyte living in soil and surface water in endemic areas (South East Asia and northern, tropical Australia), particularly in rice paddies. In endemic countries, the organism exists primarily in focal areas and is not equally distributed throughout the landscape. Sporadic cases have been reported as acquired in parts of Africa and the Americas.
The organism may exist in a viable, non-cultivable state in the environment, interacting with other organisms, particularly protozoa, which might explain its adaptation to an intracellular niche. Two outbreaks in Australia have also implicated potable water supplies rather than surface water as a potential source of the infection.
Melioidosis is a disease of the rainy season in the endemic areas. It mainly affects people who have direct contact with soil and water. Many have an underlying predisposing condition such as diabetes (commonest risk factor), renal disease, cirrhosis, thalassemia, alcohol dependence, immunosuppressive therapy, chronic obstructive lung disease, cystic fibrosis, and excess kava consumption. Kava is an herbal member of the pepper family that can be associated with chronic liver disease.
Melioidosis may present at any age, but peaks in the 4th and 5th decades of life. It affects men more than women. Although severe fulminating infection can and does occur in healthy individuals, severe disease and fatalities are much less common in those without risk factors.
The most commonly recognised presentation of melioidosis is pneumonia, associated with high fever, significant muscle aches, chest pain, and cough. Although the cough can be non-productive, respiratory secretions can be purulent, significant in quantity, and associated with on-and-off bright red blood. The lung infection can be rapidly fatal, with bacteraemia and shock, or somewhat more indolent.
Acute melioidosis septicemia is the most severe complication, presenting as a typical sepsis syndrome with hypotension, high cardiac output and low systemic vascular resistance. In many cases, a primary focus in the soft tissues or lung can be found.
The syndrome, usually in patients with risk factor comorbidities, is characteristically associated with multiple abscesses involving the cutaneous tissues, the lung, the liver, and spleen, and a very high mortality rate of 80–95 per cent. With prompt optimal therapy the case fatality rate can be decreased to 40–50 per cent.
The melioidosis bacillus is intrinsically insensitive to many antimicrobials. It should be noted that bioterrorism strains may be engineered to be even more resistant¹. B. Pseudomallei is usually inhibited by tetracyclines, chloramphenicol, trimethoprim- sulfamethoxazole (SXT), antipseudomonal penicillins, carbapenems, ceftazidime, and amoxicillin/clavulanate or ampicillin/sulbactam.
Ceftriaxone and cefotaxime have good in vitro activity but poor efficacy; and cefepime did not appear to be equivalent to ceftazidime in a mouse model. The unusual antimicrobial profile of resistance to colistin and polymyxin B and the aminoglycosides but sensitivity to amoxicillin/clavulanate is a useful tool to consider in treatment.
Randomised and quasi-randomised trials comparing melioidosis treatment have been found that the former standard therapy of chloramphenicol, doxycycline, and SXT combination had a higher mortality rate than therapy with ceftazidime, imipenem/cilastatin, or amoxicillin/clavulanate (or ampicillin/sulbactam). The betalactam-betalactamase inhibitor therapy, however, seemed to have a higher failure rate.
References
1. TolaneyP,LutwickLI:Melioidosis.In: Lutwick LI, Lutwick SM (eds). Bioterror: the weaponization of infectious diseases. Totowa NJ: Humana Press, 2008 pp 145–58
ProMED-mail 2012; 5 June