Initially, it was thought that the longest period between presumed exposure and clinical presentation is 62 years in a prisoner of war in Burma-Thailand-Malaysia. However, subsequent genotyping of the bacteria isolate from the Vietnam veteran showed that the isolate may not come from Southeast Asia, but from South America. This reinstates another report that put the longest latency period for melioidosis as 29 years. Patients with latent melioidosis may be symptom-free for decades. Less than 5% of all melioidosis cases have activation after a period of latency. Various comorbidities such as diabetes, renal failure, and alcoholism can predispose to reactivation of melioidosis. Cause
Bacteria
Melioidosis is caused by gram-negative, motile, saprophytic bacteria named Burkholderia pseudomallei. The bacteria are usually opportunistic, facultative intracellular pathogens. It is also aerobic and oxidase test positive. A granule at the centre of the bacterium makes it resemble a "safety pin" when Gram stained. The bacteria emit a strong soil smell after 24 to 48 hours of growth in culture, however smelling for the identification of the bacteria is not recommended for routine laboratory practice. One of the factors causing B. pseudomalleis resistance to various kinds of antibiotics is because of its production of a glycocalyx polysaccharide capsule. It is generally resistant to gentamicin and colistin but sensitive to co-amoxiclav. B. pseudomallei is a biosafety level 3 pathogen which requires specialized laboratory handling. In humans and animals, another similar organism named Burkholderia mallei is the causative agent of the disease glanders.
On the other hand, melioidosis is only a notifiable condition in Thailand since June 2016. However, until recently, the official notification system in Thailand has significantly underestimated the incidence of culture-positive melioidosis and its mortality. Nevertheless, Australia also embarked on awareness campaigns to increase the communitys understanding of the disease. In the United Kingdom, where reporting by laboratories is mandatory, 41.3% of cases imported since 2010 were not notified. In the United States, lab workers can handle clinical specimens of B. pseudomallei under BSL-2 conditions, while mass production of such organisms requires BSL-3 precautions. On the other hand, in other endemic areas where the B. pseudomallei samples were handled less stringently, there has been no confirmed laboratory-acquired infection reported. This phenomenon may show that the risk of infection with B. pseudomallei is less than a typical biohazard type 3 agent. There are also several cases of hospital-acquired infection of melioidosis. Therefore, healthcare providers are recommended to practice hand hygiene and universal precautions.Large-scale water chlorination has been successful at reducing B. pseudomallei in the water in Australia. In middle to low-income countries, water should be boiled before consumption. In high income countries, water could be treated with ultraviolet light for those at risk of contracting melioidosis. Those who are at high risk of contact with the bacteria should wear protective gear (such as boots and gloves) during work. Those staying in endemic areas should avoid direct contact with soil, and outdoor exposure to heavy rain or dust clouds.