Epidemiology
Melioidosis is endemic in parts of southeast Asia (including Thailand, Laos and southern China, Singapore, Malaysia, Burma and Vietnam), Taiwan and northern Australia. Multiple cases have also been described in Hong Kong and Brunei India, and sporadic cases in Central and South America, the Middle East, the Pacific and several African countries. Although only one case of melioidosis has ever been reported in Bangladesh, at least five cases have been imported to the UK from that country, which suggests that melioidosis is endemic to that country and that there is a serious problem of underdiagnosis or under-reporting, most likely due to a lack of adequate laboratory facilities.
Northeast Thailand has the highest incidence of melioidosis recorded in the world (21.3 cases of melioidosis per 100,000 people per year). In Northeast Thailand, 80% of children are positive for antibodies against B. pseudomallei by the age of 4; the figures are lower in other parts of the world.
Melioidosis is a recognised disease in animals, including cats, goats, sheep, and horses. Cattle, water buffalo, and crocodiles are considered to be relatively resistant to melioidosis despite their constant exposure to mud. An outbreak at the Paris Zoo in the 1970s ("L’affaire du jardin des plantes") was thought to have originated from an imported panda.
Burkholderia pseudomallei is normally found in soil and surface water; a history of contact with soil or surface water is therefore almost invariable in patients with melioidosis; that said, the majority of patients who do have contact with infected soil suffer no ill effects. Even within an area, the distribution of B. pseudomallei within the soil can be extremely patchy, and competition with other Burkholderia species has been suggested as a possible reason. Contaminated ground water was implicated in one outbreak in northern Australia. Also implicated are severe weather events such as flooding tsunamis and typhoons.
It has been suggested, on the basis of whole genome sequencing, that humans may play a role in moving B. pseudomallei from place to place.
The single most important risk factor for developing severe melioidosis is diabetes mellitus. Other risk factors include thalassaemia, kidney disease, occupation (rice paddy farmers), and cystic fibrosis. The mode of infection is believed to be either through a break in the skin, or through the inhalation of aerosolized B. pseudomallei. Person-to-person spread has been described but is extremely unusual.
There is a clear association with increased rainfall: with the number (and severity) of cases increasing following increased precipitation.
Read more about this topic: Melioidosis