Water Journal : Water Journal April 2011
feature article 74 APRIL 2011 water feature articles Burkholderia pseudomallei occurs in moist tropical soil and surface water and is endemic in South East Asia and northern Australia. The bacterium is transmitted by exposure to contaminated soil and water, mainly through cuts in the skin but also via inhalation and ingestion. Most people who get sick with melioidosis have underlying risk factors such as diabetes, hazardous alcohol consumption, chronic lung or kidney disease, cancer or old age. Symptoms of this infection vary enormously, from subclinical infection, to simple skin sores, to pneumonia and, at the severe end of the spectrum, systemic septic shock with very high mortality. Melioidosis is an emerging disease that has seen a large increase of cases in the Top End of the Northern Territory, with over 100 in 2010 -- more than three times the average annual incidence rate in this area. Higher rainfall, especially in the Darwin region, and increasing levels of soil disturbance are considered to be important factors in this increase. In the last 15 years, melioidosis outbreaks have been attributed to contaminated water supplies in other areas of northern Australia causing fatalities among humans and animals. Chlorination will control pathogens like B. pseudomallei but is rarely practised in private residential bores in rural areas. A second study addressed the question of whether the presence of B. pseudomallei in bores is mainly the consequence of single contamination events or whether specific conditions have to be met to allow the survival of this bacterium in bore water (Draper et al., 2010). The study investigated 47 water bores and found a significant association with lower pH and low salinity water, which is in accordance with previous studies. Some B. pseudomallei positive bores also had high water turbidity levels. More organic matter in these bores is favourable to B. pseudomallei, which as a saprophytic organism obtains nutrients from decaying organic matter. Moreover, decomposition of organic matter further contributes to acidification of the water. The occurrence was also strongly linked to high iron levels. This finding supports previous research showing enhanced B. pseudomallei growth in iron-rich media and in red-coloured soil indicating oxidised iron. Furthermore, clinical conditions causing iron overload such as thalassemia and haemochromatosis are associated with increased melioidosis rates. For some B. pseudomallei positive bores, the source of contamination was likely to be the entry of soil or surface water into the bore as suggested by concurrent high water turbidity and coliform counts. Nevertheless, this was only evident in a subset of positive bores and it seems that the above specific conditions (especially low salinity, low pH and high iron) significantly contribute to persistent colonisation. The Author Mirjam Kaestli PhD (email: email@example.com) is a Senior Research Officer at the Menzies School of Health Research, Tropical & Emerging Infectious Diseases Division, Royal Darwin Hospital Campus, Casuarina NT 0811. Note: Full versions of these studies with references were published in the Journals Applied and Environmental Microbiology, Aug. 2010, p. 5305--5307 (Draper et al., 2010) and Emerging Infectious Diseases, in press (Mayo et al, 2011). Mirjam Kaestli A study has shown that the soil bacterium Burkholderia pseudomallei, which causes the disease melioidosis, occurred in one-third of 55 tested residential bores in rural areas around Darwin (Mayo et al., 2011). There are about 5,000 residential bores in these rural areas. They are mostly unchlorinated and can be contaminated with potentially pathogenic microbes such as E. coli bacteria, Cryptosporidium or Giardia. Melioidosis Bacteria Found in Private Bores Around Darwin A study investigated 47 water bores and found a significant association of B. pseudomallei with lower pH and low-salinity water.
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