Melioidosis under the microscope
Beneath the tropical trees, under umbrellas and lower still, encased in soggy soil, lies a murderous member of the disease family. Melioidosis, also known as the ‘Darwin Disease’ thrives in the wet. It causes local and generalised infection; often pneumonia – and then, for the especially unlucky, septic shock and death.
‘Melio’, as it’s often shortened to, first hit the Australian radar in the late 1940s. Sheep were becoming infected in Queensland. By 1960, the first human case emerged.
In 2009-10, the Top End of the Northern Territory had the highest annual incidence of melioidosis documented globally from anywhere to date.
This wet season over the last Christmas period has seen further rises. Since 1 October 2011, 97 cases and nine deaths were reported, with most infections occurring in the Darwin region.
Professor Bart Currie, with Menzies and Royal Darwin Hospital colleagues has been researching melioidosis for two decades. He describes it as a disease caused by bacteria that live in soil and appear to have a symbiotic relationship with various plants
The bacteria ‘switch on’ and multiplies in the wet season. “These bacteria are then probably brought to the surface by drenching rains recharging the subterranean aquifers, which are underground layers of permeable rock or materials such as soil or silt,” he says.
“Burkholderia pseudomallei lives below the soil’s surface during the dry season but after heavy rainfall, can be found in surface water and mud and potentially become airborne,” he adds.
“It usually enters the body via cuts and sores in the skin or via inhalation of splashes, dust or droplets and, in very rare cases, by ingesting contaminated water.”
In Australia cases typically occur in the Top End of the Northern Territory (NT) and in far north Queensland and the Kimberley region of Western Australia.
These depend on where the infection develops in the first place. Often the illness starts as a chest infection with shortness of breath, productive cough and fever. Other initial indicators include fever with headache and confusion, or difficulty passing urine.
Infected patients usually fall ill one to 21 days after being infected, and symptoms may be sudden or gradual. That said, cases exist whereby the disease reared its head many years after the initial infection – indicating the person was carrying the bacteria, but they only activated once his or her immune system weakened.
The longest ever-documented time between infection and disease activation was 62 years – the case involved a war veteran who served in Southeast Asia
The last three wet seasons produced an unprecedented high number of cases, and there is concern that the coming wet season could again stretch local health resources.
Ongoing studies are assessing the relative contributions to the high case numbers of rainfall patterns, population changes in Darwin city itself and the environmental perturbations occurring with the many construction projects taking place over recent years.
To combat melio, Menzies is conducting the Darwin Prospective Melioidosis Study with colleagues at Royal Darwin Hospital, together with a number of collaborative environmental studies with colleagues from Charles Darwin University and various Australian and overseas universities.
Now in its 22nd year, the Darwin Prospective Melioidosis Study aims to understand the epidemiological, clinical and microbiological aspects of melioidosis in the Darwin region, and to use this information to lessen the burden of the disease.
It seeks to improve diagnosis and treatment of cases and provide health promotion messages for the public in conjunction with the NT Department of Health’s Centre for Disease Control.
The current mortality rate at Royal Darwin Hospital (RDH) in cases of melioidosis is lower than anywhere else in the world. Professor Currie attributes this to the excellent diagnostic skills of the RDH microbiology laboratory staff; as well as to the exceptional quality of care provided to critically ill patients with melioidosis by the medical and nursing staff of the Intensive Care Unit at RDH.
“The RDH staff are truly the world leaders and experts at saving lives when it comes to melioidosis” says Professor Currie.
These studies are funded by the National Health and Medical Research Council, the Australian Research Council, the Northern Territory Research and Innovation Fund and the US National Institutes of Health and Department of Homeland Security.
1. Mark Mayo and Ian Harrington sampling for melioidosis bacteria
2. One of the symptoms of melioidosis
3. Glenda Harrington, research assistant and Mirjam Kaestli, senior research officer