“One Health” movement tackles infectious diseases


Seventy per cent of emerging and re-emerging infectious diseases are either vector borne or zoonotic - that means that today humans catch infections from animals, and vice versa, on a never-before experienced scale.


Out of this realisation, the "One Health" theme was born. The idea behind "One Health" is a simple one: that people, animals and the environment are all connected, including the sharing of disease-causing organisms. "One Health" is a movement that seeks to forge all-inclusive collaborations between doctors, veterinarians, dentists, nurses, environmentalists and research scientists to gain real understanding and real solutions for infectious diseases.


One of these experts is Canadian, Dr Mike Grigg, who works at the United States' National Institutes of Health in Bethesda, just outside of Washington DC. Dr Grigg and his colleagues, published a series of landmark papers in the ASP's official journal, The International Journal for Parasitology, between 2002 and 2008 showing that the severity of toxoplasmosis, a water-borne zoonosis caused by the protozoan parasite, Toxoplasma gondii, varies widely from chronic and benign to acutely fatal in marine mammals off the North American west coast. And now, they've discovered that another protozoan parasite, Sarcocystis neurona, often co-infects, with Toxoplasma, the same marine mammals. And, when both parasites are present, the disease is far worse, causing encephalitis and death.


The puzzling thing is that both of these parasites are normally terrestrial - Toxoplasma is passed out in the faeces of cats and this particular form of Sarcocystis is passed in the faeces of opossums. Runoff from the land to the ocean, and into marine ecosystems, is the culprit.


And there's a chilling link to human disease: rare Toxoplasma genotypes linked to a major human outbreak in the Pacific Northwest were abundant in marine mammals of the region, emphasising wildlife as relevant sentinels for evaluation of human health risks. The message is clear - we need vigilant surveillance of public waterways to prevent faecal contamination threatening human and wildlife health.


For humans, there's some good news. "Chlorination does not kill Toxoplasma, but filtration eliminates them from the water supply," said Dr Grigg.


But for marine mammals the outlook is less positive. "Limiting serious disease in marine mammals will require larger conservation efforts to block these land pathogens from flowing into coastal waters," said Dr Grigg. During the six year study period, more than 5,000 dead marine mammals were reported on the coastal beaches of the Pacific Northwest.


A similar "One Health" story has been developing in Europe. Professor Peter Deplazes of the University of Zurich in Switzerland notes that urban recreational environments are increasingly designed closer to natural ecological systems, boosting populations of voles which represent reservoirs for Toxoplasma and also other zoonotic parasites, like Echinococcus, a tapeworm that causes terrible, cystic disease (echinococcosis or hydatids) in humans.


Large populations of freely roaming stray dogs and cats maintain a permanent infection presence for many parasites and ecological changes also contribute to parasite dispersal: fox populations have grown in many areas of Europe and human echinococcosis emerged in Europe in the context of the fox populations invading urban areas. Professor Deplazes says: "A good understanding of the parasites' epidemiology is required for planning and implementing effective prevention strategies. The continuous education of medical doctors and veterinarians and the instruction of pet owners by providing uniform recommendations are also of prime importance. A close collaboration between veterinary and public health professionals in a 'One Health' concept is required."


Both Dr Mike Grigg and Professor Peter Deplazes have been brought to Australia by the ASP under its Invited International Lectureship Scheme. As part of their tour, they will be visiting Professor Nick Smith at the newly established Queensland Tropical Health Alliance at James Cook University in Cairns. The three researchers will be discussing collaborative plans to try to find a way to prevent transmission of Toxoplasma gondii.


The two international experts will also be visiting Murdoch University in Perth, where Professor Andrew Thompson is passionately interested in parasites of wildlife, especially those that can cross between native animals and humans.


"Insufficient attention has been given to the impact of infectious diseases on the health of Australian wildlife and their conservation and there's a need to redress the balance," says Professor Thompson. "Encroachment and translocation expose wildlife to novel pathogens which may impact on their health or even establish new reservoirs for human disease."


Though Australia may be accused of lagging behind Europe and North America in embracing the "One Health" philosophy, that accusation can't be levelled at Dr Deborah Holt and colleagues at the Menzies School of Health Research in Darwin. Dr Holt notes that, "The most important human parasitic infections in northern Australia are associated with gastrointestinal diseases such as Strongyloides, Cryptosporidium, Trichuris and Giardia, all of which are also found in animals, and skin disorders, particularly scabies, which are also a significant problem in domestic animals and wildlife. 


"For Indigenous Australians living in remote community settings, extremely overcrowded living conditions and infrastructure problems that result in poor sanitation, are a significant factor in the transmission of many of these diseases," says Dr Holt. But there's hope. Community based control programs, championed by the Menzies School, using permethrin for scabies have had some success while a mass drug administration program using ivermectin for scabies and strongyloidiasis is currently underway.


Queensland Tropical Health Alliance (QTHA) scientists will present their latest research on improving health outcomes for people living in the tropics at the network's inaugural scientific conference on July 16-17 at the Pullman Reef Casino Hotel in Cairns, Australia.


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