A new way to test for the parasite which causes the potentially fatal disease leishmaniasis could help control its spread to humans and stop dogs being needlessly killed in parts of South America. Zoonotic visceral leishmaniasis is a vector-transmitted parasitic infection which can be fatal if left untreated. It generally affects the poorest of the poor, particularly malnourished children in developing countries, with an estimated 200,000 to 400,000 new cases in humans occurring annually, according to World Health Organization (WHO) figures. Dogs have been shown to be the ‘reservoir’ for the parasite, which is transmitted to humans via bites from female sandflies that have fed on blood from infected dogs. In Brazil, tens of thousands of dogs that test positive for anti-Leishmania antibodies are killed every year in an effort to control the disease. However the presence of antibodies does not necessarily mean that the dog is symptomatic or is infectious to sandflies so that it can pass the parasite onto humans. This means that it is likely many dogs are killed unnecessarily, which usually results in dog owners acquiring a new dog, often a puppy that has not encountered the parasite before and that is then likely to become infected, thus helping to drive transmission. Previous studies have questioned the effectiveness of these measures in controlling leishmaniasis in dogs and humans and the policy is also undermined by significant levels of non-compliance among dog owners. An alternative approach is outlined in a new study by scientists at the University of Warwick in the UK who have shown that parasite load – a count of the number of parasites present in a dog’s skin tissue – is related to its infectiousness to sandflies.
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