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Disappearing mosquitoes mystify scientists

Tuesday, December 27, 2011 - 02:46

Dec. 27 - The disappearance of mosquitoes from villages in north-eastern Tanzania is delighting villagers long-plagued by malaria -- but mystifying scientists who worry that this could be a new manifestation of climate change. Jim Drury reports.

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These barren huts in remote Tanzania are used for trapping mosquitoes, enabling researchers to study the deadly creature. But recently the pests, which carry the malaria parasite that's been killing humans for 50,000 years, have been almost entirely absent. Scientists at Tanzania's National Institute of Medical Research are puzzled. They say less rainfall in recent years may be partly responsible for the decline in mosquito numbers. While this looks like good news for villagers, it also presents worrying evidence about the impact of climate change. SOUNDBITE (English) DR MEWLLE MALECELA, DIRECTOR GENERAL OF TANZANIA'S NATIONAL INSTITUTE OF MEDICAL RESEARCH (NIMR), SAYING: "Why we think there is a decline in mosquitoes is that there have been changes in rainfall patterns and particularly in Masayicha, these changes in rainfall patterns have been directly linked to this decline in vector populations and so we see that climate change has a very, very important part in this decline. However, we are very careful to say that it is not the only factor." In 2004 researchers caught more than 5,000 mosquitoes. Within five years that figure had plummeted to just 14, a fall of more than 99 percent. Large reductions have been noted across the continent. Collaborators on the Joint Malaria program include experts from the University of Copenhagen. Its lead researcher - Professor Dan Meyrowitsch - is cautious about blaming climate change. SOUNDBITE (English) PROFESSOR DAN MEYROWITSCH, UNIVERSITY OF COPENHAGEN, LEAD SCIENTIST OF REPORT, SAYING: "Although the rainfall pattern has fallen over all these years, we don't think that that can entirely explain these rapid declines. We assume that there may be other factors at play. It could be a disease among the mosquitoes, it could also be a change in use of agricultural pesticides in these communities. Because the interesting thing is that there has been no systematic attempt to control mosquitoes in these communities, so there has been no major intervention targeting the mosquitoes but despite this we have observed a very rapid decline." Other scientists are sceptical. The World Health Organisation say increases to malaria-fighting budgets was pivotal in reducing deaths over the past decade. But the mystery - and the worries surrounding it, remain, especially as extreme weather events are becoming increasingly common across the region. There are also worries that in areas where the mosquitoes have disappeared, resistance to malaria is on the decrease and that if the disease returns, the impact will be devastating. Out in the village of Tongoni, however, there is much joy. For a new generation, malaria is - for now - no longer the killer it once was. Jim Drury, Reuters

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Disappearing mosquitoes mystify scientists

Tuesday, December 27, 2011 - 02:46