Spraying cattle with insecticides cuts sleeping sickness

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Sleeping sickness is endemic in 36 countries in Sub-Saharan Africa, threatening more than 60 million people, and is a major obstacle to economic development of affected rural areas, according to the WHO. It is caused by the parasite Trypanosoma brucei rhodesiense, which is transmitted by tsetse flies that feed on humans, cattle and wild animals. It can be controlled by treating cattle with insecticides that kill the tsetse vectors, or trypanocides that kill the disease parasite. To compare the two options, researchers used mathematical modelling and found that, in areas with few wild animals — where cattle provide most of the tsetse's blood meals — treating cattle with insecticides could be a cheaper and more effective method for breaking transmission of the disease.   Just 20 per cent of the cattle need to be sprayed with insecticides to control the disease in humans, whereas 65 per cent would require spraying with trypanocides to do the same, according to the findings, published in PLoS Neglected Tropical Diseases in May. "If there are many wild hosts, then the vast majority of tsetse flies may feed on wild hosts and treating cattle with insecticides may not help in killing the tsetse vectors," said Damian Kajunguri, one of the authors based at Stellenbosch University, South Africa. But, he added, "treating cattle with insecticides will work perfectly in areas with few wild hosts like Uganda where cattle provide most of tsetse blood meals." In such areas treating cattle with insecticides provides "one of the cheapest and most effective methods of controlling the diseases", said Kajunguri. Shem Wandiga, managing trustee at the Nairobi based Centre for Science & Technology Innovations, said that the reduction of tste tse flies may find some importance. But he added the researchers did not specify what kind of insecticide would be used, highlighting it should not be one of the pesticides banned under the Stockholm Convention on Persistent Organic Pollutants. Link to full paper in PLoS Neglected Tropical Diseases