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Children herding livestock
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Research on Vector-Borne Diseases of Livestock and Humans targets insects and rodents that have a major impact on health and productivity of humans and livestock, mainly by transmitting disease-causing pathogens such as malaria and trypanosomiasis but also through direct debilitating effects such as blood-feeding. The work focuses on development of cost-effective and environmentally-benign interventions.
Understanding and exploiting behavioural interactions between vectors and their hosts is an important research area. DNA markers were used to demonstrate that tsetse feed largely on legs and bellies of larger and older cattle. Analysis of odours produced by different cattle and behavioural interactions between cattle and tsetse revealed that older cattle are more frequently bitten because their odours attract more flies and they are more tolerant of feeding tsetse. By restricting insecticide application to the legs of larger cattle within a herd, insecticide use can be cut by 90%, thereby reducing cost and environmental impact. Research on cattle-feeding mosquitoes in Ethiopia and Zimbabwe has shown that they, also, feed more from the legs of older and larger cattle. These findings offer the exciting prospect that, in Africa, insecticide-treated cattle might be used to control not only tsetse but also malarial mosquitoes feeding on cattle and humans. Research on chemical ecology of other insect pests of humans and livestock has identified natural and synthetic attractants for mosquitoes, screwworm and triatomid bugs.
Impacts of large-scale interventions against vector-borne diseases have been analysed in: rice-irrigation and malaria transmission in China; aerial-spraying operations against tsetse in Botswana; and use of insecticide-treated cattle. These analyses identified key factors that contributed to success or failure, and the simulation models have provided the basis for interactive decision tools to guide practitioners in the design of tsetse control programmes and policies. Research has led to successful planning and execution of a control programme that eliminated vectors of onchocerciasis from Bioko Island, Equatorial Guinea, under WHO’s African Programme for Onchocerciasis Control. Ecological research on African rodent vectors of lassa fever, bubonic plague and leptospirosis has aided development of deterministic models of outbreak risk and transmission pathways. NRI-led projects have developed ecologically-based rodent management tools to support sustainable vector-control programmes in Africa and Asia.
Following successful research that developed baits for vectors of animal trypanosomiasis, NRI is a major partner in a new Gates Foundation-supported initiative to identify attractants for tsetse that spread human African trypanosomiasis. Research showing that cost-effective control of tsetse can be achieved by treating the legs of cattle with insecticide requires testing on a larger scale in a variety of agro-ecological settings. Artificial baits and insecticide-treated livestock also have potential for controlling mosquito- and midge-borne diseases. Accordingly, research will be directed at analysing host-orientated behaviour of the Anopheles gambiae complex and Culicoides spp., vectors of malaria and blue-tongue virus respectively. Research on the ecology of rodents as vectors and reservoirs of many zoonotic and parasitic diseases affecting humans and livestock will continue. New competitively-won EC research in SADC region is investigating rodent ecology and health impacts. Research is also planned on effects of climate change on distribution and epidemiological significance of onchocerciasis vectors throughout Africa.
Bonner, P.C., Schmidt, W.P., Belmain, S.R., Oshin,
B., Baglole D., and Borchert, M. (in press) Poor housing quality increases
risk of rodent infestation and Lassa fever infection in refugee camps of
Sierra Leone. American Journal of Tropical Medicine and Hygiene.
Cheke, R.A., Tirados, I., Mas, J., Geenan, P., Adjaru, J. M. M., Bouaha, J. L. A., Sima, A., Meyer, R. R. F. & Wilson, M. D. (2006) Onchocerciasis transmission by the Bioko form of Simulium yahense Vajime & Dunbar 1975 (Diptera: Simuliidae). Proceedings of the International Symposium on Simuliidae. Berlin 2004. Studia dipterologica. Supplement 14: 26-30.
Gibson G & Russell I (2006) Flying in tune: sexual recognition in mosquitoes. Current Biology, 16, 1311-1316.
Kgori, P.M., Modo S. & Torr, S.J. (2006) The use of aerial spraying to eliminate tsetse from the Okavango Delta of Botswana. Acta Tropica, 99, 184-199.
Morales-Hojas, R., Cheke, R. A. & Post, R. J. (2006) The molecular systematics of five Onchocerca species (Nematoda: Filarioidea) including the human parasite, O. volvulus, suggest sympatric speciation. Journal of Helminthology 80: 281-290.
Morales-Hojas, R., Cheke, R.A. & Post, R. J. (2007) No genetic differentiation in the ribosomal ITS2 sequences between different strains of Onchocerca volvulus (Nematoda: Filarioidea). International Parasitology (submitted).
Mustapha, M., McCall, P. J., Cheke, R. A. & Post, R. J. (2006) The blackflies (Diptera: Simuliidae) of Bioko (Republic of Equatorial Guinea) and the Gulf of Guinea with a description of the larvae of the 'Pomeroy' form of Simulium cervicornutum. Systematic Entomology 31: 611-620.
Stenseth, N.C, Aikimbayev, A., Atshabar, B.B., Begon, M., Belmain, S.R., Bertherat, B., Carniel, E., Gage, K.L., Leirs, H. and Rahalison, L. (in press) Plague: Past, Present and Future. PLoS Medicine.
Tirados, I., Costantini, C., Gibson, G. & Torr, S.J. (2006) Blood-feeding behaviour of the malarial mosquito Anopheles arabiensis: implications for vector control. Medical and Veterinary Entomology 20: 425-437.
Torr, S. J., Mangwiro, T.N.C. & Hall, D.R. (2006). The effects of host physiology on the attraction of tsetse (Diptera: Glossinidae) and Stomoxys (Diptera: Muscidae) to cattle. Bulletin of Entomological Research 96, 71-84.
Torr, S.J., Maudlin, I. & Vale, G.A. (2007) Less is more: the restricted application of insecticide to cattle to improve the cost and efficacy of tsetse control. Medical and Veterinary Entomology 21, 53-64.
Torr, S.J., Prior, A., Wilson, P.J. & Schofield, S. (2007) Is there safety in numbers? The effect of cattle herding on biting risk from tsetse flies. Medical and Veterinary Entomology 21, 301-311.