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      Prospects for Developing Odour Baits To Control Glossina fuscipes spp., the Major Vector of Human African Trypanosomiasis

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          Abstract

          We are attempting to develop cost-effective control methods for the important vector of sleeping sickness, Glossina fuscipes spp. Responses of the tsetse flies Glossina fuscipes fuscipes (in Kenya) and G. f. quanzensis (in Democratic Republic of Congo) to natural host odours are reported. Arrangements of electric nets were used to assess the effect of cattle-, human- and pig-odour on (1) the numbers of tsetse attracted to the odour source and (2) the proportion of flies that landed on a black target (1×1 m). In addition responses to monitor lizard ( Varanus niloticus) were assessed in Kenya. The effects of all four odours on the proportion of tsetse that entered a biconical trap were also determined. Sources of natural host odour were produced by placing live hosts in a tent or metal hut (volumes≈16 m 3) from which the air was exhausted at ∼2000 L/min. Odours from cattle, pigs and humans had no significant effect on attraction of G. f. fuscipes but lizard odour doubled the catch ( P<0.05). Similarly, mammalian odours had no significant effect on landing or trap entry whereas lizard odour increased these responses significantly: landing responses increased significantly by 22% for males and 10% for females; the increase in trap efficiency was relatively slight (5–10%) and not always significant. For G. f. quanzensis, only pig odour had a consistent effect, doubling the catch of females attracted to the source and increasing the landing response for females by ∼15%. Dispensing CO 2 at doses equivalent to natural hosts suggested that the response of G. f. fuscipes to lizard odour was not due to CO 2. For G. f. quanzensis, pig odour and CO 2 attracted similar numbers of tsetse, but CO 2 had no material effect on the landing response. The results suggest that identifying kairomones present in lizard odour for G. f. fuscipes and pig odour for G. f. quanzensis may improve the performance of targets for controlling these species.

          Author Summary

          Human African Trypanosomiasis (sleeping sickness) remains a serious threat to many of the poorest people in Africa. The trypanosomes causing the disease are transmitted by tsetse flies. There are no vaccines or prophylactic drugs to prevent people from contracting the disease. So the disease is dealt with after it has been contracted using often ineffective curative drugs with unpleasant and sometimes fatal side effects. Prospects for the development of effective vaccines or prophylactic drugs are poor. One certain means of preventing disease transmission is to remove tsetse flies, either at a local level (e.g., a group of villages) or regionally (covering large parts of a country or region). However, a major problem is the cost and logistical difficulty of implementing such fly control programmes. To overcome this, we are trying to develop cost-effective insecticide-treated targets by identifying chemicals that will increase the numbers of tsetse that will be lured to a target and killed. Here we show that two major vectors, G. f. fuscipes and G. f. quanzensis, are attracted to the odour of monitor lizards and pigs, respectively. This opens the way for further work to identify the attractants present in these natural odours which can be simply and cheaply incorporated into targets to reduce the cost of control.

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          Eliminating Human African Trypanosomiasis: Where Do We Stand and What Comes Next>

          While the number of new detected cases of HAT is falling, say the authors, sleeping sickness could suffer the "punishment of success," receiving lower priority by public and private health institutions.
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            Visual and olfactory responses of haematophagous Diptera to host stimuli.

            Key biotic and environmental constraints on the host-orientated behaviour of haematophagous Diptera are summarized. For each major group of biting Diptera, responses to host stimuli are reviewed, including activation and ranging behaviour, long-range and short-range olfactory responses and visual responses. Limitations to the comparison of results between groups of species, and the practical problems of experimental method and equipment are discussed.
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              GLIM for ecologists

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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS Negl Trop Dis
                plos
                plosntds
                PLoS Neglected Tropical Diseases
                Public Library of Science (San Francisco, USA )
                1935-2727
                1935-2735
                May 2009
                12 May 2009
                : 3
                : 5
                : e435
                Affiliations
                [1 ]International Center for Insect Physiology and Ecology, ICIPE, Nairobi, Kenya
                [2 ]Masinde Muliro University of Science & Technology, Kakamega, Kenya
                [3 ]Labovet, Kinshasa, Democratic Republic of Congo
                [4 ]Liverpool School of Tropical Medicine, Liverpool, United Kingdom
                [5 ]Institut de Recherche pour le Développement (IRD), UMR 177 IRD-CIRAD, Montpellier, France
                [6 ]Centre International de Recherche-Développement sur l'Elevage en Zone Subhumide (CIRDES), Bobo Dioulasso, Burkina Faso
                [7 ]Natural Resources Institute, University of Greenwich, Chatham, United Kingdom
                Yale University School of Medicine, United States of America
                Author notes

                Conceived and designed the experiments: MOO AH JE JL MJL PS GAV SJT IT. Performed the experiments: MOO SM JE JBR SJT IT. Analyzed the data: MOO JE PS JBR GAV SJT IT. Contributed reagents/materials/analysis tools: MOO PS. Wrote the paper: MOO JE MJL PS GAV SJT IT.

                Article
                09-PNTD-RA-0056R2
                10.1371/journal.pntd.0000435
                2674566
                19434232
                779b9043-58a0-459a-ba86-baec1624725d
                Omolo et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                History
                : 20 February 2009
                : 16 April 2009
                Page count
                Pages: 9
                Categories
                Research Article
                Infectious Diseases/Neglected Tropical Diseases
                Infectious Diseases/Protozoal Infections

                Infectious disease & Microbiology
                Infectious disease & Microbiology

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