Impact of insecticide resistance on malaria vector competence: a literature review.

Since its first report in Anopheles mosquitoes in 1950s, insecticide resistance has spread very fast to most sub-Saharan African malaria-endemic countries, where it is predicted to seriously jeopardize the success of vector control efforts, leading to rebound of disease cases. Supported mainly by four mechanisms (metabolic resistance, target site resistance, cuticular resistance, and behavioural resistance), this phenomenon is associated with intrinsic changes in the resistant insect vectors that could influence development of invading Plasmodium parasites. A literature review was undertaken using Pubmed database to collect articles evaluating directly or indiretly the impact of insecticide resistance and the associated mechanisms on key determinants of malaria vector competence including sialome composition, anti-Plasmodium immunity, intestinal commensal microbiota, and mosquito longevity. Globally, the evidence gathered is contradictory even though the insecticide resistant vectors seem to be more permissive to Plasmodium infections. The actual body of knowledge on key factors to vectorial competence, such as the immunity and microbiota communities of the insecticide resistant vector is still very insufficient to definitively infer on the epidemiological importance of these vectors against the susceptible counterparts. More studies are needed to fill important knowledge gaps that could help predicting malaria epidemiology in a context where the selection and spread of insecticide resistant vectors is ongoing.

Animal trypanosomosis in clinically healthy cattle of north Cameroon: epidemiological implications.

BACKGROUND: The control of animal trypanosomosis consists, amongst other things, of the punctual treatment of new cases, primarily diagnosed by pastoralists on the basis of clinical signs. This practice suggests that many apparently healthy infected animals are left untreated. In this study animal trypanosomosis in clinically healthy zebu cattle was evaluated, the distribution of the vectors established and the epidemiological implications discussed. METHODS: In 2014 two cross-sectional surveys were carried out in the Cambeef ranch. A total of 866 blood samples were collected from cattle in different sites: 549 in the dry season and 317 in the rainy season. The blood samples were subjected to parasitological examination using the buffy coat method and to PCV determination. An entomological survey on animal trypanosomosis vectors was undertaken during tsetse flies caught were identified and the mid-gut of each living non-teneral tsetse fly was examined for infections using a microscope. RESULTS: An overall trypanosomosis prevalence of 9% was found in the cattle examined. There were significantly (P < 0.05) more trypanosome infected cattle in the dry season than the rainy season. Trypanosome-infected cattle had significantly (P < 0.05) lower Body Condition Scores (BCS) and Packed Cell Volumes (PCV) in the dry season than in the rainy season. Anemia was positively correlated with trypanosome infection. The likelihood for an animal to be parasitologically free of trypanosome infection was at least three times as high in the Gudali breed as compared with the white and red Fulani breeds. Species of trypanosomes identified were Trypanosoma vivax (73.23%), Trypanosoma congolense (15.49%) and Trypanosoma brucei (11.27%). A total of 390 tsetse flies and 103 tabanids were trapped. Two species of tsetse flies were identified: Glossina tachinoides (33.59%) and G. morsitans submorsitans (41%). Nine of the 194 non-teneral flies were infected with trypanosomes. CONCLUSION: Carriers of trypanosomes are present amongst apparently healthy cattle in the study site. Attempts to successfully reduce the population of reservoir trypanosomes within herds and control the disease will need to consider mass screening once every year and this should be associated with drug sensitivity tests.