Reduced bio-efficacy of permethrin EC impregnated bednets against an Anopheles gambiae strain with oxidase-based pyrethroid tolerance

BACKGROUND: Insecticide-treated nets (ITNs) are an integral component of malaria control programmes in Africa. How much pyrethroid resistance in malaria vectors will impact on the efficacy of ITNs is controversial. The purpose of this study was to evaluate knockdown and killing effects of ITNs on a metabolic-based resistant or tolerant malaria vector strain. METHODS: Bio-efficacy of 500 mg/m(2 )permethrin EC treated bednets was assessed on the OCEAC laboratory (OC-Lab) strain of Anopheles gambiae s.s.. This strain is resistant to DDT and tolerant to pyrethroids, with elevated mixed function oxidases. The Kisumu reference susceptible strain of A. gambiae s.s. was used as control. Nets were impregnated in February 1998 and used by households of the Ebogo village. Then they were collected monthly over six months for Bio-assays (WHO cone test). Knockdown and mortality rates were compared between the OC-Lab and the Kisumu strains, by means of the Mantel-Haenszel chi-square test. RESULTS: During the whole trial, permethrin EC knockdown rates were impressive (mostly higher than 97%). No significant difference was observed between the two strains. However, the mortality rates were significantly decreased in the OC-Lab strain (40–80%) compared with that of the Kisumu strain (75–100%). The decrease of killing effect on the OC-Lab strain was attributed to permethrin EC tolerance, due to the high oxidase metabolic activity. CONCLUSION: These data suggested an impact of pyrethroid tolerance on the residual activity of ITNs. More attention should be given to early detection of resistance using biochemical or molecular assays for better resistance management

Malaria vectors and transmission dynamics in coastal south-western Cameroon

BACKGROUND: Malaria is a major public health problem in Cameroon. Unlike in the southern forested areas where the epidemiology of malaria has been better studied prior to the implementation of control activities, little is known about the distribution and role of anophelines in malaria transmission in the coastal areas. METHODS: A 12-month longitudinal entomological survey was conducted in Tiko, Limbe and Idenau from August 2001 to July 2002. Mosquitoes captured indoors on human volunteers were identified morphologically. Species of the Anopheles gambiae complex were identified using the polymerase chain reaction (PCR). Mosquito infectivity was detected by the enzyme-linked immunosorbent assay and PCR. Malariometric indices (plasmodic index, gametocytic index, parasite species prevalence) were determined in three age groups (<5 yrs, 5–15 yrs, >15 yrs) and followed-up once every three months. RESULTS: In all, 2,773 malaria vectors comprising Anopheles gambiae (78.2%), Anopheles funestus (17.4%) and Anopheles nili (7.4%) were captured. Anopheles melas was not anthropophagic. Anopheles gambiae had the highest infection rates. There were 287, 160 and 149 infective bites/person/year in Tiko, Limbe and Idenau, respectively. Anopheles gambiae accounted for 72.7%, An. funestus for 23% and An. nili for 4.3% of the transmission. The prevalence of malaria parasitaemia was 41.5% in children <5 years of age, 31.5% in those 5–15 years and 10.5% in those >15 years, and Plasmodium falciparum was the predominant parasite species. CONCLUSION: Malaria transmission is perennial, rainfall dependent and An. melas does not contribute to transmission. These findings are important in the planning and implementation of malaria control activities in coastal Cameroon and West Africa

Genome sequence of the tsetse fly (Glossina morsitans):Vector of African trypanosomiasis

Tsetse flies are the sole vectors of human African trypanosomiasis throughout sub-Saharan Africa. Both sexes of adult tsetse feed exclusively on blood and contribute to disease transmission. Notable differences between tsetse and other disease vectors include obligate microbial symbioses, viviparous reproduction, and lactation. Here, we describe the sequence and annotation of the 366-megabase Glossina morsitans morsitans genome. Analysis of the genome and the 12,308 predicted protein-encoding genes led to multiple discoveries, including chromosomal integrations of bacterial (Wolbachia) genome sequences, a family of lactation-specific proteins, reduced complement of host pathogen recognition proteins, and reduced olfaction/chemosensory associated genes. These genome data provide a foundation for research into trypanosomiasis prevention and yield important insights with broad implications for multiple aspects of tsetse biology.IS

Anophèles afrotropicaux : 4. Mise au point sur le complexe Anopheles moucheti, réhabilitation d'An. multicinctus et d'An. garnhami basilewskyi (Diptera : Culicidae)

International audienceAmong the species belonging to the An. moucheti complex, the authors suggest to synonymize An. moucheti nigeriensis Evans, 193] with An. moucheti Evans, 1925 and restore An. moucheti bervoetsi D' Haenens, 1961 as a subspecies. They restore An. multicinctus Edwards, 1930 as a vaJid species and An. garnhami. basilewskyi Leleup, 1960 as a subspecies.Parmi les espèces appartenant au complexe An. moucheti, les auteurs proposent la mise en synonymie d'An. moucheti nigeriensis Evans, 193] avec An. moucheti Evans, 1925 ainsi que le rétablissement d'An. moucheti bervoetsi D'Haenens, [961 au rang de sous-espèce. Ils restaurent aussi An. multicinctus Edwards, 1930 au rang d'espèce valide et An. garnhami basilewskyi Leleup, 1960 au rang de sous-espèce

Quelques données cytogénétiques sur le complexe Anopheles gambiae au sud Cameroun

Les auteurs présentent des résultats originaux sur l'appartenance spécifique de membres endophiles du complexe Anopheles gambiae, récoltés au Cameroun dans les régions du Centre ef de l'Ouest. Dans tous les cas il s'agit d'Anopheles gambiae sensu stricto. La forme chromosomique forêt prédomine dans tous les prélèvements réalisés. Dans la région de I'Ouest la forme savane, très minoritaire, est observée. L'absence d'An. arabiensis et d'An. melas esf discutée

The bionomics of Anopheles funestus and its role in malaria transmission in a forested area of southern Cameroon

International audienc

Spatial Organisation Influences Citrus Pseudocercospora Leaf and Fruit Spot Disease Severity in Cocoa-Based Agroforestry Systems

An investigation to assess the spatial structure and severity of Pseudocerco-spora leaf and fruit spot disease (PLFSD) on citrus trees in cocoa-based agro-forests was carried out in three contrasting ecological zones in southern Cameroon, viz: 1) the humid forest zone, 2) the degraded forest zone, and 3) the forest-savannah transition zone. Two main parameters were investigated viz: 1) the spatial structure of cocoa based agroforests, and 2) the disease severity. In total, the spatial structure of 19 cocoa-based agroforests was analysed using the Ripley K(r) function, meanwhile the collection of epidemiological data that consisted of noting the presence of PLFSD spots on leaves and fruits on 438 citrus trees was used to characterise the severity of the disease. Results showed that, the spatial structure of citrus trees in these agro-forests investigated were regular in seven plots, random in nine, and aggre-gated in three. Aggregated plots presented a significantly higher mean of disease severity on leaves and fruits (28.55 and 30.37 respectively), as compared to randomised (20.91 and 16.32 respectively) and regular plots (16.28 and 14.97 respectively), at P-value < 0.05. These results suggest that the spatial structure of citrus trees in the cocoa-based agroforests studied influences the severity of PFLSD. Proper integrated control measures can therefore be initiated , leading to a considerable reduction of the use of manufactured inputs, and thereby, the cost of production of citrus fruits