Vector species composition and malaria infectivity rates in Mkuzi, Muheza District, north-eastern Tanzania.

Entomological surveys were conducted in Mkuzi village in Muheza District, north-east Tanzania from April to September 2003. The objectives were to determine the species composition and infectivity rates of mosquitoes in Mkuzi village. Mosquito collection was done using CDC light trap and pyrethrum spray catch (PSC) techniques. The light trap: spray catch ratio was 2.2:1. A total of 2157 mosquitoes were collected (light trap = 1483; PSC = 674). Anopheles gambiae s.s. accounted for 56.7% (N = 1224) of all mosquitoes collected. Other species were An. funestus complex (19.2%) and Culex quinquefasciatus (24.1%).The mosquito density per room was 74.15 and 33.7 for light trap and PSC techniques, respectively. A total of 1637 Anopheles mosquitoes were tested for circumsporozoite protein by Enzyme linked Immunosobent Assay (ELISA). The overall infectivity rate for circumsporozoite protein for P. falciparum in Anopheles mosquitoes was 21.14% (346/1637). Species-specific infectivity rates were 22.7% (278/1224) in An. gambiae s.s. and 24.0% (68/283) in An. funestus funestus, 0% (0/80) for An. rivulorum and 0% (0/50) for An. parensis. Blood meal analysis indicated that 92.3% of An. gambiae s.s, 88.9% of An. funestus s.s., 64.5% of An. rivulorum and 67.7% of An. parensis had taken blood meal from human hosts. In conclusion, malaria transmission in Mkuzi area of Muheza district is mainly by the highly anthropophagic An. gambiae s.s. and An. funestus s.s. More studies are needed to identify the seasonal variation of species composition and transmission dynamics in this village.

Identification of four members of the Anopheles funestus (Diptera: Culicidae) group and their role in Plasmodium falciparum transmission in Bagamoyo coastal Tanzania.

The role of Anopheles funestus group in malaria transmission was investigated in Bagamoyo coastal Tanzania, in the process of characterizing the area as a malaria vaccine testing site. Mosquitoes were sampled inside houses and multiplex PCR was used to identify 649 specimens. The following species were found: A. funestus s.s. (84.3%), A. leesoni (13.6%), A. rivulorum (1.5%) and A. parensis (0.6%). Multiplex PCR of 147 blood-fed specimens showed that over half (57.1%) of the identifiable blood meals were taken from human hosts, and human blood index in A. funestus and A. leesoni was 55% and 82% respectively. Plasmodium falciparum infection rate determined by nested PCR was 11% in A. funestus s.s. Although the abundance was low, 26 specimens of A. leesoni, two of A. rivolurum and one of A. parensis were found positive for P. falciparum. The presence of four A. funestus species in Tanzania emphasizes the relevance to define precisely their spatial and temporal distribution, specific behaviour, ecology and exact role in malaria transmission.

Bioassay and biochemical analyses of insecticide resistance in southern African Anopheles funestus (Diptera: Culicidae).

Anopheles funestus Giles has been implicated as a major malaria vector in sub-Saharan Africa where pyrethroid insecticides are widely used in agriculture and public health. Samples of this species from northern Kwazulu/Natal in South Africa and the Beluluane region of southern Mozambique showed evidence of resistance to pyrethroid insecticides. Insecticide exposure, synergist and biochemical assays conducted on A. funestus suggested that elevated levels of mixed function oxidases were responsible for the detoxification of pyrethroids in resistant mosquitoes in these areas. The data suggested that this mechanism was also conferring cross-resistance to the carbamate insecticide propoxur.

The role of four anopheline species (Diptera: Culicidae) in malaria transmission in coastal Tanzania.

Malaria is holoendemic in coastal Tanzania with Anopheles funestus and members of the A. gambiae complex being mainly responsible for transmission. Over a 4 months' sampling period 2222 anopheline mosquitoes were collected using light-traps and indoor resting catches, of which 58.6% were A. gambiae, 7.6% A. arabiensis, 6.9% A. merus and 26.9% A. funestus. Plasmodium falciparum circumsporozoite antigen (CSA) rates were: A. funestus 6.05% (n = 479), A. gambiae 8.4% (n = 1042), A. arabiensis 7.3% (n = 136) and A. merus 9.8% (n = 122). The P. malariae CSA rate for all anophelines was 0.07% (n = 1862). Estimated sporozoite densities were less than 2000 for at least 50% of all the positive mosquitoes. Along the coast the abundance of A. merus (41.3%) and A. gambiae (46.1%) was similar, and their CSA rates were comparable (11.6% and 12.5%, respectively) and higher than those for A. arabiensis (7.7%) and A. funestus (4.6%). These results indicate that A. merus plays an unexpectedly important role in malaria transmission in coastal Tanzania.