On the conspecificity of Anopheles fluviatilis species S with Anopheles minimus species C.

Anopheles fluviatilis and An. minimus complexes,each comprising of at least three sibling species, are closely related and important malaria vectors in Oriental Region. Recently An. fluviatilis species S, which is a highly efficient malaria vector in India, has been made conspecific with An. minimus species C (senior synonym) on the basis of homology in 335 base pair nucleotide sequence of D3 domain of 28S ribosomal DNA (rDNA). We examined the conspecificity of these two nominal species by obtaining and analysing the DNA sequences of nuclear ribosomal loci internal transcribed spacer 2 (ITS2) and D2-D3 domain of 28S rDNA (28S-D2/D3) from those of An. fluviatilis S and An. minimus C. We found that the sequences of An. fluviatilis S are appreciably different from those of An. minimus C with pair-wise distance (Kimura-2-parametre model)of 3.6 and 0.7%for loci ITS2 and 28S-D2/D3, respectively. Pair-wise distance and phylogenetic analyses using ITS2 sequences of members of Minimus and Fluviatilis Complexes revealed that An. fluviatilis S is distantly related to An. minimus C as compared to any other members of the Fluviatilis Complex. These findings suggest that the two nominal species, An. fluviatilis S and An. minimus C, do not merit synonymy. The study also confirms that the reported species An. fluviatilis X is synonym with species S.

Evaluation of bifenthrin treated mosquito nets against anopheline and culicine mosquitoes.

BACKGROUND AND OBJECTIVES: The main rural malaria vector Anopheles culicifacies has developed resistance to dichloro diphenyl trichloroethane (DDT), hexachloro cyclo hexane (HCH) and malathion in the state of Haryana in northern India. An alternative synthetic pyrethroid insecticide bifenthrin was therefore evaluated on mosquito nets against anopheline and culicine mosquitoes, in two villages Jagdishpur and Garh Mirakpur of Community Health Center (CHC) Badhkhalsa in district Sonipat, Haryana state. METHODS: Two formulations of bifenthrin, suspension concentrate (SC) and micro-emulsion (ME) were compared with micro-capsule suspension (CS) of lambdacyhalothrin. The impact of three doses of bifenthrin (10, 25 and 50 mg/m(2)) impregnated on mosquito nets was compared with lambdacyhalothrin (25 mg/m(2)) and untreated control. Quality assessment of treatment on treated nets was carried out by residue analysis and the persistence of the insecticide on nets was determined by contact bioassays. Efficacy of treated nets on mosquito density was assessed by calculating mosquito entry rate, immediate mortality, delayed mortality and excito-repellency to the insecticides. RESULTS: In susceptibility tests An. culicifacies was susceptible to bifenthrin (0.1% test papers) and to lambdacyhalothrin (0.05% test papers). Bioassays on treated nets against A. culicifacies recorded 100 per cent mortality up to tenth fortnight for all the doses of impregnation with bifenthrin (SC and ME) and lambdacyhalothrin (CS). Ring-net bioassays against An. culicifacies showed median knock-down time between 3.1 to 11.4 min. Behavioural indices were also studied for anopheline and culicine mosquitoes. The reduction in entry rates of anopheline and culicine mosquitoes into the rooms with treated nets compared to control indicated good efficacy with all the formulations and doses of the insecticides. INTERPRETAION AND CONCLUSION: Indoor (immediate) mortality of mosquitoes with bifenthrin ME formulation was relatively lower compared to SC fomulation of bifenthrin and based on delayed mortility and continued susceptibility in bioassays, bifenthrin ME at the rate of 10 mg/m(2) dose was found suitable for the impregnation of mosquito nets for phase III trial.

An allele-specific polymerase chain reaction assay for the differentiation of members of the Anopheles culicifacies complex.

Anopheles culicifacies, the principal vector of malaria in India, is a complex of five cryptic species which are morphologically indistinguishable at any stage of life. In view of the practical difficulties associated with classical cytotaxonomic method for the identification of members of the complex, an allele-specific polymerase chain reaction (ASPCR) assay targeted to the D3 domain of 28S ribosomal DNA was developed. The assay discriminates An. culicifacies species A and D from species B, C and E. The assay was validated using chromosomally identified specimens of An. culicifacies from different geographical regions of India representing different sympatric associations. The assay correctly differentiates species A and D from species B, C and E. The possible use of this diagnostic assay in disease vector control programmes is discussed.

Investigation of malaria outbreak in Bahraich district, Uttar Pradesh.

BACKGROUND & OBJECTIVES: Based on the reports of 139 fever related deaths in Jarwal primary health centre (PHC) of Bahraich district, Uttar Pradesh (UP) during April to September 1999, a study was undertaken to explore the possibility of outbreak of Plasmodium falciparum malaria in the area and reasons of outbreak. METHODS: The study was undertaken during September-October 1999 in Bahraich district, UP. The study included a parasitological and an entomological survey. Blood slides from fever cases were collected and examined following standard procedures for detection of species and stage of parasite. The resting adult mosquitoes were collected from human dwellings and cattle sheds from selected villages. Susceptibility status of Anopheles culicifacies to 4 per cent DDT and 0.05 per cent deltamethrin was determined under laboratory conditions following the WHO procedure. In vitro drug sensitivity of P. falciparum to chloroquine was also estimated. RESULTS: Overall slide positivity rate (SPR) was found to be 33.8 with a preponderance of P. falciparum (88.4%). There was an outbreak of Pf malaria in Jarwal and surrounding areas as well. Foci of P. falciparum malaria were found in Jarwal, Fakharpur and Hazoorpur PHCs around Kaisarganj PHC. In addition, P. falciparum cases, were also reported from Motipur and Tejwapur. INTERPRETATION & CONCLUSION: Poor surveillance of affected areas resulting in low annual parasite incidence (API), lack of insecticidal spray in the currently affected PHCs as the API was less than 2 and development of resistance in P. falciparum to chloroquine were found as the possible reasons for the outbreak. It is recommended that surveillance be strengthened in all PHCs of Bahraich district to contain further extension of malaria in northeastern UP.

Investigation of malaria prevalence at National Thermal Power Corporation, Shaktinagar, Sonbhadra District (Uttar Pradesh), India.

Malaria in industrial complexes is promoted by extensive mosquitogenic potential generated by excavations and importation of parasite through migratory labor. The National Thermal Power Corporation (NTPC), Shaktinagar, Sonbhadra district was surveyed for malariogenic conditions from 1994 to 1996. The major mosquito breeding sites were drains, storm-water drains, lakes, outside tanks, overhead tanks, sluice-valve chambers, ornamental tanks, wells, pit wells and water reservoirs, etc. Anopheles culicifacies was the major vector of malaria in this area. Sibling species identification of An. culicifacies revealed that species C predominated during the transmission season and responsible to transmit malaria. Insecticide susceptibility tests against An. culicifacies sl showed that An.culicifacies population was 100% susceptible to malathion, fenitrothorn and deltamethrin while it was found 44% resistant to DDT. The malaria cases recorded in 1994, 1995 and 1996 were 847, 590 and 409 respectively. In vitro study on P. falciparum cases showed that 41, 70, 50% of the isolates tested were resistant to chloroquine in 1994, 1995 and 1996 respectively while an in vivo follow-up study showed 20-30% P. falciparum cases resistant to chloroquine. An integrated approach involving alternate vector control measures along with judicious use of insecticides has been suggested to bring down malaria in industrial complexes.

Anopheline species complexes & malaria control.

Species complexes comprising morphologically indistinguishable biological species that are reproductively isolated, are of common occurrence among anophelines. A list of anopheline species complexes identified so far in the world has been given. To demonstrate the importance of species complexes in malaria control, we report the Anopheles culicifacies complex as a case study. An. culicifacies is a major vector of malaria in India and neighbouring countries. This complex comprises four sibling species, A, B, C and D. Stratification of U.P. state and district Allahabad has been shown taking into consideration the biological differences among sibling species, viz., sibling species composition and vectorial potential- species B is a non-vector while others are vectors. To achieve cost effective vector control, microlevel stratification at least at the block level has been suggested. Implications of differential responses of sibling species to DDT and malathion in field operations have been discussed. To achieve selective and sustainable control, and to reduce the unnecessary selection pressure of insecticides, an insecticide spray strategy to control An. culicifacies has been provided.