Effect of house spraying with lambdacyhalothrin 10 per cent capsule suspension (CS) formulation in comparison with 10 per cent wettable powder (WP) against malaria vector in Malkangiri district, Odisha, India.

Background & objectives: Selection of an insecticide and its appropriate formulation is a prerequisite of formulating any chemical control strategy against vectors. A hut scale field trial was carried out to study the effectiveness of house spraying with capsule suspension (CS) formulation of lambdacyhalothrin in comparison with its wettable powder (WP) formulation on mortality, density and behaviour of malaria vector in Malkangiri district, Odisha, India. Methods: The two formulations were tested at 20 and 30 mg (a.i.)/m2 for their effectiveness in terms of deterrence, excito-repellency, blood-feeding success, mortality and residual activity against Anopheles fluviatilis, the major malaria vector, in experimental huts in Malkangiri district, Odisha State, India. Results: Both CS and WP formulations prevented the entry of An. fluviatilis in to the sprayed huts by >90 per cent for >6 months, the entire peak malaria transmission season in the area. The exit rate increased (90-99%) with different treatments and the feeding rate was reduced (91-97%). There was no significant difference between WP 30, CS 20 and CS 30 mg/m2 in these respects. However, WP 20 mg/m2 caused a lesser effect than the other three groups. The formulations or the dosages differed only in causing vector mortalities. Overall, the total mortality rate of An. fluviatilis was higher in the huts sprayed with CS 30 (58%) than the huts sprayed with CS 20 (48%), WP 20 (37%) and WP 30 mg/m2 (47%). Interpretation & conclusions: Considering the duration of residual action and the effect on entry, exit, feeding and mortality of An. fluviatilis, the dosage 20 mg/m2 of CS formulation of lambdacyhalothrin could be considered for further use.

Environmental management through sluice gated bed-dam: a revived strategy for the control of Anopheles fluviatilis breeding in streams.

Background & objectives: Integrated vector management (IVM) emphasizes sustainable eco-friendly methods and minimal use of chemicals. In this context, the present study highlights the environmental control of breeding of Anopheles fluviatilis, the primary malaria vector, through water management in a natural stream in Koraput district, Odisha, India. Methods: The District Rural Development Agency (DRDA), Koraput, constructed two bed-dams across streams, one in Barigaon and the other in Pipalapodar village. The bed-dam in the former village was fitted with two sluice gates whereas the bed dam constructed in the latter village was without the sluice gate. tThe sluice gates were opened once in a week on a fixed day to flush out the water from the dam. Anopheles immatures were sampled systematically in the streams using a dipper for density measurement and species composition. Results: There was a reduction of 84.9 per cent in the proportion of positive dips for aAnopheles larvae/pupae and a reduction of 98.4 per cent in immature density (number/dip) of An. fluviatilis in the experimental downstream compared to the control following opening of the sluice gates. Interpretation & conclusions: oOur findins showed that opening of sluice gates of the bed-dam regularly once in a week resulted in the control of vector breeding in the downstream due to the flushing effect of the water released with a high flow from the bed-dam that stagnated water in the upstream. The outcome of the study encourages upscaling this measure to other areas, wherever feasible.

Response of malaria vectors to conventional insecticides in the southern districts of Odisha State, India.

Background & objectives: Updating information on response (susceptible / resistant status) of vectors to the insecticides in use is essential to formulate and introduce appropriate resistance management strategy. Therefore, a study was undertaken in the 10 southern districts of Odisha State, which are endemic for Plasmodium falciparum malaria, to determine the insecticide susceptibility/ resistance status of Anopheles fluviatilis and An. culicifacies, the vectors of malaria. Methods: Mosquitoes were collected during September 2010 - February 2012 from 60 randomly selected villages in the 10 districts and blood-fed females were exposed to the diagnostic dosage of DDT (4.0%), malathion (5.0%) and deltamethrin (0.05%) for one hour. Mortality was recorded at 24 h after the exposure. The test mortality was corrected to the control mortality. Results: An. fluviatilis was susceptible to the three insecticides tested while, An. culicifacies was resistant to DDT and malathion in all the 10 districts except in two, where its response against malathion was under ‘verification required’ category. Against deltamethrin, An. culicifacies was susceptible in two districts; while in the other eight districts its response was under ‘verification required’ category. Interpretation & conclusions: Since An. fluviatilis the vector species primarily associated with transmission of malaria, was still susceptible to DDT, indoor residual spraying with DDT could be continued in the 10 districts. Also, in view of the large scale implementation of long lasting insecticidal nets and the signs of development of resistance in An. culicifacies to deltamethrin, response of the vectors to synthetic pyrethroids needs to be periodically monitored.

Seasonal prevalence & resting behaviour of Anopheles minimus Theobald & An. fluviatilis James (Diptera: Culicidae) in east-central India.

Background & objectives: Anopheles minimus has recently been reported to have re-appeared in Keonjhar district of Orissa after a period of about 45 years of launching the malaria eradication programme. An. minimus and An. fluviatilis were the incriminated major malaria vectors in the district, endemic for falciparum malaria. The information on seasonal prevalence and resting behaviour of the vectors is crucial for implementing appropriate malaria control measures. Therefore, a study was undertaken on seasonal prevalence and resting behaviour of An. minimus and An. fluviatilis in this district. Methods: Seven randomly selected villages of Keonjhar district, Orissa, were studied during August 2005 to November 2007. Daytime resting collections indoors and outdoors were made covering three seasons of the year. The Anopheles mosquitoes obtained from different habitats were identified. Collections were maintained separately according to different sites as well as heights of the walls in human dwellings. Results: Among the indoor collections, the densities of An. minimus and An. fluviatilis were higher in human dwellings than cattle sheds. An. fluviatilis was the predominant (41.5%) species followed by An. minimus (26.3%) in human dwellings. The density of both the vector species in human dwellings peaked during rainy and winter seasons followed by summer. Walls were the most preferred site by these vectors for resting and the maximum number was collected at a height of 3 to 4 ft. Interpretation & conclusions: The resting behaviour of the vector species increases their contact with the sprayed walls and therefore, a quality residual spraying of human dwellings focusing indoor walls could interrupt the malaria transmission in this area.

Distribution of sibling species of Anopheles culicifacies s.l. and Anopheles fluviatilis s.l. and their vectorial capacity in eight different malaria endemic districts of Orissa, India

The study was undertaken in eight endemic districts of Orissa, India, to find the members of the species complexes of Anopheles culicifacies and Anopheles fluviatilis and their distribution patterns. The study area included six forested districts (Keonjhar, Angul, Dhenkanal, Ganjam, Nayagarh and Khurda) and two non-forested coastal districts (Puri and Jagatsingpur) studied over a period of two years (June 2007-May 2009). An. culicifacies A, B, C and D and An. fluviatilis S and T sibling species were reported. The prevalence of An. culicifacies A ranged from 4.2-8.41 percent, B from 54.96-76.92 percent, C from 23.08-33.62 percent and D from 1.85-5.94 percent (D was reported for the first time in Orissa, except for occurrences in the Khurda and Nayagarh districts). The anthropophilic indices (AI) were 3.2-4.8 percent, 0.5-1.7 percent, 0.7-1.37 percent and 0.91-1.35 percent for A, B, C and D, respectively, whereas the sporozoite rates (SR) were 0.49-0.54 percent, 0 percent, 0.28-0.37 percent and 0.41-0.46 percent for A, B, C and D, respectively. An. fluviatilis showed a similarly varied distribution pattern in which S was predominant (84.3 percent overall); its AI and SR values ranged from 60.7-90.4 percent and 1.2-2.32 percent, respectively. The study observed that the co-existence of potential vector sibling species of An. culicifacies (A, C and D) and An. fluviatilis S (> 50 percent) was responsible for the high endemicity of malaria in forested districts such as Dhenkanal, Keonjhar, Angul, Ganjam, Nayagarh and Khurda (> 5 percent slide positivity rate). Thus, the epidemiological scenario for malaria is dependent on the distribution of the vector sibling species and their vectorial capacity.

Molecular Variation and Distribution of Anopheles fluviatilis (Diptera: Culicidae) Complex in Iran

Anopheles fluviatilis James (Diptera: Culicidae) is one of the known malaria vectors in south and southeastern Iran. Earlier ITS2 sequences analysis of specimens from Iran demonstrated only a single genotype that was identical to species Y in India, which is also the same as species T. We identified 2 haplotypes in the An. fluviatilis populations of Iran based on differences in nucleotide sequences of D3 domain of the 28S locus of ribosomal DNA (rDNA). Comparison of sequence data from 44 Iranian specimens with those publicly available in the Genbank database showed that all of the 28S-D3 sequences from Kazeroun and Khesht regions in Fars Province were identical to the database entry representing species U in India. In other regions, all the individuals showed heterozygosity at the single nucleotide position, which identifies species U and T. It is argued that the 2 species may co-occur in some regions and hybridize; however, the heterozygosity in the 28S-D3 locus was not reflected in ITS2 sequences and this locus for all individuals was identical to species T. This study shows that in a newly diverged species, like members of An. fluviatilis complex, a single molecular marker may not be sufficiently discriminatory to identify all the taxa over a vast geographical area. In addition, other molecular markers may provide more reliable information for species discrimination.

Utility of the rDNA-ITS2-PCR assay in detecting the life stages of species S of Anopheles fluviatilis complex.

Background & objectives: Anopheles fluviatilis, which ranks second among the major malarial vectors in India occurs as a complex of three morphologically identical species (species S, T and U) of which only species S is a vector. Hence, it becomes pertinent to have a method for the detection of this vector species under field conditions to map the distribution of this vector. An rDNA-ITS2-PCR assay has been developed earlier for species S of this complex using female adult specimens. In order to widen the range of samples on which this technique can be employed, the utility of this PCR assay in detecting different life stages/gender/parts of the vector species was studied. Also, its reliability in detecting a single species S in pools of species T was studied. Methods: Mosquitoes were collected from Malkangiri and Koraput districts of Orissa State where species S and T of this complex are reported. The wild caught fed females, after egg laying were subjected to PCR assay for species identification. The F1 progeny of a few PCR identified specimens was raised and samples at larval, pupal and adult stages were used for PCR assay. Single adult specimen of species S was added to pools containing different numbers of adults of species T and the pools were subjected to DNA extraction and PCR assay. Results: The PCR assay could detect species S from pure DNA extracts of the immature stages and crude DNA extracts of parts of adult/whole adult mosquito of either gender. Crude DNA extracts of pools of mosquitoes had to be diluted and used in order to obtain the species diagnostic fragment. Interpretation & conclusions: The rDNA-ITS2-PCR assay producing an amplicon of 350 bp. diagnostic for species S, could detect all stages/gender. Any part of the adult can be used for species identification. Further, a single adult of species S in pools of as many as 99 adults of species T could be detected. Application of this PCR assay will be useful in mapping the distribution of species S, an important malarial vector.