Laboratory wash-resistance and field evaluation of deltamethrin incorporated long-lasting polyethylene netting (Netprotect(®)) against malaria transmission in Assam, north-east India.

North-east India is co-endemic for Plasmodium falciparum and P. vivax malaria, and disease transmission is perennial and persistent. This study reports the results of a field-based village scale trial of deltamethrin incorporated long-lasting polyethylene netting (Netprotect(®)) conducted in P. falciparum predominant pocket of Assam, north-east India to assess operational feasibility, acceptability and sustainability against disease vectors and malaria transmission. The study monitored the residual efficacy of the long-lasting net in relation to serial washings in the laboratory and malaria prevalence in experimental villages for the first year of investigations from September 2008 to June 2009. The mosquito vector populations of Anopheles minimus were observed to be highly susceptible to deltamethrin (0.05%), and follow up investigations revealed that the vector mosquito had virtually disappeared in Netprotect(®) intervention villages. Concurrently, there was consistent decline in malaria cases in Netprotect(®) villages and transmission reduction was statistically significant compared to untreated net (net without insecticide) and no-net control villages for the corresponding study period. The contact cone-bioassay investigations against malaria transmitting mosquito species revealed that the bioavailability of the insecticide on the net fiber was persistent up to 20th serial wash resulting in ≥80% mortality. Community compliance and acceptance were high, and users reported decreased nuisance due to biting mosquitoes. It was concluded that deltamethrin incorporated polyethylene long-lasting netting was safe, wash-resistant, and assessed to be an operationally feasible, community-based intervention for sustainable management of disease vectors to prevent malaria transmission.

Wash resistance and bioefficacy of Olyset net--a long-lasting insecticide-treated mosquito net against malaria vectors and nontarget household pests.

During recent years, long-lasting insecticide-treated nets (LLINs) have been developed to overcome the problems of low retreatment rates, washing, and erratic dose of the insecticide resulting in the dilution of efficacy of the conventional insecticide-treated mosquito nets. These nets are treated at factory level with insecticide either incorporated into or coated around fibers. Olyset net, a polyethylene net with 2% permethrin incorporated within fibers, is one type of LLIN. Therefore, these nets were evaluated for their wash resistance and bioefficacy against malaria vectors Anopheles culicifacies Giles and Anopheles fluviatilis James (Diptera: Culicidae) and other nontarget species. Cone bioassay tests produced 100% mortality in these two vector species with 3-min exposure. Results of the bioassays on washed nets showed 100% mortality in An. fluviatilis even after 20 washings, whereas in An. culicifacies 100% mortality up to 11 washings and 80% mortality up to 20 washings were observed. Cone bioassay tests also were performed on nontarget mosquito species Culex quinquefasciatus Say; house fly, Musca domestica L.; American cockroach, Periplaneta americana (L.); head louse, Pediculus humanus capitis De Geer; and bed bug, Cimex lectularius L. with 30-min exposure. Except for bed bugs, 100% mortality was observed in these nontarget species after 24-h recovery period. In bed bugs, only 25% mortality was observed. The density of An. culicifacies and An. fluviatilis was significantly reduced in houses with Olyset nets compared with those with untreated nets or no nets. Thus, it may be concluded that Olyset nets are highly effective against malaria vectors and moderately against other nontarget household insects.

Effectiveness of mosquito nets treated with a tablet formulation of deltamethrin for malaria control in a hyperendemic tribal area of Sundargarh District, Orissa, India.

A village-scale trial on the efficacy of mosquito nets treated with a tablet formulation of deltamethrin (K-OTAB) against malaria in comparison to untreated nets or no net was conducted in Sundargarh District of Orissa, India, which is characterized by perennial transmission with Plasmodium falciparum accounting for more than 80% of malaria cases. Three villages with similar topographical and epidemiological situations were selected and randomly assigned to 3 arms of the study: treated net, untreated net, and no net. Distribution of nets, based on a sleeping pattern survey, was carried out to cover 100% of the population in treated-net and untreated-net villages. Longitudinal and cross-sectional surveys were conducted to measure malaria incidence, prevalence, and splenomegaly. Malaria incidence was reduced by 64.3% in the village with treated nets, 45.2% in the village with plain nets, and 21.4% in the control village without nets. Comparison of malaria incidence data after 1 year of intervention showed significant difference between villages with treated net vs. untreated net (P < 0.05) and treated net vs. no net (P < 0.005). The incidence of clinical attack rate due to P. falciparum was significantly lower in the population using treated nets than in those using untreated nets and no nets. However, no age-specific protective efficacy of treated nets or untreated nets was observed. A significant reduction occurred in spleen rate and parasite rate in children aged 2-9 years using treated nets or untreated nets. An overall significant reduction was found in parasite rate in the total population using treated and untreated nets as compared to nonusers.

Village-scale evaluation of mosquito nets treated with a tablet formulation of deltamethrin against malaria vectors.

A field trial was carried out in the Sundargarh district of Orissa, India on the efficacy of mosquito nets treated with a tablet formulation of deltamethrin (K-O TAB) against malaria vectors. Treated nets were used in one village, and in the two control villages, one used untreated nets and the other used indoor spraying with DDT, without nets. In this area the primary malaria vectors are Anopheles culicifacies Giles sensu lato (Diptera: Culicidae) and An. fluviatilis James s.l., which are both endophagic and endophilic, and fully susceptible to deltamethrin. Treatment of a 10-m(2) mosquito net with one of the tablets gave a deltamethrin deposit of 25 mg/m(2). Bioassays repeated on domestically used nets over 7 months showed persistence of almost 100% mortality of An. fluviatilis, whereas An. culicifacies showed a decline from 100% to 71% mortality over this period, after which the nets were re-treated and bioassays were not continued. The sum of collections of mosquitoes resting in village houses and those in exit traps and dead on floor sheets showed a reduction in the numbers of the two vector species due to the treated nets, compared with untreated or no nets, but no reduction in other anophelines or Culex species. Large proportions of the collections of the vector and non-vector anophelines were dead on the floor sheets, but among Culex, mortality was delayed. Treated and untreated nets reduced the proportion of anophelines that had blood-fed; the treated nets did so more effectively than the untreated in the case of An. culicifacies and of Culex mosquitoes. In rooms with treated nets a larger proportion of the total collections [dead + live] were in the exit traps, which can be attributed to the excito-repellent effect of deltamethrin. It is easier to pack and handle tablets of insecticide than liquid concentrate and the use of one tablet per net may be preferable to making up a large volume of diluted insecticide and dipping many nets at a time.

Malarial morbidity in tribal communities living in the forest and plain ecotypes of Orissa, India.

A detailed epidemiological study of malarial morbidity was carried out in 13 'tribal' villages in the forest or plain ecotypes of Sundargarh district, Orissa, India. Longitudinal and cross-sectional, parasitological surveys were conducted in all the villages, to determine the incidence of malaria and the prevalence of malarial infection. The annual numbers of malaria cases/1000 were much higher in the forest (347.9) than on the plain (61.0). In the forest clinical malaria occurred more frequently in children than in adults but on the plain all age-groups were equally affected. In cross-sectional surveys, 14.1% of the subjects from the forest but only 2.8% of those from the plain were found smear-positive for malarial infection. The prevalences of infection in the forest area were highest in the young children (aged 1-5 years) and gradually declined with increasing age. The highest incidence of Plasmodium falciparum malaria (0.90 episode/person-year) was also recorded in the subjects from the forest who were aged 1-5 years. In the forest and plain communities surveyed, 78.5%-81.5% and 36.0%-52.0% of the children aged 2-9 years had detectable splenomegaly, respectively, indicating that the forest was hyper-endemic and the plain meso-endemic for malaria. Malaria is clearly a major problem among the tribal communities of Sundargarh, causing great morbidity and, consequently, considerable economic losses.

Observations on the breeding habitat of Aedes species in the steel township, Rourkela.

Prompted by report of large number of dengue fever cases in township of Rourkela steel plant, entomological surveys were carried out to know the distribution and extent of Aedes breeding in and around the dengue fever affected areas. Out of 2062 water containers searched, 819 were positive for Aedes larvae. The house index (HI), container index (CI) and Breteau index (BI) were 53.4, 39.7 and 118.5 respectively. 27.9% of the houses had single breeding habitats. The breateau index of single storeyed houses and double storeyed buildings was 149.8 and 54.6 respectively, showing that the single storeyed houses have more potential for Aedes breeding. The breeding preference ratio (BPR) was highest for plastic containers. Three species of Aedes were found breeding in different habitats and Aedes aegypti was found breeding in coolers, cement tanks, tyres and miscellaneous containers with a prevalence rate of 13.2%. The role of entomological surveillance and health education has been highlighted for the control of disease through community participation.

Field studies on the sensitivity and specificity of an immunochromatographic test for the detection of Plasmodium falciparum malaria in tribal areas of Orissa.

A rapid immunodiagnostic test developed by an Australian Biotechnology company for the diagnosis of Plasmodium falciparum in the peripheral blood has been evaluated in the field for its sensitivity, specificity and efficacy in comparison to microscopic examination. The results showed that the tests sensitivity, specificity and efficacy were 98.2, 96.9 and 97.5 per cent respectively. The positive and negative predictive values of the test were 96.4 and 98.4 per cent respectively. The test when compared to the conventional microscopy did not show any statistically significant difference suggesting that the two diagnostic methods are equally good. The test performed did not show cross-reactions with other parasite species. It is a simple and rapid field diagnostic method, which does not require any expensive laboratory equipment or skilled personnel.

Fishes of District Sundargarh, Orissa, with special reference to their potential in mosquito control.

An extensive fish fauna survey was carried out in Sundargarh, a malaria-endemic district in Orissa, during 1988 to 1990 to identify and evaluate the indigenous larvivorous fishes for mosquito control. In all, 57 species belonging to 19 families under 6 orders were found in the local water bodies. On laboratory evaluation against anopheline and culicine larvae, six potential larvivorous fishes, viz. Aplocheilus panchax, Oryzias melastigma, Oreochromis mossambicus, Gambusia affinis, Danio (B.) rerio and Esomus danricus were selected. Feasibility of mass multiplication of these fishes in village ponds for operational use is being studied.