Insecticide susceptibility of phlebotomus argentipes & assessment of vector control in two districts of West Bengal, India.

Background & objectives: Kala-azar or visceral leishmanisis (VL) is known to be endemic in several States of India including West Bengal (WB). Only meager information is available on the vector dynamics of its vector species, Phlebotomus argentipes particularly in relation to control measure from this State. Hence, a pilot study was undertaken to assess the control strategy and its impact on vector in two endemic districts of WB, India. Methods: Two villages each from the two districts, Maldah and Burdwan, were selected for the study. Seasonal variation of sandflies was observed during pre-monsoon, post-monsoon and winter seasons. Susceptibility test of P. argentipes against DDT and bioassay on DDT sprayed wall and on long lasting insecticide nets (LN) Permanet® 2.0 were conducted as per the WHO standard methods. Results: P. argentipes density was high during March to October. Susceptibility status of P. argentipes ranged from 40 to 61.54 per cent. Bioassay test showed 57.89 per cent mortality against LN permaNet®-2.0. and 50 per cent against DDT on wall within 30 min of exposure. Interpretation & conclusions: Despite the integrated vector management approach, the sandfly population was high in the study area. The reason could be development of resistance in P. argentipes against DDT and low effectiveness of LN permaNet®-2.0. The more pragmatic step will be to conduct large studies to monitor the susceptibility level in P. argentipes against DDT.

Analysing Host Preference Behavior of Phlebotomus argentipes (Diptera: Psychodidae) Under the Impact of Indoor Residual Spray.

Background: Present scenario of Bihar and neighboring Indian states reveals dichlorodiphenyltrichloroethane (DDT) being an insecticide of choice for controlling the vector of Indian Visceral Leishmaniasis (VL) i.e., Phlebotomus argentipes, that had reported to attain resistance/tolerance against it, leading to the behavioral transition including host preference and selection by them. The relationship between insecticidal resistance and host preference/ selection is not yet well understood. Objective: Exploring the host preference/selection behavior under the influence of insecticidal pressure in different biotopes of VL endemic regions in India Methods: For this, the engorged sand flies that were collected before and after Indoor Residual Spray (IRS) were subjected for feeding behavior analysis. The parameter studied were Host Feeding Index (HFI) and Forage Ratio (FR) by analyzing Blood Meal Identification (BMI). Results: The higher percentage of sand flies were recorded to be fed on cattle host (56.05%) with respect to the human host (30.35%) before IRS while a significant increase in cattle blood index (79.17%) in contrast to significant drop in human blood index (9.43%) was recorded during post IRS session at the study site. It establishes, cattle being potentially served as a preferred host for sand flies in contrast to other available hosts. The lowered value of FR during pre- and post-IRS respectively for human (0.77 and 0.24) as compared to the cattle (1.89 and 2.67) indicates cattle host being selectively preferred by the P. argentipes also corroborate with the results of BMI. Conclusion: Through the study we can conclude that instead of being killed by IRS, P. argentipes has attained resistance against DDT. Under the insecticidal pressure the host preference as well as selection tendency of P. argentipes for cattle host gets enhanced under the influence of IRS, as abrupt increment was observed in the FR’s post-IRS. While, the avoidance tendency of insects from the human hosts in favor of other available hosts’ viz., cattle, goat, pigs, etc. with slight decrement in the forage ratios for the human hosts during the IRS was also observed. Thus, under the impact of IRS, P. argentipes has changed its behavior from endophilic to exophilic and migrated from the human hosts at the periphery area of sprayed houses towards much safer zone, i.e., deserted houses, nearby gardens, bushes, etc for their survival for feeding cattle i.e., preferred host, lying in unsprayed horizon. Therefore, change in control strategy involving the proper management of insecticide resistance is very much needed to tackle the vector outbreak and hence menace caused by them.

User friendliness, efficiency & spray quality of stirrup pumps versus hand compression pumps for indoor residual spraying.

Background & objectives: Indoor residual spraying (IRS) is a proven tool to reduce visceral leishmaniasis vectors in endemic villages. In India IRS is being done with stirrup pumps, whereas Nepal, Bangladesh, and other countries use compression pumps. The present study was conducted with the objectives to compare the efficiency, cost and user friendliness of stirrup and compression pumps. Methods: The study was carried out in Gorigawan village of the Vaishali district in north Bihar and included a total population of 3259 inhabitants in 605 households. Spraying with 50 per cent DDT was done by two teams with 6 persons per team under the supervision of investigators over 5 days with each type of pump (10 days in total using 2 stirrup pumps and 3 compression pumps) by the same sprayers in an alternate way. The spraying technique was observed using an observation check list, the number of houses and room surfaces sprayed was recorded and an interview with sprayers on their satisfaction with the two types of pumps was conducted. Results: On average, 65 houses were covered per day with the compression pump and 56 houses were covered with the stirrup pump. The surface area sprayed per squad per day was higher for the compression pump (4636 m2) than for the stirrup pump (4102 m2). Observation showed that it was easy to maintain the spray swath with the compression pump but very difficult with the stirrup pump. The wastage of insecticide suspension was negligible for the compression pump but high for the stirrup pump. Interpretation & conclusions: The compression pump was found to be more user friendly due to its lower weight, easier to operate, lower operation cost, higher safety and better efficiency in terms of discharge rate and higher area coverage than the stirrup pump.

Appraisal of Phlebotomus argentipes habitat suitability using a remotely sensed index in the kala-azar endemic focus of Bihar, India

Visceral leishmaniasis, or kala-azar, is recognised as a serious emerging public health problem in India. In this study, environmental parameters, such as land surface temperature (LST) and renormalised difference vegetation indices (RDVI), were used to delineate the association between environmental variables and Phlebotomus argentipes abundance in a representative endemic region of Bihar, India. The adult P. argentipes were collected between September 2009-February 2010 using the hand-held aspirator technique. The distribution of P. argentipes was analysed with the LST and RDVI of the peak and lean seasons. The association between environmental covariates and P. argentipes density was analysed a multivariate linear regression model. The sandfly density at its maximum in September, whereas the minimum density was recorded in January. The regression model indicated that the season, minimum LST, mean LST and mean RDVI were the best environmental covariates for the P. argentipes distribution. The final model indicated that nearly 74% of the variance of sandfly density could be explained by these environmental covariates. This approach might be useful for mapping and predicting the distribution of P. argentipes, which may help the health agencies that are involved in the kala-azar control programme focus on high-risk areas.

Delimitation of kala-azar risk areas in the district of Vaishali in Bihar (India) using a geo-environmental approach

Remote sensing and geographical information technologies were used to discriminate areas of high and low risk for contracting kala-azar or visceral leishmaniasis. Satellite data were digitally processed to generate maps of land cover and spectral indices, such as the normalised difference vegetation index and wetness index. To map estimated vector abundance and indoor climate data, local polynomial interpolations were used based on the weightage values. Attribute layers were prepared based on illiteracy and the unemployed proportion of the population and associated with village boundaries. Pearson's correlation coefficient was used to estimate the relationship between environmental variables and disease incidence across the study area. The cell values for each input raster in the analysis were assigned values from the evaluation scale. Simple weighting/ratings based on the degree of favourable conditions for kala-azar transmission were used for all the variables, leading to geo-environmental risk model. Variables such as, land use/land cover, vegetation conditions, surface dampness, the indoor climate, illiteracy rates and the size of the unemployed population were considered for inclusion in the geo-environmental kala-azar risk model. The risk model was stratified into areas of "risk"and "non-risk"for the disease, based on calculation of risk indices. The described approach constitutes a promising tool for microlevel kala-azar surveillance and aids in directing control efforts.

A comparative evaluation of end-emic and non-endemic region of visceral leishmaniasis (Kala-azar) in India with ground survey and space technology

In visceral leishmaniasis, phlebotomine vectors are targets for control measures. Understanding the ecosystem of the vectors is a prerequisite for creating these control measures. This study endeavours to delineate the suitable locations of Phlebotomus argentipes with relation to environmental characteristics between endemic and non-endemic districts in India. A cross-sectional survey was conducted on 25 villages in each district. Environmental data were obtained through remote sensing images and vector density was measured using a CDC light trap. Simple linear regression analysis was used to measure the association between climatic parameters and vector density. Using factor analysis, the relationship between land cover classes and P. argentipes density among the villages in both districts was investigated. The results of the regression analysis indicated that indoor temperature and relative humidity are the best predictors for P. argentipes distribution. Factor analysis confirmed breeding preferences for P. argentipes by landscape element. Minimum Normalised Difference Vegetation Index, marshy land and orchard/settlement produced high loading in an endemic region, whereas water bodies and dense forest were preferred in non-endemic sites. Soil properties between the two districts were studied and indicated that soil pH and moisture content is higher in endemic sites compared to non-endemic sites. The present study should be utilised to make critical decisions for vector surveillance and controlling Kala-azar disease vectors.