Understanding Behavioural Temperament of Phlebotomus argentipes Under the Influence of DDT-IRS Versus SP-IRS for Scoping New Approaches for Maximum Control Over the VL-Vector Population in Bihar

Background:After the decades of Dichlorodiphenyltrichloroethane (DDT) use, Phlebotomus argentipesreportedly developed resistance against it affecting every aspect of vector control at grass-root level. Although DDT based Indoor Residual Spray (IRS) has been replaced with Alphacypermethrine-a Synthetic Pyrethroid (SP) based insecticide, since 2016 butits successful implementation at the Visceral Leishmaniasis (VL) endemic regime of Bihar doesn’t cause much effect upon VL vector density. Furthermore, the outcomes of existing operational research works, it Original ResearchArticle had been observed that VL vectors are continuously changing its behavior under the pressure of insecticides. Methods: For validating the hypothesis, present study has been carried out at Vaishali and Patna being highly and semi-endemic sites respectively for quantifying the oriental behavior among VL vectors persuaded by the IRS and enforce them to remain alive and get trapped in light trap even after changed chemical composition of IRS i.e., SP-IRS from routine DDT-IRS. Results:Following results, a significant reduction in sand fly density (i.e., 33.09% and 29.16%) was observed for outdoor and indoor caught sand flies, collected with light trap and aspirator respectively. Significant higher no. of sand fly collection in terms of per light traps per night was recorded from the outdoor sites than thosefrom indoor habitat for each village of Vaishali and Saran district of Bihar. Higher no. of male sand flies than to that of female ones were collected from outdoor sites and only unfed female sand flies (i.e., 100%) were caught following SP-IRS from each study villages of Vaishali and Saran districts of Bihar.Conclusions:The results of higher no. of sand flies collection from the outdoor sites as compared with the indoor habitat validate the hypothesis of gradual shifting of habitat of VL vectors from endophilic to exophilic which is undoubtedly followed due to the fact of developed resistance among them against chemical constituent of IRS. Results provide very useful information about the sand fly dynamics under the impact of IRS and accordingly, advocates the combined approach of IRS along with insecticidal fogging together at a same time that could be an effective dividend for maximum VL vector control along for negotiating VL cases at par for longer duration during the maintenance phase at the VL foci.

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.

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.

Insecticide susceptibility status of Phlebotomus argentipes, a vector of visceral leishmaniasis in different foci in three states of India.

Background & objectives: Phlebotomus argentipes is the vector for visceral leishmaniasis in India. The development of resistance in kala-azar vector to DDT has been reported from various parts of India. The main objective of this study was to generate information on insecticides susceptibility status of P. argentipes to DDT, malathion and deltamethrin in different parts in three states of India. Methods: Phlebotomus argentipes were collected from different villages, identified and used to investigate the susceptibility status against DDT, malathion and deltamethrin as per the WHO standard methods. Results: Phlebotomus argentipes was resistant to DDT in different areas, viz. PHCs Murumgaon in Maharashtra; Ramgarh in Jharkhand; Kodah, Falka, Mahua and Lalganj in Bihar. In Phulwari Shareef PHC of Patna district in Bihar, DDT produced 89% mortality in P. argentipes, indicating resistant/tolerance (verification required) to DDT. The corrected percent mortality to malathion (5%) in different areas ranged between 98 and 100%; and to deltamethrin (0.05%) between 98.4 and 100%. The results showed that the tested P. argentipes are susceptible to malathion and deltamethrin. Conclusion: Phlebotomus argentipes are still susceptible to malathion and deltamethrin, but resistant to DDT. The susceptibility status of P. argentipes should be monitored regularly in diversified situations to ascertain the judicious use of insecticides being used for indoor residual spraying in the programme for rational use of appropriate insecticide.

Vector control interventions for visceral leishmaniasis elimination initiative in South Asia, 2005-2010.

The Visceral Leishmaniasis (VL) Elimination Initiative in the Indian subcontinent was launched in 2005 as a joint effort between the governments in the Region (India, Nepal and Bangladesh) and the World Health Organization (WHO). The objective is to reduce the annual VL incidence below 1/10,000 inhabitants by 2015 based on detection and treatment of VL cases and vector control. We present here a review of studies published in the period 2005-2010 on the efficacy of different tools to control Phlebotomus argentipes. The review indicates that the current indoor residual spraying (IRS) and novel vector control methods mainly insecticide treated nets (ITN) have low effectiveness for several reasons. Efforts to improve quality of IRS operations and further research on alternative and integrated vector control methods need to be promoted to reach the VL elimination target by 2015.

A morphologically distinct Phlebotomus argentipes population from active cutaneous leishmaniasis foci in central Sri Lanka

Although the reported aetiological agent of cutaneous leishmaniasis (CL) in Sri Lanka is Leishmania donovani, the sandfly vector remains unknown. Ninety-five sandflies, 60 females and 35 males, collected in six localities in the district of Matale, central Sri Lanka, close to current active transmission foci of CL were examined for taxonomically relevant characteristics. Eleven diagnostic morphological characters for female sandflies were compared with measurements described for Indian and Sri Lankan sandflies, including the now recognised Phlebotomus argentipes sensu lato species complex. The mean morphometric measurements of collected female sandflies differed significantly from published values for P. argentipes morphospecies B, now re-identified as Phlebotomus annandalei from Delft Island and northern Sri Lanka, from recently re-identified P. argentipes s.s. sibling species and from Phlebotomus glaucus. Furthermore, analysis of underlying variation in the morphometric data through principal component analysis also illustrated differences between the population described herein and previously recognised members of the P. argentipes species complex. Collectively, these results suggest that a morphologically distinct population, perhaps most closely related to P. glaucus of the P. argentipess. I. species complex, exists in areas of active CL transmission. Thus, research is required to determine the ability of this population of flies to transmit cutaneous leishmaniasis.

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.

Effect of untreated bed nets on blood-fed Phlebotomus argentipes in kala-azar endemic foci in Nepal and India

Observational studies in the Indian subcontinent have shown that untreated nets may be protective against visceral leishmaniasis (VL). In this study, we evaluated the effect of untreated nets on the blood feeding rates of Phlebotomus argentipes as well as the human blood index (HBI) in VL endemic villages in India and Nepal. The study had a "before and after intervention" design in 58 households in six clusters. The use of untreated nets reduced the blood feeding rate by 85 percent (95 percent CI 76.5-91.1 percent) and the HBI by 42.2 percent (95 percent CI 11.1-62.5 percent). These results provide circumstantial evidence that untreated nets may provide some degree of personal protection against sand fly bites.

Vector density and the control of kala-azar in Bihar, India

Bihar, India has been in the grip of kala-azar for many years. Its rampant and severe spread has made life miserable in most parts of the state. Such conditions require a comprehensive understanding of this affliction. The numbers coming out of the districts prone to the disease in the north and south Ganges have provided us with several startling revelations, as there are striking uniformities on both sides, including similar vegetation, water storage facilities, house construction and little change in risk factors. The northern areas have been regularly sprayed with DDT since 1977, but eradication of the disease appears to be a distant dream. In 2007 alone, there were as many as 37,738 cases in that region. In contrast, the southern districts of Patna and Nalanda have never had the disease in its epidemic form and endemic disease has been present in only some pockets of the two districts. In those cases, two rounds of spraying with DDT had very positive results, with successful control and no new established foci. In addition, an eleven-year longitudinal study of the man hour density and house index for the vector Phlebotomus argentipes demonstrated that they were quite high in Patna and Nalanda and quite low in north Bihar. Given these facts, an attempt has been made to unravel the role of P. argentipes saliva (salivary gland) in the epidemiology of kala-azar. It was determined that patchy DDT spraying should be avoided for effective control of kala-azar.

A report on the indoor residual spraying (IRS) in the control of Phlebotomus argentipes, the vector of visceral leishmaniasis in Bihar (India): an initiative towards total elimination targeting 2015 (Series-1).

Background & objectives: Visceral leishmaniasis, commonly known as kala-azar is endemic in Bihar state, India. Current vector control programme in Bihar focuses mainly on spraying the sandfly infested dwellings with DDT. The Government of India in collaboration with WHO has fixed the target 2015 for total elimination of kala-azar. The present study was carried out to see the impact of DDT and improved IEC in the containment of vector density vis-à-vis disease transmission. Methods: Before the start of the spraying operations training was imparted to all the medical and paramedical personnel regarding the methods of spraying operations. Pre- and post-sandfly density was monitored in four selected districts. Incidences of kala-azar cases were compared for pre- and post-spray periods. Social acceptability and perceptions of households was collected through questionnaires from 500 randomly selected households in the study districts. Results: House index in three study districts reduced considerably during post-spray when compared to pre-spray. Kala-azar incidence in many districts was reduced after the DDT spray. Either partial or complete refusal was reported in 14.4%, while 35% were not satisfied with the suspension concentration and coverage; and 46.6% were found satisfied with the spraying procedure. Interpretation & conclusion: Strengthening the IEC activities to sensitise the community, proper training of health personnel, monitoring of spray, good surveillance, proper treatment of cases and two rounds of DDT spray with good coverage in the endemic districts up to three years are essential to achieve the desired total elimination of kala-azar in Bihar state.