Seasonal variation of sand fly populations in Kala-azar endemic areas of the Malda district, West Bengal, India

Sardar, Ashif Ali; Chatterjee, Moytrey; Jana, Kingsuk; Saha, Pabitra; Maji, Ardhendu Kumar; Guha, Subhasish Kamal; Kundu, Prabir Kumar

doi:10.1016/j.actatropica.2020.105358

“…Based on the previous studies and information on seasonality [ 13 , 47 , 48 ], the national VL elimination program in Nepal has been following the schedule of two rounds of IRS using synthetic pyrethroids (alphacypermethrin, deltamethrin or lambda-cyhalothrin) in the reported VL areas or villages, the first round in the months of May–June and second in September–October [ 6 ]. The observed seasonality of vector sand fly density in this study was similar to other studies conducted in Nepal [ 13 , 47 ] and bordering areas of India [ 49 – 51 ] and aligns with the existing practice of IRS. Nevertheless, the seasonality of vector abundance is conducive for Leishmania transmission throughout the year except in the months of January and February and raises concerns about the suitability of two rounds of IRS with pyrethroids, the insecticide group that is reported effective to reduce the vector sand fly density up to 4 weeks only in Nepal and Bangladesh [ 12 , 27 , 52 , 53 ].…”

Section: Discussionsupporting

confidence: 90%

The ongoing risk of Leishmania donovani transmission in eastern Nepal: an entomological investigation during the elimination era

Roy,

Cloots,

Uranw

et al. 2023

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Background Visceral leishmaniasis (VL), a life-threatening neglected tropical disease, is targeted for elimination from Nepal by the year 2026. The national VL elimination program is still confronted with many challenges including the increasingly widespread distribution of the disease over the country, local resurgence and the questionable efficacy of the key vector control activities. In this study, we assessed the status and risk of Leishmania donovani transmission based on entomological indicators including seasonality, natural Leishmania infection rate and feeding behavior of vector sand flies, Phlebotomus argentipes, in three districts that had received disease control interventions in the past several years in the context of the disease elimination effort. Methods We selected two epidemiologically contrasting settings in each survey district, one village with and one without reported VL cases in recent years. Adult sand flies were collected using CDC light traps and mouth aspirators in each village for 12 consecutive months from July 2017 to June 2018. Leishmania infection was assessed in gravid sand flies targeting the small-subunit ribosomal RNA gene of the parasite (SSU-rRNA) and further sequenced for species identification. A segment (~ 350 bp) of the vertebrate cytochrome b (cytb) gene was amplified from blood-fed P. argentipes from dwellings shared by both humans and cattle and sequenced to identify the preferred host. Results Vector abundance varied among districts and village types and peaks were observed in June, July and September to November. The estimated Leishmania infection rate in vector sand flies was 2.2% (1.1%–3.7% at 95% credible interval) and 0.6% (0.2%–1.3% at 95% credible interval) in VL and non-VL villages respectively. The common source of blood meal was humans in both VL (52.7%) and non-VL (74.2%) villages followed by cattle. Conclusions Our findings highlight the risk of ongoing L. donovani transmission not only in villages with VL cases but also in villages not reporting the presence of the disease over the past several years within the districts having disease elimination efforts, emphasize the remaining threats of VL re-emergence and inform the national program for critical evaluation of disease elimination strategies in Nepal. Graphical Abstract

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“…This is the first comprehensive field study that has made a direct comparison between CDC-LTs and two types of large battery-powered aspirators used in mosquito surveillance for the capture of P. argentipes females. Traditionally, CDC-LTs and mouth aspirators, rather than large battery-powered aspirators, are used in field studies performed in India to capture P. argentipes females (11, 17, 21, 26). However, a decision was made to avoid using mouth aspirators in the present study due to health and scientific concerns.…”

Section: Discussionmentioning

confidence: 99%

“…However, this study was performed over a single year, and morphological identifications were not confirmed using molecular methods, so further work is required to examine seasonal trends. Since then, studies have collected P. argentipes using CDC-LTs and/or mouth aspirators (14, 17) but no natural infection rates of P. argentipes for L. donovani DNA were published in the last seven years prior to the commencement of the present study.…”

Section: Introductionmentioning

confidence: 99%

Comparison of collection methods forPhlebotomus argentipessand flies to use in a molecular xenomonitoring system for the surveillance of visceral leishmaniasis

McIntyre-Nolan

¹

,

Kumar

²

,

Carew

³

et al. 2023

Preprint

0

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BackgroundThe kala-azar elimination programme has resulted in a significant reduction in visceral leishmaniasis (VL) cases across the Indian Subcontinent. To detect any resurgence of transmission, a sensitive cost-effective surveillance system is required. Molecular xenomonitoring (MX), detection of pathogen DNA/RNA in vectors, provides a proxy of human infection in the lymphatic filariasis elimination programme. To determine whether MX can be used for VL surveillance in a low transmission setting, large numbers of the sand fly vectorPhlebotomus argentipesare required. This study will determine the best method for capturingP. argentipesfemales for MX.Methodology/Principal FindingsThe field study was performed in two programmatic and two non-programmatic villages in Bihar, India. A total of 48 households (12/village) were recruited. Centers for Disease Control and Prevention light traps (CDC-LTs) were compared with Improved Prokopack (PKP) and mechanical vacuum aspirators (MVA) using standardised methods. Four 12×12 Latin squares, 576 collections, were attempted (12/house, 144/village,192/method). Molecular analyses of collections were conducted to confirm identification ofP. argentipesand to detect human andLeishmaniaDNA. Operational factors, such as time burden, acceptance to householders and RNA preservation, were also considered. A total of 562 collections (97.7%) were completed with 6,809 sand flies captured. Females comprised 49.0% of captures, of which 1,934 (57.9%) were identified asP. argentipes. CDC-LTs collected 4.04 times moreP. argentipesfemales than MVA and 3.62 times more than PKP (p<0.0001 for each). Of 21,735 mosquitoes in the same collections, no significant differences between collection methods were observed. CDC-LTs took less time to install and collect than to perform aspirations and their greater yield compensated for increased sorting time. CDC-LTs were favoured by householders.Conclusions/SignificanceCDC-LTs are the most useful collection tool of those tested for MX surveillance since they collected higher numbers ofP. argentipesfemales without compromising mosquito captures or the preservation of RNA. However, capture rates are still low.Author SummaryMolecular xenomonitoring, screening insects for pathogen DNA/RNA, may be used for surveillance of diseases transmitted by insects. Since the proportion of insects infected with pathogens is very low in areas targeted for disease elimination, large numbers of females need to be screened. We compared three different methods for collectingPhlebotomus argentipessand fly females, the vector of parasites causing the disease visceral leishmaniasis in the Indian subcontinent, to determine which collected the largest number of females. Other factors that may also influence selection of a particular method of collection by a disease control programme, such as the time it takes to collect and sort samples, the acceptance of householders for a particular collection method and whether RNA degradation in insect samples differed between collection methods, were also considered. Centers for Disease Control and Prevention light traps (CDC-LTs) proved to be more useful than two types of aspiration methods for collecting higher numbers of sand fly females and RNA preservation was retained. Furthermore, they took less time to install than to perform aspirations and were favoured by householders. Therefore, CDC-LTs were considered to be the most suitable collection method for molecular xenomonitoring of sand flies in India.

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“…However, this study was performed over a single year, and morphological identifications were not confirmed using molecular methods, so further work is required to examine seasonal trends. Since then, studies have collected P. argentipes using CDC-LTs and/or mouth aspirators [16,19] but no natural infection rates of P. argentipes for L. donovani DNA were published in the last seven years prior to the commencement of the present study.…”

Section: Rationale For MX System For Vl Surveillance In Indiamentioning

confidence: 99%

“…Since then, studies have collected P . argentipes using CDC-LTs and/or mouth aspirators [ 16 , 19 ] but no natural infection rates of P . argentipes for L .…”

Section: Introductionmentioning

confidence: 99%

Comparison of collection methods for Phlebotomus argentipes sand flies to use in a molecular xenomonitoring system for the surveillance of visceral leishmaniasis

McIntyre-Nolan,

Kumar,

Mark-Carew

et al. 2023

PLoS Negl Trop Dis

1

0

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Background The kala-azar elimination programme has resulted in a significant reduction in visceral leishmaniasis (VL) cases across the Indian Subcontinent. To detect any resurgence of transmission, a sensitive cost-effective surveillance system is required. Molecular xenomonitoring (MX), detection of pathogen DNA/RNA in vectors, provides a proxy of human infection in the lymphatic filariasis elimination programme. To determine whether MX can be used for VL surveillance in a low transmission setting, large numbers of the sand fly vector Phlebotomus argentipes are required. This study will determine the best method for capturing P. argentipes females for MX. Methodology/Principal findings The field study was performed in two programmatic and two non-programmatic villages in Bihar, India. A total of 48 households (12/village) were recruited. Centers for Disease Control and Prevention light traps (CDC-LTs) were compared with Improved Prokopack (PKP) and mechanical vacuum aspirators (MVA) using standardised methods. Four 12x12 Latin squares, 576 collections, were attempted (12/house, 144/village,192/method). Molecular analyses of collections were conducted to confirm identification of P. argentipes and to detect human and Leishmania DNA. Operational factors, such as time burden, acceptance to householders and RNA preservation, were also considered. A total of 562 collections (97.7%) were completed with 6,809 sand flies captured. Females comprised 49.0% of captures, of which 1,934 (57.9%) were identified as P. argentipes. CDC-LTs collected 4.04 times more P. argentipes females than MVA and 3.62 times more than PKP (p<0.0001 for each). Of 21,735 mosquitoes in the same collections, no significant differences between collection methods were observed. CDC-LTs took less time to install and collect than to perform aspirations and their greater yield compensated for increased sorting time. No significant differences in Leishmania RNA detection and quantitation between methods were observed in experimentally infected sand flies maintained in conditions simulating field conditions. CDC-LTs were favoured by householders. Conclusions/Significance CDC-LTs are the most useful collection tool of those tested for MX surveillance since they collected higher numbers of P. argentipes females without compromising mosquito captures or the preservation of RNA. However, capture rates are still low.

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Seasonal variation of sand fly populations in Kala-azar endemic areas of the Malda district, West Bengal, India

Cited by 4 publications

References 31 publications

The ongoing risk of Leishmania donovani transmission in eastern Nepal: an entomological investigation during the elimination era

The ongoing risk of Leishmania donovani transmission in eastern Nepal: an entomological investigation during the elimination era

Comparison of collection methods forPhlebotomus argentipessand flies to use in a molecular xenomonitoring system for the surveillance of visceral leishmaniasis

Comparison of collection methods for Phlebotomus argentipes sand flies to use in a molecular xenomonitoring system for the surveillance of visceral leishmaniasis

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