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. 2021 Aug 9;15(8):e0009101.
doi: 10.1371/journal.pntd.0009101. eCollection 2021 Aug.

Impact of IRS: Four-years of entomological surveillance of the Indian Visceral Leishmaniases elimination programme

Rinki Deb  1 , Rudra Pratap Singh  1 , Prabhas Kumar Mishra  2 , Lisa Hitchins  1 , Emma Reid  1 , Arti Manorama Barwa  2 , Debanjan Patra  2 , Chandrima Das  2 , Indranil Sukla  2 , Ashish Kumar Srivastava  2 , Shilpa Raj  2 , Swikruti Mishra  2 , Madhuri Swain  2 , Swapna Mondal  2 , Udita Mandal  2 , Geraldine M Foster  1 , Anna Trett  1 , Gala Garrod  1 , Laura McKenzie  1 , Asgar Ali  2 , Karthick Morchan  2 , Indrajit Chaudhuri  2 , Nupur Roy  3 , Naresh K Gill  3 , Chandramani Singh  4 , Neeraj Agarwal  4 , Sadhana Sharma  4 , Michelle C Stanton  1 , Janet Hemingway  1 , Sridhar Srikantiah  2 , Michael Coleman  1
Affiliations

Impact of IRS: Four-years of entomological surveillance of the Indian Visceral Leishmaniases elimination programme

Rinki Deb et al. PLoS Negl Trop Dis. .

Abstract

Background: In 2005, Bangladesh, India and Nepal agreed to eliminate visceral leishmaniasis (VL) as a public health problem. The approach to this was through improved case detection and treatment, and controlling transmission by the sand fly vector Phlebotomus argentipes, with indoor residual spraying (IRS) of insecticide. Initially, India applied DDT with stirrup pumps for IRS, however, this did not reduce transmission. After 2015 onwards, the pyrethroid alpha-cypermethrin was applied with compression pumps, and entomological surveillance was initiated in 2016.

Methods: Eight sentinel sites were established in the Indian states of Bihar, Jharkhand and West Bengal. IRS coverage was monitored by household survey, quality of insecticide application was measured by HPLC, presence and abundance of the VL vector was monitored by CDC light traps, insecticide resistance was measured with WHO diagnostic assays and case incidence was determined from the VL case register KAMIS.

Results: Complete treatment of houses with IRS increased across all sites from 57% in 2016 to 70% of houses in 2019, rising to >80% if partial house IRS coverage is included (except West Bengal). The quality of insecticide application has improved compared to previous studies, average doses of insecticide on filters papers ranged from 1.52 times the target dose of 25mg/m2 alpha-cypermethrin in 2019 to 1.67 times in 2018. Resistance to DDT has continued to increase, but the vector was not resistant to carbamates, organophosphates or pyrethroids. The annual and seasonal abundance of P. argentipes declined between 2016 to 2019 with an overall infection rate of 0.03%. This was associated with a decline in VL incidence for the blocks represented by the sentinel sites from 1.16 per 10,000 population in 2016 to 0.51 per 10,000 in 2019.

Conclusion: Through effective case detection and management reducing the infection reservoirs for P. argentipes in the human population combined with IRS keeping P. argentipes abundance and infectivity low has reduced VL transmission. This combination of effective case management and vector control has now brought India within reach of the VL elimination targets.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Map of the three VL endemic areas in India with the sentinel site districts labelled.
(Base layers for map can be found at https://www.statsilk.com/maps/download-free-shapefile-maps).
Fig 2
Fig 2. Percentage of household structures that were completely sprayed in each IRS round as reported by; A spray operators in all 8 sites, and B sentinel sites surveys.
R1 = Round one R2 = Round two. Solid colours represent complete spray and lined colours partial spray.
Fig 3
Fig 3. Percentage of household structures that received the correct dose, overdose and under dose of alpha-cypermethrin.
R1-Round 1; R2-Round 2; % over sprayed- >30 mg/m2; % on target-20-30mg/m2; % under sprayed—<20 mg/m2 alpha-cypermethrin.
Fig 4
Fig 4. Aggregated P. argentipes abundance collected in all sentinel sites for IRS and non-IRS villages.
See this image and copyright information in PMC

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