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

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.

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

“…The inability to detect L. donovani DNA in P. argentipes in the Saran villages is surprising considering that VL and PKDL cases were reported on the KAMIS system in months leading up to and after when the work was performed. However, similar low infections rates in P. argentipes were also reported in eight VL sentinel sites undergoing routine entomological and IRS surveillance in three VL endemic States in India (27). Of 14,775 P. argentipes females tested, L. donovani DNA was detected in only four females collected in the district of East Champaran, Bihar (3/991 and 1/704 females collected 2017 and 2018, respectively).…”

“…argentipes females/trap night found in a previous study performed in Saran, but higher than the mean capture rate of 2.0 P. argentipes females/trap night reported in Muzaffarpur, Bihar, another VL endemic district bordering Saran (11,21) and in other sentinel sites in India where, even during the June-September peak, densities of P. argentipes females/trap night declined from 2014-2019 (27).…”

“…Nevertheless, it is worth noting that the mean capture rates of P. argentipes females/trap night using CDC-LTs placed in human dwellings, of 4.2-4.8 or 6.0-6.1 P. argentipes females/trap night in Nalanda and Saran villages, respectively, were consistent with a mean capture rate of 5.5 P. argentipes females/trap night found in a previous study performed in Saran, but higher than the mean capture rate of 2.0 P. argentipes females/trap night reported in Muzaffarpur, Bihar, another VL endemic district bordering Saran (11, 21) and in other sentinel sites in India where, even during the June-September peak, densities of P. argentipes females/trap night declined from 2014-2019 (27).…”

An Opinion based on a Retrospective Study on Vector Management for the Elimination of Visceral Leishmaniasis and its Sustenance

“…62 Another source of concern in terms of quality IRS is logistics. 51,55 Due to limited coverage, a suboptimal or defective spray may raise the cost of the programme and, as a result, the usage of insecticide.…”

“…Despite the fact that IRS has been the mainstay for the elimination of Kala-azar and DDT has been the insecticide of choice, IRS has been severely harmed due to a lack of proper monitoring and evaluation tools, 6,31,37,53,54 whilst a four-year assessment of IRS coverage revealed that while there has been progress, much more improvement is needed. 55 In 2009, TDR/WHO and German collaboration (BMZ/GIZ) developed an IRS toolkit for use in a multi-country study in India, Bangladesh, and Nepal. This tool set for IRS quality assurance included a number of indicators.…”