Abstract
BackgroundThe sand fly Phlebotomus argentipes is the vector for visceral leishmaniasis (VL) in the Indian sub-continent. In Bangladesh since 2012, indoor residual spraying (IRS) was applied in VL endemic areas using deltamethrin. In Nepal, IRS was initiated in 1992 for VL vector control using lambda-cyhalothrin. Irrational use of insecticides may lead to vector resistance but very little information on this subject is available in both countries. The objective of this study was to generate information on the susceptibility of the vector sand fly, P. argentipes to insecticide, in support of the VL elimination initiative on the Indian sub-continent.MethodsSusceptibility tests were performed using WHO test kits following the standard procedures regarding alpha cypermethrin (0.05%), deltamethrin (0.05%), lambda-cyhalothrin (0.05%), permethrin (0.75%), malathion (5%) and bendiocarb (0.1%) in six upazilas (sub-districts) in Bangladesh. In Nepal, the tests were performed for two insecticides: alpha cypermethrin (0.05%) and deltamethrin (0.05%). Adult P. argentipes sand flies were collected in Bangladesh from six VL endemic upazilas (sub-districts) and in Nepal from three endemic districts using manual aspirators.ResultsThe results show that VL vectors were highly susceptible to all insecticides at 60 minutes of exposure in both countries. In Bangladesh, corrected mortality was 100% at 15 minutes as well as 30 minutes of exposure. The study sites in Nepal, however, showed some diverse results, with a mortality rate less than 90% for 15 minutes of exposure with alpha cypermethrin and deltamethrin in two districts but was above 95% after 30 minutes of exposure.ConclusionsThese results suggest that the insecticides tested can still be used in the national programmes of Bangladesh and Nepal. However, insecticide rotation should be performed to mitigate the possible development of insecticide resistance. Periodic susceptibility tests should be performed by the countries to get timely alerts regarding insecticide resistance.
Highlights
The sand fly Phlebotomus argentipes is the vector for visceral leishmaniasis (VL) in the Indian sub-continent
The mortality rate was 100 % for 60 minutes of exposure for both insecticides in all three study districts but different results were found for 15 and 30 minutes of exposure (Table 14). These results indicate the need for establishing the susceptibility status of vector sand flies for above tested as well as other insecticides in the pipeline for indoor residual spraying (IRS) in Nepal
Two insecticides were tested in the both countries and the findings indicate that the P. argentipes populations are on the way to developing tolerance against both insecticides in Nepal whereas they are still 100% susceptible in Bangladesh
Summary
The sand fly Phlebotomus argentipes is the vector for visceral leishmaniasis (VL) in the Indian sub-continent. The objective of this study was to generate information on the susceptibility of the vector sand fly, P. argentipes to insecticide, in support of the VL elimination initiative on the Indian sub-continent. Visceral leishmanisis (VL) known as kala-azar in the Indian sub-continent is a deadly parasitic disease (if untreated) caused by Leishmania donovani Laveran & Mesnil (Kinetoplastida: Trypanosomatidae) which is transmitted by the bite of a female sand fly Phlebotomus argentipes Annandale & Brunneti (Diptera: Psychodidae). VL was virtually eliminated from this part of world during the malaria eradication era through massive DDT spraying for malaria vector control [1]. The use of DDT was banned in Bangladesh and Nepal in 1998 and 1995, respectively, due to its environmental hazard [2, 3]
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