Abstract
Control of malaria vectors in Yemen relies on both indoor residual spraying using carbamate (bendiocarb) and long-lasting pyrethroids-treated nets. This paper reports the results of studies conducted to monitor the insecticide resistance of the main malaria vector, Anopheles arabiensis, to the insecticides currently used in the vector control in four different locations. Susceptibility tests were performed following the WHO test procedures. Two pyrethroids (lambda-cyhalothrin 0.05% and deltamethrin 0.05%) and one carbamate (bendiocarb 0.1%) were tested at diagnostic doses (DD). The five-fold DD of lambda-cyhalothrin and deltamethrin (0.25%) were also used to yield information on the intensity of resistance. Besides, tests with synergists were performed to assess the involvement of detoxifying enzyme in the phenotypic resistance of the populations of An. arabiensis to pyrethroids. The results of the performed susceptibility bioassay showed that the vector is susceptible to bendiocarb and resistant to lambda-cyhalothrin and deltamethrin in the four studied areas. The pyrethroids resistance is solely metabolic. This information could help policy-makers to plan insecticide resistance management. Bendiocarb is still an effective insecticide in the form of IRS. Concerning LLINS, it would be interesting to assess their effectiveness, combining a pyrethroid with PBO for the control of the pyrethroid-resistant malaria vector.
Highlights
Malaria is a significant public health problem in Yemen with 65% of the population living in areas where transmission is thought to occur resulting in an estimated one million cases per year and a case fatality rate of about 1% [1]. e predominant parasite species is Plasmodium falciparum, and the overall prevalence of infections was 1.5% in 2009, with 97% of infections occurring in governorates predominantly below altitudes of 1000 m [2]
Two cycles of indoor residual spraying (IRS) are targeted in all areas below 600 m altitude (Stratum 1), one cycle of IRS supplemented with long lasting insecticidetreated nets (LLINs) in areas from 600 m to 1000 m altitude (Stratum 2) and LLINs only in areas from 1000 to 1500 m altitude (Stratum 3). e residual insecticides used for IRS were lambda-cyhalothrin (ICON 10 wp and ICON 10 CS) until 2014 after which a shift was made to using bendiocarb (FICAM 80% WP). e LLINs distributed for populations have included the following product
® and Yorkool [4]. ® e first susceptibility tests were conducted in 2009. Results of these tests showed the full susceptibility of An. arabiensis to lambda-cyhalothrin in ten sites, to permethrin in two sites, to deltamethrin in one site, to bendiocarb in one site, and to DDT in four sites [5]. e first pyrethroid resistance was detected in 2012-2013 in several localities: in Al Qanawis (Stratum 1), resistance to lambda-cyhalothrin and permethrin and in Wadi Sulkmal (Stratum 2), and Zabied (Stratum 1), resistance to lambda-cyhalothrin and deltamethrin [5]
Summary
Malaria is a significant public health problem in Yemen with 65% of the population living in areas where transmission is thought to occur resulting in an estimated one million cases per year and a case fatality rate of about 1% [1]. e predominant parasite species is Plasmodium falciparum, and the overall prevalence of infections was 1.5% in 2009, with 97% of infections occurring in governorates predominantly below altitudes of 1000 m [2]. ® e first susceptibility tests were conducted in 2009 Results of these tests showed the full susceptibility of An. arabiensis to lambda-cyhalothrin in ten sites, to permethrin in two sites, to deltamethrin in one site, to bendiocarb in one site, and to DDT in four sites [5]. The pyrethroid resistance detected represents a threat for malaria vector control strategy. Is study was developed in this context It aims to evaluate and characterize the current insecticide resistance of the main malaria vector, An. Arabiensis, in Yemen, to the insecticides currently used in the vector control. Ree insecticides were tested at diagnostic doses (DD) as defined by the WHO [7]: two pyrethroids (lambdacyhalothrin 0.05% and deltamethrin 0.05%) and one carbamate (bendiocarb 0.1%). Mortalities were recorded after 24 hours, and susceptibility status of mosquito populations was graded according to the WHO protocol [7]
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