Status of insecticide resistance in Anopheles mosquitoes in Ubon Ratchathani province, Northeastern Thailand

Abstract

BackgroundMalaria is common in hilly, forested areas along national borders in Southeast Asia. Insecticide resistance in malaria vectors has been detected in a few countries in the Greater Mekong sub-region (GMS), representing a threat to malaria control and prevention. This study aims to determine the insecticide resistance status of Anopheles mosquitoes in Ubon Ratchathani province, northeastern Thailand, where increasing number of malaria cases were reported recently.MethodsMosquitoes were collected in 2013–2015 using human landing and cattle bait collections in six sites during both the rainy and dry seasons. Mosquitoes were first morphologically identified to species and their susceptibility status to deltamethrin (0.05%), permethrin (0.75%) and DDT (4%) investigated, according to WHO guidelines. Bioassays with the synergists PBO and DEF were carried out to address the role of detoxifying enzymes in insecticide resistance. DNA sequencing of a fragment of the voltage-gated sodium channel gene was carried out to detect knock-down resistance (kdr) substitutions at position 1014 in resistant species.ResultsDue to low vector abundance, complete bioassays (n ≥ 100 mosquitoes) were only achieved for Anopheles hyrcanus s.l., which was resistant to all insecticides tested (mortality ranged from 45 to 87%). Suspected resistance to DDT was found in Anopheles barbirostris s.l. (mortality 69%), but it was susceptible to deltamethrin (mortality 97–100%) and permethrin (mortality 100%). Although insufficient number of primary vectors were collected, results showed that Anopheles dirus s.l. and Anopheles maculatus s.l. were susceptible to deltamethrin (mortality 100%). Anopheles nivipes and Anopheles philippinensis were susceptible to all three insecticides. PBO significantly increased mortality to deltamethrin and permethrin in pyrethroid-resistant An. hyrcanus s.l. None of the sequenced specimens presented the L1014F or L1014S mutation.DiscussionThis study shows that insecticide resistance is present in potential malaria vectors in northeastern Thailand. The absence of kdr mutations in all Anopheles species tested suggests that metabolic resistance is the main mechanism of pyrethroid resistance. This study provides new findings about insecticide susceptibility status of potential malaria vectors in northeastern Thailand that are deemed important to guide malaria vector control.

Discriminating Lethal Concentrations for Transfluthrin, a Volatile Pyrethroid Compound for Mosquito Control in Thailand

“…Anopheles dirus s.l. from Khong Chiam and Buntharik districts, Ubon Ratchathani Province, were also found susceptible to deltamethrin (0.05%) (Sumarnrote et al 2017). Recently, suspected resistance to deltamethrin was detected in An.…”

Human and Simian Malaria in the Greater Mekong Subregion and Challenges for Elimination

“…With current efforts focusing on malaria elimination [72], there is considerable interest in vector behaviour that is not influenced by application of core interventions (i.e., conventional IRS and Insecticide Treated Nets (ITNs)), such as feeding earlier and resting outdoors when humans are not protected. For example, an unprecedented malaria outbreak, related to illegal rosewood logging, occurred in 2014 with a seven-fold increase of cases in 1 year in Ubon Ratchathani Province, Northeastern Thailand [73]. Insecticide-susceptible and exophilic An.…”

“…maculatus s.l. collected remote villages with potentially low insecticide pressure [73]. These susceptible vector species are less amenable to control interventions due to their behaviour and their interactions with humans contribute to persistent residual transmission and represent barrier to success [74,75].…”

The Overview of Malaria Cases in Trenggalek District based on The Epidemiological Triangle

“…Terdapat beberapa penelitian mengenai resistensi insektisida terhadap vektor malaria, akan tetapi dengan hasil yang tidak sejalan dengan hasil penelitian ini. Penelitian di Thailand Asia Tenggara menyatakan bahwa resistensi insektisida pada vektor malaria di daerah timur laut Thailand menunjukkan hasil tidak adanya mutasi Knock Down Resistence (KDR) pada semua spesies Anopheles yang diuji akan tetapi terjadi resistansi metabolik terutama pada mekanisme resistensi piretroid (Sumarnrote et al, 2017). Penelitian di Afrika khususnya di empat wilayah bagian Uganda menunjukkan bahwa Anopheles gambiae telah resistensi terhadap Deltamethrin dan Permethrin (Okia et al, 2018).…”