Abstract
Background: The Thailand-Myanmar borderland is an area endemic for malaria where transmission is low, seasonal and unstable. The epidemiology has been described but there is relatively few data on the entomological determinants of malaria transmission. Methods: As part of a pilot study on Targeted Malaria Elimination, entomological investigations were conducted during 24 months in four villages located in Kayin state, Myanmar. Anopheles mosquitoes were identified by morphology, and molecular assays were used in order to discriminate between closely related sibling species of malaria vectors. Plasmodium infection rate was determined using quantitative real-time PCR. Results: The biodiversity of Anopheles entomo-fauna was very high and multiple species were identified as malaria vectors. The intensity of human-vector contact (mean human-biting rate= 369 bites/person/month) compensates for the low infection rate in naturally infected populations of malaria vectors (mean sporozoite index= 0.4 and 1.7 /1,000 mosquitoes for P. falciparum and P. vivax respectively), yielding intermediary level of transmission intensity (mean entomological inoculation rate= 0.13 and 0.64 infective bites/person/month for P. falciparum and P. vivax, respectively). We estimated that 65% of the potential infective bites are not prevented by mosquito bed nets because of outdoor and early biters. Conclusion: This study provided a unique opportunity to describe the entomology of malaria in low transmission settings of Southeast Asia. Our data are important in the context of malaria elimination in the Greater Mekong Subregion.
Highlights
Artemisinin resistance in Plasmodium falciparum has emerged and spread in the Greater Mekong Sub-region (GMS)[1], leading to the failure of several artemisinin-based combination therapies (ACTs)[2]
We report the occurrence of 10 Groups of Anopheles on the basis of morphological identification: Barbirostris, Hyrcanus (Anopheles Subgenus, Myzorynchus Series), Annularis, Jamesii, Maculatus (Cellia Subgenus, Neocellia Series), Funestus (Cellia Subgenus, Myzomyia Series), Kochi, Leucosphyrus, Tessellatus (Cellia Subgenus, Neomyzomyia Series) and Subpictus (Cellia Subgenus, Pyretophorus Series)
A priori malaria vectors in the Annularis, Barbirostris, Funestus, Leucosphyrus and Maculatus Groups (i.e. Anopheles taxa that were previously reported to be infected with human malaria parasites in the Thailand-Myanmar border area) accounted for 84–96% and for 40–70% of the Anopheles mosquitoes collected by human-landing catch (HLC) and cow-bait trap (CBT) collection methods respectively (Figure 2)
Summary
Artemisinin resistance in Plasmodium falciparum has emerged and spread in the Greater Mekong Sub-region (GMS)[1], leading to the failure of several artemisinin-based combination therapies (ACTs)[2]. In Myanmar (western GMS), the incidence of clinical malaria cases has declined[4]. In this area, dihydroartemisinin-piperaquine and artemether-lumefantrine remain effective against P. falciparum. It is urgent to eliminate falciparum malaria in Myanmar, the main gateway to India and Bangladesh, before these two ACTs fall to resistance. Entomological aspects of malaria transmission are important in the context of elimination as they largely determine intervention design and outcome. The Thailand-Myanmar borderland is an area endemic for malaria where transmission is low, seasonal and unstable. The epidemiology has been described but there is relatively few data on the entomological determinants of malaria transmission. Conclusion: This study provided a unique opportunity to describe the entomology of malaria in low transmission settings of Southeast Asia. Our data are important in the context of malaria elimination in the Greater Mekong Subregion
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