Entomological determinants of malaria transmission in Kayin state, Eastern Myanmar: A 24-month longitudinal study in four villages

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.

Natural Wolbachia infections in malaria vectors in Kayin state, Myanmar

“…The vector status of species in the Thailand-Myanmar border area has been Anopheles determined previously (Somboon, Aramrattana et al 1998, Chaumeau, Fustec et al 2018 Tables 1-3 provide a breakdown of the species composition collected at the different villages but I think it would be more informative to have all the different species grouped according to villages. Currently it's difficult to determine mosquito species prevalence on a village level.…”

Impact of outdoor residual spraying on the biting rate of malaria vectors: A pilot study in four villages in Kayin state, Myanmar

“…s .) (Aconitus Subgroup, Funestus Group) and some members in the Annularis and Barbirostris Groups are secondary vectors [ 7 – 9 ]. Biting rate can be very high, thereby playing a disproportionate role in driving transmission intensity in this setting where Plasmodium -infection rates in mosquito populations are low [ 7 , 10 ].…”

“…(Aconitus Subgroup, Funestus Group) and some members in the Annularis and Barbirostris Groups are secondary vectors [ 7 – 9 ]. Biting rate can be very high, thereby playing a disproportionate role in driving transmission intensity in this setting where Plasmodium -infection rates in mosquito populations are low [ 7 , 10 ]. Bed-nets and indoor residual spraying fail to prevent most of malaria infections [ 11 – 13 ] because of the ecology and biology of relevant Anopheles species, including exophily and exophagy, zoophagy and opportunistic blood type selection, and activity peaks at dusk and dawn [ 7 , 14 , 15 ].…”

“…Biting rate can be very high, thereby playing a disproportionate role in driving transmission intensity in this setting where Plasmodium -infection rates in mosquito populations are low [ 7 , 10 ]. Bed-nets and indoor residual spraying fail to prevent most of malaria infections [ 11 – 13 ] because of the ecology and biology of relevant Anopheles species, including exophily and exophagy, zoophagy and opportunistic blood type selection, and activity peaks at dusk and dawn [ 7 , 14 , 15 ]. Larval source management is difficult to implement because of the diverse and fragmented nature of larval habitats [ 16 ], and because incredibly high densities of vector larvae can be found over large areas covered with paddy fields [ 17 ].…”

Bayesian spatiotemporal analysis of malaria infection along an international border: Hlaingbwe Township in Myanmar and Tha-Song-Yang District in Thailand

“…It was also noted that their feeding patterns (early versus late) were sometimes contradictory, even in the same site and species across different years or locations. A few studies of the entomological determinants of malaria transmission in the same areas as this study along the Thai–Myanmar border also reported that Anopheles mosquitoes exhibited an outdoor and early biting pattern with active timing between 06:00 and 07:00 [ 53 , 54 ]. Several studies have reported high malaria morbidity among children [ 55 , 56 ]; interestingly, one study in the Laiza refugee camp along the Myanmar–China border [ 57 ] speculated that daytime malaria transmission might occur near the primary school attended by younger children.…”