Knockdown Resistance Mutations in the Voltage-Gated Sodium Channel of Aedes aegypti (Diptera: Culicidae) in Myanmar

Abstract

Aedes aegypti is an important mosquito vector transmitting diverse arboviral diseases in Myanmar. Pyrethroid insecticides have been widely used in Myanmar as the key mosquito control measure, but the efforts are constrained by increasing resistance. Knockdown resistance (kdr) mutations in the voltage-gated sodium channel (VGSC) are related to pyrethroid resistance in Ae. aegypti. We analyzed the patterns and distributions of the kdr mutations in Ae. aegypti in the Mandalay area of Myanmar. The segment 6 regions of domains II and III of vgsc were separately amplified from individual Ae. aegypti genomic DNA via polymerase chain reaction. The amplified gene fragments were sequenced. High proportions of three major kdr mutations, including S989P (54.8%), V1016G (73.6%), and F1534C (69.5%), were detected in the vgsc of Ae. aegypti from all studied areas. Other kdr mutations, T1520I and F1534L, were also found. These kdr mutations represent 11 distinct haplotypes of the vgsc population. The S989P/V1016G/F1534C was the most prevalent, followed by S989P/V1016V and V1016G/F1534C. A quadruple mutation, S989P/V1016G/T1520I/F1534C, was also identified. High frequencies of concurrent kdr mutations were observed in vgsc of Myanmar Ae. aegypti, suggesting a high level of pyrethroid resistance in the population. These findings underscore the need for an effective vector control program in Myanmar.

Keywords: Aedes aegypti; Myanmar; knockdown resistance; voltage-gated sodium channel.

Figure 1

Map of the mosquito collection sites. Aedes aegypti larvae and pupae were collected at 4 townships in Mandalay Region [Patheingyi (21°57′44.7″ N, 96°24′20.9″ E), Pyin Oo Lwin (21°59′25.9″ N, 96°04′13.0″ E), Chan Aye Thazan (21°57′44.7″ N, 96°24′20.9″ E), and Aung Myae Tharsan (21°58′39.6″ N, 96°05′54.3″ E)] and 1 township in Shan State [Naung Cho (22°19′48.7″ N, 96°47′24.0″ E)]. Yellow and blue colors represent Mandalay Region and Shan State, respectively. Closed black circles indicated the collection sites of the mosquito samples.

Figure 2

Frequencies of major kdr mutations associated with pyrethroid resistance in Ae. aegypti populations collected in Mandalay area, Myanmar. (A) Frequencies of major kdr mutations detected in vgsc DII-S6 and DIII-S6 of Myanmar Ae. aegypti populations. (B) Frequencies of major kdr mutations detected in Myanmar Ae. aegypti populations collected at 5 townships, Mandalay area, Myanmar.

Figure 3

Patterns and frequencies of vgsc haplotypes based on major kdr mutations in Ae. aegypti vgsc from 5 study sites. The wild type amino acids are the column rows and colored boxes indicate mutations. Single or concurrent kdr mutations in the vgsc DII-S6 and DIII-S6 generated 11 distinct haplotypes of the gene. Patterns and frequencies of each haplotype differed by study site.