Investigation of Armigeres subalbatus, a vector of zoonotic Brugia pahangi filariasis in plantation areas in Suratthani, Southern Thailand

In recent years, children in Thailand have been infected with zoonotic Brugia pahangi. However, the local environment of rubber or oil palm plantations, which would increase their exposure to risk factors of the infection due to mosquito transmission, is unclear. The present study first sought to determine the extent to which variations in the local landscape, such as the elevated versus low-lying ecotope of rubber or oil palm plantations, in a 2-km radius of the geographically defined landscape in a rural area of Suratthani, Southern Thailand could influence the abundance of Armigeres subalbatus and its susceptibility to zoonotic filarial parasite infections compared to Mansonia, Aedes, and Culex, and Coquillettidia. Thereafter, the filarial larvae found in the infected mosquitoes were molecularly investigated. Ar. subalbatus plantation ecotype was not only found to outnumber the local mosquitoes, but was identified as the predominant species that adapted well to the elevated ecotopes of the rubber or oil palm plantations, which existed at altitudes of 60–80 m. The overall rate of zoonotic filarial parasite infections (L(1), L(2), or L(3) larvae) of Ar. subalbatus was 2.5% (95% CI, −0.2 to 4.1), with an average L(3) load of 2.3 larvae per infected Ar. subalbatus (95% CI, −0.6 to 13.0); this is because the infections were found to be concentrated in the elevated ecotopes alone. Based on filarial orthologous β-tubulin gene-specific touchup-nested PCR and sequence analysis using 30 L(3) larva clones as representatives of 9 Ar. subalbatus infectious pools, Ar. subalbatus either carried B. pahangi or Dirofilaria immitis, or both species. Such findings suggest that Ar. subalbatus might have played an imperative role in the transmission of B. pahangi in the plantation areas infested with Ar. subalbatus.