Human arboviral diseases transmitted by Aedes aegypti such as dengue, Zika, chikungunya and yellow fever remain global public health threats to date. Of these diseases, dengue fever is particularly prevalent in Southeast Asia. Relentless vector control efforts are performed to curtail disease transmissions through which pyrethroid insecticides are broadly used as the first line of defense to control Ae. aegypti, especially in the course of disease outbreaks. Here, we compile the largest contemporary database for susceptibility profiles and underlying mechanisms involved in Ae. aegypti resistant to pyrethroids in Southeast Asia. The extensive use of pyrethroids inevitably elicit different levels of resistance to numerous populations despite the presence of geographical isolation. The most common mechanisms of pyrethroid resistance that have been identified in Ae. aegypti includes mutations in the voltage sensitive sodium channel gene (Vssc gene) and metabolic-mediated insecticide resistance. Aedes aegypti develops resistance to pyrethroids by acquisition of one or several amino acid substitution(s) in this Vssc gene. Enzymes involved in metabolic-mediated detoxification (i.e. monooxygenases, glutathione-S-transferases and esterases) have been reported to be related to pyrethroid resistance but many specific contributory enzymes are not completely studied. An inadequate amount of data from some countries indicates an urgent need for further study to fill the knowledge gaps. Perspectives and future research needs are also discussed.

The morphotaxonomy of Rhipicephalus microplus complex has been challenged in the last few years and prompted many biologists to adopt a DNA-based method for distinguishing the members of this group. In the present study, we used a mitochondrial DNA analysis to characterise the genetic assemblages, population structure and dispersal pattern of R. microplus from Southeast Asia, the region where the species originated. A phylogeographic analysis inferred from the 16S rRNA and cytochrome oxidase subunit I (COI) genes was performed with five populations of R. microplus collected from cattle in Malaysia. Malaysian R. microplus sequences were compared with existing COI and 16S rRNA haplotypes reported globally in NCBI GenBank. A total of seven and 12 unique haplotypes were recovered by the 16S rRNA and COI genes, respectively. The concatenated sequences of both 16S rRNA and COI revealed 18 haplotypes. Haplotype network and phylogenetic analyses based on COI+16S rRNA sequences revealed four genetically divergent groups among Malaysian R. microplus. The significantly low genetic differentiation and high gene flow among Malaysian R. microplus populations supports the occurrence of genetic admixture. In a broader context, the 16S rRNA phylogenetic tree assigned all isolates of Malaysian R. microplus into the previously described African/the Americas assemblage. However, the COI phylogenetic tree provides higher resolution of R. microplus with the identification of three main assemblages: clade A sensu Burger et al. (2014) comprises ticks from Southeast Asia, the Americas and China; clade B sensu Burger et al. (2014) is restricted to ticks that originated from China; and clade C sensu Low et al. (2015) is a new genetic assemblage discovered in this study comprising ticks from India and Malaysia. We conclude that the R. microplus complex consisting of at least five taxa: R. australis, R. annulatus, R. microplus clade A sensu Burger et al. (2014), R. microplus clade B sensu Burger et al. (2014) and the new taxon, R. microplus clade C sensu Low et al. (2015). The use of COI as the standard genetic marker in discerning the genetic assemblages of R. microplus from a broad range of biogeographical regions is proposed.

Plasmodium knowlesi, a simian malaria parasite, has been in the limelight since a large focus of human P. knowlesi infection was reported from Sarawak (Malaysian Borneo) in 2004. Although this infection is transmitted across Southeast Asia, the largest number of cases has been reported from Malaysia. The increasing number of knowlesi malaria cases has been attributed to the use of molecular tools for detection, but environmental changes including deforestation likely play a major role by increasing human exposure to vector mosquitoes, which coexist with the macaque host. In addition, with the reduction in human malaria transmission in Southeast Asia, it is possible that human populations are at a greater risk of P. knowlesi infection due to diminishing cross-species immunity. Furthermore, the possibility of increasing exposure of humans to other simian Plasmodium parasites such as Plasmodium cynomolgi and Plasmodium inui should not be ignored. We here review the current status of these parasites in humans, macaques, and mosquitoes to support necessary reorientation of malaria control and elimination in the affected areas.

Perspicuous assessments of taxonomic boundaries and discovery of cryptic taxa are of paramount importance in interpreting ecological and evolutionary phenomena among black flies (Simuliidae) and combating associated vector-borne diseases. Simulium tani Takaoka & Davies is the largest and perhaps the most taxonomically challenging species complex of black flies in the Oriental Region. We use a DNA sequence-based method to delineate currently recognized chromosomal and morphological taxa in the S. tani complex on the Southeast Asian mainland and Taiwan, while elucidating their phylogenetic relationships. A molecular approach using multiple genes, coupled with morphological and chromosomal data, supported recognition of cytoform K and morphoform ‘b’ as valid species; indicated that S. xuandei, cytoform L and morphoform ‘a’ contain possible cryptic species; and suggested that cytoform B is in the early stages of reproductive isolation whereas lineage sorting is incomplete in cytoforms A, C and G.

Background: The endosymbiont bacteriumWolbachiais maternally inherited and naturally infects some filarial nematodes and a diverse range of arthropods, including mosquito vectors responsible for disease transmission in humans. Previously, it has been found infecting most mosquito species but absent inAnophelesandAedes aegypti. However, recently these two mosquito species were found to be naturally infected withWolbachia. We report here the extent ofWolbachiainfections in field-collected mosquitoes from Malaysia based on PCR amplification of theWolbachia wspand16SrRNA genes.Methods: The prevalence ofWolbachiain Culicinae mosquitoes was assessedviaPCR withwspprimers. For some of the mosquitoes, in which thewspprimers failed to amplify a product,Wolbachiascreening was performed using nested PCR targeting the16SrRNA gene.Wolbachiasequences were aligned using Geneious 9.1.6 software, analyzed with BLAST, and the most similar sequences were downloaded. Phylogenetic analyses were carried out with MEGA 7.0 software. Graphs were drawn with GraphPad Prism 8.0 software.Results: A total of 217 adult mosquitoes representing 26 mosquito species were screened. Of these, infections withWolbachiawere detected in 4 and 15 mosquito species usingwspand16SrRNA primers, respectively. To our knowledge, this is the first timeWolbachiawas detected using16SrRNA gene amplification, in someAnophelesspecies (some infected withPlasmodium),Culex sinensis,Culex vishnui,Culex pseudovishnui,Mansonia bonneaeandMansonia annulifera. Phylogenetic analysis based onwsprevealedWolbachiafrom most of the mosquitoes belonged toWolbachiaSupergroup B. Based on16SrRNA phylogenetic analysis, theWolbachiastrain fromAnophelesmosquitoes were more closely related toWolbachia infectingAnophelesfrom Africa than from Myanmar.Conclusions: Wolbachia was found infectingAnophelesand other important disease vectors such asMansonia. SinceWolbachiacan affect its host by reducing the life span and provide resistance to pathogen infection, several studies have suggested it as a potential innovative tool for vector/vector-borne disease control. Therefore, it is important to carry out further studies on naturalWolbachiainfection in vector mosquitoes’ populations as well as their long-term effects in new hosts and pathogen suppression.