Sylvatic dengue virus type 4 in Aedes aegypti and Aedes albopictus mosquitoes in an urban setting in Peninsular Malaysia

Abstract

Dengue fever is endemic in Malaysia, contributing to significant economic and health burden in the country. Aedes aegypti and Ae. albopictus are the main vectors of the dengue virus (DENV), which circulates in sylvatic and human transmission cycles and has been present in Malaysia for decades. The study investigated the presence and distribution of DENV in urban localities in the Klang Valley, Peninsular Malaysia. A total of 364 Ae. aegypti and 1,025 Ae. albopictus larvae, and 10 Ae. aegypti and 42 Ae. albopictus adult mosquitoes were screened for the presence of DENV. In total, 31 (2.2%) samples were positive, of which 2 Ae. albopictus larvae were co-infected with two serotypes, one with DENV-2 and DENV-3 and the other with DENV-3 and DENV-4. Phylogenetic analysis determined that the isolates belonged to DENV-1 genotype I (1 Ae. aegypti adult), DENV-2 (1 Ae. albopictus larva), DENV-3 genotype V (3 Ae. aegypti larvae and 10 Ae. albopictus larvae) and DENV-4 genotype IV (6 Ae. aegypti larvae and 12 Ae. albopictus larvae), a sylvatic strain of DENV-4 which was most closely related with sylvatic strains isolated from arboreal mosquitoes and sentinel monkeys in Peninsular Malaysia in the 1970s. All four DENV serotypes were co-circulating throughout the study period. The detection of a sylvatic strain of DENV-4 in Ae. aegypti and Ae. albopictus mosquitoes in urban areas in Peninsular Malaysia highlights the susceptibility of these vectors to infection with sylvatic DENV. The infectivity and vector competence of these urban mosquitoes to this strain of the virus needs further investigation, as well as the possibility of the emergence of sylvatic virus into the human transmission cycle.

Fig 1. Map of Peninsular Malaysia with a transect line diagram of the sampling sites selected within Selangor and Kuala Lumpur.

Fig 2. Phylogenetic analysis of the CprM gene sequences of DENV-1 isolates from the Klang Valley.

Sample sequence of DENV-1 (429 nt) from adult Ae. aegypti collected from Selangor in this study (marked with a white triangle) is labelled with the GenBank accession number, sample ID and year of collection. Bootstrap values (1,000 replicates) are shown next to the branches. Taxa of reference sequences are labelled as the GenBank accession numbers, year and country of sample collection.

Fig 3. Phylogenetic analysis of the CprM gene sequences of DENV-3 isolates from the Klang Valley.

Sample sequences of DENV-3 (240 nt) from Ae. aegypti (indicated with an asterisk *) and Ae. albopictus collected from Selangor (indicated with a white triangle) and Kuala Lumpur (indicated with a black triangle) in this study are labelled with the GenBank accession number, sample ID and year of collection. Bootstrap values (1,000 replicates) are shown next to the branches. Taxa of reference sequences are labelled as the GenBank accession numbers, year and country of sample collection.

Fig 4. Phylogenetic analysis of the CprM gene sequences of DENV-4 isolates from the Klang Valley.

Sample sequences of DENV-4 (351 nt) from Ae. aegypti (indicated with an asterisk *) and Ae. albopictus collected from Selangor (indicated with a white triangle) and Kuala Lumpur (indicated with a black triangle) in this study are labelled with the GenBank accession number, sample ID and year of collection. Bootstrap values (1,000 replicates) are shown next to the branches. Taxa of reference sequences are labelled as the GenBank accession numbers, year and country of sample collection.