Trouble from the tiger: First detection of dengue virus in Aedes albopictus in Australia during a 2024 dengue outbreak on Masig Island

Background Dengue is not endemic in Australia and outbreaks occur occasionally after viraemic travellers visit parts of Queensland where dengue vectors are prevalent. Prior to 2016, Aedes aegypti was the primary vector of dengue in Australia. However, several dengue outbreaks have occurred more recently on islands in the Torres Strait region where Ae. aegypti has been displaced by Ae. albopictus following its first detection in the islands in 2005. Methods In November 2024, adult female Ae. albopictus were collected during a dengue outbreak on Masig Island where Ae. aegypti is now absent after displacement by Ae. albopictus. Collected mosquitoes were pooled and screened for the presence of dengue virus by qRT-PCR and direct RNA sequencing. Results Dengue virus was detected by qRT-PCR in 9 of 12 mosquito pools. RNA sequencing of three positive pools confirmed the virus as belonging to dengue serotype 3 (DENV-3), consistent with the clinical serotype identified during the 2024 outbreak. Sequencing further detected four insect-specific viruses, including Bio Sioux River virus, reported in Australia for the first time. Conclusions These results represent the first detection and whole genome sequencing of dengue virus in Ae. albopictus collected in Australia. The detection of DENV-3 in Ae. albopictus during a concurrent outbreak of the same serotype in the absence of Ae. aegypti supports the ability of Ae. albopictus to drive independent dengue outbreaks. The findings confirm the risk of dengue outbreaks in mainland Australia if Ae. albopictus were to invade and expand beyond its current distribution in the Torres Strait.