Peridomestic Aedes malayensis and Aedes albopictus are capable vectors of arboviruses in cities

Abstract

Background

Dengue and chikungunya are global re-emerging mosquito-borne diseases. In Singapore, sustained vector control coupled with household improvements reduced domestic mosquito populations for the past 45 years, particularly the primary vector Aedes aegypti. However, while disease incidence was low for the first 30 years following vector control implementation, outbreaks have re-emerged in the past 15 years. Epidemiological observations point to the importance of peridomestic infection in areas not targeted by control programs. We investigated the role of vectors in peri-domestic areas.

Methods

We carried out entomological surveys to identify the Aedes species present in vegetated sites in highly populated areas and determine whether mosquitoes were present in open-air areas frequented by people. We compared vector competence of Aedes albopictus and Aedes malayensis with Ae. aegypti after oral infection with sympatric dengue serotype 2 and chikungunya viruses. Mosquito saliva was tested for the presence of infectious virus particles as a surrogate for transmission following oral infection.

Results

We identified Aedes albopictus and Aedes malayensis throughout Singapore and quantified their presence in forested and opened grassy areas. Both Ae. albopictus and Ae. malayensis can occupy sylvatic niches and were highly susceptible to both arboviruses. A majority of saliva of infected Ae. malayensis contained infectious particles for both viruses.

Conclusions

Our study reveals the prevalence of competent vectors in peri-domestic areas, including Ae. malayensis for which we established the vector status. Epidemics can be driven by infection foci, which are epidemiologically enhanced in the context of low herd immunity, selective pressure on arbovirus transmission and the presence of infectious asymptomatic persons, all these conditions being present in Singapore. Learning from Singapore’s vector control success that reduced domestic vector populations, but has not sustainably reduced arboviral incidence, we suggest including peri-domestic vectors in the scope of vector management.

Author summary

Dengue and chikungunya are mosquito-borne diseases and re-emerging as a global burden of the 21 ^st century. Because of the absence of cure and limitations of the current vaccine, vector control remains the sole efficient intervention to mitigate epidemics. The highly-populated city of Singapore represents an example of successful vector control, where the primary vector Aedes aegypti has practically disappeared from households. However, there as well, dengue and chikungunya are re-emerging. In this study, we surveyed peridomestic sites for mosquito vectors and identified Aedes albopictus and Aedes malayensis throughout Singapore and in open-air areas frequented by people. We further showed that both mosquito species are highly susceptible to dengue and chikungunya viruses and detected infectious virus particles in mosquito saliva, indicating their transmission capacity. Our study provides evidence that Ae. albopictus and Ae. malayensis possess all the traits necessary to contribute to virus transmission in cities and suggest that peridomestic areas be included in vector management programme.