Transovarial Transmission of Dengue Virus in Aedes aegypti and Aedes albopictus in Malaysia Transovarial Transmission of Dengue Virus in Aedes aegypti and Aedes albopictus in Relation to Dengue Outbreak in an Urban Area in Malaysia

The transovarial transmission of dengue virus in field populations of Aedes aegypti and Ae. albopictus was monitored in an urbanized residential area in Malaysia. The mosquito larval populations were monitored using standard ovitraps and the larvae retrieved were subjected to dengue virus isolation by culturing in C6/36 cells and detected by peroxidase anti peroxidase staining. Data on serologicallyconfirmed dengue cases in the study area were obtained. Ae. albopictus was the dominant mosquito vector in the study area as indicated by ovitrap survey. Similarly, transovarial dengue virus was detected in Ae. albopictus in seven instances, compared to three in Ae. aegypti larvae. The minimum infection rate (MIR) for Ae. albopictus and Ae. aegypti larvae ranged between 2.35–14.30 and 5.77–40.00 respectively. When dengue occurrences were analysed together with transovarial transmission of dengue virus in Ae. albopictus, it was found that transovarial dengue virus often occurred prior to the reporting of human cases. The intervals between detecting the transovarial dengue virus and the occurrence of first clinical case/human case ranged from 7 to 41 days. However, occurrence of many viraemic asymptomatic and mildly symptomatic individuals before detection of clinical cases put limitations in forestalling the potential outbreak. Transovarial dengue infection in Ae. aegypti larvae appeared to maintain or enhance the epidemics.