Transovarial Transmission of Dengue Virus in Aedes aegypti: A Case in Quezon City, Philippines

Ralph Julius G. Bawalan1 Nelia P. Salazar2 and Francisco M. Heralde III3

1The Graduate School, University of the East
Ramon Magsaysay Memorial Medical Center, Inc., Quezon City, Philippines
2Research Institute for Tropical Medicine, Department of Health, Muntinlupa City, Philippines
3Department of Biochemistry and Molecular Biology,
College of Medicine, University of the Philippines Manila

Background. The changing nature of dengue epidemiology and control makes dengue one of the challenging infectious disease problems in the present time with certain inadequacies in existing knowledge base becoming apparent.

Objective. This quantitative and experimental study was conducted to provide recent local evidence that dengue virus transovarial transmission among field collected Aedes aegypti mosquitoes does occur and presents an important factor in the epidemiology and control of dengue.

Methods. Households in Quezon City, Philippines, a known dengue infection hotspot in 2011, were randomly selected (H9 and H14) for Aedes aegypti egg and larval collection. Mosquito larvae were captured using standard ovitraps and reared to adulthood in the entomology unit of the Molecular Diagnostics and Genotyping Laboratory at the University of the Philippines (UP), College of Medicine, Manila. Whole organism homogenate of adult mosquitoes were prepared for subsequent dengue virus molecular characterization and virulence testing. Both egg samples and their infection profile for dengue virus was determined by serotype specific RT-PCR.

Results. Molecular test results show that in each household and in each generation (parent, F1 and F2), there were detectable and strong dengue viral presence, predominantly the serotypes DEN-2, DEN-3 and DEN-4 in the Aedes aegypti mosquito homogenates.

Conclusions. These laboratory evidences indicate that thransovarial transmission of dengue virus does occur in a high urban city like Quezon City where incidence of dengue is high.Thus, it is important to consider the existence of this phenomenon in existing and future dengue control programs to ensure effectiveness of community-based intervention strategies.

Key Words: Aedes aegypti, transovarial transmission, dengue PCR, serotype-specific RT-PCR, community-based intervention