Pathogenesis of Dengue Vaccine Viruses in Mosquitoes

Techniques were developed and improved for the study of dengue virus in the mosquito vector. A technique for oral infection of mosquitoes using freshly prepared virus stocks proved to be efficient. An improved in vitro assay for transmission of dengue parent and vaccine viruses was deployed and is being assessed. Using an oil-charged capillary feeding system, saliva can rapidly and reliably be collected from even moribund mosquitoes. This technique will greatly facilitate studies on the assessment of vector competence. The dengue-2 vaccine virus (S-1) and its parent virus (PR 159) were compared for their ability to infect orally, to replicate in, and subsequently to be transmited by Aedes aegypti mosquitoes. The vaccine virus was markedly less efficient in its ability to infect mosquitoes orally. After ingesting infectious bloodmeals containing 3.7 to 8.2 log 10 TCID50/ml of the respective viruses, 56% (220/396) of the mosquitoes became orally infected with the parent virus contrasted to 16% (66/397) for the vaccine virus. None of the 16 infected mosquitoes transmitted the vaccine virus, while 14% (3/22) of the mosquitoes transmitted the parent virus. The vaccine virus remained temperature sensitive (39 C) after orally infecting and replicating in Ae. aegypti mosquitoes.