Pathogenesis of Dengue Vaccine Viruses in Mosquitoes

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 transmitted 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 TCID 50/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 degrees C) after orally infecting and replicating in Ae. aegypti mosquitoes. An improved in vitro assay for transmission of dengue parent and vaccine viruses is being developed. 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.