Horizontal and vertical transmission of dengue virus type 2 in highly and lowly susceptible strains of Aedes aegypti mosquitoes

Isofemale lines of Aedes aegypti mosquitoes highly and lowly susceptible to dengue type 2 (DEN-2) virus (DEN(h) and DEN(l), respectively) were establi shed by oral feeding and individual rearing. The susceptibility at Fl3 gene ration was found to be 61% and 25% for the DEN(h) and DEN(l) line, respecti vely. The virus-infected mosquito females were allowed to probe on bovine a lbumin phosphate saline pH 7.2 (BAPS) through membrane feeders. The presenc e of virus in the probed BAPS was determined either by ELISA or by intratho racic (i.t.) inoculation of mosquitoes or by both methods. The rate of oral transmission of virus was found to be 2 times higher in the DEN(h) isofema le line than in the DEN(l) one. Similarly, vertical transmission rate of th e virus was found to be 7 times higher in the DEN(h) line. When batches of eggs obtained from infected female mosquitoes were allowed to hatch after t wo months the vertical transmission rate of the virus was very high. It is possible that, at room temperature, the virus gets an opportunity to multip ly and increase its copy number in the quiescent embryos. The progeny obtai ned from the infected mosquitoes was found to be capable of transmitting th e virus horizontally when allowed to probe on BAPS through the membrane fee der. This is the first report demonstrating horizontal transmission of DEN- 2 virus by mosquitoes infected through vertical transmission. The higher ve rtical transmission rate of the virus in the progeny obtained from the eggs dessicated for a longer time and the horizontal transmission of the virus from the progeny is of very high epidemiological significance.