Effects of initial dose on eastern equine encephalomyelitis virus dependent mortality in intrathoracically inoculated Culiseta melanura (Diptera : culicidae)

Viral growth characteristics that favor rapid and prodigious virion product ion may increase virus transmission but be detrimental to infected hosts. S everal arboviruses, including eastern equine encephalomyelitis (EEE) virus, negatively affect the survival of their infected mosquito vectors. To test the hypothesis that the mosquito virulent properties of EEE virus are caus ed by the presence of intrinsic viral growth properties, we investigated th e effects of infecting dose on the survival of intrathoracically inoculated Culiseta melanura (Coquillett). Daily survival of age-matched females inoc ulated with either a low initial dose of 10(1.5) plaque-forming units (PFUs ) per mosquito or a high initial dose of 10(5.5) PFUs per mosquito was moni tored for 8 wk. Compared with diluent inoculated controls, mosquitoes from both dosage groups displayed highly significant decreases in survival. No s ignificant differences in daily survival were detected between the two infe cted groups. Virus production within inoculated mosquitoes was assessed by sampling mosquitoes every 12 h for 96 h after inoculation. Rapid virus ampl ification occurred in both dosage groups, and by 24 h after exposure the me an viral loads in mosquitoes inoculated with the low dose were comparable t o those inoculated with the high dose. Likewise, although detectable virion s appeared sooner in the saliva of high dosage mosquitoes, by 72 h after in oculation no significant differences in virus transmission were detected be tween the two exposure groups. These results indicate that the virulence of EEE virus for its enzootic North American mosquito vector is not dosage de pendent and likely reflects the inherent growth propel-ties of this virus w ithin infected mosquitoes.