Retrospective analysis of epidemic eastern equine encephalomyelitis transmission in Massachusetts
The study presented in this dissertation concerns the epidemiology of eastern equine encephalitis (EEE) in Massachusetts.
Human serosurveys were conducted in case neighborhoods to determine the inapparent infection rate and to test the hypothesis of focality of EEE virus transmission. An inapparent transmission rate of up to 1.85% was observed at epidemic foci. Focality of transmission was supported by the identification of an inapparent infection less than 10 meters from a 1990 case site.
Putative epidemic EEE virus vector populations were compared at 15 case sites in Massachusetts. Carbon dioxide baited American Biophysics Corporation (ABC) light traps were used for trapping mosquitoes to estimate biting risk. These population data along with biological and behavioral data from other studies suggest that Coquillettidia perturbans (Walker), Aedes canadensis (Theobald), and Culex salinavius (Coquillett) may be more important vectors than the other potential vectors for EEE virus in Massachusetts, Aedes vexans (Meigen), Anopheles punctipennis (Say) and Anopheles quadrimaculatus (Say).
Stepwise linear regression models were constructed from remotely sensed landscape data and Geographic Information System (GIS) Technology. Wetlands accounted for up to 72.5% of the observed variation in the host seeking populations of Ae. canadensis, Ae. vexans, and Culesita melanura.
Stepwise linear regressions also demonstrated deciduous wetlands to be the specific wetland category contributing to the major class models. Pesticide targeting of deciduous (or coniferous) wetlands may be an effective way of controlling the abundance of Cs. melanura, Ae. canadensis and Ae. vexans.
The effect of EEE virus on survivorship was determined for three possible epidemic vectors: Aedes albopictus, An. quadrimaculatus and Cq. perturbans. Female mosquitoes of these three species were exposed to EEE virus through infected blood meals and compared to uninfected controls for differential survival. Additionally, survival of Cq. perturbans and An. quadrimaculatus mosquitoes intrathoracically inoculated with EEE virus was compared to controls receiving diluent inoculations. It was shown that neither Ae. albopictus nor An. quadrimaculatus experienced reduced survivorship. Reduced survival was observed among Cq. perturbans orally infected with EEE virus. Damage to the midgut epithelium by EEE virus may be the cause of the increased mortality in this vector.
0573: Public health