Transmission of Eastern Equine Encephalomyelitis Virus in Central Alabama

Abstract

A site near Tuskegee, Alabama was examined for vector activity of eastern equine encephalomyelitis (EEE) virus in 2001. More than 23,000 mosquitoes representing 8 genera and 34 species were collected during a 21-week period, and five species, Culiseta melanura, Aedes vexans, Coquillettidia perturbans, Culex erraticus, and Uranotaenia sapphirina, were examined for the presence of virus using a nested reverse transcriptase-polymerase chain reaction for EEE virus. Each species was infected at various times of the mosquito season (May-September) with different minimum infection rates (MIRs). Culiseta melanura had the highest MIR (20.2) and positive pools were detected from late May to mid-September. Aedes vexans had an MIR of 2.2 and was infected early in the season (June), while Cq. perturbans exhibited a much higher field infection rate (9.9) with all positive pools collected in August. Culiseta melanura is a likely endemic vector in central Alabama, while Ae. vexans and Cq. perturbans probably function as bridge vectors. Culex erraticus, the most common mosquito in the habitat (54% of total collections), had an MIR of 3.2, and was persistently infected from mid-June to mid-September. This is the first report of high rates of EEE virus infection in this species, a member of the tropical subgenus Melanoconion. Uranotaenia sapphirina, considered to feed on amphibians and possibly reptiles, had an MIR of 5.6, with positive pools spanning a four-month period. This suggests that species other than birds may serve as a reservoir for EEE in hardwood swamps in the Southeastern United States and elsewhere. The lengthy period of mosquito infection with EEE virus, coupled with the diverse habits of the vectors and their proximity to a population center, indicate the importance of monitoring EEE virus activity in the Mid-South.

Competency of Reptiles and Amphibians for Eastern Equine Encephalitis Virus

“…sappharina . 21 EEEV-positive pools from all these species have been collected from the TNF site, indicating that all three species have come into contact with EEEV-infected hosts. Uranotaenia sapphirina has previously been implicated as a potential bridge vector for EEEV.…”

“…erraticus has been shown to feed upon reptiles at the TNF site. This is the most common species found at the TNF site and throughout the Southeastern United States 21,[28][29][30] and it is believed to represent a major potential vector of EEEV in this region. 21,28 It is therefore possible that any or all of these four mosquito species might be responsible for initiating the enzootic transmission cycle through feeding upon EEEV-infected snakes exiting hibernation in the spring.…”

“…The species were chosen because data obtained from long-term field studies of the ecology of EEEV transmission at the TNF site suggested that they were among the most common and frequently fed upon ectotherms present. 13,14,[21][22][23] …”

Phylogenetic Analysis of Eastern Equine Encephalitis Virus Isolates from Florida

“…1,2 In the northeastern United States, the primary vector responsible for maintaining the enzootic cycle of the virus is the ornithophilic mosquito Culiseta melanura , 3,4 although other mosquito species may be responsible for enzootic maintenance in the south central United States. 5,6 Enzootic cycles are often located in hardwood swamp habitats, where vector and avian hosts are found. There are also numerous species of bridge vectors with catholic feeding patterns important in epizootic transmission of the virus to humans, horses, and other mammals, which are generally considered dead end hosts for the virus.…”

Bats as Potential Reservoir Hosts for Vector-Borne Diseases

“…erraticus and Cs. melanura from June till mid-September (Cupp et al 2003). In most publications, the ornithophilic mosquito Cs.…”