Abstract
Eastern equine encephalitis virus (EEEV) causes a highly pathogenic mosquito-borne zoonosis that is responsible for sporadic outbreaks of severe illness in humans and equines in the eastern USA. Culiseta (Cs.) melanura is the primary vector of EEEV in most geographic regions but its feeding patterns on specific avian and mammalian hosts are largely unknown in the mid-Atlantic region. The objectives of our study were to: 1) identify avian hosts of Cs. melanura and evaluate their potential role in enzootic amplification of EEEV, 2) assess spatial and temporal patterns of virus activity during a season of intense virus transmission, and 3) investigate the potential role of Cs. melanura in epidemic/epizootic transmission of EEEV to humans and equines. Accordingly, we collected mosquitoes at 55 sites in Suffolk, Virginia in 2013, and identified the source of blood meals in engorged mosquitoes by nucleotide sequencing PCR products of the mitochondrial cytochrome b gene. We also examined field-collected mosquitoes for evidence of infection with EEEV using Vector Test, cell culture, and PCR. Analysis of 188 engorged Cs. melanura sampled from April through October 2013 indicated that 95.2%, 4.3%, and 0.5% obtained blood meals from avian, mammalian, and reptilian hosts, respectively. American Robin was the most frequently identified host for Cs. melanura (42.6% of blood meals) followed by Northern Cardinal (16.0%), European Starling (11.2%), Carolina Wren (4.3%), and Common Grackle (4.3%). EEEV was detected in 106 mosquito pools of Cs. melanura, and the number of virus positive pools peaked in late July with 22 positive pools and a Maximum Likelihood Estimation (MLE) infection rate of 4.46 per 1,000 mosquitoes. Our findings highlight the importance of Cs. melanura as a regional EEEV vector based on frequent feeding on virus-competent bird species. A small proportion of blood meals acquired from mammalian hosts suggests the possibility that this species may occasionally contribute to epidemic/epizootic transmission of EEEV.
Highlights
Eastern equine encephalitis virus (EEEV) (Togaviridae, Alphavirus) is a highly pathogenic mosquito-borne virus that occurs in discrete foci in the eastern USA
Our findings highlight the importance of Cs. melanura as a regional EEEV vector based on frequent feeding on virus-competent bird species with occasional blood meals from mammalian hosts
Collections were comprised of 62.0% Cs. melanura (Figs 1B and 3), 7.0% Culex (Cx.) salinarius, 6.7%, Coquillettidia perturbans, 5.9% Cx. erraticus, 3.3% Aedes albopictus, 3.1% Ochlerotatus canadensis, and less than 3% of each of the remaining 26 species (Table 1)
Summary
Eastern equine encephalitis virus (EEEV) (Togaviridae, Alphavirus) is a highly pathogenic mosquito-borne virus that occurs in discrete foci in the eastern USA. EEEV is amplified in a bird-mosquito transmission cycle that depends on frequent feeding of Cs. melanura on virus-competent bird species [3,4,5,6,7]. Humans and horses become infected when mosquitoes act as bridge vectors by feeding opportunistically on viremic birds and mammalian hosts. Cs. melanura is considered an unlikely bridge vector because it feeds mainly on birds [2, 8]. Recent analyses of Cs. melanura sampled from the northeastern USA revealed that 1–11% of blood meals were obtained from mammals including equines and humans [5,6,7, 9], suggesting that this species may occasionally transmit EEEV to horses and possibly humans
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