Epidemiology and Transmission Dynamics of West Nile Virus Disease

Centers for Disease Control and Prevention, Fort Collins, Colorado 80526, USA.
Emerging infectious diseases (Impact Factor: 6.75). 08/2005; 11(8):1167-73. DOI: 10.3201/eid1108.050289a
Source: PubMed


From 1937 until 1999, West Nile virus (WNV) garnered scant medical attention as the cause of febrile illness and sporadic encephalitis in parts of Africa, Asia, and Europe. After the surprising detection of WNV in New York City in 1999, the virus has spread dramatically westward across the United States, southward into Central America and the Caribbean, and northward into Canada, resulting in the largest epidemics of neuroinvasive WNV disease ever reported. From 1999 to 2004, >7,000 neuroinvasive WNV disease cases were reported in the United States. In 2002, WNV transmission through blood transfusion and organ transplantation was described for the first time, intrauterine transmission was first documented, and possible transmission through breastfeeding was reported. This review highlights new information regarding the epidemiology and dynamics of WNV transmission, providing a new platform for further research into preventing and controlling WNV disease.

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Available from: Nicholas Komar, Feb 02, 2015
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    • "The passive system of reporting of equine cases by sentinel veterinarians in France was found to be a cost-effective and efficient method of early detection of virus activity when compared to sentinel horses, sentinel chickens, and mosquito testing by using mathematical modeling to simulate data for low activity and endemic and epidemic situations (Chevalier et al. 2011). Although equines frequently are vaccinated in California (American Association of Equine Practitioners 2012) and, therefore, our horse population has not experienced the recent epizootics seen in France (Hayes et al. 2005), our results for areas with a susceptible bird population agree that passive surveillance is the most cost-effective system for WNV surveillance. Higher densities of mosquito traps resulted in more precise estimates of infection prevalence in both trap types. "
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    ABSTRACT: Surveillance systems for West Nile virus (WNV) combine several methods to determine the location and timing of viral amplification. The value of each surveillance method must be measured against its efficiency and costs to optimize integrated vector management and suppress WNV transmission to the human population. Here we extend previous comparisons of WNV surveillance methods by equitably comparing the most common methods after standardization on the basis of spatial sampling density and costs, and by estimating optimal levels of sampling effort for mosquito traps and sentinel chicken flocks. In general, testing for evidence of viral RNA in mosquitoes and public-reported dead birds resulted in detection of WNV approximately 2-5 weeks earlier than serological monitoring of sentinel chickens at equal spatial sampling density. For a fixed cost, testing of dead birds reported by the public was found to be the most cost effective of the methods, yielding the highest number of positive results per $1000. Increased spatial density of mosquito trapping was associated with more precise estimates of WNV infection prevalence in mosquitoes. Our findings also suggested that the most common chicken flock size of 10 birds could be reduced to six to seven without substantial reductions in timeliness or sensitivity. We conclude that a surveillance system that uses the testing of dead birds reported by the public complemented by strategically timed mosquito and chicken sampling as agency resources allow would detect viral activity efficiently in terms of effort and costs, so long as susceptible bird species that experience a high mortality rate from infection with WNV, such as corvids, are present in the area.
    Vector borne and zoonotic diseases (Larchmont, N.Y.) 02/2015; 15(2):147-155. DOI:10.1089/vbz.2014.1689 · 2.30 Impact Factor
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    • "However, its importance is likely to be higher outside urban areas where their preferred breeding sites are more common and the abundance of wild animals is higher. Outside of Austria, Ae. vexans has been shown to serve as a vector for WNV (USA; Hayes et al. 2005) and for dirofilariasis (Slovakia; Bocková et al. 2013). Similar to Ae. vexans, the preferred breeding sites of Oc. sticticus are temporary water bodies after floodings (Becker et al. 2010). "
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    ABSTRACT: Mosquitoes (Diptera: Culicidae) are important vectors for a wide range of pathogenic organisms. As large parts of the human population in developed countries live in cities, the occurrence of vector-borne diseases in urban areas is of particular interest for epidemiologists and public health authorities. In this study, we investigated the mosquito occurrence in the city of Vienna, Austria, in order to estimate the risk of transmission of mosquito-borne diseases. Mosquitoes were captured using different sampling techniques at 17 sites in the city of Vienna. Species belonging to the Culex pipiens complex (78.8 %) were most abundant, followed by Coquillettidia richiardii (10.2 %), Anopheles plumbeus (5.4 %), Aedes vexans (3.8 %), and Ochlerotatus sticticus (0.7 %). Individuals of the Cx. pipiens complex were found at 80.2 % of the trap sites, while 58.8 % of the trap sites were positive for Cq. richiardii and Ae. vexans. Oc. sticticus was captured at 35.3 % of the sites, and An. plumbeus only at 23.5 % of the trap sites. Cx. pipiens complex is known to be a potent vector and pathogens like West Nile virus (WNV), Usutu virus (USUV), Tahyna virus (TAHV), Sindbis virus (SINV), Plasmodium sp., and Dirofilaria repens can be transmitted by this species. Cq. richiardii is a known vector species for Batai virus (BATV), SINV, TAHV, and WNV, while Ae. vexans can transmit TAHV, USUV, WNV, and Dirofilaria repens. An. plumbeus and Oc. sticticus seem to play only a minor role in the transmission of vector-borne diseases in Vienna. WNV, which is already wide-spread in Europe, is likely to be the highest threat in Vienna as it can be transmitted by several of the most common species, has already been shown to pose a higher risk in cities, and has the possibility to cause severe illness.
    Parasitology Research 12/2014; 114:707-713. DOI:10.1007/s00436-014-4237-6 · 2.10 Impact Factor
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    • "The distributions of these vectors vary across the country due to biotic and abiotic requirements of the species. From 2001-2004, Culex pipiens, Culex restuans, Culex salinarius , Culex quinquefasciatus and Culex tarsalis were in the top three infected mosquitoes in at least one year in the USA (Hayes et al., 2005). Studies from Northeast and Great Lakes regions of the USA have often implicated Cx. pipiens and Cx. "
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    ABSTRACT: After several years of low West Nile virus (WNV) occurrence in the United States of America (USA), 2012 witnessed large outbreaks in several parts of the country. In order to understand the outbreak dynamics, spatial clustering and landscape, demographic and climatic associations with WNV occurrence were investigated at a regional level in the USA. Previous research has demonstrated that there are a handful of prominent WNV mosquito vectors with varying ecological requirements responsible for WNV transmission in the USA. Published range maps of these important vectors were georeferenced and used to define eight functional ecological regions in the coterminous USA. The number of human WNV cases and human populations by county were attained in order to calculate a WNV rate for each county in 2012. Additionally, a binary value (high/low) was calculated for each county based on whether the county WNV rate was above or below the rate for the region it fell in. Global Moran's I and Anselin Local Moran's I statistics of spatial association were used per region to examine and visualize clustering of the WNV rate and the high/low rating. Spatial data on landscape, demographic and climatic variables were compiled and derived from a variety of sources and then investigated in relation to human WNV using both Spearman rho correlation coefficients and Poisson regression models. Findings demonstrated significant spatial clustering of WNV and substantial inter-regional differences in relationships between WNV occurrence and landscape, demographic and climatically related variables. The regional associations were consistent with the ecologies of the dominant vectors for those regions. The large outbreak in the Southeast region was preceded by higher than normal winter and spring precipitation followed by dry and hot conditions in the summer.
    Geospatial health 11/2014; 9(1):153-68. DOI:10.4081/gh.2014.13 · 1.19 Impact Factor
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