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United States Articles found through PubMed 2000-2012

Description

West Nile Virus (WNV) is a mosquito-borne virus that can infect humans. Originally known in East Africa, WNV has now spread throughout the world. The first case of WNV in the western hemisphere was identified in New York in 1999, and within 5 years the disease had spread throughout the United States and into Canada, Latin America, and the Caribbean. While most of WNV infections cause no symptoms, the remaining cases show flu-like symptoms, and can lead to neurological disease or death.

latest article added on November 2013

ArticleFirst AuthorPublished
Assessment of methods for prediction of human West Nile virus (WNV) disease from WNV-infected dead birdsVeksler, Anna2009

Assessment of methods for prediction of human West Nile virus (WNV) disease from WNV-infected dead birds

Keywords

WNV

Abstract

BACKGROUND: West Nile virus (WNV) is currently the leading cause of arboviral-associated encephalitis in the U.S., and can lead to long-term neurologic sequelae. Improvements in dead bird specimen processing time, including the availability of rapid field laboratory tests, allows reassessment of the effectiveness of using WNV-positive birds in forecasting human WNV disease. METHODS: Using New York State integrated WNV surveillance data from transmissions seasons in 2001-2003, this study determined which factors associated with WNV-positive dead birds are most closely associated with human disease. The study also addressed the 'delay' period between the distribution of the dead bird variable and the distribution of the human cases. In the last step, the study assessed the relative risk of contracting WNV disease for people who lived in counties with a 'signal' value of the predictor variable versus people who lived in counties with no 'signal' value of the predictor variable. RESULTS: The variable based on WNV-positive dead birds [(Positive/Tested)*(Population/Area)] was identified as the optimum variable for predicting WNV human disease at a county level. The delay period between distribution of the variable and human cases was determined to be approximately two weeks. For all 3 years combined, the risk of becoming a WNV case for people who lived in 'exposed' counties (those with levels of the positive dead bird variable above the signal value) was about 2 times higher than the risk for people who lived in 'unexposed' counties, but risk varied by year. CONCLUSION: This analysis develops a new variable based on WNV-positive dead birds, [(Positive/Tested)*(Population/Area)] to be assessed in future real-time studies for forecasting the number of human cases in a county. A delay period of approximately two weeks between increases in this variable and the human case onset was identified. Several threshold 'signal' values were assessed and found effective at indicating human case risk, although specific thresholds are likely to vary by region and surveillance system differences.

Authors

Veksler, Anna, Eidson, Millicent and Zurbenko, Igor

Year Published

2009

Publication

Emerging Themes in Epidemiology

Locations
DOI

10.1186/1742-7622-6-4

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/19500367

Ecological correlates of risk and incidence of West Nile virus in the United StatesAllan, Brian F.2009

Ecological correlates of risk and incidence of West Nile virus in the United States

Keywords

WNV

Abstract

West Nile virus, which was recently introduced to North America, is a mosquito-borne pathogen that infects a wide range of vertebrate hosts, including humans. Several species of birds appear to be the primary reservoir hosts, whereas other bird species, as well as other vertebrate species, can be infected but are less competent reservoirs. One hypothesis regarding the transmission dynamics of West Nile virus suggests that high bird diversity reduces West Nile virus transmission because mosquito blood-meals are distributed across a wide range of bird species, many of which have low reservoir competence. One mechanism by which this hypothesis can operate is that high-diversity bird communities might have lower community-competence, defined as the sum of the product of each species' abundance and its reservoir competence index value. Additional hypotheses posit that West Nile virus transmission will be reduced when either: (1) abundance of mosquito vectors is low; or (2) human population density is low. We assessed these hypotheses at two spatial scales: a regional scale near Saint Louis, MO, and a national scale (continental USA). We found that prevalence of West Nile virus infection in mosquito vectors and in humans increased with decreasing bird diversity and with increasing reservoir competence of the bird community. Our results suggest that conservation of avian diversity might help ameliorate the current West Nile virus epidemic in the USA.

Authors

Allan, Brian F., Langerhans, R. Brian, Ryberg, Wade A., Landesman, William J., Griffin, Nicholas W., Katz, Rachael S., Oberle, Brad J., Schutzenhofer, Michele R., Smyth, Kristina N., St. Maurice, Annabelle, Clark, Larry, Crooks, Kevin R., Hernandez, Daniel E., McLean, Robert G., Ostfeld, Richard S. and Chase, Jonathan M.

Year Published

2009

Publication

Oecologia

Locations
DOI

10.1007/s00442-008-1169-9

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/18941794

Spatially Explicit West Nile Virus Risk Modeling in Santa Clara County, CaliforniaKonrad, Sarah K.2009

Spatially Explicit West Nile Virus Risk Modeling in Santa Clara County, California

Keywords

WNV

Abstract

A geographic information system model designed to identify regions at risk for West Nile virus (WNV) transmission was calibrated and tested with data collected in Santa Clara County, California. American Crows that died from WNV infection in 2005 provided spatial and temporal ground truth. When the model was run with parameters based on Culex tarsalis infected with the NY99 genotype of the virus, it underestimated WNV occurrence in Santa Clara Co. The parameters were calibrated to fit the field data by reducing the number of degree-days necessary to reach the mosquito's extrinsic incubation period from 109 to 76. The calibration raised model efficiency from 61% to 92% accuracy, and the model performed well the following year in Santa Clara Co.

Authors

Konrad, Sarah K., Miller, Scott N., Reeves, Will K. and Tietze, Noor S.

Year Published

2009

Publication

Vector-Borne and Zoonotic Diseases

Locations
DOI

10.1089/vbz.2008.0084

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/19514810

Seasonal Patterns for Entomological Measures of Risk for Exposure to Culex Vectors and West Nile Virus in Relation to Human Disease Cases in Northeastern ColoradoBolling, Bethany G.2009

Seasonal Patterns for Entomological Measures of Risk for Exposure to Culex Vectors and West Nile Virus in Relation to Human Disease Cases in Northeastern Colorado

Keywords

Culex pipiens, Culex tarsalis, Colorado, seasonal risk, West Nile virus, WNV

Abstract

We examined seasonal patterns for entomological measures of risk for exposure to Culex vectors and West Nile virus (family Flaviviridae, genus Flavivirus, WNV) in relation to human WNV disease cases in a five-county area of northeastern Colorado during 2006–2007. Studies along habitat/ elevation gradients in 2006 showed that the seasonal activity period is shortened and peak numbers occur later in the summer for Culex tarsalis Coquillett females in foothills-montane areas > 1,600 m compared with plains areas 1,600 m. The vector index for abundance of WNV-infected Cx. tarsalis females for the plains sites combined exceeded 0.50 from mid-July to mid-August, with at least one site exceeding 1.00 from early July to late August. Finally, we found that abundance of Cx. tarsalis females and the vector index for infected females were strongly associated with weekly numbers of WNV disease cases with onset 4–7 wk later (female abundance) or 1–2 wk later (vector index).

Authors

Bolling, Bethany G., Barker, Christopher M., Moore, Chester G., Pape, W. John and Eisen, Lars

Year Published

2009

Publication

Journal of Medical Entomology

Locations
DOI

10.1603/033.046.0641

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/19960707

Equine West Nile virus disease occurrence and the Normalized Difference Vegetation IndexWard, Michael P.2009

Equine West Nile virus disease occurrence and the Normalized Difference Vegetation Index

Keywords

West Nile virus; Equine; Spatial; GIS; NDVI; Texas, WNV

Abstract

The association between the Normalized Difference Vegetation Index (NDVI) and periods of above- or below-average reported cases of equine West Nile virus encephalomyelitis, reported in Texas between 2002 and 2004, was investigated. A time-series of case reports, using a biweekly window, was constructed. Because of the disparity in number of cases reported (1698, 672 and 101 in 2002, 2003 and 2004, respectively), data were standardized by calculating the number of cases reported during each biweekly period as a ratio of the annual average number of cases reported. The mean NDVI (0.439) in Texas in biweekly periods in which cases were reported was significantly higher (P < 0.001) than the mean NDVI (0.396) in periods in which cases were not reported. The best-fitting model of standardized case ratios included the mean NDVI in the preceding 4-week period. This association was further investigated in the two ecological regions of Texas in which most cases were reported during the study period—Prairies and Lakes, and the Panhandle Plains. Standardized case ratios in the Prairies and Lakes ecoregion were best predicted by NDVI estimated 19–20 weeks previously, whereas standardized case ratios in the Panhandle Plains region were most strongly associated with NDVI estimated 1–4 weeks previously, indicating that the temporal lag between appropriate environmental conditions and resulting increased risk of WNV transmission can vary in different regions. The associations identified could be useful in an early-warning system of increased disease risk.

Authors

Ward, Michael P.

Year Published

2009

Publication

Preventive Veterinary Medicine

Locations
DOI

10.1016/j.prevetmed.2008.10.003

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/19054585

Environmental risk factors for equine West Nile virus disease cases in TexasWard, Michael P.2009

Environmental risk factors for equine West Nile virus disease cases in Texas

Keywords

WNV

Abstract

West Nile Virus (WNV) was first detected in the Texas equine population during June 2002. Infection has since spread rapidly across the state and become endemic in the equine population. Environmental risk factors associated with equine WNV attack rates in Texas counties during the period 2002 to 2004 were investigated. Equine WNV attack rates were smoothed using an empirical Bayesian model, because of the variability among county equine populations (range 46-9,517). Risk factors investigated included hydrological features (lakes, rivers, swamps, canals and river basins), land cover (tree, mosaic, shrub, herbaceous, cultivated and artificial), elevation, climate (rainfall and temperature), and reports of WNV-positive mosquito and wild bird samples. Estimated county equine WNV attack rate was best described by the number of lakes, presence of broadleaf deciduous forest, presence of cultivated areas, location within the Brazos River watershed, WNV-positive mosquito status and average temperature. An understanding of environmental factors that increase equine WNV disease risk can be used to design and target disease control programs.

Authors

Ward, Michael P., Wittich, Courtney A., Fosgate, Geoffrey and Srinivasan, Raghavan

Year Published

2009

Publication

Veterinary Research Communications

Locations
DOI

10.1007/s11259-008-9192-1

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/19031106

An examination of the effect of landscape pattern, land surface temperature, and socioeconomic conditions on WNV dissemination in ChicagoLiu, Hua2009

An examination of the effect of landscape pattern, land surface temperature, and socioeconomic conditions on WNV dissemination in Chicago

Keywords

WNV

Abstract

This paper developed an approach by the synthesis of remote sensing, landscape metrics, and statistical methods to examine the effects of landscape pattern, land surface temperature, and socioeconomic conditions on the spread of West Nile virus (WNV) caused by mosquitoes and animal hosts in Chicago, USA. Land use/land cover and land surface temperature images were derived from Terra's Advanced Spaceborne Thermal Emission and Reflection Radiometer imagery. An analytical procedure using landscape metrics was developed, applying configuration analysis of landscape patterns in the study area. The positive reports of mosquitoes and animal hosts for WNV in fall, 2001-2006, were collected from the Cook County Public Health Department. Forty-nine municipalities were found to have WNV-positive records in mosquitoes and animal hosts in fall 2004. Socioeconomic data were obtained from the 2000 US Census. Statistical analysis was applied to WNV data in fall 2004 to identify the relationship between potential predictors and WNV spread. As a result, landscape factors, such as landscape aggregation index and the urban areas and areas of grass and water, showed strong correlations with the WNV-positive records. Socioeconomic conditions, such as the population over 65 years old, also showed a strong correlation with WNV-positive records. Thermal conditions of water showed a less but still considerable correlation to WNV-positive records. This research offers an opportunity to explore the effects of landscape pattern, land surface temperature, and socioeconomic conditions on the spread of WNV caused by mosquitoes and animal hosts. Results can contribute to public health and environmental management in the study area.

Authors

Liu, Hua and Weng, Qihao

Year Published

2009

Publication

Environmental Monitoring and Assessment

Locations
DOI

10.1007/s10661-008-0618-6

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/19107566

Investigation of Fathead Minnows (Pimephales promelas) as a Biological Control Agent of Culex Mosquitoes Under Laboratory and Field ConditionsIrwin, Patrick2009

Investigation of Fathead Minnows (Pimephales promelas) as a Biological Control Agent of Culex Mosquitoes Under Laboratory and Field Conditions

Keywords

WNV

Abstract

Many urban areas have engineered storm-water runoff control structures such as ditches and detention ponds. These often serve as excellent habitats for Culex pipiens and Culex restuans, the primary enzootic vectors of West Nile virus in the Midwest. We evaluated predation and control of these species by a fish species native to Wisconsin, the fathead minnow (Pimephales promelas). In the lab, a single minnow consumed an average of 74 Cx. pipiens larvae in a 24-h period. Minnow gender and age had minimal effect on predation of 2nd and 4th instars. In the field, fathead minnows (1,000 fish/ha) were introduced 1 time into 3 storm-water ditches with an additional 9 sites serving as controls. Sites where fish were introduced required no Bacillus sphaericus (VectoLex) treatments during the 10-week experiment. The control sites required 19 VectoLex treatments during the same 10-week time span. Survival analysis revealed a statistically significant difference in time to first VectoLex treatment between fish sites and control sites. Our results suggest fathead minnows may provide a long-lasting and ecologically and economically feasible alternative to the use of VectoLex for Culex larval control.

Authors

Irwin, Patrick and Paskewitz, Susan

Year Published

2009

Publication

Journal of the American Mosquito Control Association

Locations
DOI

10.2987/09-0013.1

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/19852220

Seasonal Blood-Feeding Behavior of Culex tarsalis (Diptera: Culicidae) in Weld County, Colorado, 2007Kent, Rebekah2009

Seasonal Blood-Feeding Behavior of Culex tarsalis (Diptera: Culicidae) in Weld County, Colorado, 2007

Keywords

WNV

Abstract

Studies on Culex tarsalis Coquillett in Colorado have shown marked seasonal variation in the proportion of blood meals from birds and mammals. However, limitations in the specificity of antibodies used in the precipitin test and lack of vertebrate host availability data warrant revisiting Cx. tarsalis blood feeding behavior in the context of West Nile virus (WNV) transmission. We characterized the host preference of Cx. tarsalis during peak WNV transmission season in eastern Colorado and estimated the relative contribution of different avian species to WNV transmission. Cx. tarsalis preferred birds to mammals each month, although the proportion of blood meals from mammals increased in July and August. The distribution of blood meals differed significantly across months, in part because of changes in the proportion of blood meals from American robins, a preferred host. The estimated proportion of WNV-infectious vectors derived from American robins declined from 60 to 1% between June and August. The majority of avian blood meals came from doves, preferred hosts that contributed 25-40% of the WNV-infectious mosquitoes each month. Active WNV transmission was observed in association with a large house sparrow communal roost. These data show how seasonal patterns in Cx. tarsalis blood feeding behavior relate to WNV transmission in eastern Colorado, with the American robin contributing greatly to early-season virus transmission and a communal roost of sparrows serving as a focus for late-season amplification.

Authors

Kent, Rebekah, Juliusson, Lara, Weissmann, Michael, Evans, Sara and Komar, Nicholas

Year Published

2009

Publication

Journal of Medical Entomology

Locations
DOI

10.1603/033.046.0226

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/19351092

Role of Communally Nesting Ardeid Birds in the Epidemiology of West Nile Virus RevisitedReisen, William K.2009

Role of Communally Nesting Ardeid Birds in the Epidemiology of West Nile Virus Revisited

Keywords

WNV

Abstract

Although herons and egrets in the family Ardeidae frequently have been associated with viruses in the Japanese encephalitis virus serocomplex, communal nesting colonies do not appear to be a focus of early season and rapid amplification of West Nile virus (WNV) in California. Evidence for repeated WNV infection was found by testing living and dead nestlings collected under trees with mixed species ardeid colonies nesting above in an oak grove near the University of California arboretum in Davis and in a Eucalyptus grove at a rural farmstead. However, mosquito infection rates at both nesting sites were low and positive pools did not occur earlier than at comparison sites within the City of Davis or at the Yolo Bypass wetlands managed for rice production and waterfowl habitat. Black-crowned night herons (Nycticorax nycticorax) were the most abundant and frequently infected ardeid species, indicating that WNV may be an important cause of mortality among nestlings of this species.

Authors

Reisen, William K., Wheeler, Sarah, Armijos, M. Veronica, Fang, Ying, Garcia, Sandra, Kelley, Kara and Wright, Stan

Year Published

2009

Publication

Vector-Borne and Zoonotic Diseases

Locations
DOI

10.1089/vbz.2008.0104

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/19125659

Recent Articles

Effects of Temperature on Emergence and Seasonality of West Nile Virus in California

by Hartley, D. M., Barker, C. M., Le Menach, A., Niu, T., Gaff, H. D. and Reisen, W. K.

Temperature has played a critical role in the spatiotemporal dynamics of West Nile virus transmission throughout California from its introduction in 2003 through establishment by 2009. We compared two novel mechanistic measures of transmission risk, the temperature-dependent ratio of virus extrinsic incubation period to the mosquito gonotrophic period (BT), and the fundamental reproductive rati...

published 2012 in American Journal of Tropical Medicine and Hygiene

Weather Variability Affects Abundance of Larval culex (diptera: Culicidae) in Storm Water Catch Basins in Suburban Chicago

by Gardner, Allison M., Hamer, Gabriel L., Hines, Alicia M., Newman, Christina M., Walker, Edward D. and Ruiz, Marilyn O.

Culex pipiens L. (Diptera: Culicidae) and Culex restuans Theobald are the primary enzootic and bridge vectors of West Nile virus in the eastern United States north of 36° latitude. Recent studies of the natural history of these species have implicated catch basins and underground storm drain systems as important larval development sites in urban and suburban locales. Although the presence of la...

published 2012 in Journal of Medical Entomology


Wild Birds as Sentinels for Multiple Zoonotic Pathogens Along an Urban to Rural Gradient in Greater Chicago, Illinois

by Hamer, S. A., Lehrer, E. and Magle, S. B.

Wild birds are important in the maintenance and transmission of many zoonotic pathogens. With increasing urbanization and the resulting emergence of zoonotic diseases, it is critical to understand the relationships among birds, vectors, zoonotic pathogens, and the urban landscape. Here, we use wild birds as sentinels across a gradient of urbanization to understand the relative risk of diseases ...

published 2012 in Zoonoses and Public Health

Completeness of West Nile Virus Testing in Patients with Meningitis and Encephalitis During an Outbreak in Arizona, Usa

by WEBER, I. B., LINDSEY, N. P., BUNKO-PATTERSON, A. M., BRIGGS, G., WADLEIGH, T. J., SYLVESTER, T. L., LEVY, C., KOMATSU, K. K., LEHMAN, J. A., FISCHER, M. and STAPLES, J. E.

Accurate data on West Nile virus (WNV) cases help guide public health education and control activities, and impact regional WNV blood product screening procedures. During an outbreak of WNV disease in Arizona, records from patients with meningitis or encephalitis were reviewed to determine the proportion tested for WNV. Of 60 patients identified with meningitis or encephalitis, 24 (40%) were te...

published 2012 in Epidemiology and Infection