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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
West Nile Virus and Greater Sage-Grouse: Estimating Infection Rate in a Wild Bird PopulationWalker, Brett L.2007

West Nile Virus and Greater Sage-Grouse: Estimating Infection Rate in a Wild Bird Population

Keywords

Centrocercus urophasianus, coal-bed natural gas, energy development, flavivirus, greater sage-grouse, infection rate, sagebrush-steppe, West Nile virus

Abstract

Understanding impacts of disease on wild bird populations requires knowing not only mortality rate following infection, but also the proportion of the population that is infected. Greater sage-grouse (Centrocercus urophasianus) in western North America are known to have a high mortality rate following infection with West Nile virus (WNv), but actual infection rates in wild populations remain unknown. We used rates of WNv-related mortality and seroprevalence from radiomarked females to estimate infection rates in a wild greater sage-grouse population in the Powder River basin (PRB) of Montana and Wyoming from 2003 to 2005. Minimum WNv-related mortality rates ranged from 2.4% to 13.3% among years and maximum possible rates ranged from 8.2% to 28.9%. All live-captured birds in 2003 and 2004 tested seronegative. In spring 2005 and spring 2006, 10.3% and 1.8% respectively, of newly captured females tested seropositive for neutralizing antibodies to WNv. These are the first documented cases of sage-grouse surviving infection with WNv. Low to moderate WNv-related mortality in summer followed by low seroprevalence the following spring in all years indicates that annual infection rates were between 4% and 29%. This suggests that most sage-grouse in the PRB have not yet been exposed and remain susceptible. Impacts of WNv in the PRB in the near future will likely depend more on annual variation in temperature and changes in vector distribution than on the spread of resistance. Until the epizootiology of WNv in sagebrush-steppe ecosystems is better understood, we suggest that management to reduce impacts of WNv focus on eliminating man-made water sources that support breeding mosquitoes known to vector the virus. Our findings also underscore problems with using seroprevalence as a surrogate for infection rate and for identifying competent hosts in highly susceptible species.

Authors

Walker, Brett L.; Naugle, David E.; Doherty, Kevin E.; Cornish, Todd E.

Year Published

2007

Publication

Avian Diseases

Locations
DOI

10.1637/0005-2086(2007)51[691:WNVAGS]2.0.CO;2

The Role of Hydrogeography and Climate in the Landscape Epidemiology of West Nile Virus in New York State from 2000 to 2010Walsh, Michael G.2012

The Role of Hydrogeography and Climate in the Landscape Epidemiology of West Nile Virus in New York State from 2000 to 2010

Keywords

WNV

Abstract

The epidemiology and ecology of West Nile virus (WNV) have not yet been completely described. In particular, the specific roles of climate and water in the landscape in the occurrence of human WNV cases remain unknown. This study used Poisson regression to describe the relationships between WNV cases and temperature, precipitation, and the hydrogeography of the landscape in New York State from 2000 to 2010. Fully adjusted models showed that hydrogeographic area was significantly inversely associated with WNV cases (incidence rate ratio (IRR) = 0.99; 95% C.I. = 0.98-0.997< p = 0.04), such that each one square kilometer increase in hydrogeographic area was associated with a 1% decrease in WNV incidence. This association was independent of both temperature, which was also associated with WNV incidence (IRR = 2.06; 95% C.I. = 1.84-2.31, ps express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Authors

Walsh, Michael G.

Year Published

2012

Publication

PLOS One

Locations
DOI

10.1371/journal.pone.0030620

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/22328919

Dry weather induces outbreaks of human West Nile virus infectionsWang, Guiming2010

Dry weather induces outbreaks of human West Nile virus infections

Keywords

WNV

Abstract

BACKGROUND: Since its first occurrence in the New York City area during 1999, West Nile virus (WNV) has spread rapidly across North America and has become a major public health concern in North America. By 2002, WNV was reported in 40 states and the District of Columbia with 4,156 human and 14,539 equine cases of infection. Mississippi had the highest human incidence rate of WNV during the 2002 epidemic in the United States. Epidemics of WNV can impose enormous impacts on local economies. Therefore, it is advantageous to predict human WNV risks for cost-effective controls of the disease and optimal allocations of limited resources. Understanding relationships between precipitation and WNV transmission is crucial for predicting the risk of the human WNV disease outbreaks under predicted global climate change scenarios. METHODS: We analyzed data on the human WNV incidences in the 82 counties of Mississippi in 2002, using standard morbidity ratio (SMR) and Bayesian hierarchical models, to determine relationships between precipitation and human WNV risks. We also entertained spatial autocorrelations of human WNV risks with conditional autocorrelative (CAR) models, implemented in WinBUGS 1.4.3. RESULTS: We observed an inverse relationship between county-level human WNV incidence risk and total annual rainfall during the previous year. Parameters representing spatial heterogeneity in the risk of human exposure to WNV improved model fit. Annual precipitation of the previous year was a predictor of spatial variation of WNV risk. CONCLUSIONS: Our results have broad implications for risk assessment of WNV and forecasting WNV outbreaks. Assessing risk of vector-born infectious diseases will require understanding of complex ecological relationships. Based on the climatologically characteristic drought occurrence in the past and on climate model predictions for climate change and potentially greater drought occurrence in the future, we suggest that the frequency and relative risk of WNV outbreaks could increase.

Authors

Wang, Guiming, Minnis, Richard B, Belant, Jerrold L and Wax, Charles L

Year Published

2010

Publication

BMC Infectious Diseases

Locations
DOI

10.1186/1471-2334-10-38

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/20181272

WILD BIRD MORTALITY AND WEST NILE VIRUS SURVEILLANCE: BIASES ASSOCIATED WITH DETECTION, REPORTING, AND CARCASS PERSISTENCEWard, Marsha R.2006

WILD BIRD MORTALITY AND WEST NILE VIRUS SURVEILLANCE: BIASES ASSOCIATED WITH DETECTION, REPORTING, AND CARCASS PERSISTENCE

Keywords

American crow, carcass, house sparrow, persistence, scavenging, surveillance, West Nile virus, WNV

Abstract

Surveillance targeting dead wild birds, in particular American crows (Corvus brachyrhynchos), plays a critical role in West Nile virus (WNV) surveillance in the United States. Using crow decoy surrogates, detection and reporting of crow carcasses within urban and rural environments of DeKalb County, Georgia were assessed for potential biases that might occur in the county's WNV surveillance program. In each of two replicated trials, during July and September 2003, 400 decoys were labeled with reporting instructions and distributed along randomly chosen routes throughout designated urban and rural areas within DeKalb County. Information-theoretic methods were used to compare alternative models incorporating the effects of area and trial on probabilities of detection and reporting. The model with the best empirical support included the effects of area on both detection and reporting of decoys. The proportion of decoys detected in the urban area (0.605, SE=0.024) was approximately twice that of the rural area (0.293, SE=0.023), and the proportion of decoys reported in the urban area (0.273, SE=0.023) was approximately three times that of the rural area (0.103, SE=0.028). These results suggest that human density and associated factors can substantially influence dead crow detection and reporting and, thus, the perceived distribution of WNV. In a second and separate study, the persistence and fate of American crow and house sparrow (Passer domesticus) carcasses were assessed in urban and rural environments in Athens-Clarke, Madison, and Oconee counties, Georgia. Two replicated trials using 96 carcasses of each species were conducted during July and September 2004. For a portion of the carcasses, motion sensitive cameras were used to monitor scavenging species visits. Most carcasses (82%) disappeared or were decayed by the end of the 6-day study. Carcass persistence averaged 1.6 days in rural areas and 2.1 days in urban areas. We analyzed carcass persistence rates using a known-fate model framework in program MARK. Model selection based on Akaike's Information Criteria (AIC) indicated that the best model explaining carcass persistence rates included species and number of days of exposure; however, the model including area and number of days of exposure received approximately equal support. Model-averaged carcass persistence rates were higher for urban areas and for crow carcasses. Six mammalian and one avian species were documented scavenging upon carcasses. Dead wild birds could represent potential sources of oral WNV exposure to these scavenging species. Species composition of the scavenger assemblage was similar in urban and rural areas but “scavenging pressure” was greater in rural areas.

Authors

Ward, Marsha R., Stallknecht, David E., Willis, Juanette, Conroy, Michael J. and Davidson, William R.

Year Published

2006

Publication

Journal of Wildlife Diseases

Locations
DOI

10.7589/0090-3558-42.1.92

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/16699152

Investigation of an outbreak of encephalomyelitis caused by West Nile virus in 136 horsesWard, Michael P.2004

Investigation of an outbreak of encephalomyelitis caused by West Nile virus in 136 horses

Keywords

WNV

Abstract

No abstract available

Authors

Ward, Michael P., Levy, Michel, Thacker, H. Leon, Ash, Marianne, Norman, Sandra K. L., Moore, George E. and Webb, Paul W.

Year Published

2004

Publication

Journal of the American Veterinary Medical Association

Locations
DOI

10.2460/javma.2004.225.84

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/15239478

Rural Cases of Equine West Nile Virus Encephalomyelitis and the Normalized Difference Vegetation IndexWard, Michael P.2005

Rural Cases of Equine West Nile Virus Encephalomyelitis and the Normalized Difference Vegetation Index

Keywords

WNV

Abstract

Data from an outbreak (August to October, 2002) of West Nile virus (WNV) encephalomyelitis in a population of horses located in northern Indiana was scanned for clusters in time and space. One significant (p = 0.04) cluster of case premises was detected, occurring between September 4 and 10 in the south-west part of the study area (85.70°N, 45.50°W). It included 10 case premises (3.67 case premises expected) within a radius of 2264 m. Image data were acquired by the Advanced Very High Resolution Radiometer (AVHRR) sensor onboard a National Oceanic and Atmospheric Administration polar-orbiting satellite. The Normalized Difference Vegetation Index (NDVI) was calculated from visible and near-infrared data of daily observations, which were composited to produce a weekly-1km2 resolution raster image product. During the epidemic, a significant (p < 0.01) decrease (0.025 per week) in estimated NDVI was observed at all case and control premise sites. The median estimated NDVI (0.659) for case premises within the cluster identified was significantly (p < 0.01) greater than the median estimated NDVI for other case (0.571) and control (0.596) premises during the same period. The difference in median estimated NDVI for case premises within this cluster, compared to cases not included in this cluster, was greatest (5.3% and 5.1%, respectively) at 1 and 5 weeks preceding occurrence of the cluster. The NDVI may be useful for identifying foci of WNV transmission. Vector-Borne Zoonotic Dis. 5, 181–188.

Authors

Ward, Michael P., Ramsay, Bruce H. and Gallo, Kevin

Year Published

2005

Publication

Vector-Borne and Zoonotic Diseases

Locations
DOI

10.1089/vbz.2005.5.181

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/16011435

Characteristics of an outbreak of West Nile virus encephalomyelitis in a previously uninfected population of horsesWard, Michael P.2006

Characteristics of an outbreak of West Nile virus encephalomyelitis in a previously uninfected population of horses

Keywords

Equine; West Nile virus; Epidemiology; Outbreak; Risk factors; Geostatistical analysis, WNV

Abstract

Equine West Nile virus (WNV) encephalomyelitis cases – based on clinical signs and ELISA serology test results – reported to Texas disease control authorities during 2002 were analyzed to provide insights into the epidemiology of the disease within a previously disease-free population. The epidemic occurred between June 27 and December 17 (peaking in early October) and 1698 cases were reported. Three distinct epidemic phases were identified, occurring mostly in southeast, northwest and then central Texas. Significant (P < 0.05) disease clusters were identified in northwest and northern Texas. Most (91.1%) cases had no recent travel history, and most (68.9%) cases had not been vaccinated within the previous 12 months. One-third of cases did not survive, 71.2% of which were euthanatized. The most commonly reported presenting signs included ataxia (69%), abnormal gait (52%), muscle fasciculations (49%), depression (32%) and recumbency (28%). Vaccination status, ataxia, falling down, recumbency and lip droop best explained the risk of not surviving WNV disease. Results suggest that the peak risk period for encephalomyelitis caused by WNV may vary substantially among regions within Texas. Recumbent horses have a poor prognosis for survival. Vaccines, even if not administered sufficiently in advance of WNV infection within a district, may reduce the risk of death by at least 44%.

Authors

Ward, Michael P., Schuermann, James A., Highfield, Linda D. and Murray, Kristy O.

Year Published

2006

Publication

Veterinary Microbiology

Locations
DOI

10.1016/j.vetmic.2006.07.016

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/16971067

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

Field-Based Estimates of Avian Mortality from West Nile Virus InfectionWard, Michael P.2010

Field-Based Estimates of Avian Mortality from West Nile Virus Infection

Keywords

WNV

Abstract

One of the unique characteristics of West Nile virus (WNV) in North America is the large number of bird species for which the virus can be fatal. WNV mortality has been documented through experimental infections of captive birds and necropsies of free-ranging birds. Investigations of WNV-related mortality in wild birds often focus on species with dramatic population declines (e.g., American Crow, Corvus brachyrhynchos); however, few studies have addressed WNV-related mortality in species not exhibiting marked population declines since the arrival of WNV. We conducted a mark-recapture study of 204 Northern Cardinals (Cardinalis cardinalis) in an area with endemic WNV activity to estimate WNV-related mortality. Previous research has shown that once a bird is infected and recovers from WNV it develops antibodies making it resistant to future infection. Assuming that mortality risks from non-WNV causes were the same for individuals with (had been exposed to WNV) and without antibodies (had not been exposed to WNV), we compared the survival rates of birds with and without WNV antibodies to estimate the impact of WNV on wild birds. An information theoretic approach was used, and the apparent survival was found to be 34.6% lower for individuals without antibodies during the period when WNV was most active (July-September). However, the apparent survival rate was 9.0% higher for individuals without antibodies over the rest of the year. These differences in apparent survival suggest that WNV increases mortality during the WNV season and that chronic effects of WNV infection may also be contributing to mortality. Although WNV appears to have increased mortality rates within the population, population trend data do not indicate declines, suggesting that some cardinal populations can compensate for WNV-related mortality.

Authors

Ward, Michael P., Beveroth, Tara A., Lampman, Richard, Raim, Arlo, Enstrom, David and Novak, Robert

Year Published

2010

Publication

Vector-Borne and Zoonotic Diseases

Locations
DOI

10.1089/vbz.2008.0198

Additional Information:

http://www.ncbi.nlm.nih.gov/pubmed/20370425

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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

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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...

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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