| Mosquito Larval Habitat Mapping Using Remote Sensing and GIS: Implications of Coalbed Methane Development and West Nile Virus | Zou, Li | 2006 |
KeywordsCulex tarsalis, risk, discharge water, WNV AbstractPotential larval habitats of the mosquito Culex tarsalis (Coquillett), implicated as a primary vector of West Nile virus in Wyoming, were identified using integrated remote sensing and geographic information system (GIS) analyses. The study area is in the Powder River Basin of north central Wyoming, an area that has been undergoing a significant increase in coalbed methane gas extractions since the late 1990s. Large volumes of water are discharged, impounded, and released during the extraction of methane gas, creating aquatic habitats that have the potential to support immature mosquito development. Landsat TM and ETM+ data were initially classified into spectrally distinct water and vegetation classes, which were in turn used to identify suitable larval habitat sites. This initial habitat classification was refined using knowledge-based GIS techniques requiring spatial data layers for topography, streams, and soils to reduce the potential for overestimation of habitat. Accuracy assessment was carried out using field data and high-resolution aerial photography commensurate with one of the Landsat images. The classifier can identify likely habitat for ponds larger than 0.8 ha (2 acres) with generally satisfactory results (72.1%) with a lower detection limit of ≈0.4 ha (1 acre). Results show a 75% increase in potential larval habitats from 1999 to 2004 in the study area, primarily because of the large increase in small coalbed methane water discharge ponds. These results may facilitate mosquito abatement programs in the Powder River Basin with the potential for application throughout the state and region. AuthorsMiller, Scott N., Zou, Li and Schmidtmann, Edward T. Year Published2006 PublicationJournal of Medical Entomology LocationsDOI10.1603/0022-2585(2006)43[1034:MLHMUR]2.0.CO;2 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/17017244 |
| Identification of hyperendemic foci of horses with West Nile virus disease in Texas | Wittich, Courtney A. | 2008 |
KeywordsWNV AbstractObjective—To determine whether West Nile virus (WNV) disease hyperendemic foci (hot spots) exist within the horse population in Texas and, if detected, to identify the locations.
Sample Population—Reports of 1,907 horses with WNV disease in Texas from 2002 to 2004.
Procedures—Case data with spatial information from WNV epidemics occurring in 2002 (1,377 horses), 2003 (396 horses), and 2004 (134 horses) were analyzed by use of the spatial scan statistic (Poisson model) and kriging of empirical Bayes smoothed county attack rates to determine locations of horses with WNV disease in which affected horses were consistently (in each of the 3 study years) clustered (hyperendemic foci, or hot spots).
Results—2 WNV hot spots in Texas, an area in northwestern Texas and an area in eastern Texas, were identified with the scan statistic. Risk maps of the WNV epidemics were qualitatively consistent with the hot spots identified.
Conclusions and Clinical Relevance—WNV hot spots existed within the horse population in Texas (2002 to 2004). Knowledge of disease hot spots allows disease control and prevention programs to be made more efficient through targeted surveillance and education. AuthorsWard, Michael P., Wittich, Courtney A., Fosgate, Geoffrey T. and Srinivasan, Raghavan Year Published2008 PublicationAmerican Journal of Veterinary Research LocationsDOI10.2460/ajvr.69.3.378 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/18312137 |
| Vector Surveillance for West Nile Virus | WHITE, DENNIS J. | 2001 |
KeywordsWNV AbstractWest Nile virus (WNV) was detected in the metropolitan New York City (NYC) area during the summer and fall of 1999. Sixty-two human cases, including seven fatalities, were documented. The New York State Department of Health (NYSDOH) initiated and implemented a statewide mosquito and WNV surveillance system. We developed a WNV response plan designed to provide local health departments (LHD) a standardized means to begin to assess basic mosquito population data and to detect WNV circulation in mosquito populations. During the 2000 arbovirus surveillance season, local health agencies collected 317,676 mosquitoes and submitted 9,952 pools for virus testing. NYSDOH polymerase chain reaction (PCR) testing detected 363 WNV-positive pools. Eight species of mosquitoes were found to be infected. Of the 26 counties conducting mosquito surveillance, WNV-positive mosquitoes were detected only in NYC, on Long Island, and in four counties in the lower Hudson River valley region. LHD larval surveillance provided initial or enhanced mosquito habitat location and characterization and mosquito species documentation. Adult mosquito surveillance provided LHD information on species' presence, density, seasonal fluctuations, virus infection, minimum infection ratios (MIR) and indirect data on mosquito control efficacy after larval or adult control interventions. Collective surveillance activities conducted during 1999 and 2000 suggest that WNV has dispersed throughout the state and may affect local health jurisdictions within NYS, adjacent states, and Canada in future years. Vector surveillance will remain a critical component of LHD programs addressing public health concerns related to WNV. AuthorsWHITE, DENNIS J. Year Published2001 PublicationAnnals of the New York Academy of Sciences LocationsDOI10.1111/j.1749-6632.2001.tb02686.x Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/11797806 |
| Aquatic Effects of Aerial Spraying for Mosquito Control over an Urban Area | Weston, Donald P. | 2006 |
KeywordsWNV AbstractIn an effort to combat West Nile Virus, planes dispersed insecticide over Sacramento, CA, treating nearly 50,000 hectares with pyrethrins and the synergist piperonyl butoxide (PBO). Widespread dispersal of insecticide over a metropolitan area, coupled with extensive pretreatment data on the area's urban creeks, provided a unique opportunity to study effects of mosquito control agents on aquatic habitats within an urban setting. There was no evidence of aquatic toxicity from the two active ingredients in the product applied. However, PBO concentrations were high enough to enhance toxicity of pyrethroids already existing in creek sediments from general urban pesticide use. PBO concentrations of 2−4 μg/L were high enough to nearly double the toxicity of sediments to the amphipod Hyalella azteca. Though the increase in toxicity was modest, it was unexpected to find environmental synergy at all. Risk assessments for mosquito control agents have focused on the active ingredients but have failed to recognize the potential for interactions with pesticides previously existing in the environment, which in this case appeared to represent a risk to aquatic life greater than that of the active ingredients themselves. AuthorsWeston, Donald P., Amweg, Erin L., Mekebri, Abdou, Ogle, R. Scott and Lydy, Michael J. Year Published2006 PublicationEnvironmental Science & Technology LocationsDOI10.1021/es0601540 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/17007146 |
| Completeness of West Nile virus testing in patients with meningitis and encephalitis during an outbreak in Arizona, USA | WEBER, I. B. | 2012 |
KeywordsWNV AbstractAccurate 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 tested for WNV. Only 12 (28%) of 43 patients aged <0·01). Patients with clinical signs of weakness or paralysis, elevated CSF protein, admitted to an inpatient facility, or discharged to a rehabilitation facility were also more likely to have WNV testing performed. The lack of testing in younger age groups and in those with less severe disease probably resulted in substantial underestimates of WNV neuroinvasive disease burden. AuthorsWEBER, 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. Year Published2012 PublicationEpidemiology and Infection LocationsDOI10.1017/S0950268811002494 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/22123531 |
| Investigation of an outbreak of encephalomyelitis caused by West Nile virus in 136 horses | Ward, Michael P. | 2004 |
KeywordsWNV AbstractNo abstract available AuthorsWard, Michael P., Levy, Michel, Thacker, H. Leon, Ash, Marianne, Norman, Sandra K. L., Moore, George E. and Webb, Paul W. Year Published2004 PublicationJournal of the American Veterinary Medical Association LocationsDOI10.2460/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 Index | Ward, Michael P. | 2005 |
KeywordsWNV AbstractData 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. AuthorsWard, Michael P., Ramsay, Bruce H. and Gallo, Kevin Year Published2005 PublicationVector-Borne and Zoonotic Diseases LocationsDOI10.1089/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 horses | Ward, Michael P. | 2006 |
KeywordsEquine; West Nile virus; Epidemiology; Outbreak; Risk factors; Geostatistical analysis, WNV AbstractEquine 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%. AuthorsWard, Michael P., Schuermann, James A., Highfield, Linda D. and Murray, Kristy O. Year Published2006 PublicationVeterinary Microbiology LocationsDOI10.1016/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 Index | Ward, Michael P. | 2009 |
KeywordsWest Nile virus; Equine; Spatial; GIS; NDVI; Texas, WNV AbstractThe 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. AuthorsWard, Michael P. Year Published2009 PublicationPreventive Veterinary Medicine LocationsDOI10.1016/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 Texas | Ward, Michael P. | 2009 |
KeywordsWNV AbstractWest 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. AuthorsWard, Michael P., Wittich, Courtney A., Fosgate, Geoffrey and Srinivasan, Raghavan Year Published2009 PublicationVeterinary Research Communications LocationsDOI10.1007/s11259-008-9192-1 Additional Information:http://www.ncbi.nlm.nih.gov/pubmed/19031106 |
