A GIS tool to estimate West Nile virus risk based on a degree-day model.

West Nile virus (Flaviviridae: Flavivirus) is a serious infectious disease that recently spread across the North America continent. A spatial analysis tool was developed on the ArcMap 9.x platform to estimate potential West Nile virus activity using a spatially explicit degree-day model. The model identifies when the virus Extrinsic Incubation Period (EIP) is completed within the vector longevity during mid-summer months. The EIP is treated as a threshold indicator of the potential for virus emergence and activity. Comparing the number of West Nile virus cases in Wyoming reported from 2003 to 2005 with model results, actual cases and predicted events of West Nile virus activity match relatively well. The model represents a useful method for estimating potential West Nile virus activity in a large spatial scale.

A Rift Valley fever risk surveillance system for Africa using remotely sensed data: potential for use on other continents.

The authors developed a monitoring and risk mapping system using normalized difference vegetation index (NDVI) times series data derived from the advanced very high resolution radiometer (AVHRR) instrument on polar orbiting national oceanographic and atmospheric administration (NOAA) satellites to map areas with a potential for a Rift Valley fever (RVF) outbreaks in sub-Saharan Africa. This system is potentially an important tool for local, national and international organisations involved in the prevention and control of animal and human disease, permitting focused and timely implementation of disease control strategies several months before an outbreak. We are currently developing a geographic information system (GIS)-based remotely sensed early warning system for potential RVF vectors in the United States. Forecasts of the potential emergence of mosquito vectors will be disseminated throughout the United States, providing several months' warning in advance of potentially elevated mosquito populations. This would allow timely, targeted implementation of mosquito control, animal quarantine and vaccine strategies to reduce or prevent animal and human disease.

Mosquito larval habitat mapping using remote sensing and GIS: implications of coalbed methane development and West Nile virus.

Potential 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 approximately 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.

Risk factors associated with herd-level exposure of cattle in Nebraska, North Dakota, and South Dakota to bluetongue virus.

OBJECTIVE: To evaluate herd-level risk factors for seropositive status of cattle to 1 or more bluetongue viruses. ANIMALS: 110 herds of cattle in Nebraska, North Dakota, and South Dakota. PROCEDURE: Blood samples were collected before and after the vector season. Samples were tested for antibodies against bluetongue virus by use of a commercially available competitive ELISA. Factors evaluated included descriptors of geographic location and management practices. Trapping of insect vectors was conducted to evaluate vector status on a subset of 57 operations. A multivariable logistic regression model was constructed to evaluate associations. RESULTS: For the full data set, altitude and latitude were associated with risk of having seropositive cattle (an increase in altitude was associated with an increase in risk, and a more northerly location was associated with a decrease in risk of a premise having seropositive cattle). Import of cattle from selected states was associated with an increase in risk of having seropositive cattle. From the subset of herds with data on vector trapping, altitude and latitude were associated with risk of having seropositive cattle, similar to that for the full model. However, commingling with cattle from other herds was associated with a decrease in risk of seropositivity. CONCLUSIONS AND CLINICAL RELEVANCE: Findings reported here may be useful in generating additional hypotheses regarding the ecologic characteristics of bluetongue viruses and other vector-borne diseases of livestock. Sentinel surveillance programs are useful for documenting regionalization zones for diseases, which can be beneficial when securing international markets for animals and animal products.

Culture-independent analysis of midgut microbiota in the arbovirus vector Culicoides sonorensis (Diptera: Ceratopogonidae).

Differences in midgut microbial communities inhabiting Culicoides spp., insect vectors of virus pathogens, may affect the variation observed in the ability of these biting midges to propagate arthropod-borne viruses. As a first step toward addressing this hypothesis, midgut bacterial communities were compared between Culicoides species expected to be efficient and inefficient vectors of virus pathogens. We used 16S rDNA sequence and restriction fragment information to provisionally identify 36 bacterial genera from guts of wild adult female biting midges, Culicoides sonorensis Wirth and Jones and Culicoides variipennis (Coquillet), from two geographical locations. Bacterial identification was made by sequence analysis of 16S rDNA fragments and by terminal restriction fragment length polymorphism analysis of polymerase chain reaction-amplified 16S rDNA fragments from adult guts. Of 36 bacterial genera identified, 12 had been previously identified in other insects: Comomonas, Enterobacter, Klebsiella, Acinetobacter, Pseudomonas, Stenotrophomonas, Staphylococcus, Chryseobacterium, Moraxella, Acholeplasma, Flavobacterium, and Rickettsia, Significant differences in bacterial community composition were found between all three groups of wild adult females analyzed: live-trapped C. sonorensis, laboratory-emerged C. sonorensis, and laboratory-emerged C. variipennis.