Distribution Of West Nile Virus Research Articles

West Nile Virus Seroprevalence in a Selected Donkey Population of Namibia.

West Nile Virus (WNV) is a mosquito-borne virus enzootically maintained in birds. However, it can incidentally infect other species, leading to sometimes severe clinical consequences like in horses and especially human beings. Despite the topic relevance, the presence and distribution of WNV are currently unknown in Namibia. Several countries implement surveillance systems based on virus detection in birds, mosquitoes, and vertebrate species including horses. The present study aimed to fill this knowledge gap by serologically evaluating WNV exposure in Namibian donkeys, whose population is remarkably bigger than the horse one. Forty-seven out of 260 sampled animals showed neutralizing antibodies against WNV (18.07% [95% CI = 13.59–23.30%]), demonstrating its circulation in all country territory, although, with apparent regional differences. On the contrary, no association with animal age or sex could be identified. The present study demonstrates the widespread presence of WNV in Namibia as well as the practical utility and effectiveness of donkeys as sentinels for infection surveillance. Due to clinical relevance, vaccination campaigns should be considered for horses of high economic or genetic value. Additionally, the burden of WNV infection on human health should be carefully evaluated.

Flaviviruses at the territory of Serbia – present situation and challenges

The aim of this study is to summarize the data on the occurrence, presence and prevalence of some zoonotic flaviviruses, which have been actively circulating in the territory of the Republic of Serbia during past decade. The genus Flavivirus, family Flaviviridae,encompasses vector-transmitted viruses with zoonotic potential. The genus is comprised of more than 70 viruses transmitted to humans by mosquitoes and ticks. Some of those are associated only with human diseases (such as yellow fever and dengue fever), whereas others can cause diseases in both humans and animals. Animals are major reservoirs and primary hosts for the latter group. The virus transmission to other animal species or humans occurs via diverse vectors – mostly mosquitoes and ticks. A range of these virus species is widely distributed worldwide, especially in tropical and sub-tropical climatic zones. Some representatives of these species have only recently been identified at the territory of Republic of Serbia. This paper gives an evidence on the presence and distribution of West-Nile virus, tick-borne encephalitis (TBE) virus and Usutu virus that were conducted within the study in Serbia. The research pointed out the presence of recently detected West-Nile virus and Usutu virus as well as the current circulation of tick-borne encephalitis virus, for which only limited serological evidence on the presence of virus-specific antibodies in humans was available so far. In the aspect of public health, the full understanding of the importance of identification and prevalence of different flaviviruses still require further comprehensive entomologicalacarological, seroepidemiological, clinical and virological research.

Identifying Environmental Risk Factors and Mapping the Distribution of West Nile Virus in an Endemic Region of North America.

Understanding the geographic distribution of mosquito‐borne disease and mapping disease risk are important for prevention and control efforts. Mosquito‐borne viruses (arboviruses), such as West Nile virus (WNV), are highly dependent on environmental conditions. Therefore, the use of environmental data can help in making spatial predictions of disease distribution. We used geocoded human case data for 2004–2017 and population‐weighted control points in combination with multiple geospatial environmental data sets to assess the environmental drivers of WNV cases and to map relative infection risk in South Dakota, USA. We compared the effectiveness of (1) land cover and physiography data, (2) climate data, and (3) spectral data for mapping the risk of WNV in South Dakota. A final model combining all data sets was used to predict spatial patterns of disease transmission and characterize the associations between environmental factors and WNV risk. We used a boosted regression tree model to identify the most important variables driving WNV risk and generated risk maps by applying this model across the entire state. We found that combining multiple sources of environmental data resulted in the most accurate predictions. Elevation, late‐season humidity, and early‐season surface moisture were the most important predictors of disease distribution. Indices that quantified interannual variability of climatic conditions and land surface moisture were better predictors than interannual means. We suggest that combining measures of interannual environmental variability with static land cover and physiography variables can help to improve spatial predictions of arbovirus transmission risk.

Focal amplification and suppression of West Nile virus transmission associated with communal bird roosts in northern Colorado.

To explain the patchy distribution of West Nile virus (WNV), we propose that avian immunity encountered by Culex vectors regulates WNV transmission, particularly at communal bird roosts. To test this hypothesis, we selected two test sites with communally roosting American robins (Turdus migratorius) and two control sites that lacked communal roosts. The density of vector-vertebrate contacts, represented by engorged Culex pipiens, was 23-fold greater at test sites compared to control sites, and the density of blood-engorged Cx. pipiens measured in resting mosquito traps correlated positively with the presence of robins and negatively with the presence of other birds, confirming an attraction to robins for blood feeding. WNV transmission was alternately up-regulated (amplification) and down-regulated (suppression) at both test sites. At one test site, infection in resting Cx. pipiens surged from zero to 37.2 per thousand within four weeks, and robin immunity rose from 8.4% to 64% before reducing to 33%. At this site, ten potentially infectious contacts between vector and vertebrates (including nine robins and a mourning dove [Zenaida macroura]) were documented. Infectious vector-vertebrate contacts were absent from control sites. The use of infectious vector-vertebrate contacts, rather than infected mosquitoes, to evaluate a transmission focus is novel.

Seroprevalence, risk factors and spatial distribution of West Nile virus in Jordan.

This is the first countrywide study of the seroprevalence, risk factors and spatial distribution of West Nile virus (WNV) in Jordan. A cross-sectional sample of 801 participants was administered a comprehensive questionnaire survey and tested for WNV immunoglobulin G antibodies. The point seroprevalence rate for WNV infection was 8.61% (95% confidence interval 6.8 to 10.8). Multivariate regression analysis demonstrated that sex, age, climate, income and drinking water source were significantly associated with seropositivity (p≤0.05). Males had 1.73 greater odds of infection compared with females. Compared with 15 to 29-year-olds, adults 30-49 y old and adults ≥50 y old had 2.0 and 3.1 greater odds of infection, respectively. Individuals living in the Jordan Valley and Badia had 22.2 and 7.2 times greater odds of infection, respectively, compared with individuals living in the highlands. Households with an income of <US$750/month had 1.8 greater odds of infection compared with those with higher household incomes. Individuals using spring lakes as a drinking water source had 5.1 greater odds of infection than people who used water from any other source. This study demonstrates that WNV is circulating in Jordan and should be considered as a differential diagnosis in medical cases presenting with nervous system symptoms, especially for older populations living in the Jordan Valley and Badia areas.

Exposure to West Nile virus and tick-borne encephalitis virus in dogs in Spain.

In the past decade, the spread of emerging zoonotic flaviviruses (genus Flavivirus, family Flaviviridae) has been reported in many regions worldwide, representing a threat to both human and animal health. A serosurvey was carried out to assess exposure and risk factors associated with antigenically related flaviviruses, particularly West Nile virus (WNV), Usutu virus (USUV) and tick-borne encephalitis virus (TBEV), in dogs in Spain. Flavivirus antibodies were detected in 39 of 815 dogs (4.8%; 95% CI: 3.3-6.3) by bELISA. Significantly higher seropositivity was observed in hunting dogs compared to pet dogs. Virus neutralization tests confirmed WNV-specific and TBEV-specific antibodies in 11 and 14 bELISA-positive dogs, respectively. This is the first serosurvey of WNV and TBEV in dogs in Spain and the first report of TBEV circulation in this country. The seropositivity obtained indicates widespread, but not homogeneous, distribution of WNV and TBEV in dogs in Spain. In 2013 and 2015, WNV-seropositive dogs were detected in those areas of Andalusia where the highest number of WNV outbreaks were reported in both horses and humans. Antibodies against TBEV have been found in dogs sampled in two different periods and regions in Spain. Serosurveillance in dogs could be a complementary way of monitoring the activity of emerging flaviviruses in Spain.

Spatial distribution of West Nile virus in humans and mosquitoes in Israel, 2000–2014

ObjectivesIsrael has a long history of West Nile virus (WNV) morbidity, and the rate of detection of WNV in mosquitoes has been high since 2000. The aim of this study was to integrate several WNV datasets in order to gain an insight into the geographical distribution of WNV in Israel. MethodsThree choropleth maps were generated showing WNV human morbidity, WNV prevalence in mosquitoes, and the results of a nationwide serological survey, based on the division of Israel into 15 sub-districts. ResultsThe maps show a high endemicity of WNV in Israel. In respect to the morbidity map, the population residing in the central part of the country and in Arava Region is at higher risk of developing the disease than the population of the rest of Israel. Interestingly, high prevalence rates of both WNV serology and WNV-infected mosquitoes were detected in Arava Region, but lower prevalence rates were detected in most areas of the coastal region, suggesting that other factors might also be important in the development of symptomatic WNV infections. ConclusionsThese results underline the high prevalence of WNV in Israel and point to specific risk areas for WNV infections across the country.

The study of the area of distribution of west nile virus in the territory of the European part of Russia; the results of seroepidemiological research. report 1: Astrakhan region, Krasnodar region, Stavropol region, Saratov region

Sera of inhabitants of the European part of Russia, collected in 2010-2013 were studied with the use of ELISA and neutralization test. Antibodies to West Nile virus were detected in 19.6% of cases in the Astrakhan region, 4.5% - in the Krasnodar region, 0.9% - in the Saratov region and 5.4% - in the Stavropol region. The coincidence of the results of the examination of sera in ELISA-IgG and neutralization test accounted of 80.7% in the Astrakhan region, 72.2% - in the Krasnodar region and 69.2% - in the Saratov region. The presented results correlate with the incidence and duration of known epidemiological activity of West Nile fever in the territories of these regions. Analysis of our data, as well as statistics of the morbidity rate of West Nile fever in the Volgograd and Rostov regions and Dagestan confirm endemic and expanding foci of this infection in the southern regions of Russia, currently including Astrakhan, Volgograd, Rostov, Saratov, Krasnodar and Stavropol regions and Dagestan. The most active and stable foci are located on the territory of Astrakhan, Volgograd and Rostov regions.

Evaluation of the Control of West Nile Virus in Ontario: Did Risk Patterns Change from 2005 to 2012?

The goal of this study was to evaluate and compare the risk distribution of human cases of West Nile virus (WNV) disease in Ontario in 2005 to 2012. The objectives were to: map the risk distribution of WNV in 2005 and 2012, identify clusters of human WNV disease and determine whether the clusters are significantly different between the years 2005 and 2012. West Nile virus surveillance data were used to calculate empirical Bayesian smoothed estimates of disease incidence in southern Ontario for 2005 and 2012. Choropleth maps were generated to visualize the spatial risk distribution, and the spatial scan test was performed to identify clusters of disease. Following identification of clusters for 2005 and 2012, a Poisson model was applied to the 2012 human WNV incidence adjusted for the smoothed human WNV incidence rate from 2005 and the scan test was repeated. Two significant clusters were identified in both the year 2005 and 2012. In 2005, the primary cluster was located in the Windsor-Essex and Chatham-Kent public health units (PHUs). For 2012, the primary cluster was identified in the Golden Horseshoe area. A cluster analysis for 2012 adjusted for those identified in 2005 resulted in one significant cluster in the Windsor-Essex PHU. In 2012, the Windsor-Essex PHU remained as a high-risk area for human WNV disease when compared with the rest of southern Ontario. Although overall risk may change from year to year, public health programming should be employed to decrease the relative risk of WNV in this area.

Climate change impacts on West Nile virus transmission in a global context.

West Nile virus (WNV), the most widely distributed virus of the encephalitic flaviviruses, is a vector-borne pathogen of global importance. The transmission cycle exists in rural and urban areas where the virus infects birds, humans, horses and other mammals. Multiple factors impact the transmission and distribution of WNV, related to the dynamics and interactions between pathogen, vector, vertebrate hosts and environment. Hence, among other drivers, weather conditions have direct and indirect influences on vector competence (the ability to acquire, maintain and transmit the virus), on the vector population dynamic and on the virus replication rate within the mosquito, which are mostly weather dependent. The importance of climatic factors (temperature, precipitation, relative humidity and winds) as drivers in WNV epidemiology is increasing under conditions of climate change. Indeed, recent changes in climatic conditions, particularly increased ambient temperature and fluctuations in rainfall amounts, contributed to the maintenance (endemization process) of WNV in various locations in southern Europe, western Asia, the eastern Mediterranean, the Canadian Prairies, parts of the USA and Australia. As predictions show that the current trends are expected to continue, for better preparedness, any assessment of future transmission of WNV should take into consideration the impacts of climate change.

Spatial and temporal distribution of West Nile virus in horses in Israel (1997-2013)--from endemic to epidemics.

With the rapid global spread of West Nile virus (WNV) and the endemic state it has acquired in new geographical areas, we hereby bring a thorough serological investigation of WNV in horses in a longstanding endemic region, such as Israel. This study evaluates the environmental and demographic risk factors for WNV infection in horses and suggests possible factors associated with the transition from endemic to epidemic state. West Nile virus seroprevalence in horses in Israel was determined throughout a period of more than a decade, before (1997) and after (2002 and 2013) the massive West Nile fever outbreak in humans and horses in 2000. An increase in seroprevalence was observed, from 39% (113/290) in 1997 to 66.1% (547/827) in 2002 and 85.5% (153/179) in 2013, with persistent significantly higher seroprevalence in horses situated along the Great Rift Valley (GRV) area, the major birds' migration route in Israel. Demographic risk factors included age and breed of the horse. Significantly lower spring precipitation was observed during years with increased human incidence rate that occurred between 1997–2007. Hence, we suggest referring to Israel as two WNV distinct epidemiological regions; an endemic region along the birds' migration route (GRV) and the rest of the country which perhaps suffers from cyclic epidemics. In addition, weather conditions, such as periods of spring drought, might be associated with the transition from endemic state to epidemic state of WNV.

Towards an early warning system for forecasting human west nile virus incidence.

We have identified environmental and demographic variables, available in January, that predict the relative magnitude and spatial distribution of West Nile virus (WNV) for the following summer. The yearly magnitude and spatial distribution for WNV incidence in humans in the United States (US) have varied wildly in the past decade. Mosquito control measures are expensive and having better estimates of the expected relative size of a future WNV outbreak can help in planning for the mitigation efforts and costs. West Nile virus is spread primarily between mosquitoes and birds; humans are an incidental host. Previous efforts have demonstrated a strong correlation between environmental factors and the incidence of WNV. A predictive model for human cases must include both the environmental factors for the mosquito-bird epidemic and an anthropological model for the risk of humans being bitten by a mosquito. Using weather data and demographic data available in January for every county in the US, we use logistic regression analysis to predict the probability that the county will have at least one WNV case the following summer. We validate our approach and the spatial and temporal WNV incidence in the US from 2005 to 2013. The methodology was applied to forecast the 2014 WNV incidence in late January 2014. We find the most significant predictors for a county to have a case of WNV to be the mean minimum temperature in January, the deviation of this minimum temperature from the expected minimum temperature, the total population of the county, publicly available samples of local bird populations, and if the county had a case of WNV the previous year.

Towards an early warning system for forecasting human west nile virus incidence.

We have identified environmental and demographic variables, available in January, that predict the relative magnitude and spatial distribution of West Nile virus (WNV) for the following summer. The yearly magnitude and spatial distribution for WNV incidence in humans in the United States (US) have varied wildly in the past decade. Mosquito control measures are expensive and having better estimates of the expected relative size of a future WNV outbreak can help in planning for the mitigation efforts and costs. West Nile virus is spread primarily between mosquitoes and birds; humans are an incidental host. Previous efforts have demonstrated a strong correlation between environmental factors and the incidence of WNV. A predictive model for human cases must include both the environmental factors for the mosquito-bird epidemic and an anthropological model for the risk of humans being bitten by a mosquito. Using weather data and demographic data available in January for every county in the US, we use logistic regression analysis to predict the probability that the county will have at least one WNV case the following summer. We validate our approach and the spatial and temporal WNV incidence in the US from 2005 to 2013. The methodology was applied to forecast the 2014 WNV incidence in late January 2014. We find the most significant predictors for a county to have a case of WNV to be the mean minimum temperature in January, the deviation of this minimum temperature from the expected minimum temperature, the total population of the county, publicly available samples of local bird populations, and if the county had a case of WNV the previous year.

Modeling Monthly Variation of Culex tarsalis (Diptera: Culicidae) Abundance and West Nile Virus Infection Rate in the Canadian Prairies

The Canadian prairie provinces of Alberta, Saskatchewan, and Manitoba have generally reported the highest human incidence of West Nile virus (WNV) in Canada. In this study, environmental and biotic factors were used to predict numbers of Culex tarsalis Coquillett, which is the primary mosquito vector of WNV in this region, and prevalence of WNV infection in Cx. tarsalis in the Canadian prairies. The results showed that higher mean temperature and elevated time lagged mean temperature were associated with increased numbers of Cx. tarsalis and higher WNV infection rates. However, increasing precipitation was associated with higher abundance of Cx. tarsalis and lower WNV infection rate. In addition, this study found that increased temperature fluctuation and wetland land cover were associated with decreased infection rate in the Cx. tarsalis population. The resulting monthly models can be used to inform public health interventions by improving the predictions of population abundance of Cx. tarsalis and the transmission intensity of WNV in the Canadian prairies. Furthermore, these models can also be used to examine the potential effects of climate change on the vector population abundance and the distribution of WNV.

Dispersal ofCulexMosquitoes (Diptera: Culicidae) From a Wastewater Treatment Facility

A mark-recapture project examined dispersal and flight distances of Culex mosquitoes from a wastewater treatment plant in Albany, NY, during 2007 and 2008. A self-marking device was constructed to mark egressing mosquitoes with fluorescent marking powder. Mosquitoes were recaptured using 30 CDC miniature light traps located within a 2.0 km radius of the marking site. A total of 13 and 10 marked Culex mosquitoes were recaptured in 2007 and 2008, respectively. Culex mosquitoes traveled a minimum of 0.16 km, a maximum of 1.98 km and, following correction for decreasing trap density with distance, had a mean distance traveled of 1.33 km. Characterizing the dispersal patterns of these mosquitoes is important for understanding the distribution of West Nile virus and other pathogens.

Meteorological and Hydrological Influences on the Spatial and Temporal Prevalence of West Nile Virus in &lt;I&gt;Culex&lt;/I&gt; Mosquitoes, Suffolk County, New York

The factors determining the spatial and temporal distribution of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) activity are not well understood. Here, we explore the effects of hydrological and meteorological conditions on WNV infection among Culex genus mosquitoes collected during 2001-2009 in Suffolk County, Long Island, NY. We show that WNV infection rates in assayed pools of Culex mosquitoes are associated in both space and time with hydrological and meteorological variability. Specifically, wet winter, warm and wet spring conditions, and dry summer conditions are associated with the increased local prevalence of WNV among Culex mosquitoes during summer and fall. These findings indicate that within Suffolk County, and for a given year, areas at risk for heightened WNV activity may be identified in advance by using hydrology model estimates of land surface wetness and observed meteorological conditions.

Using Volunteered Geographic Information to Assess the Spatial Distribution of West Nile Virus in Detroit, Michigan

West Nile Virus is a vector-borne flavivirus that affects mainly birds, horses, and humans. The disease emerged in the United States in 1999 and by 2001 had reached Michigan. In clinical human cases, the most common symptoms are fever, weakness, nausea, headache, and changes in mental state. The crow is the most common wildlife host in the life cycle of the virus. The state of Michigan, through the Michigan Department of Community Health, collected the spatial locations of over 8,000 dead birds (Corvidae), statewide, during 2002. The large number of samples made spatial and temporal hotspot detection possible. However, the volunteer reporting method produced a dataset with a direct correlation between the numbers and locations of the dead birds and human population density and accurately identifying hotspots remains a challenge. Geographic variation in dead bird intensity was modeled using both global and local spatial clustering algorithms. Statistical models identified overall spatial structure and local clustering. Identification of hotspots was confounded by limited information about the collection procedures, data availability and quality, and the limitations of each method.

Temporal Variations in the Distribution of West Nile Virus Within the United States; 2000-2008.

West Nile Virus (WNV) is a serious illness that has affected thousands of people in the United States. Over 1,000 disease related deaths have occurred since its introduction to American soil in 1999. Spatial statistics are used to analyze distributional trends of human WNV cases from 2000 to 2008 through four analyses: Weighted Mean Center, Standard Deviational Ellipses, Global Moran’s I, and Getis-Ord-Gi* statistic (hot spot analysis). We conclude that the directional trend in cases has been from East to West with the area affected increasing with time. Hot spot analysis reveals that recurring counties with a high number of human cases have been in the metro areas of large cities. However, normalized results indicate that the rate of humans showing symptoms of WNV is greatest in rural areas, particularly the Great Plains. These results provide a foundation for future research in analyzing the most persistent hot spots in more detail. Furthermore, these findings may aid decision makers in identifying areas to target for mitigation strategies such as spraying, larval control, and public awareness.

Antigenic distribution of west nile virus in various organs of wildly infected American crows (Corvus Brachyrhynchos)

Objective:Since its discovery in the western hemisphere in 1999, West Nile virus (WNv) has caused extensive bird mortality across North America, especially in American crows (Corvus brachyrhynchos) which are highly susceptible to WNv. In this study, antigenic distribution of WNv among different organs of American crows was studied, using the immunohistochemistry technique (IHC).Materials and Methods:Dead crows reported by residents were collected, transported on ice, and were necropsied for heart, lung, brain, intestine, kidney, liver, spleen, pancreas, and gonad tissues. Gross examination was performed on brain, heart, lung, liver, kidney, spleen, bursa of fabricius, gastrointestinal tract, skeletal muscle, pancreas, reproductive tract, and skin. Gross hemorrhage of brain, splenomegaly, meningoencephalitis, myocarditis, and trauma were sporadically observed in some of the infected carcasses. Formalin-fixed paraffin-embedded tissue sections were stained with IHC technique followed by counter staining with hematoxylin and eosin.Results:WNv antigen was detected in brain, spleen, heart, kidney, liver, gonads, intestine, lung, and pancreas. The spleen was found to be positive in all infected crows, followed by kidney, liver, and duodenum (95% each). Heart and pancreas were positive in 63% while brain was positive in 36.5% of the infected crows.Conclusion:More than one tissue sample is suggested to screen WNv infection using IHC technique. IHC has the advantage of correlating the visual destruction of tissue architecture with the presence of stained WNv antigen but as compared to PCR, IHC has the disadvantage of longer turnaround time, which is critical when used as a surveillance tool.

Geographic distribution of West Nile virus reported in humans and corvids in southern Ontario, 2006

This study analyzes the spatial risk distribution of West Nile virus (WNv) in humans and birds across southern Ontario for 2006. The relationship between bird and human risk is also investigated. Surveillance data was obtained for the number of human WNv cases and the fraction of dead birds testing positive in each public health unit. The presence of disease clustering in humans and birds was investigated using a spatial scan test. Choropleth risk maps of regional empirical Bayesian smoothed estimates were created to investigate the spatial distribution of WNv in humans and birds. Isopleth risk maps were created through kriging of smoothed estimates, and were used to identify high-risk areas as well as investigate the relationship between human and bird risk. One disease cluster was found in both humans and birds. The human disease cluster was not significant when the bird data was used as a covariate in the analysis. The choropleth and isopleth maps identified the southern portion of southern Ontario to be the highest risk area for both humans and birds. This study indicates that bird outbreaks are a potential indicator for an increase in human risk. As well, WNv risk is greatest in the southern portion of southern Ontario and is geographically spreading in comparison to previous years.