Prevalence Of West Nile Virus Infection Research Articles

Effect of climate change on West Nile virus transmission in Italy: a systematic review

Abstract Background West Nile Virus (WNV) is a pathogen transmitted by mosquitoes of the Culex genus, affecting both humans and animals such as horses and birds. The prevalence of WNV infection has increased dramatically in recent years in Europe, especially in Italy, and has been related to climate and environmental changes linked to global warming. Our review aims to assess the relation between the spread of WNV in Italy and the different climate change-related factors. Methods We conducted a literature search in the PubMed, Web of Science, Embase and Scopus databases, actualised as of 20 February 2024, using as search terms WNV, its vectors and climate change, and limiting our analysis to studies conducted in to avoid an overly heterogeneous setting. We registered the review in PROSPERO (CRD42023430636). Results Of the 252 unique records retrieved, we eventually included 25 articles after full-text screening. These studies were published between 2011 and 2023 and evaluated the distribution of WNV or its vectors according to various climatic and environmental factors. Despite rather heterogeneous results, we found a consistently positive association with temperature, especially spring temperature, agricultural land use, demography, and soil moisture, and a negative one with evapotranspiration and wind, while the relationship with other environmental variables and water cycle-related factors was weak, null or conflicting. Conclusions Despite some inconsistencies in the results, likely related to differences in study methodologies as well as complex environmental interactions, we found unequivocal evidence that climate change-related factors, such as the lengthening of the warm season, extensive farming, and invasive human activities towards natural environments, favour WNV spread in Italy. Consequently, actions against global warming and preservation of natural environments may counteract the WNV epidemic. Key messages • WNV epidemic seems to be linked to specific climate change-related factors, such as the lengthening of the warm season, extensive farming, and invasive human activities towards natural environments. • Actions against global warming and preservation of natural environments may counteract WNV spread.

First detection of WNV RNA presence in field-collected mosquitoes in Cyprus

West Nile virus (WNV) infections have increased over recent years to the extent that WNV has become one of the most widespread arboviruses in the world, with potential consequences for both human and animal health. While much is known about WNV and the vectors that transmit it from their primary hosts across continental Europe, little is known about the epidemiology of the disease on the island of Cyprus. In this study, the aim was to investigate the prevalence of WNV infection in potential mosquito vectors for the first time in the Republic of Cyprus, using WNV surveillance of mosquitoes. Mosquitoes were collected in 2019, during which an outbreak in humans had occurred, and sampled mosquitoes were then examined for WNV infection by testing them for the presence of WNV RNA. Of 126 mosquito pools tested, one pool, containing Culex pipiens mosquitoes sampled from the Nicosia district, was found to be positive for the presence of WNV RNA. The positive pool found in this study represents the first demonstration of WNV in mosquitoes in Cyprus and confirms that human cases in Cyprus are likely the result of transmission via local Culex mosquitoes.

Emergence and Associated Risk Factors of Vector Borne West Nile Virus In¬fection in Ilorin, Nigeria

West Nile Virus (WNV) is a mosquito-borne viral pathogen that is the causative agent of West Nile fever and encephalitis. Diagnostic tools for WNV infection in Nigeria are not well established hence the current prevalence rate of WNV infection in Nigeria is unknown. We aimed to establish the serological prevalence of WNV infection in febrile patients in Ilorin, Nigeria in 2016, and to assess the risk factors associated with the acquisition of the virus. This was a cross-sectional study involving the screening of subjects presenting with febrile illnesses. While specific IgM ELISA was used to determine the seroprevalence, a closed-ended questionnaire was used to ascertain the risk factors associated with this viral infection. Fifteen (7.5%) of the respondents were positive for WNV infection. Subjects living in areas in close proximity to trees and bushes (P= 0.011) and stagnant water (P= 0.001) were at a higher risk of having WNV infection. Other risk factors associated with WNV among the respondents include the none use of insecticide (P= 0.001), sitting out at night (P= 0.044), HIV positivity (P= 0.003) and having an organ transplant (P= 0.002). This study clearly shows a considerable WNV infection in Ilorin, with the presence of factors that can promulgate an outbreak, hence a need for further surveillance in the study area.

Climate change projections of West Nile virus infections in Europe: implications for blood safety practices.

BackgroundWest Nile virus (WNV) is transmitted by mosquitoes in both urban as well as in rural environments and can be pathogenic in birds, horses and humans. Extrinsic factors such as temperature and land use are determinants of WNV outbreaks in Europe, along with intrinsic factors of the vector and virus.MethodsWith a multivariate model for WNV transmission we computed the probability of WNV infection in 2014, with July 2014 temperature anomalies. We applied the July temperature anomalies under the balanced A1B climate change scenario (mix of all energy sources, fossil and non-fossil) for 2025 and 2050 to model and project the risk of WNV infection in the future. Since asymptomatic infections are common in humans (which can result in the contamination of the donated blood) we estimated the predictive prevalence of WNV infections in the blood donor population.ResultsExternal validation of the probability model with 2014 cases indicated good prediction, based on an Area Under Curve (AUC) of 0.871 (SD = 0.032), on the Receiver Operating Characteristic Curve (ROC). The climate change projections for 2025 reveal a higher probability of WNV infection particularly at the edges of the current transmission areas (for example in Eastern Croatia, Northeastern and Northwestern Turkey) and an even further expansion in 2050. The prevalence of infection in (blood donor) populations in the outbreak-affected districts is expected to expand in the future.ConclusionsPredictive modelling of environmental and climatic drivers of WNV can be a valuable tool for public health practice. It can help delineate districts at risk for future transmission. These areas can be subjected to integrated disease and vector surveillance, outreach to the public and health care providers, implementation of personal protective measures, screening of blood donors, and vector abatement activities.Electronic supplementary materialThe online version of this article (doi:10.1186/s12940-016-0105-4) contains supplementary material, which is available to authorized users.

WEST NILE VIRUS-RELATED TRENDS IN AVIAN MORTALITY IN CALIFORNIA, USA, 2003-12.

West Nile virus (WNV) is an arbovirus transmitted enzootically by Culex mosquitoes among avian hosts. Since 2000, the California Dead Bird Surveillance Program (DBSP) has tracked avian mortality reported by the public on a telephone hotline and website and measured the prevalence of WNV infection in dead birds. We summarize herein WNV prevalence in dead birds tested and variation of WNV transmission over time and space with the use of DBSP data from 2003 to 2012. Prevalence among dead birds was highest in 2004, 2008, and 2012. This pattern was similar to peak WNV infection years for mosquitoes but not to human WNV incidence. Although American Crows (Corvus brachyrhynchos) were most frequently reported and tested, this species ranked third in infection prevalence (44%) after Yellow-billed Magpies (Pica nuttalli; 62%) and Western Scrub-Jays (Aphelocoma californica; 48%). Overall prevalence in American Robin (Turdus migratorius), House Finch (Haemorhous mexicanus), and House Sparrow (Passer domesticus) carcasses ranged from 18% to 22%. Corvid WNV prevalence was highest in South Coast, Bay/Delta, Sacramento, and San Joaquin valleys, and Klamath/North Coast bioregions, overlapping areas of elevated WNV activity in other surveillance measurements. Bioregional analysis revealed the avian species most likely to be reported and found positive in each bioregion. Our results may be useful to WNV surveillance and control efforts and provide insight into bird population trends in California.

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.

West Nile Virus Prevalence across Landscapes Is Mediated by Local Effects of Agriculture on Vector and Host Communities

Arthropod-borne viruses (arboviruses) threaten the health of humans, livestock, and wildlife. West Nile virus (WNV), the world’s most widespread arbovirus, invaded the United States in 1999 and rapidly spread across the county. Although the ecology of vectors and hosts are key determinants of WNV prevalence across landscapes, the factors shaping local vector and host populations remain unclear. Here, we used spatially-explicit models to evaluate how three land-use types (orchards, vegetable/forage crops, natural) and two climatic variables (temperature, precipitation) influence the prevalence of WNV infections and vector/host distributions at landscape and local spatial scales. Across landscapes, we show that orchard habitats were associated with greater prevalence of WNV infections in reservoirs (birds) and incidental hosts (horses), while increased precipitation was associated with fewer infections. At local scales, orchard habitats increased the prevalence of WNV infections in vectors (mosquitoes) and the abundance of mosquitoes and two key reservoir species, the American robin and the house sparrow. Thus, orchard habitats benefitted WNV vectors and reservoir hosts locally, creating focal points for the transmission of WNV at landscape scales in the presence of suitable climatic conditions.

Serologic Evidence of West Nile Virus Infection among Humans, Morocco

To the Editor: West Nile virus (WNV) infections were reported in horses in Morocco in 1996, 2003 (1), and 2010 (2). The isolates from 1996 and 2003 belong to WNV lineage 1, clade 1a (1). In 1996, WNV infection was reported in a human in Morocco (3), and in 2008, a serosurvey of wild birds confirmed the circulation of WNV in native birds (4). To our knowledge, there are no seroprevalence data for WNV antibodies in humans in Morocco. Thus, we evaluated the prevalence of WNV neutralizing bodies in serum samples collected during March–April 2011 from 499 healthy persons living in the vicinities of Meknes, Rabat, or Kenitra. All persons consented to study participation. The participants were divided into 3 cohorts, A, B, and C. Cohort A consisted of 150 persons from the Meknes area, where no WNV infections among horses have been reported. The mean age of persons in cohort A was 52 years (SD ± 15 years), and 31% were male. Cohort B consisted of 200 persons living in the region of Rabat (median age 49 years [SD ± 12 years]; 38% male), where the WNV outbreaks among horses were described in 1996 (3) and 2010 (2). Cohort C consisted of 149 participants living in the region of Kenitra (median age 48 years [SD ± 17 years]; 43% male), which was affected by the WNV outbreaks among horses in 1996, 2003, and 2010. Serum was stored at −20°C until tested. Just before testing, serum samples were heated at 56°C for 30 minutes. The samples were screened for neutralizing antibody against the equine WNV strain, Morocco 96–111 (3), by using a micro virus-neutralization test in 96-well plates and an adaptation of a described method (5). Dilutions of test serum (50 µL) were incubated with one hundred 50% tissue culture infectious doses of the virus in the same volume (50 μL) for 1 hour at 37°C in Dulbecco minimum Eagle medium. We then added 150 μL (105 cells/mL) of a Vero cell suspension with 5% fetal calf serum. This mixture was incubated for 5–6 days at 37°C until cytopathic effects were observed in a negative control well containing a 50% tissue culture infectious dose of virus. Serum samples were screened in duplicate at dilutions of 1:6, 1:18, and 1:54. Samples that neutralized the virus, characterized by absence of cytopathic effects, at 1 of the dilutions tested were retested in 4 replicates to confirm the result. We then titrated the samples by testing 6 serial dilutions ranging from 1:6 to 1:1,458. Titers were calculated by using the Spearman-Karber method (6). Titers >18 were considered positive. Of the 499 participants, 59 (11.8%) had WNV neutralizing bodies (7 of 150 in cohort A, 24 of 200 in cohort B, and 28 of 149 in cohort C). Titers determined by the micro virus-neutralization test ranged from 18 to 2,630 (Table).The prevalence of WNV neutralizing bodies was significantly higher in cohort B and C participants than in cohort A participants (p<0.01). A significant correlation was not observed between the presence of WNV neutralizing bodies and the age or sex of participants. Table West Nile virus neutralizing antibody titers in human serum samples obtained during March–April 2011, Morocco The low prevalence of WNV neutralizing antibodies (4.7%; median ± SD titer 54 ± 42.5) in persons from Meknes (cohort A) suggests a low level of WNV circulation in the area. This finding is likely related to the ecosystem of this region (arid and semi-arid, with an average altitude of 500 m), which is unfavorable for survival of the vectors. Infections are more likely the result of travel to areas where WNV is endemic. In persons from Rabat (cohort B), the medium prevalence reported (12%; median ± SD titer 54 ± 31) confirms human infection with epidemic WNV strains found in horses during WNV epidemics of 1996 and 2010. However, this prevalence is lower than that for persons in Kenitra (cohort C) (18.8%; median titer 95 ± 72). High titers were obtained in cohort C, which is located in an extremely humid area that includes several wetlands and rice fields flooded through regulated channels from the Sebou River. In addition, this region includes 2 natural bird reserves along a principal migratory Europe–sub-Saharan route. These conditions are favorable for WNV circulation and are likely related to the high prevalence of WNV infection registered in this region. We found evidence for local circulation of WNV in Morocco. The Moroccan WNV strains most often cause mild and self-limiting illnesses. These illnesses are difficult to distinguish from many other febrile illnesses, making it less likely that viral testing would be performed for WNV. Our results show that WNV is an emerging disease in Morocco, and a national response plan should be implemented by public health authorities.

Avian Hosts of West Nile Virus in Puerto Rico

West Nile virus (WNV) ecology in neotropical ecosystems is poorly understood, and vertebrate hosts responsible for infecting mosquitoes remain unidentified throughout the Caribbean Basin. After a period of intense WNV transmission among sentinel chickens near Ceiba, Puerto Rico, we measured abundance of resident birds and species-specific prevalence of WNV infection. Taking the product of these measures indicates the relative number of WNV infections by species. Greater Antillean grackle (Quiscalus niger) accounted for the most WNV infections among birds in our 100-km(2) study site. In urban habitats, the house sparrow (Passer domesticus) was frequently infected. Immature birds less than one year of age were more likely to have detectable WNV-reactive antibodies than older birds of the same species.

No evidence of West Nile virus infection in Dutch blood donors

West Nile virus (WNV) can be transmitted by transfusion through infected blood components. This study aimed to determine the prevalence of WNV infection among Dutch blood donors to assess whether WNV is a possible threat for the Dutch blood supply. Plasma samples from 61 992 blood donations were pooled in 7,749 test pools of eight donations using a Tecan robot. These samples were collected between April and October 2004. The pools were tested for the presence of WNV RNA by using the Procleix WNV assay. No WNV RNA-positive pools were detected. Based on Poisson distribution statistics, extrapolation of our data to all the Dutch donations in 2004 revealed that between 0 and 55 cases of WNV infection could be expected. No evidence of the presence of WNV RNA in Dutch blood donor samples from 2004 was found. However, surveillance of this emerging infection is of importance to safeguard the blood supply in the future because the transmission cycle of WNV is complex and hard to predict.

Serologic Evidence of West Nile Virus Infection in Three Wild Raptor Populations

We assayed for West Nile virus (WNV) antibodies to determine the presence and prevalence of WNV infection in three raptor populations in southeast Wisconsin during 2003-04. This study was conducted in the framework of ongoing population studies that started before WNV was introduced to the study area. For 354 samples, 88% of 42 adult Cooper's hawks (Accipiter cooperii), 2.1% of 96 nestling Cooper's hawks, 9.2% of 141 nestling red-tailed hawks (Buteo jamaicensis), and 12% of 73 nestling great horned owls (Bubo virginianus) tested positive for WNV antibodies by the constant virus-serum dilution neutralization test. Samples that tested positive for WNV antibodies were collected across a wide variety of habitat types, including urban habitats (both high and low density), roads, parking areas, recreational areas, croplands, pastures, grasslands, woodlands, and wetlands. Based on the increased prevalence and significantly higher WNV antibody titers in adults compared with nestlings, we suggest that nestlings with detectable antibody levels acquired these antibodies through passive transmission from the mother during egg production. Low levels of WNV antibodies in nestlings could serve as a surrogate marker of exposure in adult raptor populations. Based on breeding population densities and reproductive success over the past 15 yr, we found no apparent adverse effects of WNV infections on these wild raptor populations.

Seroepidemiological study of infection with West Nile virus in Karachi, Pakistan, in 1983 and 1985.

The prevalence of West Nile (WN) virus infection in Karachi, Pakistan, was unknown until 1982. It had been noticed that there were more than a few patients with encephalitides in Karachi, and it was supposed that Japanese encephalitis (JE) cases would be found among them. Therefore, a seroepidemiological study was conducted to define the prevalence of WN virus infection and the possible occurrence of JE virus infection in the Karachi area. Prevalences of haemagglutination inhibition (HI) and neutralization (NT) antibodies against WN virus were studied among 81 serum samples (in July, 33 samples; in September, 48) during 1983, and among 156 paired serum samples that were collected twice, in July and October of 1985. Nearly the same antibody-positive rates were obtained in July of both years (1983: HI 55%; 1985: HI 53%; NT 50%); the rates increased slightly during September/October (1983: HI 65%; 1985: HI 59%, NT 54%). Among 156 paired samples in 1985, 20 (13%) and 12 (8%) showed positive- or negative-antibody conversion between July and October. Two serum samples from each of 156 residents obtained in July had a significantly higher NT antibody titre against JE virus than against WN virus (in case 1, JE 1:80, WN less than 1:10; in case 2, JE 1:40, WN less than 1:10). This is the first report to show the prevalence of WN virus infection in Karachi, Pakistan.

Neutralizing antibody response to Japanese encephalitis inactivated mouse brain vaccine among laboratory personnel

Among vaccinees given two doses of JE Nakayama strain liquid vaccine, 41·8% had significant neutralizing (N) antibody response to the P20778 strain and 48·6% to the Japanese Nakayama strain. Among vaccinees who received three doses of the freeze-dried vaccine, the proportion of positive reactors was 53·8% when the sera were tested with the P20778 strain and 47·4% with the Nakayama strain. A fairly large proportion of those vaccinees who had responded positively to the latter vaccine were found to have lost detectable N antibodies to the P20778 strain and a smaller proportion to the Nakayama strain 13 to 17 months after the third dose of vaccine. Following the administration of a booster dose of the vaccine after this time interval, 65·2% and 56·5% of vaccinees responded positively to the P20778 strain and the Nakayama strain, respectively. The differences between the proportion of positive reactors to the two strains were not significant either for the liquid vaccine or the freeze-dried vaccine. An important finding was the priming effect of infection with West Nile (WN) virus before vaccination. Those vaccinees who had N antibody to WN virus before vaccination had a significantly higher N antibody response to the P20778 strain of JE virus than those who had no detectable antibody to WN virus. These findings indicate that the JE Nakayama strain vaccine would be efficacious in India, particularly in view of the widespread prevalence of WN virus infection.