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1.
The primary objectives of this study were to determine the seroprevalence of West Nile virus (WNV) infection of horses in Saskatchewan in 2003 and to identify risk factors for the infection. Blood samples were collected in August and October from 212 horses in 20 herds in 5 geographic zones. After accounting for within-herd clustering, the proportion of horses that had been infected with WNV, as determined by IgG and IgM antibody response, was 55.7% (95% confidence interval, 44.9% to 65.8%). The proportion of antibody-positive horses differed among herds (0% to 100%) and across ecoregions (20% to 76%). Horses in southern ecoregions were more likely to have either IgM antibodies or IgG concentrations suggesting infection than were horses in northern ecoregions. The use of mosquito-control measures was associated with decreased risk. After accounting for ecoregion, there was no difference between recipients of an inactivated WNV vaccine and nonrecipients in the occurrence of antibodies reflecting natural infection.  相似文献   

2.
The circulation of West Nile virus (WNV) in horses was investigated in the Southwest Indian ocean. In 2010, blood samples were collected from a total of 303 horses originating from Madagascar, Mauritius, Reunion and the Seychelles and tested for WNV-specific antibodies. An overall seroprevalence of 27.39% was detected in the Indian Ocean with the highest WNV antibody prevalence of 46.22% (95% CI: [37.4–55.2%]) in Madagascar. The age and origin of the horses were found to be associated with the WNV infection risk. This paper presents the first seroprevalence study investigating WN fever in horses in the Southwest Indian Ocean area and indicates a potential risk of infection for humans and animals. In order to gain a better understanding of WN transmission cycles, WNV surveillance needs to be implemented in each of the countries.  相似文献   

3.
REASONS FOR PERFORMING STUDY: West Nile virus (WNV) infection is endemic in southern Africa. With the recent emergence of WNV infection of horses in Europe and the USA the present study was performed to estimate the risk of seroconversion to WNV in a cohort of 488 young Thoroughbred (TB) horses. OBJECTIVES: To estimate the risk of seroconversion to WNV among a cohort of South African TB yearlings sold at the 2001 National Yearling Sales (NYS) and to determine whether the risk varied geographically. Two horses were also infected with a recent South African isolate of WNV to evaluate its virulence in horses. METHODS: Serum samples were collected from the cohort of 488 TB yearlings at the 2001 NYS. Serum samples that were collected from the same horses at the time that they were identified were sourced from our serum bank. Sera from 243 of the dams that were collected at the time that the foals were identified were also sourced from our serum bank. These sera were subjected to serum neutralisation (SN) tests for antibody to WNV. RESULTS: Approximately 11% of yearlings seroconverted to WNV on paired serum samples collected from each animal approximately 12 months apart. Studfarms with WNV-seropositive yearlings were widely distributed throughout South Africa and SN tests on sera from their dams indicated that exposure to WNV was even more prevalent (75%) in this population. Neurological disease was not described in any of the horses included in this study and 2 horses inoculated with a recent lineage 2 South African isolate of WNV showed no clinical signs of disease after infection and virus was not detected in their blood. CONCLUSIONS: Infection of horses with WNV is common in South Africa, but infection is not associated with neurological disease. POTENTIAL RELEVANCE: In contrast to recent reports from Europe, North Africa, Asia and North America, the results of our field and experimental studies indicated that exposure of horses to the endemic southern African strains of WNV was not associated with neurological disease.  相似文献   

4.
OBJECTIVE: 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.  相似文献   

5.
Two horses had a history of ataxia and weakness or recumbency. One recovered and was diagnosed with West Nile virus (WNV) infection by serologic testing. The other was euthanized; it had meningoencephalomyelitis, WNV was detected by polymerase chain reaction. West Nile virus infection is an emerging disease. Year 2002 is the first year in which cases have been seen in Saskatchewan.  相似文献   

6.
The objectives of the study were to describe the regional and provincial incidence rates and the weekly distribution of 842 reported West Nile virus (WNV) cases in horses in Canada between 2003 and 2019. This study also investigated characteristics of cases reported to the Canadian Food Inspection Agency (CFIA) between 2015 and 2019. The western region (British Columbia, Alberta, Saskatchewan, and Manitoba) had higher incidence rates than the eastern region (Ontario, Quebec, and Atlantic provinces) and overall, Saskatchewan registered the highest incidence. Over the study period, an earlier weekly preliminary onset of WNV cases was observed in the western region. The vast majority of cases were unvaccinated (96%), most cases were Quarter Horses (68%) and the risk of mortality was 31.9%. The findings of this study may be useful in informing veterinary equine practitioners about measures to prevent WNV disease in horses in Canada.  相似文献   

7.
Since 2008, West Nile Virus (WNV) has expanded its range in several Italian regions, and its yearly recurrence suggests the virus may have become endemic in some areas. In 2011, a new plan based also on the detection of IgM antibodies was implemented in the north‐eastern Italian regions of Veneto and Friuli Venezia Giulia, aiming to early detect WNV infections in areas where the virus had already circulated during the previous summers, and in adjacent zones. From July to November 2011, 1880 sera from 521 equine premises were screened by a commercial IgM capture ELISA. Mosquitoes were captured by CDC‐CO2 traps at 61 locations in the two regions. Collected mosquitoes were identified, pooled by species/date/location and examined by real‐time RT‐PCR and sequencing. Passive surveillance was carried out on clinically affected horses and non‐migratory wild birds found dead. IgM sero‐positive equines were detected in 19 holdings, five in the area with WNV circulation (AWC) and 14 in the surveillance area (SA); 10 more horse premises tested positive to further serological controls within 4 km of the positive holdings. A total of 85 398 mosquitoes of 15 species were collected and 2732 pools examined. Five Culex pipiens pools tested positive for the presence of WNV. Passive surveillance on non‐migratory wild birds allowed detection of the virus only in one found dead collared dove (Streptopelia decaocto), of 82 birds sampled. The WNV belonged to the lineage 2, which had been isolated for the first time in Italy earlier in 2011. By the first week of October, nine human cases had been confirmed in the same area. The implementation of a protocol combining IgM screening of horses with surveillance on mosquito vectors proved to be valuable for early detecting WNV circulation.  相似文献   

8.
West Nile virus (WNV) and Usutu virus (USUV) are arboviruses that are maintained in enzootic transmission cycles between mosquitoes and birds and are occasionally transmitted to mammals. As arboviruses are currently expanding their geographic range and emerging in often unpredictable locations, surveillance is considered an important element of preparedness. To determine whether sera collected from resident and migratory birds in the Netherlands as part of avian influenza surveillance would also represent an effective source for proactive arbovirus surveillance, a random selection of such sera was screened for WNV antibodies using a commercial ELISA. In addition, sera of jackdaws and carrion crows captured for previous experimental infection studies were added to the selection. Of the 265 screened serum samples, 27 were found to be WNV–antibody‐positive, and subsequent cross‐neutralization experiments using WNV and USUV confirmed that five serum samples were positive for only WNV‐neutralizing antibodies and seven for only USUV. The positive birds consisted of four Eurasian coots (Fulica atra) and one carrion crow (Corvus corone) for WNV, of which the latter may suggest local presence of the virus, and only Eurasian coots for USUV. As a result, the screening of a small selection of serum samples originally collected for avian influenza surveillance demonstrated a seroprevalence of 1.6% for WNV and 2.8% for USUV, suggesting that this sustained infrastructure could serve as a useful source for future surveillance of arboviruses such as WNV and USUV in the Netherlands.  相似文献   

9.
Background: The spread of lineage 2 West Nile virus (WNV) from sub‐Saharan regions to Europe and the unpredictable change in pathogenicity indicate a potential public and veterinary health threat and requires scientific awareness. Objectives: To describe the results of clinical and virological investigations of the 1st outbreak of a genetic lineage 2 WNV encephalomyelitis in horses. Animals: Seventeen horses with neurologic signs. Methods: Information regarding signalment, clinical signs, and outcome was obtained for each animal. Serology was performed in 15 cases, clinicopathological examination in 7 cases, and cerebrospinal fluid was collected from 2 horses. Histopathology was carried out in 4 horses, 2 of which were assessed for the presence of WNV in their nervous system. Results: WNV neutralizing antibody titers were between 10 and 270 (median, 90) and the results of other serological assays were in agreement with those of the plaque reduction neutralization test. Common signs included ataxia, weakness, asymmetric gait, muscle tremors, hypersensitivity, cranial nerve deficits, and recumbency. Twelve animals survived. Amplicons derived from the infection‐positive specimens allowed molecular characterization of the viral strain. Conclusions and Clinical Importance: From our results, we conclude that this outbreak was caused by a lineage 2 WNV strain, even though such strains often are considered nonpathogenic. Neurological signs and survival rates were similar to those reported for lineage 1 virus infections. The disease occurrence was not geographically limited as had been the typical case during European outbreaks; this report describes a substantial northwestern spread of the pathogen.  相似文献   

10.
Distribution of finite levels of resources between multiple competing tasks can be a challenging problem. Resources need to be distributed across time periods and geographic locations to increase the probability of detection of a disease incursion or significant change in disease pattern. Efforts should focus primarily on areas and populations where risk factors for a given disease reach relatively high levels. In order to target resources into these areas, the overall risk level can be evaluated periodically across locations to create a dynamic national risk landscape. Methods are described to integrate the levels of various risk factors into an overall risk score for each area, to account for the certainty or variability around those measures and then to allocate surveillance resources across this risk landscape. In addition to targeting resources into high risk areas, surveillance continues in lower risk areas where there is a small yet positive chance of disease occurrence. In this paper we describe the application of portfolio theory concepts, routinely used in finance, to design surveillance portfolios for a series of examples. The appropriate level of resource investment is chosen for each disease or geographical area and time period given the degree of disease risk and uncertainty present.  相似文献   

11.
In 2003, an outbreak of West Nile virus (WNV) occurred in Saskatchewan, Canada from July to September. One-hundred thirty-three horse cases and 947 human cases were recorded and data were analyzed retrospectively for evidence of clustering to determine if clinical infection in the horse population could be used to estimate human risk of infection with WNV. Kulldorff's scan statistic was used to identify spatial-temporal clusters in both the human and horse cases. In most areas, human clusters were not preceded by horse clusters. In one area, a significant cluster of horse cases preceded human cases by 1 week; however, 1 week does not provide sufficient time for human-health authorities to act and provide advance warning for the public.  相似文献   

12.
West Nile virus (WNV) is a single-stranded, enveloped RNA virus capable of causing encephalitic disease in horses. Unvaccinated horses are at risk for developing WNV disease in endemic geographic regions. Effective vaccination reduces disease frequency and diminishes disease severity in vaccinated individuals that become infected with WNV. Recent data indicate CD4+ lymphocytes are required for effective protection against disease; in particular, cross talk between CD4+ and CD8+ lymphocytes must be functional. The objective of this project was to investigate immune responses in horses throughout a series of three vaccinations using a commercial inactivated vaccine under natural conditions. Immune responses to vaccination were determined by neutralizing antibody titers with plaque reduction neutralization test (PRNT), IgM titer (capture ELISA), WNV specific antibody Ig subclass responses, WNV lymphocyte proliferative responses and intracellular cytokine expression. Horses were vaccinated with a series of three vaccines at 3-week intervals using an inactivated product. An initial measure of immune activation following vaccination was determined by evaluating changes in lymphocyte cytokine expression. Interferon (IFN) gamma and interleukin (IL)-4 expressing CD4+ lymphocytes significantly increased 14 days following initial vaccination compared to unvaccinated horses (P<0.05). IFN-gamma expressing CD8+ lymphocytes also increased and remained elevated for 110 days. Antigen specific lymphocyte proliferative responses were significantly increased up to 90 days following the third vaccination (P<0.05). As expected, vaccinated horses produced increased neutralizing antibody based on PRNT data and WNV antigen-specific Ig subclass responses compared with unvaccinated horses (P<0.05). Our data indicate that WNV vaccination with an inactivated product effectively induced an antigen-specific antibody responses, as well as CD4+ and CD8+ lymphocyte activation.  相似文献   

13.
OBJECTIVE: To compare neutralizing antibody response between horses vaccinated against West Nile virus (WNV) and horses that survived naturally occurring infection. DESIGN: Cross-sectional observational study. ANIMALS: 187 horses vaccinated with a killed WNV vaccine and 37 horses with confirmed clinical WNV infection. PROCEDURE: Serum was collected from vaccinated horses prior to and 4 to 6 weeks after completion of an initial vaccination series (2 doses) and 5 to 7 months later. Serum was collected from affected horses 4 to 6 weeks after laboratory diagnosis of infection and 5 to 7 months after the first sample was obtained. The IgM capture ELISA, plaque reduction neutralization test (PRNT), and microtiter virus neutralization test were used. RESULTS: All affected horses had PRNT titers > or = 1:100 at 4 to 6 weeks after onset of disease, and 90% (18/20) maintained this titer for 5 to 7 months. After the second vaccination, 67% of vaccinated horses had PRNT titers > or = 1:100 and 14% had titers < 1:10. Five to 7 months later, 33% (28/84) of vaccinated horses had PRNT titers > or = 1:100, whereas 29% (24/84) had titers < 1:10. Vaccinated and clinically affected horses' end point titers had decreased by 5 to 7 months after vaccination. CONCLUSIONS AND CLINICAL RELEVANCE: A portion of horses vaccinated against WNV may respond poorly. Vaccination every 6 months may be indicated in certain horses and in areas of high vector activity. Other preventative methods such as mosquito control are warranted to prevent WNV infection in horses.  相似文献   

14.
Surveillance for West Nile virus (WNV) and other mosquito‐borne pathogens involves costly and time‐consuming collection and testing of mosquito samples. One difficulty faced by public health personnel is how to interpret mosquito data relative to human risk, thus leading to a failure to fully exploit the information from mosquito testing. The objective of our study was to use the information gained from historic West Nile virus mosquito testing to determine human risk relative to mosquito infection and to assess the usefulness of our mosquito infection forecasting models to give advance warning. We compared weekly mosquito infection rates from 2004 to 2013 to WNV case numbers in Illinois. We then developed a weather‐based forecasting model to estimate the WNV mosquito infection rate one to 3 weeks ahead of mosquito testing both statewide and for nine regions of Illinois. We further evaluated human illness risk relative to both the measured and the model‐estimated infection rates to provide guidelines for public health messages. We determined that across 10 years, over half of human WNV cases occurred following the 29 (of 210) weeks with the highest mosquito infection rates. The values forecasted by the models can identify those time periods, but model results and data availability varied by region with much stronger results obtained from regions with more mosquito data. The differences among the regions may be related to the amount of surveillance or may be due to diverse landscape characteristics across Illinois. We set the stage for better use of all surveillance options available for WNV and described an approach to modelling that can be expanded to other mosquito‐borne illnesses.  相似文献   

15.
REASON FOR PERFORMING STUDY: West Nile virus (WNF) is a Flavivirus responsible for a life-threatening neurological disease in man and horses. Development of improved vaccines against Flavivirus infections is therefore important. OBJECTIVES: To establish that a single immunogenicity dose of live Flavivirus chimera (WN-FV) vaccine protects horses from the disease and it induces a protective immune response, and to determine the duration of the protective immunity. METHODS: Clinical signs were compared between vaccinated (VACC) and control (CTRL) horses after an intrathecal WNV challenge given at 10 or 28 days, or 12 months post vaccination. RESULTS: Challenge of horses in the immunogenicity study at Day 28 post vaccination resulted in severe clinical signs of WNV infection in 10/10 control (CTRL) compared to 1/20 vaccinated (VACC) horses (P<0.01). None of the VACC horses developed viraemia and minimal histopathology was noted. Duration of immunity (DPI) was established at 12 months post vaccination. Eight of 10 CTRL exhibited severe clinical signs of infection compared to 1 of 9 VACC horses (P<0.05). There was a significant reduction in the occurrence of viraemia and histopathology lesion in VACC horses relative to CTRL horses. Horses challenged at Day 10 post vaccination experienced moderate or severe clinical signs of WNV infection in 3/3 CTRL compared to 5/6 VACC horses (P<0.05). CONCLUSIONS: This novel WN-FV chimera vaccine generates a protective immune response to WNV infection in horses that is demonstrated 10 days after a single vaccination and lasts for up to one year. POTENTIAL RELEVANCE: This is the first USDA licensed equine WNV vaccine to utilise a severe challenge model that produces the same WNV disease observed under field conditions to obtain a label claim for prevention of viraemia and aid in the prevention of WNV disease and encephalitis with a duration of immunity of 12 months.  相似文献   

16.
A prospective cohort study was used to estimate the incidence of West Nile virus (WNV) infection in a group of unvaccinated horses (n = 37) in California and compare the effects of natural WNV infection in these unvaccinated horses to a group of co-mingled vaccinated horses (n = 155). Horses initially were vaccinated with either inactivated whole virus (n = 87) or canarypox recombinant (n = 68) WNV vaccines during 2003 or 2004, prior to emergence of WNV in the region. Unvaccinated horses were serologically tested for antibodies to WNV by microsphere immunoassay incorporating recombinant WNV E protein (rE MIA) in December 2003, December 2004, and every two months thereafter until November 2005. Clinical neurologic disease attributable to WNV infection (West Nile disease (WND)) developed in 2 (5.4%) of 37 unvaccinated horses and in 0 of 155 vaccinated horses. One affected horse died. Twenty one (67.7%) of 31 unvaccinated horses that were seronegative to WNV in December, 2004 seroconverted to WNV before the end of the study in November, 2005. Findings from the study indicate that currently-available commercial vaccines are effective in preventing WND and their use is financially justified because clinical disease only occurred in unvaccinated horses and the mean cost of each clinical case of WND was approximately 45 times the cost of a 2-dose WNV vaccination program.  相似文献   

17.
West Nile virus (WNV) is a flavivirus that is maintained in an enzootic cycle between ornithophilic mosquitoes, mainly of the Culex genus, and certain wild bird species. Other bird species like ravens, jays and raptors are highly susceptible to the infection and may develop deadly encephalitis, while further species of birds are only going through subclinical infection. The objective of this study was to continue in years 2009-2011 the serological and molecular surveillance in wild birds in Germany (see Vector Borne Zoonotic Dis. 10, 639) and to expand these investigations for the first time also to sera from domestic poultry and horses collected between 2005 and 2009. All three cohorts function as indicators for the endemic circulation of WNV. The presence of WNV-specific antibodies was detected in all samples by virus neutralization test (VNT), indirect immunofluorescence test (IFT) and/or enzyme-linked immunosorbent assay (ELISA). The presence of WNV genomes was monitored in relevant sera using two qRT-PCRs that amplify lineage 1 and 2 strains. A total of 364 migratory and resident wild bird serum samples (with emphasis on Passeriformes and Falconiformes) as well as 1119 serum samples from domestic poultry and 1282 sera from horses were analysed. With the exception of one hooded crow, antibody carriers were exclusively found in migratory birds, but not in resident birds/domestic poultry or in local horses. Crows are facultative, short-distance winter migrants in Germany. WNV-specific nucleic acids could not be demonstrated in any of the samples. According to these data, there is no convincing evidence for indigenous WNV infections in equines and in wild/domestic birds in Germany. However, since a few years, WNV infections are endemic in other European countries such as Austria, Hungary, Greece and Italy, a state-of-the-art surveillance system for the detection of incursions of WNV into Germany deems mandatory.  相似文献   

18.
In 2003, the occurrence and location of horses with clinical signs of West Nile virus infection were identified in the southern portion of Saskatchewan with the help of veterinarians, owners, and the regional laboratory. A total of 133 clinical cases were reported between July 30 and September 19, 2003; however, postseason surveillance suggests that the number of cases was underestimated. The case fatality rate was 43.8% (95% CI 35.2, 52.4). Factors associated with fatality in clinical cases included sex, week of onset of clinical signs, and coat color. Reported clinical cases clustered within regional health authority districts, suggesting regional differences in geographic factors, potentially including climate and mosquito control, that could contribute to the risk of disease. However, most of the variation in the risk of fatality in clinical cases is explained at the individual level rather than the Regional Health Authority level, which suggests the outcome of clinical disease is primarily determined by characteristics of, or management factors affecting, the individual horse.  相似文献   

19.
OBJECTIVE: To determine the onset of immunity after IM administration of a single dose of a recombinant canarypox virus vaccine against West Nile virus (WNV) in horses in a blind challenge trial. ANIMALS: 20 mixed-breed horses. PROCEDURE: Horses with no prior exposure to WNV were randomly assigned to 1 of 2 groups (10 horses/group). In 1 group, a recombinant canarypox virus vaccine against WNV was administered to each horse once (day 0). The other 10 control horses were untreated. On day 26, 9 treated and 10 control horses were challenged via the bites of mosquitoes (Aedes albopictus) infected with WNV. Clinical responses and WNV isolation were monitored for 14 days after challenge exposure; antibody responses against WNV after administration of the vaccine and challenge were also assessed in both groups. RESULTS: Following challenge via WNV-infected mosquitoes, 1 of 9 treated horses developed viremia. In contrast, 8 of 10 control horses developed viremia after challenge exposure to WNV-infected mosquitoes. All horses seroconverted after WNV challenge; compared with control horses, antibody responses in the horses that received the vaccine were detected earlier. CONCLUSIONS AND CLINICAL RELEVANCe: In horses, a single dose of the recombinant canarypox virus-WNV vaccine appears to provide early protection against development of viremia after challenge with WNV-infected mosquitoes, even in the absence of measurable antibody titers in some horses. This vaccine may provide veterinarians with an important tool in controlling WNV infection during a natural outbreak or under conditions in which a rapid onset of protection is required.  相似文献   

20.
WNV encephalitis in horses, previously reported in Africa, Asia, and Europe, occurred for the first time in the Western Hemisphere in 1999. The causative agent, WNV, is a flavivirus maintained in nature by a bird-mosquito cycle. The disease in horses is manifested primarily by ataxia of variable severity. Outbreaks of encephalitis may have a case fatality rate in excess of 40%, although this virus infection is inapparent in some horses. Early evidence indicates that WNV has overwintered in the northeastern United States and poses a threat for future disease occurrences in horses. No vaccine is available to protect against WNV infection in horses; disease control is predicated on mosquito abatement.  相似文献   

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