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1.
In 1998, bluetongue (BT) was introduced in northern Africa and then extended to northern latitudes including the French island of Corsica. Following the outbreaks in Corsica in 2000 and 2001, cross-sectional studies and surveillances have been set up in Corsica and also in the southern part of mainland France, a disease-free area but considered at high risk because of its proximity. The surveillance was based on regular blood sampling of susceptible species and antibody detection by a commercial competitive ELISA kit (cELISA). The performance of this cELISA was evaluated on both field results obtained during the 2001 surveillance campaigns and experimental results. ROC analyses were carried out using RT-PCR results as gold standard for determining the infection status of animals. From all these sets of data, cut-off values optimising the diagnostic accuracy of the test were computed. Their values ranged around the manufacturer's 50% threshold from 41% to 63%. The area under the ROC curve obtained from field data was 0.843 (95% CI: 0.762-0.923). In all our results, it appeared also that the specificity of the cELISA test was always perfect if the cut-off was at least at 80%. This cELISA test does not seem sufficient to diagnose BT disease in animals with BT-like symptoms. However, complementary data are needed to better estimate sensitivity and specificity values of this BT test for its use either as a diagnostic tool in infected areas or as a screening test in BT-free areas. The use and validity of RT-PCR results as gold standard are discussed. As the lack of suitable data strongly limited the applicable analyses, a discussion based on the OIE recommendations about test evaluation is initiated.  相似文献   

2.
Bluetongue (BT) is a reportable re-emerging vector-borne disease of animal health concern. Enzyme-linked immunosorbent assays (ELISA) are frequently used in BT surveillance programs in domestic ruminants, but their diagnostic accuracy has not been evaluated for wild ruminants, which can play an important role as natural reservoirs of bluetongue virus (BTV). The aim of this study was to assess two commercial ELISAs for BT diagnosis in wild ruminants using control sera of known BTV infection status and field samples. When control sera were tested, the double recognition ELISA (DR-ELISA) showed 100 % sensitivity (Se) and specificity (Sp), while the competitive ELISA (C-ELISA) had 86.4 % Se and 97.1 % Sp. Using field samples, the selected latent-class analysis model showed 95.7 % Se and 85.9 % Sp for DR-ELISA, 58.2 % Se and 95.8 % Sp for C-ELISA and 84.2 % Se for the serum neutralization test (SNT). Our results indicate that the DR-ELISA may be a useful diagnostic method to assess BTV circulation in endemic areas, while the C-ELISA should be selected when free-areas are surveyed. The discrepancy between control and field samples point out that the inclusion of field samples is required to assess the accuracy of commercial ELISAs for the serological diagnosis of BTV in wild ruminants.  相似文献   

3.
In recent years the vector-borne diseases (VBD) are (re)-emerging and spreading across the world having a profound impact on human and veterinary health, ecology, socio-economics and disease management. Arguably the best-documented example of veterinary importance is the recent twofold invasion of bluetongue (BT) in Europe. Much attention has been devoted to derive presence-absence habitat distribution models and to model transmission through direct contact. Limited research has focused on the dynamic modelling of wind mediated BT spread. This paper shows the results of a stochastic predictive model used to assess the spread of bluetongue by vectors considering both wind-independent and wind-mediated movement of the vectors. The model was parameterised using epidemiological knowledge from the BTV8 epidemic in 2006/2007 and the BTV1 epidemic in 2008 in South-France. The model correctly reflects the total surface of the infected zone (overall accuracy=0.77; sensitivity=0.94; specificity=0.65) whilst slightly overestimating spatial case density. The model was used operationally in spring 2009 to predict further spread of BTV1. This allowed veterinary officers in Belgium to decide whether there was a risk of introduction of BTV1 from France into Belgium and thus, whether there was a need for vaccination. Given the far distance from the predicted infected zone to the Belgian border, it was decided not to vaccinate against BTV1 in 2009 in Belgium.  相似文献   

4.
The performance of the standard agar gel immunodiffusion (AGID) test and the competitive enzyme-linked immunosorbent assay (cELISA) for the detection of serum antibody against bluetongue virus (BTV) in clinically healthy and diseased camels in Gujarat state were compared. Out of 176 sera tested, 22 (12.5%) and 34 (19.3%) were positive for group-specific bluetongue antibodies by AGID and cELISA, respectively. Maximum seropositivities of 18.0% by AGID and 25.8% by cELISA were recorded in the Kutchhi breed, and of 6.9% and 12.6%, respectively, in the Marwari breed. The seroprevalence detected by AGID and cELISA in clinically healthy and diseased camels did not differ significantly with regard to bluetongue disease in these breeds.  相似文献   

5.
A serologic survey was conducted in yearling cattle imported into Alberta feedlots from Montana during October 2001 to estimate the prevalence of antibodies to bluetongue virus (BTV) and Anaplasma marginale in Montana yearling cattle. The apparent prevalence of antibodies to BTV when the competitive enzyme-linked immunosorbent assay (cELISA) was used was 0.37% (21/5608). Test positive cELISA samples were also all positive when tested by virus neutralization (VN) and they reacted to 1 or more BTV serotypes, including 2, 10, 11, 13, and 17. The apparent prevalence of antibodies to A. marginale when a recombinant cELISA (rcELISA) was used with a positive cutoff at 30% inhibition was 1.93% (108/5608). When the rcELISA positive cutoff was at 42% inhibition, the apparent prevalence was 0.73% (41/5608). After the reported sensitivity and specificity of the test had been accounted for, the A. marginale antibody results were consistent with a population that was either free of exposure or had a very low prevalence for A. marginale.  相似文献   

6.
Bluetongue virus serotype 8 (BTV-8) emerged in Central Western Europe in 2006 causing a large scale epidemic in 2007 that involved several European Union (EU) countries including Belgium. As in several other EU member states, vaccination against BTV-8 with inactivated vaccines was initiated in Belgium in spring 2008 and appeared to be successful. Since 2009, no clinical cases of Bluetongue (BT) have been reported in Belgium and BTV-8 circulation seemed to have completely disappeared by spring 2010. Therefore, a series of repeated cross-sectional surveys, the BT sentinel surveillance program, based on virus detection in blood samples by means of real-time RT-PCR (RT-qPCR) were carried out in dairy cattle from the end of 2010 onwards with the aim to demonstrate the absence of BTV circulation in Belgium. This paper describes the results of the first two sampling rounds of this BT sentinel surveillance program carried out in October-November 2010 and January-February 2011. In addition, the level of BTV-specific maternal antibodies in young non-vaccinated animals was monitored and the level of herd immunity against BTV-8 after 3 consecutive years of compulsory BTV-8 vaccination was measured by ELISA. During the 1st sampling round of the BT sentinel surveillance program, 15 animals tested positive and 2 animals tested doubtful for BTV RNA by RT-qPCR. During the 2nd round, 17 animals tested positive and 5 animals tested doubtful. The positive/doubtful animals in both rounds were re-sampled 2-4 weeks after the original sampling and then all tested negative by RT-qPCR. These results demonstrate the absence of BTV circulation in Belgium in 2010 at a minimum expected prevalence of 2% and 95% confidence level. The study of the maternal antibodies in non-vaccinated animals showed that by the age of 7 months maternal antibodies against BTV had disappeared in most animals. The BTV seroprevalence at herd level after 3 years of compulsory BTV-8 vaccination was very high (97.4% [95% CI: 96.2-98.2]). The overall true within-herd BTV seroprevalence in 6-24 month old Belgian cattle in early 2011 was estimated at 73.4% (95% CI: 71.3-75.4).  相似文献   

7.
A competitive enzyme-linked immunosorbent assay (cELISA) was developed to detect antibodies to the group antigen of bluetongue virus (BTV). The epitope recognized by the BTV-specific monoclonal antibody was confirmed, by immunofluorescence staining of monolayers of virus-infected Vero cells, to be present on BTV serotypes 2, 10, 11, 13, and 17 but not on epizootic hemorrhagic disease virus (EHDV) serotypes 1 and 2. Sera from BTV-inoculated ruminants and rabbits were used to evaluate the cELISA and to compare its specificity and sensitivity with that of the conventional BTV-specific agar gel immunodiffusion (AGID) and serum neutralization (SN) tests. Rabbit antisera to the 5 serotypes of BTV present in the United States had cELISA titers (inverse of the final dilution of serum that gave greater than 20% inhibition) that ranged from 32 to greater than 1.024. Seroconversion of the 8 calves and lambs inoculated with BTV was detected by all 3 serologic tests (SN, AGID, cELISA) by 6 weeks after inoculation. Specificity of the cELISA test was confirmed with bovine sera that contained neutralizing antibodies to EHDV but not to the 5 serotypes of BTV present in the United States; these sera gave positive results by AGID test but were negative by cELISA. The sensitivity and specificity of the cELISA test was further confirmed by analysis of a panel of bovine test sera supplied by the National Veterinary Services Laboratories, indicating that the cELISA is a superior test for detection of BTV group-specific antibodies in sera from ruminants in the United States.  相似文献   

8.
This paper records the results of a bluetongue virus (BTV) serological survey and reports the first isolation of BTV on the French Island of Reunion. In January 2003, the French Island of Reunion, located off the coast of Madagascar, reported an outbreak of disease in cattle that resembled clinical bluetongue (BT) in sheep. The suspected causal agent was isolated and identified as epizootic haemorrhagic disease of deer virus (EHDV). However, because of the similarity in the clinical signs to those of BT, a retrospective survey against BTV was carried out using sera collected in 2002. Results revealed the presence of antibody in all sera tested indicating that BTV has been resident on the Island since 2002, and probably earlier. Although up to July 2003 no clinical BT had ever been reported in sheep, BTV viral RNA was amplified by RT-PCR from a single sheep blood collected in February that year, which strongly suggested that BTV was currently circulating on the Island. Following a second outbreak of disease in August 2003, this time involving a flock of Merino sheep, infectious BTV was finally isolated, and identified by both traditional and molecular techniques as serotype 3. The nucleotide and amino-acid sequences of the RT-PCR products amplified for BTV segments 7 and 10 from the sheep blood collected in February and August from different areas of the Island, were sufficiently diverse as to suggest that they were of different origins and/or different BTV serotypes.  相似文献   

9.
An outbreak of epizootic haemorrhagic disease virus (EHDV) in cattle in Israel in 2006 enabled a comparison of the spatial distribution of epidemic exposure to EHDV with that of exposure to bluetongue virus (BTV), which is endemic in the country. The seroprevalence of both viruses was examined in 1650 serum samples collected from 139 farms representative of the spatial distribution of dairy cattle in Israel. A significant association between exposure to EHDV and BTV was demonstrated in both univariate and multivariate analyses. Recent exposure to BTV and EHDV (demonstrated by seroprevalence in calves) was clustered in different geographical locations, indicating that the two viruses had different patterns of spread, that of EHDV being influenced by winds and terrain barriers and that of BTV by herd immunity.  相似文献   

10.
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11.
A recently developed indirect ELISA for the detection of bluetongue virus (BTV)-specific antibodies in bovine milk samples was compared to that of the routinely used competitive ELISA on serum samples. During the bluetongue outbreak in the Netherlands in 2006, caused by BTV serotype 8, coupled serum and milk samples were obtained from 470 individual cows from 10 BTV-infected farms with an average seroprevalence of 57%. In addition, bulk milk samples of the same farms, and historically BT-negative samples were tested. Compared to the ELISA for sera, the relative specificity and sensitivity of the ELISA for milk samples is 96.5% and 98.9%, respectively when using a S/P% cut-off value of 50% as advised by the manufacturer. The optimal cut-off value was found at S/P% of 90% revealing an optimal specificity (99.0%) combined with an optimal sensitivity (98.1%). Titres in positive individual milk samples ranged from 1 to 2048 with a peak titre of 128. Bulk milk samples contained antibodies with titres ranging from 64 to 512. The ELISA for milk samples was found to be a reliable and robust test. This diagnostic tool is very useful, and may replace the ELISA for serum samples as first choice in order to get insight into the status of lactating individual animals and therewith of the entire herd with respect to BTV infection.  相似文献   

12.
After 44 years of epidemiological silence, bluetongue virus (BTV) was reintroduced in Portugal in the autumn of 2004. The first clinical cases of bluetongue disease (BT) were notified in sheep farms located in the South of Portugal, close to the Spanish border. A total of six BTV, five of serotype 4 and one of serotype 2 were isolated from sheep and cattle during the 2004-2006 epizootics. The nucleotide sequence of gene segments L2, S7 and S10 of BTV-4 prototype strain (BTV4/22045/PT04) obtained from the initial outbreak and of BTV-2 (BTV2/26629/PT05) was fully determined and compared with those from other parts of the world. The phylogenetic analysis revealed that BTV4/22045/PT04 is related to other BTV-4 strains that circulate in the Mediterranean basin since 1998, showing the highest identity (99%) with BTV-4 isolates of 2003 from Sardinia and Corsica, whereas BTV2/26629/PT05 is almost indistinguishable from the Onderstepoort BTV-2 live-attenuated vaccine strain and its related field strain isolated in Italy. Since live-attenuated BTV-2 vaccine was never used in Portugal, the isolation of this strain may represent a natural circulation of the vaccine virus used in other countries in Mediterranean Europe.  相似文献   

13.
为了解广西地区山羊蓝舌病(BT)流行现状,本研究采用免疫扩散试验对采自广西11个地区的3 646份山羊血清进行BT血清学调查,结果表明,广西地区山羊群普遍存在BT感染,并且血清阳性率存在地域性差异,阳性率为6.3%～45.1%,平均阳性率为20.5%。对不同生长阶段山羊的血清阳性率进行统计,结果显示成年羊的阳性率高于羔羊,分别为22.1%和17.4%,这可能与成年羊接触媒介昆虫的机会较多有关。对BT流行区域分布与地理位置和气候等自然因素之间的相关性分析表明,广西山羊BT血清阳性率与地理位置有一定相关性,与年平均气温显著相关,与年平均降雨量无显著相关性,由此可见,地理位置和气温是BT流行病学的影响因素。  相似文献   

14.
Bluetongue (BT) was notified for the first time in several Northern European countries in August 2006. The first reported outbreaks of BT were confirmed in herds located near the place where Belgium, The Netherlands and Germany share borders. The disease was rapidly and widely disseminated throughout Belgium in both sheep and cattle herds. During the epidemic, case reporting by the Veterinary Authorities relied almost exclusively on the identification of herds with confirmed clinical infected ruminants. A cross-sectional serological survey targeting all Belgian ruminants was then undertaken during the vector-free season. The first objective of this study was to provide unbiased estimates of BT-seroprevalence for different regions of Belgium. Since under-reporting was suspected during the epidemic, a second goal was to compare the final dispersion of the virus based on the seroprevalence estimates to the dispersion of the confirmed clinical cases which were notified in Belgium, in order to estimate the accuracy of the case detection based on clinical suspicion. True within-herd seroprevalence was estimated based on a logistic-normal regression model with prior specification on the diagnostic test's sensitivity and specificity. The model was fitted in a Bayesian framework. Herd seroprevalence was estimated using a logistic regression model. To study the linear correlation between the BT winter screening data and the case-herds data, the linear predicted values for the herd prevalence were compared and the Pearson correlation coefficient was estimated. The overall herd and true within-herd seroprevalences were estimated at 83.3 (79.2-87.0) and 23.8 (20.1-28.1)%, respectively. BT seropositivity was shown to be widely but unevenly distributed throughout Belgium, with a gradient decreasing towards the south and the west of the country. The analysis has shown there was a strong correlation between the outbreak data and the data from the survey (r=0.73, p<0.0001). The case detection system based on clinical suspicion underestimated the real impact of the epidemic, but indicated an accurate spatial distribution of the virus at the end of the epidemic.  相似文献   

15.
A cross-sectional study was carried out to assess the prevalence and circulation of bluetongue virus (BTV) in Spanish ibexes (Capra pyrenaica hispanica). A total of 770 sera samples, 380 blood samples and 34 spleen samples were collected between 2006 and 2009 in Andalusia (southern Spain), a region and time period with a wide circulation of BTV in livestock. Thirty-one out of 770 (4.0%; CI(95%): 2.6-5.4) sera samples analyzed by ELISA showed antibodies against BTV. Twenty-four out of 31 seropositive samples were tested against BTV serotypes 1, 4 and 8 by serum neutralization test (SNT). Neutralizing antibodies against BTV-1 and BTV-4 were detected in seven and ten animals, respectively, four of them showed neutralizing antibodies to both serotypes. The animals seropositive to BTV-4 were sampled between 2006 and 2008, while BTV-1 circulation was confirmed in ibexes sampled between 2007 and 2009. None of the ibexes presented neutralizing antibodies against BTV-8. Statistically significant differences were found among regions and years, which is in coincidence with what occurred in domestic ruminants. There were no statistically significant differences between sexes, age classes and habitats (captivity vs. free-living). BTV RNA was not found in any of the 380 blood samples analyzed. However, BTV-1 RNA was detected from spleen in one Spanish ibex from Málaga province in August 2008. This finding evidences the presence of BTV-1 in Spanish ibex in a municipality where BT outbreaks were not detected in domestic ruminants during that period. Results of the present study show that Spanish ibexes were exposed and responded serologically to both BTV-1 and BTV-4. The low seroprevalence obtained suggests that Spanish ibex is not a relevant species in the dissemination of BT. However, the detection of BTV-1 RNA and the presence of seropositive ibexes in areas where BT outbreaks were not detected in livestock, could not exclude a significant role in the epidemiology of BTV in certain areas.  相似文献   

16.
This study reports on an outbreak of disease that occurred in central Algeria during July 2006. Sheep in the affected area presented clinical signs typical of bluetongue (BT) disease. A total of 5245 sheep in the affected region were considered to be susceptible, with 263 cases and thirty-six deaths. Bluetongue virus (BTV) serotype 1 was isolated and identified as the causative agent. Segments 2, 7 and 10 of this virus were sequenced and compared with other isolates from Morocco, Italy, Portugal and France showing that they all belong to a ‘western’ BTV group/topotype and collectively represent a western Mediterranean lineage of BTV-1.  相似文献   

17.
Bluetongue virus (BTV) exists around the world in a broad band covering much of the Americas, Africa, southern Asia and northern Australia. Historically, it also occasionally occurred in the southern fringes of Europe. It is considered to be one of the most important diseases of domestic livestock. Recently BTV has extended its range northwards into areas of Europe never before affected and has persisted in many of these locations causing the greatest epizootic of bluetongue (BT), the disease caused by BTV, on record. Indeed, the most recent outbreaks of BT in Europe are further north than this virus has ever previously occurred anywhere in the world. The reasons for this dramatic change in BT epidemiology are complex but are linked to recent extensions in the distribution of its major vector, Culicoides imicola, to the involvement of novel Culicoides vector(s) and to on-going climate-change. This paper investigates these recent outbreaks in the European theatre, up to the beginning of 2006, highlights prospects for the future and sets the scene for the following papers in this special issue.  相似文献   

18.
Clinical disease of bluetongue (BT) in sheep may differ depending on breed, age and immunity of infected sheep and may also vary between serotype and strain of BT virus (BTV). Since there are no data available on the susceptibility of Swiss sheep breeds for BT, we performed experimental infection of the 4 most common Swiss sheep breeds and the highly susceptible Poll Dorset sheep with the BTV serotype 8 (BTV-8) circulating in Northern Europe since 2006. Clinical signs were assessed regarding severity, localisation, progression and time point of their appearance. The results clearly show that the Swiss sheep breeds investigated were susceptible to BTV-8 infection. They developed moderate, BT-characteristic symptoms, which were similar to those observed in Poll Dorset sheep. Regardless of breed, the majority of infected animals showed fever, swelling of the head as well as erosions of the mouth and subcutaneous haemorrhages.  相似文献   

19.
Bluetongue (BT) is an infectious disease of wild and domestic ruminants caused by bluetongue virus (BTV). BTV-4 spread through southern Spain from 2004 to 2006, whereas a BTV-1 outbreak that started in southern Spain in 2007 is still ongoing. Vaccination and movement restriction regulations are applied to domestic ruminants to control BT, but the potential reservoir role of wild European ungulates has not been clarified so far. The aim of this study was to describe the epidemiology of BTV in the wild free-ranging red deer (Cervus elaphus) population of Caba?eros National Park (CNP) in central Spain during the BTV-4 and BTV-1 epizootics, assessing the potential role of this deer population as a BTV reservoir. Blood samples from 2885 (2542 adults, 208 calves and 135 undetermined) wild red deer were collected from 2005 to 2010 in CNP and surrounding hunting estates. All sera were tested for antibodies against the BTV VP7 protein by ELISA. Ninety-four of the ELISA-positive samples were analysed by serum neutralization to detect BTV-4 and BTV-1 specific antibodies, and 142 blood samples were analysed by RT-PCR for BTV RNA. A total of 371 (12.9%) out of the 2,885 deer (35/208 calves, 307/2,542 adults, and 29/135 undetermined) were positive for antibodies against BTV. Prevalence increased in adult deer from 2005-2006 to 2008-2009, declining thereafter. No positive samples for BTV-1 were found by serum neutralization, whereas 43 deer (38 adults, four calves and one undetermined) were positive for BTV-4 specific antibodies. No BTV RNA positive deer were found by RT-PCR. Antibody detection throughout the study period suggests a maintained circulation of BTV in red deer. However, the lack of BTV RNA detection suggests a minor transmission risk to livestock.  相似文献   

20.
ABSTRACT: Even though bluetongue virus (BTV) transmission is apparently interrupted during winter, bluetongue outbreaks often reappear in the next season (overwintering). Several mechanisms for BTV overwintering have been proposed, but to date, their relative importance remain unclear. In order to assess the probability of BTV overwintering by persistence in adult vectors, ruminants (through prolonged viraemia) or a combination of both, a quantitative risk assessment model was developed. Furthermore, the model allowed the role played by the residual number of vectors present during winter to be examined, and the effect of a proportion of Culicoides living inside buildings (endophilic behaviour) to be explored. The model was then applied to a real scenario: overwintering in Germany between 2006 and 2007. The results showed that the limited number of vectors active during winter seemed to allow the transmission of BTV during this period, and that while transmission was favoured by the endophilic behaviour of some Culicoides, its effect was limited. Even though transmission was possible, the likelihood of BTV overwintering by the mechanisms studied seemed too low to explain the observed re-emergence of the disease. Therefore, other overwintering mechanisms not considered in the model are likely to have played a significant role in BTV overwintering in Germany between 2006 and 2007.  相似文献   

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