Bluetongue Virus Surveillance Research Articles

Bluetongue Virus in the Iberian Lynx (Lynx pardinus), 2010-2022.

Clinical infection and death caused by bluetongue virus infection has been reported in the Eurasian lynx. Bluetongue virus surveillance in the Iberian lynx revealed widespread and repeated exposure to serotypes 1 and 4 in wild and captive populations of this species. This exposure is possibly from a spillover event from sympatric ruminants.

Evaluating the most appropriate pooling ratio for EDTA blood samples to detect Bluetongue virus using real-time RT-PCR

The control of Bluetongue virus (BTV) presents a significant challenge to European Union (EU) member states as trade restrictions are placed on animals imported from BTV-affected countries. BTV surveillance programs are costly to maintain, thus, pooling of EDTA blood samples is used to reduce costs and increase throughput. We investigated different pooling ratios (1:2, 1:5, 1:10 and 1:20) for EDTA blood samples to detect a single BTV positive animal. A published real-time RT-PCR assay (Hofmann et al., 2008) and a commercial assay (ThermoFisher VetMax™ BTV NS3 kit) were used to analyse BTV RNA extracted from pooled EDTA blood samples. The detection rate was low for the onset of infection sample (0–2 days post infection (dpi); CT 36) irrespective of the pooling ratio. Both assays could reliably detect a single BTV-positive animal at early viraemia (3–6 dpi; CT 33) when pooled, however, detection rate diminished with increasing pooling ratio. A statistical model indicated that pooling samples up to 1:20, is suitable to detect a single BTV positive animal at peak viraemia (7–12 dpi) or late infection (13–30 dpi) with a probability of detection of >80% and >94% using the Hofmann et al. (2008) and VetMAX assays, respectively. Using the assays highlighted in our study, pooling at ratios of 1:20 would be technically suitable in BTV-endemic countries for surveillance purposes. As peak viraemia occurs between 7–12 days post infection, a 1:10 pooling ratio is appropriate for post-import testing when animals are sampled within a similar time frame post-import.

Cost distribution of bluetongue surveillance and vaccination programmes in Austria and Switzerland (2007–2016)

Bluetongue virus (BTV) is an emerging transboundary disease in Europe, which can cause significant production losses among ruminants. The analysis presented here assessed the costs of BTV surveillance and vaccination...

Understanding Spatio-Temporal Variability in the Reproduction Ratio of the Bluetongue (BTV-1) Epidemic in Southern Spain (Andalusia) in 2007 Using Epidemic Trees.

Andalusia (Southern Spain) is considered one of the main routes of introduction of bluetongue virus (BTV) into Europe, evidenced by a devastating epidemic caused by BTV-1 in 2007. Understanding the pattern and the drivers of BTV-1 spread in Andalusia is critical for effective detection and control of future epidemics. A long-standing metric for quantifying the behaviour of infectious diseases is the case-reproduction ratio (Rt), defined as the average number of secondary cases arising from a single infected case at time t (for t>0). Here we apply a method using epidemic trees to estimate the between-herd case reproduction ratio directly from epidemic data allowing the spatial and temporal variability in transmission to be described. We then relate this variability to predictors describing the hosts, vectors and the environment to better understand why the epidemic spread more quickly in some regions or periods. The Rt value for the BTV-1 epidemic in Andalusia peaked in July at 4.6, at the start of the epidemic, then decreased to 2.2 by August, dropped below 1 by September (0.8), and by October it had decreased to 0.02. BTV spread was the consequence of both local transmission within established disease foci and BTV expansion to distant new areas (i.e. new foci), which resulted in a high variability in BTV transmission, not only among different areas, but particularly through time, which suggests that general control measures applied at broad spatial scales are unlikely to be effective. This high variability through time was probably due to the impact of temperature on BTV transmission, as evidenced by a reduction in the value of Rt by 0.0041 for every unit increase (day) in the extrinsic incubation period (EIP), which is itself directly dependent on temperature. Moreover, within the range of values at which BTV-1 transmission occurred in Andalusia (20.6°C to 29.5°C) there was a positive correlation between temperature and Rt values, although the relationship was not linear, probably as a result of the complex relationship between temperature and the different parameters affecting BTV transmission. Rt values for BTV-1 in Andalusia fell below the threshold of 1 when temperatures dropped below 21°C, a much higher threshold than that reported in other BTV outbreaks, such as the BTV-8 epidemic in Northern Europe. This divergence may be explained by differences in the adaptation to temperature of the main vectors of the BTV-1 epidemic in Andalusia (Culicoides imicola) compared those of the BTV-8 epidemic in Northern Europe (Culicoides obsoletus). Importantly, we found that BTV transmission (Rt value) increased significantly in areas with higher densities of sheep. Our analysis also established that control of BTV-1 in Andalusia was complicated by the simultaneous establishment of several distant foci at the start of the epidemic, which may have been caused by several independent introductions of infected vectors from the North of Africa. We discuss the implications of these findings for BTV surveillance and control in this region of Europe.

Bluetongue virus surveillance in the Islamic Republic of Mauritania: Is serotype 26 circulating among cattle and dromedaries?

In March 2013, EDTA-blood and serum samples were collected from 119 cattle and 159 dromedaries at the slaughterhouse of Nouakchott, the capital city of the Islamic Republic of Mauritania. Serum samples were screened for the presence of Bluetongue (BT) antibodies by competitive ELISA (cELISA). Positive samples were then tested by serum-neutralization (SN) to determine BTV serotype. RNA from blood samples was first tested by a genus-specific quantitative RT-PCR assay which is able to detect all 27 existing BTV serotypes (RT-qPCR1–27). Positive samples were further screened by a RT-qPCR assay which, instead, is able to detect the classical 24 BTV serotypes only (RT-qPCR1–24). Of the 278 serum samples tested, 177 (mean=63.7%; 95% CI: 57.9%–69.1%) resulted positive by cELISA. Of these, 69 were from cattle (mean=58.0%; 95% CI: 49.0%–66.5%) and 108 from dromedaries (mean=67.9%; 95% CI: 60.3%–74.7%). BTV-26 neutralizing antibodies were by far the most frequently found as they were detected in 146 animals with titres ranging from 1:10 to 1:80. Out of 278 blood samples, 25 (mean=9.0%; 95% CI: 6.2%–12.9%) were found positive for BTV by RT-qPCR1–27, 20 (mean=16.8%; 95% CI: 11.2%–24.6%) were from cattle and 5 (mean=3.1%; 95% CI: 1.4%–7.1%) from dromedaries. When tested by RT-qPCR1–24 the 25 BTV positive samples were negative. Unfortunately, no genetic information by molecular typing or by next generation sequencing has been obtained as for the very low levels of RNA in the blood samples.

Whole genome sequence analysis of circulating Bluetongue virus serotype 11 strains from the United States including two domestic canine isolates.

Bluetongue virus (BTV) is a vector-transmitted pathogen that typically infects and causes disease in domestic and wild ruminants. BTV is also known to infect domestic canines as discovered when dogs were vaccinated with a BTV-contaminated vaccine. Canine BTV infections have been documented through serological surveys, and natural infection by the Culicoides vector has been suggested. The report of isolation of BTV serotype 11 (BTV-11) from 2 separate domestic canine abortion cases in the states of Texas in 2011 and Kansas in 2012, were apparently unrelated to BTV-contaminated vaccination or consumption of BTV-contaminated raw meat as had been previously speculated. To elucidate the origin and relationship of these 2 domestic canine BTV-11 isolates, whole genome sequencing was performed. Six additional BTV-11 field isolates from Texas, Florida, and Washington, submitted for diagnostic investigation during 2011 and 2013, were also fully sequenced and analyzed. The phylogenetic analysis indicates that the BTV-11 domestic canine isolates are virtually identical, and both share high identity with 2 BTV-11 isolates identified from white-tailed deer in Texas in 2011. The results of the current study further support the hypothesis that a BTV-11 strain circulating in the Midwestern states could have been transmitted to the dogs by the infected Culicoides vector. Our study also expands the short list of available BTV-11 sequences, which may aid BTV surveillance and epidemiology.

Isolation of a Bluetongue virus group-specific monoclonal antibody and application to a diagnostic competitive ELISA.

The Bluetongue virus (BTV) VP7 protein represents an important group-specific antigen that can serve as a basis for diagnostic tests. Here, we report the generation of a novel BTV group-specific monoclonal antibody (Mab; herein named 4H7) that recognizes a conformational epitope in the VP7 protein. We used a phage-displayed peptide screen and site-directed mutagenesis to define the VP7 amino acid residues that most strongly contribute to the conformational epitope recognized by Mab 4H7. Amino acid residues at positions 175, 185, 186, and 278 of the BTV VP7 protein strongly contributed to Mab 4H7 binding. These key amino acid residues are conserved among all BTV serotypes, whereas related Orbiviruses possess at least one amino acid substitution at these positions. We developed a competitive enzyme-linked immunosorbent assay (c-ELISA) using Mab 4H7 and recombinant BTV VP7 protein to detect serum antibodies against this BTV group-specific VP7 epitope. The c-ELISA was used to screen 833 clinical samples collected from animals in three provinces of China. BTV seroprevalence in the three provinces ranged from 25.42 to 47.45 %. This work provides the foundation for a new diagnostic c-ELISA that can be further applied to BTV surveillance activities and informs our understanding of the structure of the BTV VP7 protein.

Novel Serotype of Bluetongue Virus, Western North America

To the Editor: Bluetongue is an arboviral disease of domestic and wild ruminants characterized by vascular injury that produces widespread edema and tissue necrosis (1). Bluetongue virus (BTV), the causative agent of bluetongue, is the prototype virus of the family Reoviridae and the genus Orbivirus (2). BTV occurs throughout temperate and tropical areas of the world coincident with the distribution of vector Culicoides spp. midges (3–5). Different midge species transmit different constellations of BTV serotypes in distinct global episystems (3,5). For example, C. sonorensis is the principal, if not exclusive, vector of BTV serotypes 10, 11, 13, and 17 in much of North America, whereas C. insignis is the major vector of multiple BTV serotypes (including BTV 1–4, 6, 8, 12, 17, 19, 20, and probably others) in the Caribbean basin, Central America, and South America. C. insignis is also found in the southeastern United States, and although this species might have recently expanded its range in the region, its distribution in North America remains poorly defined. Serotypes of BTV other than 10, 11, 13, and 17 are found in areas of the United States: BTV-2 was first reported in Florida in 1982. Since 1998, ten additional serotypes (BTV-1, 3, 5, 6, 9, 12, 14, 19, 22, and 24) have been identified in the southeastern United States (6). Approximately 26 BTV serotypes have been described and the global distribution of BTV has recently been altered (2,4). Coincident with the invasion of novel BTV serotypes into the southeastern United States (6), likely by extension from the adjacent Caribbean basin, multiple BTV serotypes have spread throughout much of continental Europe and parts of the British Isles and Scandinavia, precipitating an economically devastating epidemic (7). Similarly, ongoing surveillance has identified novel BTV serotypes in regions to which it historically has been endemic (e.g., Australia and the Middle East) (2). Climate change may have contributed to this dramatic recent expansion in global distribution of BTV, most notably in Europe (8). Bluetongue was first described in the late 19th century among sheep brought from Europe to South Africa, and later in North America in ≈1950 (4). Surveillance in western North America since that time has confirmed that only BTV-10, 11, 13 and 17 are present in this region, including our recent intensive surveillance of sentinel cattle on dairy farms throughout California, USA (9,10). However, during investigation of an outbreak of acute coronitis and ulcerative stomatitis among cattle at a dairy farm in the northern Sacramento Valley in California in August 2010, a blood sample from a heifer was found by using described methods (10) to be positive for BTV by serogroup-specific quantitative reverse transcription PCR (qRT-PCR) but negative by serotype-specific RT-qPCRs for BTV-10, 11, 13, and 17. Further analysis using additional serotype-specific RT-qPCRs identified virus in the blood sample as BTV-2. BTV was isolated in primary bovine endothelial cells from blood collected from the heifer. Sequence analysis of the serotype-specific L2 gene of the virus isolate confirmed it to be BTV-2 (2), and phylogenetic analyses showed it to be most closely related to a strain of BTV-2 isolated in Florida in 1999 (Figure). However, sequence analysis of the entire genome of the virus from California indicated that it is a reassortant that includes genes from BTV-6 and BTV-2. Specifically, genes encoding the viral protein 1 polymerase and viral protein 3 major core protein segregate with those of the US prototype strain of BTV-6 (isolated in 2006), but other genes are derived from BTV-2. BTV-2 and BTV-6 have been isolated only in the southeastern United States, which indicates translocation within the United States of reassortant BTV-2. Figure Cladogram comparing the L2 genes of different bluetongue virus (BTV) serotypes and global strains of BTV serotype 2 (BTV-2) with that of a virus isolated in northern California, USA (2-California-2010; GenBank accession nos. {type:entrez-nucleotide-range,attrs:{text:JQ822248-JQ822257,start_term:JQ822248,end_term:JQ822257,start_term_id:390980698,end_term_id:390980714}} ... How this virus spread to California is not known, and its distribution in the United States is uncertain because there is no comprehensive national BTV surveillance program. However, BTV-2 was not detected previously in California, suggesting that this serotype was recently introduced into the region or that it is uncommon. Identification of this novel BTV serotype in western North America emphasizes the need for ongoing entomologic and livestock surveillance, particularly in light of recent changes in the global distribution and nature of BTV infection (4,6,8).

Experimental infection of European red deer ( Cervus elaphus) with bluetongue virus serotypes 1 and 8

Bluetongue (BT) is a climate change-related emerging infectious disease in Europe. Outbreaks of serotypes 1, 2, 4, 6, 8, 9, 11, and 16 are challenging Central and Western Europe since 1998. Measures to control or eradicate bluetongue virus (BTV) from Europe have been implemented, including movement restrictions and vaccination of domestic BTV-susceptible ruminants. However, these measures are difficult to apply in wild free-ranging hosts of the virus, like red deer ( Cervus elaphus), which could play a role in the still unclear epidemiology of BT in Europe. We show for the first time that BTV RNA can be detected in European red deer blood for long periods, comparable to those of domestic ruminants, after experimental infection with BTV-1 and BTV-8. BTV RNA was detected in experimentally infected red deer blood up to the end of the study (98–112 dpi). BTV-specific antibodies were found in serum both by enzyme-linked immunosorbent assay (ELISA) and virus neutralization (VNT) from 8 to 12 dpi to the end of the study, peaking at 17–28 dpi. Our results indicate that red deer can be infected with BTV and maintain BTV RNA for long periods, remaining essentially asymptomatic. Thus, unvaccinated red deer populations have the potential to be a BT reservoir in Europe, and could threaten the success of the European BTV control strategy. Therefore, wild and farmed red deer should be taken into account for BTV surveillance, and movement restrictions and vaccination schemes applied to domestic animals should be adapted to include farmed or translocated red deer.

Programme national bulgare de surveillance du virus de la fièvre catarrhale : études de terrain et évaluation du risque en 2009

Bluetongue is a non-contagious, arthropod-borne viral disease of both domestic and wild ruminants. Bluetongue virus (BTV) is endemic in some areas where cattle and wild ruminants serve as reservoirs for the virus. Some authors suggest that a fundamental change in the European ecosystem since 1998, mostly linked to climate change, may have influenced the introduction and sur­vival of BTV in Europe. Genetic analyses of bluetongue viruses isolated in Europe during this period showed that six virus types (1, 2, 4, 8, 9 and 16) have entered the region since that period. The aim of this presentation was to summarize the results of the National BTV Surveillance Programme, field studies, and risk assessment of BTV entry into Bulgaria in 2009. As part of the Surveillance Programme of the disease in 2009, seroprevalence was performed in 19 sentinel BTV-seronegative animal herds, 7 of which were located in the western part of the country and the other 12 in the southern part, about 10 to 20 kil­ometres from the border. Each sentinel herd consisted of 10 large ear-tagged ruminants. The sentinel animals were tested every 30 days for the presence of BTV antibodies. Competitive enzyme-linked immunosorbent assays (cELISAs) were used to determine the antibodies against the common group antigen. Fourteen Onderstepoort black light traps were set up for Culicoides surveil­lance and monitoring in southern and western border districts of the country after April 1, 2009. Catches of Culicoides were sorted by traditional identification keys. The risk of BTV invasion was assessed according to the World Organisation for Animal Health standards. The hazard identification, possibility of BT outbreaks, and assessment of the epidemiological situation in neighbour­ing countries were made based on other authors’ reports on the density of small and large ruminants, and economical and trade relations between countries. In addition, the BTV situation on a Greek Aegean Sea Island was closely monitored in 2008-09. During the 2009 serum surveillance period, 3340 serum sam­ples from different species of ruminants were investigated, all with negative results for BTV antibodies; C. imicola was never detected in more than 12 years of Culicoides surveillance in Bulgaria. Analysis of 274 midges caught during 2009 showed that dominating Culicoides species were of the Obsoletus and Pulicaris complexes, well-known Palaearctic midges in Europe. The negative results from the Surveillance Programme supported the evidence of absence of active BTV circulation on the whole territory of Bulgaria during 2009. During the 2008-09 season, Greek Authorities reported several circulating BTV serotypes (1, 8, 16) on Lesvos Island. As the epidemiological situation on Greek islands in the Aegean Sea is complicated and not very clear, the risk of BTV entering Bulgaria ranges from high (in spring and summer) to moderate (in winter and autumn).

Bluetongue epidemiology in wild ruminants from Southern Spain

Serum samples from 210 wild ruminants collected between 2006 and 2007 in southern Spain were tested for antibodies against bluetongue virus (BTV) by means of a competitive ELISA assay. Eighty-seven of the 210 wild ruminants analysed (41%) showed antibodies against BTV. Statistically significant differences were found in the seroprevalence among species: 66% (65 of 98) for red deer (Cervus elaphus), 50% (ten of 20) for fallow deer (Dama dama), 33% (three of nine) for mouflon (Ovis aries musimon) and 11% (nine of 83) for Spanish ibex (Capra pyrenaica). Overall, the sites where seropositive wild ruminants were found coincide with the areas where BTV had been detected in livestock, but in eastern Sierra Morena, the virus circulated in wild ruminants, although it had not been detected in domestic ruminants in the same areas. Wild ruminants over 1-year of age (sub-adults and adults) had significantly higher seroprevalences than juvenile animals. Statistically significant differences were also observed between BTV seroprevalence and management (free-ranging vs. captivity) with higher prevalence in free-ranging animals. The high seroprevalences obtained suggest that BTV is widespread in wild ruminants in southern Spain. This factor could have an important influence on the evolution of the infection in domestic livestock and indicates the need to include wild ruminant species in BTV surveillance or control programs.