Epidemiological characteristics and clinicopathological features of bluetongue in sheep and cattle, during the 2014 BTV serotype 4 incursion in Greece.

During 2014, an outbreak of Bluetongue virus (BTV) infections attributed to serotype 4 occurred in Greece and spread to south-eastern Europe. In the present article, the clinical and epidemiological data of 15 sheep flocks and 5 dairy cattle herds affected in Greece are described. In sheep, the most frequent clinical signs observed were fever, hyporexia, and edema of the face. A number of clinically affected sheep had chronic laminitis resulting in chronic lameness. Confirmation of suspect clinical cases was performed using BTV-specific real-time RT-PCR, and serotype 4-specific RT-PCR. The average morbidity of bluetongue in the sheep flocks was estimated to be 15.3 % (95 % C.I. 6.8-23.8 %) and the average mortality and case fatality were 4.5 % (95 % C.I. 1.5-7.6 %) and 32.0 % (95 % C.I. 18.1-42.9 %), respectively. The BTV seroprevalence and the ratio of clinical manifestations-to-infections determined in seven of these flocks, were on average 36.5 % (95 % C.I. 15.7-57.3 %) and 24.6 % (95 % C.I. 12.8-36.3 %). BTV ratio of clinical manifestations-to-infections was higher in the imported western European sheep breeds examined compared to the local ones. In dairy cattle, the average herd prevalence of viremia was 48.8 % (95 % C.I. 15.3-82.4 %) and none had signs associated with bluetongue. The results of this study indicate that the 2014 Greek BTV-4 has significant impact on the health status and the viability of sheep in affected flocks but does not cause clinical signs in cattle, despite the high prevalence of viremia.

The impact of the bluetongue serotype 3 outbreak on sheep and goat mortality in the Netherlands in 2023.

In September 2023, bluetongue virus serotype 3 (BTV-3) emerged in the Netherlands, infecting over five thousand livestock farms. In sheep, high morbidity and mortality rates were reported that were unlike previously described bluetongue outbreaks. This study aimed to quantify the impact of BTV-3 in the small ruminant population in the Netherlands in 2023. Sheep and goat movement census data and BTV-3 notification data were available from 2020 until the end of 2023. Data were aggregated to farm and week level and mortality indicators were calculated for lambs (<1 year) and adult animals (≥1 year). Population averaged GEE models with a Negative-binomial distribution and a log-link function correcting for repeated measures per farm in time were used to quantify the association between BTV-3 and mortality. In 2023, 2994 sheep farmers and 89 goat farmers notified clinical signs of BTV-3 to the NVWA. During this BTV-3 outbreak period, an additional 55,000 sheep died compared to the same period in 2020-2022. At flock level a high variety in mortality was observed, with a clear increase in mortality in both flocks that were not notified but that were located in infected areas and in flocks of which the farmer notified clinical signs. During the BTV-3 outbreak period, mortality in infected areas increased 4.2 (95 % CI: 4.0-4.3) times in sheep lambs (<1 year) and 4.6 (95 % CI: 4.4-4.8) times in sheep (≥1 year) compared to BTV-3 free areas. Flocks with a confirmed BTV-3 infection that were notified in September showed a 12.8 (95 % CI: 11.4-14.3) times higher mortality in lambs and a 15.1 (95 % CI: 13.7-16.6) times higher mortality in sheep compared to flocks in BTV-3 areas. In flocks of which the farmer notified clinical signs after September, mortality was 4.6 (95 % CI: 4.2-5.0) and 5.6 (95 % CI: 5.1-6.0) times higher in lambs and sheep compared BTV-3 areas respectively. In goats, around 4000 additional deaths were recorded during the BTV-3 outbreak period. In farms that were notified, mortality of goats (≥1 year) was 1.8 (95 % CI: 1.2-2.8) times higher compared to BTV-3 free areas. Since May 2024, multiple BTV-3 vaccines are available in the Netherlands. In June 2024, the first new infections of BTV-3 were confirmed in Dutch sheep flocks. Hopes are that with the possibility to vaccinate, the spread and impact of BTV-3 in the Netherlands will rapidly decline and that losses as observed in 2023 will no longer be seen.

A Mortality-Based Description of EHDV and BTV Prevalence in Farmed White-Tailed Deer (Odocoileus virginianus) in Florida, USA.

Hemorrhagic disease (HD) caused by bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV) is the most important viral disease of farmed and wild white-tailed deer (WTD; Odocoileus virginianus) and can cause substantial mortality in susceptible hosts. Captive cervid farming is an emerging industry in Florida, an HD-enzootic region. Morbidity and mortality due to HD are major concerns among deer farmers, but the impact of HD on Florida's cervid farming industry is unknown. Our primary objective was to determine the prevalence of epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) among WTD submitted to the University of Florida Institute of Food and Agricultural Sciences Cervidae Health Research Initiative (CHeRI) for post-mortem diagnostics. Our secondary objectives were to identify the predominant circulating EHDV serotypes during each sampling year and to determine the age class with the greatest proportion of EHDV- and BTV-positive post-mortem specimens. From 2016 to 2020, spleen samples from 539 farmed WTD with unexplained mortality were tested for the presence of EHDV and BTV by RT-qPCR. Overall, the prevalence of EHDV, BTV, or EHDV/BTV coinfection was 26%, 16%, and 10%, respectively, and 44% of deer (237/539) were diagnosed with HD by RT-qPCR. The predominant circulating EHDV serotype varied by year. Overall, EHDV-2 was the most commonly identified serotype (55% of PCR-positive cases), and EHDV-1 was the least frequently identified serotype (16% of PCR-positive cases). The greatest proportion of EHDV/BTV positives among mortality cases was observed in young WTD aged 3-6 months (50%-82% positive). There was a significant difference in the prevalence of EHDV/BTV by age when comparing specimens from WTD over 1 year old (p = 0.029, n = 527). Among these samples, the number of reported mortalities and the prevalence of EHDV/BTV were highest in yearling animals (56%). These data provide the first estimate of EHDV and BTV prevalence and virus serotypes among farmed WTD in Florida, identify the WTD age groups with the greatest proportions of EHDV- and BTV-positive specimens, and suggest that HD caused by these two viruses may be a major source of mortality challenging the captive cervid farming industry in Florida.

Origin of Bluetongue Virus Serotype 8 Outbreak in Cyprus, September 2016.

In September 2016, clinical signs, indicative of bluetongue, were observed in sheep in Cyprus. Bluetongue virus serotype 8 (BTV-8) was detected in sheep, indicating the first incursion of this serotype into Cyprus. Following virus propagation, Nextera XT DNA libraries were sequenced on the MiSeq instrument. Full-genome sequences were obtained for five isolates CYP2016/01-05 and the percent of nucleotide sequence (% nt) identity between them ranged from 99.92% to 99.95%, which corresponded to a few (2-5) amino acid changes. Based on the complete coding sequence, the Israeli ISR2008/13 (98.42-98.45%) was recognised as the closest relative to CYP2016/01-05. However, the phylogenetic reconstruction of CYP2016/01-05 revealed that the possibility of reassortment in several segments: 4, 7, 9 and 10. Based on the available sequencing data, the incursion BTV-8 into Cyprus most likely occurred from the neighbouring countries (e.g., Israel, Lebanon, Syria, or Jordan), where multiple BTV serotypes were co-circulating rather than from Europe (e.g., France) where a single BTV-8 serotype was dominant. Supporting this hypothesis, atmospheric dispersion modelling identified wind-transport events during July-September that could have allowed the introduction of BTV-8 infected midges from Lebanon, Syria or Israel coastlines into the Larnaca region of Cyprus.

Epidemiology of bluetongue virus serotype 8, Germany.

In Germany, bluetongue disease had not been reported before 2006. During August 2006-August 2008, >24,000 bluetongue virus serotype 8 infections were reported, most (20,635) in 2007. In 2006 and 2007, respectively, case-fatality rates were 6.4% and 13.1% for cattle and 37.5% and 41.5% for sheep. Vaccination in 2008 decreased cases.

Laboratory tests for evaluating the level of attenuation of bluetongue virus.

One of the most important steps when preparing a live attenuated vaccine is the assessment of the level of attenuation in target animals. It is costly and time consuming as it requires, on each occasion, a large number of susceptible animals and contained accommodation. This study assessed the consistency of the bovine foetal aorta endothelial (BFA) cell line and newborn mice for evaluating the attenuation level of BTV4, BTV9 and BTV16 Italian field isolates. Following serial passages in BHK(21c13) or Vero cell cultures, BTV attenuated clones demonstrated a reduced replication capability in the BFA cells compared to the homologous virulent strains. Similarly, following intracerebral inoculation, the attenuated clones were completely innocuous to newborn mice contrary to the homologous virulent strains which killed all animals within 10 days. Vaccines produced with the BTV9 or BTV4 attenuated clones were safe, immunogenic and capable of preventing clinical symptoms and viraemia in sheep following challenge with homologous virulent virus. The two assays may be valuable indicators of the gradual changes occurring in the BTV population leading to virus attenuation, they can predict the safety of a BTV attenuated vaccine and, in turn, reduce the number of sheep and cattle required to assess the level of attenuation attained.

Field observations during the Bluetongue serotype 8 epidemic in 2006. II. Morbidity and mortality rate, case fatality and clinical recovery in sheep and cattle in the Netherlands.

Data collected in the Netherlands during the Bluetongue serotype 8 (BTV-8) epidemic indicated that in outbreak cattle herds, predominantly dairy and nursing cows were clinically affected and not young stock, beef cattle, beef calves, or breeding animals. In outbreak sheep flocks, mainly ewes and--if present--rams, were clinically affected and not the lambs. Median morbidity rate in outbreak herds was 1.85 per 100 sheep-month at risk and 0.32 per 100 cattle-month at risk for sheep and cattle, respectively. The mean proportion of BT-affected animals in outbreak herds that recovered from clinical disease was approximately eight times higher for cattle compared to sheep in the Netherlands. Median mortality rate in outbreak herds was 0.5 per 100 sheep-month at risk of dying and 0 per 100 cattle-month at risk of dying for sheep and cattle, respectively. Median recovery time of both sheep and cattle that recovered from clinical disease in outbreak herds was 14 days. Median case fatality was 50% in sheep outbreak flocks and 0% in outbreak cattle herds. It is concluded that morbidity and mortality in outbreak cattle herds was very limited during the BTV-8 epidemic in the Netherlands in 2006. In outbreak sheep flocks, morbidity was limited, with exceptions for a few flocks. However, almost 50% of the clinically sick sheep died in outbreak sheep herds.

[Bluetongue disease reaches Switzerland]. / Blauzungenkrankheit erreicht die Schweiz.

Since 2006 bluetongue disease is rapidly spreading across Europe and reached Switzerland in October 2007. In the present article a short overview about the disease and the virus is given, and the first three clinical bluetongue disease cases in cattle, and the respective laboratory findings are presented.

[Epidemiology of bluetongue virus serotype 8 outbreaks in the Netherlands in 2006]. / Beschrijvende epidemiologie van de bluetongue serotype 8-uitbraken in Nederland in 2006.

In August 2006 a major epidemic of Bluetongue (BT) occurred in north-western Europe, affecting The Netherlands, Belgium, Germany, Luxemburg, and the north of France. It was caused by Br virus serotype 8 (BTV-8), a serotype previously unknown to the EU. Although clinical disease is usually restricted to sheep, this virus also caused clinical disease in a small proportion of cattle. The last clinical outbreak of BT in The Netherlands occurred mid-December 2006. The delay between observation of the first clinical signs by the owner and reporting of a clinically suspect BT situation to the veterinary authorities was approximately 2 weeks. BTV-8-associated clinical signs were more prominent in sheep than in cattle, and the relative frequency of specific clinical signs was different in cattle and sheep. Morbidity and mortality rates were significantly higher among sheep than among cattle, and a higher proportion of cattle than sheep recovered from clinical disease.

Multiple bluetongue virus serotypes causing death in Brazilian dwarf brocket deer (Mazama nana) in Brazil, 2015-2016.

Bela Vista Biological Sanctuary (RBV) is a protected area of Itaipu Binacional, a hydroelectric power company located on the border of Brazil and Paraguay. A captive population of Brazilian dwarf brocket deer (Mazama nana, Cervidae, Artiodactyla) is maintained for conservation purposes. Despite the reproductive success of the animals, outbreaks of a fatal hemorrhagic disease have been registered over the years, compromising conservation efforts. In order to identify the etiological agents of these hemorrhagic diseases, 32 captive Brazilian dwarf brockets were sampled to investigate bluetongue virus (BTV), epizootic hemorrhagic disease (EHD), and adenovirus hemorrhagic disease (AHD), in 2015. Only one deer (1/32; 3.12%) was seropositive for BTV. After this survey, five animals died in the early autumn of 2015 and 2016, again presenting clinical signs of hemorrhagic disease. Using RT-qPCR, RT-PCR and DNA sequencing, five BTV serotypes (3, 14, 18, 19, and 22) were identified in blood and tissues collected during necropsies. These BTV serotypes had not been previously described or isolated in Brazil, either in wild or domestic ruminants. Additionally, differential diagnosis was performed for EHD and AHD, but all samples were negative for both diseases. The multiple distinct BTV serotypes identified in these outbreaks resulted in a high lethality (100%) of Brazilian dwarf brockets and indicated that various BTV serotypes are circulating in the area.

[Bluetongue in The Netherlands; description of the first clinical cases and differential diagnosis. Common symptoms just a little different and in too many herds]. / Bluetongue voor het eerst in Nederland: beschrijving van de klinische verschijnselen en differentiaaldiagnose.

For the first time Bluetongue (BT) has been diagnosed in the Netherlands. The clinical symptoms of BT on five farms during the first outbreak ever in the Netherlands are described. Fever and swollen sensitive coronets leading to reluctance to stand and walk were sometimes the first symptoms. Later lesions in the mouth occurred with foamy salivation and respiratory problems. In other cases a swollen head with swollen lips and foamy salivation were the first clinical signs. Also sudden death occurred. In the first sixteen confirmed cases morbidity and mortality were lower than described in outbreaks in other countries. Good collaboration between practitioners, specialists of the Animal Health Service (GD-Deventer), and specialists of the Food and Consumer Product Safety Authority (VWA) and CIDC-Lelystad (Wageningen UR) led to a rapid notification and ultimately confirmation of the suspected diagnosis BT.

Simulation analysis of the effect of herd immunity and age structure on infection of a cattle herd with bluetongue viruses in Queensland, Australia.

A state-transition model based on Leslie matrix formulation was used to investigate the effects of herd immunity and age structure on the infection of a simulated cattle herd with bluetongue viruses under Australian climatic conditions. Increasing duration of immunity decreased the prevalence of infection. A duration of immunity of 33 months was consistent with prevalence estimates made from previous serological studies of bluetongue virus. Herd prevalence displayed slowly dampening cyclical variation over time (most pronounced when a short duration of immunity was simulated). Increasing calving and mortality risk rates in the simulated herd increased prevalence, whereas increasing age at first calving decreased prevalence. Manipulation of calving rates had the greatest effect on the predicted prevalence of infection in the herd. Simulation of a number of herd-management scenarios suggested that management systems in which cattle are bred early and where high calving rates are achieved are likely to contribute to high levels of infection with bluetongue viruses. Results confirm the importance of management factors in influencing the prevalence of infectious diseases in animal populations.

Bluetongue in free-ranging pronghorn antelope (Antilocapra americana) in Wyoming: 1976 and 1984.

At least 3,200 pronghorn (Antilocapra americana) died during a bluetongue (BT) epizootic in eastern Wyoming during late September and early October 1976. In August and September 1984, another BT epizootic occurred in northeastern Wyoming resulting in 300 known pronghorn deaths. In 17 pronghorn examined postmortem, hemorrhages and edema were the most common gross pathologic changes. Microscopic changes included hemorrhage, edema, arterial fibrinoid necrosis, lymphoid depletion in splenic and lymphatic follicles, and neuronal necrosis. Bluetongue virus serotype 17 was isolated from pronghorn in both epizootics. Mortalities ceased with the advent of cool weather in late September and October. Seventy-six of 94 pronghorn killed by hunters during the latter period of the 1976 epizootic, and 14 of 24 pronghorn killed 1 yr later had serologic evidence of exposure to BT virus. The reproductive rate in pronghorn was depressed to 47 fawns per 100 does in August 1977, but returned to 93 fawns per 100 does by 1978. Following the 1984 outbreak, the reproductive rate was similarly depressed, but the cause was confounded by other environmental and range conditions. Deer, mostly mule deer (Odocoileus hemionus), also died during both epizootics of what was presumed to be BT.

Bluetongue in sheep and goats.

A description is given of the symptomatology, pathology and pathogenesis of bluetongue in sheep and goats. The economic significance of the disease in South Africa is discussed.

Mortality attributable to bluetongue virus serotype 8 infection in Dutch dairy cows.

In 2007, bluetongue virus serotype 8 (BTV-8) re-emerged in the Netherlands and a large number of farmers notified morbidity and mortality associated with BTV-8 to the authorities. All dead cows in the Netherlands are registered in one of the three age classes: newborn calves <3 days, calves 3 days to 1 year, and cows >1 year. These registrations result in a complete data set of dead cattle per herd per day from 2003 until 2007. In this study, the mortality associated with BTV-8 for the Dutch dairy industry was estimated, based on this census data. Default, mortality associated with BTV-8 was estimated for the confirmed notification herds. Moreover, an additional analysis was performed to determine if mortality associated with BTV-8 infection occurred in non-notification herds located in BTV-8 infected compartments. A multivariable population-averaged model with a log link function was used for analyses. Separate analyses were conducted for the three different age groups. Confirmed notification herds had an increased cow mortality rate ratio (MRR) (1.4 (95% CI: 1.2-1.6)); calf MRR (1.3 (95% CI: 1.1-1.4)); and newborn calf MRR (1.2 (95% CI: 1.1-1.3)). Furthermore, in non-notification herds in BTV-8 infected compartments, mortality significantly increased 1.1 times (95% CI: 1.1-1.1) in cows, 1.2 times (95% CI: 1.2-1.2) in calves and 1.1 times (1.1-1.1) in newborn calves compared with BTV-8 non-infected months. Using objective census data over a 5-year period, the MRRs indicated increased mortality associated with BTV-8 infection not only in herds of which the farmer notified clinical signs but also in non-notification herds in infected compartments.

Occurrence of dual infection of peste-des-petits-ruminants and goatpox in indigenous goats of central India.

Peste-des-petits-ruminants (PPR), bluetongue (BT) and goatpox (GP) have been well recognized as causes of significant economic losses in the small ruminant population of Asia and Africa. We describe here the occurrence of these three in an outbreak noticed in non-descript goats from a subtropical region of central India. An investigation was carried out to confirm the aetiology of the heavy mortality in goats (74.6%, 112/150), with testing of samples from 12 surviving animals exhibiting mixed clinical signs indicative of PPR, BT and GP. Sandwich ELISA was used to detect PPR virus antigen and competition ELISA to detect PPR virus and BT virus antibodies. GP was confirmed on the basis of nodular lesions and an immunodiffusion assay. Eight of the 12 affected animals (66.7%) were positive for PPR virus and BT virus antibodies, and two goats (16.7%, 2/12) exhibiting clinical lesions of pox were also found positive for PPR virus/antibodies and BT virus antibodies, respectively. Although BT virus could not be identified in any sample, detection of BT virus antibodies indicated previous or possibly concurrent infection with BT virus in these goats. The N-gene-based RT-PCR was used to confirm the PPR infection in these goats, and one of the amplicons was sequenced. The sequence and phylogenetic analysis revealed close proximity to PPR virus isolates from Tibet and China, with sequence homology of up to 96.9%. The sequence homology was relatively low with the majority of other Indian isolates (72.7-93.5%). The detection of this new PPR virus sequence indicates the circulation of cross-border strains in this region of India. It is presumed that the heavy mortality observed in goats is possibly attributable to the occurrence of mixed infection of PPR and GP, or PPR, BT and GP.

Using the National Cattle Register to estimate the excess mortality during an epidemic: application to an outbreak of Bluetongue serotype 8.

National Cattle Registers have been widely used to examine animal movements and their role in disease transmission, but less frequently for other epidemiological applications. Our study shows how routinely collected identification data can be used to evaluate the population impact of an epidemic in cattle and to derive an indirect estimate of the associated mortality. We adapted a method developed by Human health agencies, based on the modelling of historical mortality fluctuations, to analyze the evolution of mortality in a cattle population subjected to a Bluetongue serotype 8 (BT8) outbreak. Between 01/07/2007 and 01/07/2008, 21,017 cattle died in the considered population whereas 16,691 deaths were expected according to the model. 43% of the 4326 extra deaths were found in calves less than 7 days of age, but excess mortality was found in each age group. The temporal distribution of extra-deaths, described at a weekly scale, suggests that they were related to the BT8 epidemic. The presented method could be an appreciable tool for estimating the global burden of epidemics since it is based on data already routinely collected in each European Member State. This study was conducted retrospectively but considering the promptness of the notification system, the method could be used to monitor the evolution of epidemics in near-real time.