Bluetongue virus serotype 8 (BTV-8) infection reduces fertility of Dutch dairy cattle and is vertically transmitted to offspring

In 2007, BTV-8 re-emerged for the second year in the Netherlands and caused morbidity and increased mortality in cattle herds. In addition, cattle farmers reported reduced fertility in their cows. For this study, fifteen herds that were not vaccinated were selected. These were matched to 10 vaccinated herds by geographic region. At the start of the study, in July 2008, all cattle in the non-vaccinated herds >1 year old were sampled. All seronegative cows entered the study program and blood samples from these cows were tested for antibodies against BTV-8 in an ELISA. Cows were sampled at intervals of three weeks and sampling was stopped once a cow tested seropositive. Sampling ceased in all remaining cows in December 2008.Newborn calves originating from infected dams or from vaccinated dams were tested by PCR for BTV-8. Fertility data were obtained from the Royal Dutch Cattle Syndicate (CRV). Multi-level generalized latent and linear models were used for analyses.In 2008, 185 (17.2%) out of 1,074 initially seronegative non-vaccinated cattle seroconverted and were assumed to be infected with BTV-8. Infected cows were 5 (95% CI: 1.9-14.3) times more likely to return for insemination within 56 days after first insemination. In addition, these cows needed 1.7 (95% CI: 1.4-2.0) times more inseminations for an assumed pregnancy, and needed 2.5 (95% CI: 2.4-2.6) times more days between first and last insemination compared to the period prior to seroconversion and compared to cows not infected by BTV-8 in 2008. No association between BTV-8 infection and the chance to abort between 100 and 260 days after last insemination was found.In total, 48 calves originating from infected cows were tested by PCR for the presence of BTV-8. Ten (20.8%) out of these 48 calves were born PCR-positive. None of 256 calves from vaccinated dams tested PCR-positive. Further, cows infected during the second half of gestation had a 15.5 times (95% CI: 1.3-190.4) higher chance of a PCR-positive newborn calf compared to cows infected in the first half of gestation. This study showed that BTV-8 has a negative effect on fertility of dairy cattle.     

Increase in the occurrence of abortions associated with exposure to the Bluetongue virus serotype 8 in naïve dairy herds

The transplacental transmission capacity demonstrated for Bluetongue virus serotype 8 (BTV-8) in cattle probably is associated with an increased occurrence of abortions. The objectives of this study were to quantify the effect of BTV-8 exposure on the occurrence of abortions in previously naive dairy cow herds under natural infection conditions, and to determine a possible risk period during pregnancy associated with this increase. Two criteria were considered in order to estimate the occurrence of abortion: late return-to-service after a first artificial insemination (AI), and short gestations. A late return-to-service was defined as a return taking place 90 to 200 days after a first AI. These criteria were compared between cows in herds exposed during the 2007 epizootic in France and cows in herds that were not exposed. To determine the risk period during a pregnancy, variations in the occurrence of abortions were quantified according to the stage of the pregnancy during which the exposure took place. Survival analyses were used to estimate the risk of increased occurrence of abortion associated with BTV-8 exposure, adjusted by the principal factors known to influence the risk of abortion. Exposure to the BTV-8 virus under natural conditions in previously naive dairy herds notified after clinical suspicion during the 2007 epizootic was associated with an increase in the occurrence of abortions, regardless of the stage of pregnancy. The at-risk gestation period depended on the criteria used to detect abortions. The mean effect of BTV-8 exposure in the ensemble of detected outbreaks corresponded to an increase of 6.7% in late return-to-service. BTV-8 exposure during the first 3 mo of gestation was associated with a 15% increase in late return-to-service for cows with no return-to-service at 90 days, while this increase was 6% for exposure starting from the third month of gestation (in outbreaks detected in September). BTV-8 exposure from the third month of gestation was associated with a 1.9% increase of short gestations. The effect of exposure was more pronounced for outbreaks detected early in the epizootic compared with those detected later.     

中国蓝舌病病毒流行株血清型实时荧光定量RT-PCR检测方法的建立与应用

【背景】蓝舌病病毒(Bluetongue virus,BTV)是一种严重危害反刍动物的虫媒病毒,我国存在12种血清型BTV (BTV-1、-2、-3、-4、-5、-7、-9、-12、-15、-16、-21和-24)的流行。【目的】建立12种血清型BTV的RT-qPCR定型方法,为BTV的诊断与流行病学研究提供技术保障。【方法】根据我国流行BTV基因节段2 (Seg-2)序列设计引物和TaqMan探针,对引物的特异性与敏感性进行评估;以12种血清型BTV毒株和核酸阳性血液样本验证建立的血清型RT-qPCR检测方法;将其应用于库蠓与动物血液样本中BTV的定型。【结果】建立的BTV血清型RT-qPCR检测方法具有良好的特异性与灵敏性,反应的扩增效率(E)值90.3%,相关系数(R2)值在0.991-0.999之间,对12种血清型BTV核酸的检测下限在25-48拷贝之间。对165株BTV的RT-qPCR定型结果与病毒的Seg-2测序鉴定结果一致;对194份采集于哨兵动物的BTV核酸阳性血液样本的RT-qPCR定型结果与感染动物上分离BTV的血清型一致。采用建立的方法,从2019年云南省师宗县与景洪市采集的库蠓与牛血液样本中鉴定出6种血清型的BTV(BTV-1、-2、-4、-5、-16和-24)。【结论】研究建立的12种BTV血清型RT-qPCR定型方法具有特异、敏感和省时的优点,可用于媒介与动物感染BTV的血清型定型,具有良好的应用与推广价值。     

Protection of Spanish Ibex (Capra pyrenaica) against Bluetongue virus serotypes 1 and 8 in a subclinical experimental infection

Many wild ruminants such as Spanish ibex (Capra pyrenaica) are susceptible to Bluetongue virus (BTV) infection, which causes disease mainly in domestic sheep and cattle. Outbreaks involving either BTV serotypes 1 (BTV-1) and 8 (BTV-8) are currently challenging Europe. Inclusion of wildlife vaccination among BTV control measures should be considered in certain species. In the present study, four out of fifteen seronegative Spanish ibexes were immunized with a single dose of inactivated vaccine against BTV-1, four against BTV-8 and seven ibexes were non vaccinated controls. Seven ibexes (four vaccinated and three controls) were inoculated with each BTV serotype. Antibody and IFN-gamma responses were evaluated until 28 days after inoculation (dpi). The vaccinated ibexes showed significant (P<0.05) neutralizing antibody levels after vaccination compared to non vaccinated ibexes. The non vaccinated ibexes remained seronegative until challenge and showed neutralizing antibodies from 7 dpi. BTV RNA was detected in the blood of non vaccinated ibexes from 2 to the end of the study (28 dpi) and in target tissue samples obtained at necropsy (8 and 28 dpi). BTV-1 was successfully isolated on cell culture from blood and target tissues of non vaccinated ibexes. Clinical signs were unapparent and no gross lesions were found at necropsy. Our results show for the first time that Spanish ibex is susceptible and asymptomatic to BTV infection and also that a single dose of vaccine prevents viraemia against BTV-1 and BTV-8 replication.     

An equine herpesvirus type 1 (EHV-1) expressing VP2 and VP5 of serotype 8 bluetongue virus (BTV-8) induces protection in a murine infection model

Bluetongue virus (BTV) can infect most species of domestic and wild ruminants causing substantial morbidity and mortality and, consequently, high economic losses. In 2006, an epizootic of BTV serotype 8 (BTV-8) started in northern Europe that caused significant disease in cattle and sheep before comprehensive vaccination was introduced two years later. Here, we evaluate the potential of equine herpesvirus type 1 (EHV-1), an alphaherpesvirus, as a novel vectored DIVA (differentiating infected from vaccinated animals) vaccine expressing VP2 of BTV-8 alone or in combination with VP5. The EHV-1 recombinant viruses stably expressed the transgenes and grew with kinetics that were identical to those of parental virus in vitro. After immunization of mice, a BTV-8-specific neutralizing antibody response was elicited. In a challenge experiment using a lethal dose of BTV-8, 100% of interferon-receptor-deficient (IFNAR(-/-)) mice vaccinated with the recombinant EHV-1 carrying both VP2 and VP5, but not VP2 alone, survived. VP7 was not included in the vectored vaccines and was successfully used as a DIVA marker. In summary, we show that EHV-1 expressing BTV-8 VP2 and VP5 is capable of eliciting a protective immune response that is distinguishable from that after infection and as such may be an alternative for BTV vaccination strategies in which DIVA compatibility is of importance.     

The Spread of Bluetongue Virus Serotype 8 in Great Britain and Its Control by Vaccination

Background

Bluetongue (BT) is a viral disease of ruminants transmitted by Culicoides biting midges and has the ability to spread rapidly over large distances. In the summer of 2006, BTV serotype 8 (BTV-8) emerged for the first time in northern Europe, resulting in over 2000 infected farms by the end of the year. The virus subsequently overwintered and has since spread across much of Europe, causing tens of thousands of livestock deaths. In August 2007, BTV-8 reached Great Britain (GB), threatening the large and valuable livestock industry. A voluntary vaccination scheme was launched in GB in May 2008 and, in contrast with elsewhere in Europe, there were no reported cases in GB during 2008.

Methodology/Principal Findings

Here, we use carefully parameterised mathematical models to investigate the spread of BTV in GB and its control by vaccination. In the absence of vaccination, the model predicted severe outbreaks of BTV, particularly for warmer temperatures. Vaccination was predicted to reduce the severity of epidemics, with the greatest reduction achieved for high levels (95%) of vaccine uptake. However, even at this level of uptake the model predicted some spread of BTV. The sensitivity of the predictions to vaccination parameters (time to full protection in cattle, vaccine efficacy), the shape of the transmission kernel and temperature dependence in the transmission of BTV between farms was assessed.

Conclusions/Significance

A combination of lower temperatures and high levels of vaccine uptake (>80%) in the previously-affected areas are likely to be the major contributing factors in the control achieved in England in 2008. However, low levels of vaccination against BTV-8 or the introduction of other serotypes could result in further, potentially severe outbreaks in future.     

Embryo transfer as a means of controlling viral infections. VI. Bluetongue virus-free calves from infectious semen

Four Holstein heifers were superovulated and inseminated with infectious semen from a bull experimentally infected with type 17 bluetongue virus (BTV). A total of 20 embryos were collected at donor slaughter and transferred to 16 recipients. Ten recipients became pregnant of which one subsequently aborted, one gave birth to twins which died at birth, one was killed at term because of dystocia, and 7 gave birth to live calves one of which died perinatally. All animals were tested for BTV antibodies at the time of slaughter which was at least 30 days post partum for surviving heifers and calves. Two of the four donor heifers were retrospectively determined to have been infected by the semen (viremia demonstrated) and their embryos accounted for 9 of the 10 pregnancies including the six surviving calves. None of the recipients or calves developed BTV antibody by the termination of the experiment. This study suggests that BTV-free calves can be readily obtained from the use of BTV-positive semen.     

Full Genome Characterisation of Bluetongue Virus Serotype 6 from the Netherlands 2008 and Comparison to Other Field and Vaccine Strains

In mid September 2008, clinical signs of bluetongue (particularly coronitis) were observed in cows on three different farms in eastern Netherlands (Luttenberg, Heeten, and Barchem), two of which had been vaccinated with an inactivated BTV-8 vaccine (during May-June 2008). Bluetongue virus (BTV) infection was also detected on a fourth farm (Oldenzaal) in the same area while testing for export. BTV RNA was subsequently identified by real time RT-PCR targeting genome-segment (Seg-) 10, in blood samples from each farm. The virus was isolated from the Heeten sample (IAH “dsRNA virus reference collection” [dsRNA-VRC] isolate number NET2008/05) and typed as BTV-6 by RT-PCR targeting Seg-2. Sequencing confirmed the virus type, showing an identical Seg-2 sequence to that of the South African BTV-6 live-vaccine-strain. Although most of the other genome segments also showed very high levels of identity to the BTV-6 vaccine (99.7 to 100%), Seg-10 showed greatest identity (98.4%) to the BTV-2 vaccine (RSAvvv2/02), indicating that NET2008/05 had acquired a different Seg-10 by reassortment. Although Seg-7 from NET2008/05 was also most closely related to the BTV-6 vaccine (99.7/100% nt/aa identity), the Seg-7 sequence derived from the blood sample of the same animal (NET2008/06) was identical to that of the Netherlands BTV-8 (NET2006/04 and NET2007/01). This indicates that the blood contained two different Seg-7 sequences, one of which (from the BTV-6 vaccine) was selected during virus isolation in cell-culture. The predominance of the BTV-8 Seg-7 in the blood sample suggests that the virus was in the process of reassorting with the northern field strain of BTV-8. Two genome segments of the virus showed significant differences from the BTV-6 vaccine, indicating that they had been acquired by reassortment event with BTV-8, and another unknown parental-strain. However, the route by which BTV-6 and BTV-8 entered northern Europe was not established.     

Brucella abortus in captive bison. I. Serology, bacteriology, pathogenesis, and transmission to cattle

Two groups of six, non-brucellosis vaccinated, brucellosis seronegative pregnant American bison (Bison bison) were individually challenged with 1 x 10(7) colony forming units (CFU) of Brucella abortus strain 2308. Three days after challenge, each bison group was placed in a common paddock with six non-vaccinated, brucellosis susceptible, pregnant domestic heifers. In a parallel study, two groups of six susceptible, pregnant cattle were simultaneously challenged with the identical dose as the bison and each group was placed with six susceptible cattle in order to compare bison to cattle transmission to that observed in cattle to cattle transmission. Blood samples were collected from bison and cattle weekly for at least 1 mo prior to exposure to B. abortus and for 180 days post-exposure (PE). Sera from the bison and cattle were evaluated by the Card, rivanol precipitation, standard plate agglutination, standard tube agglutination, cold complement fixation tube, warm complement fixation tube, buffered acidified plate antigen, rapid screening, bovine conjugated enzyme linked immunosorbent assay, bison or bovine conjugated enzyme linked immunosorbent assay, and the hemolysis-in-gel techniques for the presence of antibodies to Brucella spp. At the termination of pregnancy by abortion or birth of a live-calf, quarter milk samples, vaginal swabs, and placenta were collected from the dam. Rectal swabs were collected from live calves, and mediastinal lymph nodes, abomasal contents and lung were taken at necropsy from aborted fetuses for culture of Brucella spp. These tissues and swabs were cultured on restrictive media for the isolation and identification of Brucella spp. Pathogenesis of brucellosis in bison was studied in an additional group of six pregnant bison which were challenged with 1 x 10(7) CFU of B. abortus strain 2308. One animal was euthanatized each week PE. Tissues were collected at necropsy and later examined bacteriologically and histologically. Lesions of brucellosis in bison did not significantly differ grossly or histologically from those in cattle. There were six abortions and two nonviable calves in the bison group, as compared to nine abortions in the 12 similarly inoculated cattle. As determined by bacterial isolations, transmission of B. abortus from bison to cattle (five of 12 susceptible cattle became infected) did not differ statistically from cattle to cattle transmission (six of 12 susceptible cattle became infected) under identical conditions. No single serologic test was constantly reliable to diagnosing B. abortus infected bison for 8 wk PE.(ABSTRACT TRUNCATED AT 400 WORDS)     

Transplacental Transmission of Bluetongue Virus Serotype 1 and Serotype 8 in Sheep: Virological and Pathological Findings

The Bluetongue virus serotype 8 (BTV-8) strain, which emerged in Europe in 2006, had an unusually high ability to cause foetal infection in pregnant ruminants. Other serotypes of BTV had already been present in Europe for more than a decade, but transplacental transmission of these strains had never been demonstrated. To determine whether transplacental transmission is a unique feature of BTV-8 we compared the incidence and pathological consequences of transplacental transmission of BTV-8 to that of BTV-1. Nine pregnant ewes were infected with either BTV-8 or BTV-1. The BTV strains used for the infection were field strains isolated on embryonated chicken eggs and passaged twice on mammalian cells. Blood samples were taken to monitor the viraemia in the ewes. Four weeks after the infection, the foetuses were examined for pathological changes and for the presence of BTV. BTV-8 could be demonstrated in 12 foetuses (43%) from 5 ewes (56%). %). BTV-1 was detected in 14 foetuses (82%) from 6 ewes (67%). Pathological changes were mainly found in the central nervous system. In the BTV-8 group, lympho-histiocytic infiltrates, gliosis and slight vacuolation of the neuropil were found. BTV-1infection induced a severe necrotizing encephalopathy and severe meningitis, with macroscopic hydranencephaly or porencephaly in 8 foetuses. In our experimental setting, using low passaged virus strains, BTV-1 was able to induce transplacental transmission to a higher incidence compared to BTV-8, causing more severe pathology.     

Embryo transfer as a means of controlling viral infections. III non transmission of bluetongue virus from viremic cattle

Ten holstein heifers were made viremic by inoculation with type 17 or type 18 bluetongue virus (BTV), superovulated, bred artificially with semen from a BTV seronegative bull and slaughtered for the collection of 8-day embryos. A total of 28 embryos were transferred into 28 BTV seronegative recipients.Fourteen transfers resulted in pregnancies. None of the recipients developed BTV antibody during pregnancy or within 30 days of parturition. No antibody or virus was detected in the 14 calves at parturition (of which 4 were lost due to dystocia), in one recumbent calf at the time of euthanasia at 5 days of age or in the remaining 9 healthy calves at 30 days of age. This study suggests that BTV-free calves can be obtained from infected dams by embryo transfer.     

Abortion risk in progeny of cows after a Neospora caninum epidemic

A study was done of the descendants of cows from 4 dairy herds in which there had been N. caninum abortion outbreaks. Precolostral antibodies to N. caninum were demonstrated in 34 of 50 (68%) F1 calves and in 14 of 17 (82%) F2 calves from cows that aborted during the outbreaks. In 214 F1 progeny, N. caninum seroprevalence was nearly 50%, and there was a significant association between serostatus of the offspring and serostatus of dams. These observations indicated that congenital infection was an important mode of transmission after abortion outbreaks in these herds. A total of 52 abortions was recorded in 293 pregnancies of F1 progeny cows (1 to 3 pregnancies per animal). It was found that seropositive F1 cows had a three-fold increased abortion risk compared with seronegative F1 cows. In 2 of 10 abortions in seronegative cows evidence for N. caninum infection was found, suggesting that a low level of postnatal infection may also have occurred. It is concluded that N. caninum-infected calves should not be used as replacement stock, to decrease the future risk of abortion in dairy herds.     

Fetal infection with Neospora caninum in dairy and beef cattle in Belgium

Neospora caninum is a protozoan parasite, which causes fetal and neonatal mortality in livestock and companion animals. In 224 abortions in Belgian cattle, different diagnostic methods were used to demonstrate infection, and the presence of N. caninum. An indirect fluorescent antibody test (IFAT) was used to analyze fetal and maternal sera and immunohistochemistry (IHC) was performed when lesions consistent with neosporosis were observed in the brain, heart or liver. Twenty dairy cattle sera out of 70 (29%) and 13 beef cattle sera out of 93 (14%) were positive by IFAT. A positive titer to N. caninum was found in seven and three fetuses born to beef and dairy cows, respectively. Lesions consistent with N. caninum infection were observed in 17 fetuses. Of nine positive beef fetuses, five were confirmed by IHC while, all but one dairy fetus were confirmed using the same technique.Age had no influence on the serological status of the mother (P = 0.486) whereas husbandry system had a borderline influence (P = 0.082). However, a strong association (P = 0.004) between the level of antibodies in the dam and the occurrence of lesions in the fetus was observed and lesions were more prominent in dairy than in beef fetuses. Additionally, the distribution of intra-cerebral lesions was more extensive in dairy than in beef fetuses (P < 0.0001). Age and serological status of the fetus were found to influence the occurrence of lesions in beef fetuses (both P < 0.001) but no such significant relationships could be demonstrated in dairy fetuses. The study indicated that N. caninum must be considered as an important cause of bovine abortion in Belgium.     

Embryo transfer as a means of controlling the transmission of viral infections. XV. Failure to transmit bluetongue virus through the transfer of embryos from viremic sheep donors

The first experiment involved in vitro exposure of clean embryos to bluetongue virus (BTV) while three subsequent experiments involved the collection of embryos from BTV-infected donor ewes and their transfer to disease-free recipients. In Experiment I, 22 embryos/ova were exposed to BTV type 11 (BTV-11) for 1 h, washed 10 times in PBS and assayed in pairs for BTV. All 11 samples were positive for BTV in the 11-d-old embryonated chicken egg (ECE) assay system and 5/11 samples were positive in baby hamster kidney-21 (BHK-21) cells. In Experiment II, 5 donors were infected with BTV type 10 (BTV-10). All embryos were washed 10 times prior to assay or transfer. Thirty-three embryos/ova were assayed in groups of 2 or 3 and none yielded virus in ECE. Two BTV-seronegative recipients each received 6 embryos and a total of 3 lambs free of BTV antibodies were delivered. In Experiments III and IV, a total of 9 donors were infected with BTV-11. All embryos were washed 10 times prior to assay or transfer. Seventy-four embryos/ova were assayed in groups of 2 or 3 and none yielded virus in ECE, while for each experiment, 6 embryos were transferred into 2 BTV-seronegative recipients. The four recipients and their 3 lambs and 2 aborted fetuses were also seronegative for BTV.     

Identification of a neutralizing epitope shared by bluetongue virus serotypes 2 and 13

The serotypes of bluetongue virus (BTV) are classified by differences in neutralization commonly induced by P2, a major surface protein. A BTV serotype 13 (BTV-13) monoclonal antibody, 4B13-207A, immunoprecipitated P2s of BTV-13 and BTV-2 and also neutralized both viruses. These data indicate that P2s from BTV-13 and BTV-2 share a common neutralizing epitope that is not detected by neutralizing polyclonal antibody to BTV-13.     

Characterization of protection afforded by a bivalent virus-like particle vaccine against bluetongue virus serotypes 1 and 4 in sheep

Background

Bluetongue virus (BTV) is an economically important, arthropod borne, emerging pathogen in Europe, causing disease mainly in sheep and cattle. Routine vaccination for bluetongue would require the ability to distinguish between vaccinated and infected individuals (DIVA). Current vaccines are effective but are not DIVA. Virus-like particles (VLPs) are highly immunogenic structural mimics of virus particles, that only contain a subset of the proteins present in a natural infection. VLPs therefore offer the potential for the development of DIVA compatible bluetongue vaccines.

Methodology/Principal Findings

Merino sheep were vaccinated with either monovalent BTV-1 VLPs or a bivalent mixture of BTV-1 VLPs and BTV-4 VLPs, and challenged with virulent BTV-1 or BTV-4. Animals were monitored for clinical signs, antibody responses, and viral RNA. 19/20 animals vaccinated with BTV-1 VLPs either alone or in combination with BTV-4 VLPs developed neutralizing antibodies to BTV-1, and group specific antibodies to BTV VP7. The one animal that showed no detectable neutralizing antibodies, or group specific antibodies, had detectable viral RNA following challenge but did not display any clinical signs on challenge with virulent BTV-1. In contrast, all control animals'' demonstrated classical clinical signs for bluetongue on challenge with the same virus. Six animals were vaccinated with bivalent vaccine and challenged with virulent BTV-4, two of these animals had detectable viral levels of viral RNA, and one of these showed clinical signs consistent with BTV infection and died.

Conclusions

There is good evidence that BTV-1 VLPs delivered as monovalent or bivalent immunogen protect from bluetongue disease on challenge with virulent BTV-1. However, it is possible that there is some interference in protective response for BTV-4 in the bivalent BTV-1 and BTV-4 VLP vaccine. This raises the question of whether all combinations of bivalent BTV vaccines are possible, or if immunodominance of particular serotypes could interfere with vaccine efficacy.     

Reassortment between Two Serologically Unrelated Bluetongue Virus Strains Is Flexible and Can Involve any Genome Segment

Coinfection of a cell by two different strains of a segmented virus can give rise to a “reassortant” with phenotypic characteristics that might differ from those of the parental strains. Bluetongue virus (BTV) is a double-stranded RNA (dsRNA) segmented virus and the cause of bluetongue, a major infectious disease of livestock. BTV exists as at least 26 different serotypes (BTV-1 to BTV-26). Prompted by the isolation of a field reassortant between BTV-1 and BTV-8, we systematically characterized the process of BTV reassortment. Using a reverse genetics approach, our study clearly indicates that any BTV-1 or BTV-8 genome segment can be rescued in the heterologous “backbone.” To assess phenotypic variation as a result of reassortment, we examined viral growth kinetics and plaque sizes in in vitro experiments and virulence in an experimental mouse model of bluetongue disease. The monoreassortants generated had phenotypes that were very similar to those of the parental wild-type strains both in vitro and in vivo. Using a forward genetics approach in cells coinfected with BTV-1 and BTV-8, we have shown that reassortants between BTV-1 and BTV-8 are generated very readily. After only four passages in cell culture, we could not detect wild-type BTV-1 or BTV-8 in any of 140 isolated viral plaques. In addition, most of the isolated reassortants contained heterologous VP2 and VP5 structural proteins, while only 17% had homologous VP2 and VP5 proteins. Our study has shown that reassortment in BTV is very flexible, and there is no fundamental barrier to the reassortment of any genome segment. Given the propensity of BTV to reassort, it is increasingly important to have an alternative classification system for orbiviruses.     

Prevalence of, and risk factors associated with, perinatal calf mortality in pasture-based Holstein-Friesian cows

Recent publications indicate that the prevalence of perinatal mortality has increased in some dairy industries and an increased proportion of this loss is not associated with the traditional risk factors for perinatal mortality. The objectives of this study were to establish the prevalence of perinatal mortality (calf death within 24 h of calving) in Irish dairy herds and to determine the current significance of putative risk factors in pasture-based management systems. A total of 182 026 records of full-term calvings from Holstein-Friesian dams served by artificial insemination (AI) sires of seven breeds in herds of 20 calvings or more per year were available from the Irish national breeding database over 4 years (2002 to 2005). The prevalence of perinatal mortality was 4.29% (7.7% in primiparae and 3.5% in pluriparae). The likelihood of perinatal mortality increased between 2002 and 2005 and was greatest in June and in winter. There was an interaction (P < 0.001) between the effect of calving assistance and parity with the effect of dystocia on perinatal mortality being greater in primiparae. The odds of perinatal mortality were greater in male (OR = 1.12; P < 0.001) and in twin calves (OR = 5.70-13.36; P < 0.001) and in dams that had perinatal mortality at the previous calving (OR = 4.21; P < 0.001). The logit of the probability of perinatal mortality increased by 0.099 per unit increase in sire predicted transmitting ability (PTA) for direct perinatal mortality. The probability of perinatal mortality increased at an increasing rate in primiparae as animals calved at a younger age relative to the median age at first calving. The only herd-level factor examined, herd size did not affect the odds of perinatal mortality. These data indicate that the prevalence of perinatal mortality in this cattle population is similar to that in other pasture-based dairy systems worldwide. The putative exposures and attributes traditionally associated with perinatal mortality were associated with perinatal mortality in this pasture-based dairy cow population. The practical implication of these results is that as many of the significant risk factors are largely not under management control (year of calving, month of calving, twin calving, primiparity, previous perinatal mortality and foetal gender), herd owners must focus on the significant determinants under their control (age at first calving, sire genetic merit for direct perinatal mortality and both the extent of calving supervision and the degree of assistance), in order to reduce the prevalence of perinatal mortality and improve perinatal welfare.     

A Dynamic Spatio-Temporal Model to Investigate the Effect of Cattle Movements on the Spread of Bluetongue BTV-8 in Belgium

When Bluetongue Virus Serotype 8 (BTV-8) was first detected in Northern Europe in 2006, several guidelines were immediately put into place with the goal to protect farms and stop the spreading of the disease. This however did not prevent further rapid spread of BTV-8 across Northern Europe. Using information on the 2006 Bluetongue outbreak in cattle farms in Belgium, a spatio-temporal transmission model was formulated. The model quantifies the local transmission of the disease between farms within a municipality, the short-distance transmission between farms across neighbouring municipalities and the transmission as a result of cattle movement. Different municipality-level covariates such as farm density, land composition variables, temperature and precipitation, were assessed as possibly influencing each component of the transmission process. Results showed a significant influence of the different covariates in each model component, particularly the significant effect of temperature and precipitation values in the number of infected farms. The model which allowed us to predict the dynamic spreading of BTV for different movement restriction scenarios, also affirmed the significant impact of cattle movement in the 2006 BTV outbreak pattern. Simulation results further showed the importance of considering the size of restriction zones in the formulation of guidelines for animal infectious diseases.