An investigation into the transmission and control of pestivirus in sheep in Australia

Border disease virus (BDV) is a member of the pestivirus genus that primarily affects sheep, causing reproductive losses through abortion, still births and the birth of weak lambs. The key characteristic of this disease is the birth of persistently infected (PI) lambs which, after surviving transplacental infection, are born antibody negative, yet virus positive, and thus shed the virus for their entire life and are the primary source of spread within a flock. The cornerstones of BDV control are detection and elimination of PI animals, biosecurity measures to prevent re-infection, and surveillance programs. Recommendations for the control of BDV in sheep are centred around the approach to bovine viral diarrhoea virus (BVDV), the prominent cattle pestivirus species, due to a lack of specific research into BDV control and elimination. In this study, two aspects of a BDV control program were investigated: the effectiveness of the BVDV vaccine, Pestigard®, and the rate of seroconversion in a flock deliberately exposed to known PI lambs. The vaccine appeared to be safe, and the optimal dose was the full cattle dose (2 mL). While vaccination induced high virus neutralising titres to BVDV when administered as either a quarter, half or full dose registered for cattle, the BDV titres achieved were low and unlikely to prevent transplacental infection. In a second study, after exposure of between 2 and 15 days exposure to two PI lambs in confined conditions, only 3 of 66 previously naïve sheep demonstrated seroconversion. This demonstrated a very low rate of transmission and suggested that deliberate exposure to PI lambs at low-risk times for less than 15 days was not likely to be an effective means of achieving seroconversion throughout a flock and, therefore, not provide protection against BDV challenge during gestation.

New Potential Role of European Mouflon (Ovis aries musimon) in the Epidemiology of Border Disease in the Pyrenees

Since 2001, high-mortality outbreaks of border disease (BD) have negatively affected populations of Pyrenean chamois (Rupicapra pyrenaica pyrenaica). Studies in the affected areas determined that sympatric wild ruminants did not seem to have an epidemiologic role in the circulation of border disease virus (BDV). However, the recent increase in European mouflon (Ovis aries musimon) densities might enhance the risk of pathogen transmission among chamois and mouflons. We conducted a serologic and virologic investigation of BDV in European mouflon from the Spanish Pyrenees, with the aim of determining potential changes in the role of this species in BDV epidemiology. From 2018 to 2022, we detected antibodies against BDV in 31/185 (16.7%) animals but did not detect BDV RNA in any spleen sample (0/65). These results indicate that BDV infection is occurring in these mouflon populations to a greater extent than previously described, which could shift the current understanding of BD epidemiology in the Pyrenees and cause an unpredictable effect on both chamois and mouflon populations. Further studies on the molecular identification of BDV in mouflon and chamois are required to better understand the contribution of mouflon in the epidemiology of BD.

Global Distribution and Genetic Heterogeneity of Border Disease Virus

Border disease virus (BDV) belongs to the genus Pestivirus of the family Flaviviridae. Interspecies transmission of BDV between sheep, cattle, and pigs occurs regularly, sometimes making diagnosis a challenge. BDV can yield substantial economic losses, including prenatal and postnatal infections in lambs, which are the primary source of infection and maintenance of the virus in the population. Since BDV is antigenically and genetically related to bovine viral diarrhea virus (BVDV), it might pose a significant risk to cattle, influencing BVDV eradication campaigns. Similarly, the presence of BDV in swine herds due to pestivirus spillover between small ruminants and pigs might cause uncertainty in classical swine fever virus (CSFV) diagnostics. Therefore, knowledge of BDV epidemiology in different geographical regions will help prevent its spread and optimize control measures. Previous epidemiological studies have shown that various BDV genotypes are predominant in different countries. This review provides an overview of the spread of BDV world-wide in different host species.

Seroprevalence of border disease virus and other pestiviruses in sheep in Algeria and associated risk factors

BACKGROUND

Border disease virus (BDV) is a pestivirus responsible for significant economic losses in sheep industry. The present study was conducted between 2015 and 2016 to determine the flock seroprevalence of the disease in Algeria and to identify associated risk factors. 56 flocks from nine departments were visited and 689 blood samples were collected from adult sheep between 6 and 24 months of age (n = 576) and from lambs younger than 6 months (n = 113). All samples were tested by RT-PCR as well as by Ag-ELISA, to detect Persistently Infected (PI) animals. Serum samples from adults were tested by Ab-ELISA (Enzyme Linked Immuno-Sorbent Assay), to detect specific antibodies against pestivirus and 197 of them were further characterized by VNT (virus neutralization test) for the detection of neutralizing antibodies specific for BDV and for Bovine virus diarrhea virus (BVDV-1 and BVDV-2).

RESULTS

No PI animals were found among the 689 sheep tested. 144/197 sera were positive in VNT for BDV, and 2 sera were strongly positive BVDV-2. Fifty-five flocks (98%) had at least one seropositive animal and the apparent within-flock seroprevalence was estimated to be 60.17% (95% C.I.: 52.96-66.96). The true seroprevalence based on estimated sensitivity and specificity of the Ab-ELISA was 68.20% (95% C.I.; 60.2-76.3). Several risk factors were identified as linked to BDV such as climate, landscape, flock management and presence of other ruminant species in the farm.

CONCLUSION

These high seroprevalence rates suggest that BDV is widespread and is probably endemic all over the country. Further studies are needed to detect and isolate the virus strains circulating in the country and understand the distribution and impact of pestiviruses in the Algerian livestock.

Spatial and Temporal Phylogeny of Border Disease Virus in Pyrenean Chamois (Rupicapra p. pyrenaica)

Border disease virus (BDV) affects a wide range of ruminants worldwide, mainly domestic sheep and goat. Since 2001 several outbreaks of disease associated to BDV infection have been described in Pyrenean chamois (Rupicapra pyrenaica pyrenaica) in Spain, France and Andorra. In order to reconstruct the most probable places of origin and pathways of dispersion of BDV among Pyrenean chamois, a phylogenetic analysis of 95 BDV 5'untranslated sequences has been performed on chamois and domestic ungulates, including novel sequences and retrieved from public databases, using a Bayesian Markov Chain Monte Carlo method. Discrete and continuous space phylogeography have been applied on chamois sequences dataset, using centroid positions and latitude and longitude coordinates of the animals, respectively. The estimated mean evolutionary rate of BDV sequences was 2.9×10-3 subs/site/year (95% HPD: 1.5-4.6×10-3). All the Pyrenean chamois isolates clustered in a unique highly significant clade, that originated from BDV-4a ovine clade. The introduction from sheep (dated back to the early 90s) generated a founder effect on the chamois population and the most probable place of origin of Pyrenean chamois BDV was estimated at coordinates 42.42 N and 1.9 E. The pathways of virus dispersion showed two main routes: the first started on the early 90s of the past century with a westward direction and the second arise in Central Pyrenees. The virus spread westward for more than 125 km and southward for about 50km and the estimated epidemic diffusion rate was about 13.1 km/year (95% HPD 5.2-21.4 km/year). The strong spatial structure, with strains from a single locality segregating together in homogeneous groups, and the significant pathways of viral dispersion among the areas, allowed to reconstruct both events of infection in a single area and of migrations, occurring between neighboring areas.

[PESTIVIRUSES IN RUMINANTS]

The genus Pestivirus includes four species: bovine viral diarrhea virus 1, bovine viral diarrhea virus 2, classical swine fever disease virus, and ovine border disease virus. Pestiviruses infect many species of domestic and wild animals. Bovine viral diarrhea virus is a prototypical representative of the pestiviruses of ruminant animals. Recently, new candidates appeared for including in this genus: two viruses of the wild ruminant animals that have not been officially classified and one HoBi-like virus discovered for the first time in the bovine fetal serum. The circulation of the ruminant animal pestiviruses within population of domestic and wild animals, the presence of these viruses in bioproducts stimulates studies of the infection reservoirs and their influence on the effect of the bovine viral diarrhea control programs.

Characterization of one sheep border disease virus in China

BACKGROUND

Border disease virus (BDV) causes border disease (BD) affecting mainly sheep and goats worldwide. BDV in goat herds suffering diarrhea was recently reported in China, however, infection in sheep was undetermined. Here, BDV infections of sheep herds in Jiangsu, China were screened; a BDV strain was isolated and identified from the sheep flocks in China. The genomic characteristics and pathogenesis of this new isolate were studied.

RESULTS

In 2012, samples from 160 animals in 5 regions of Jiangsu province of China were screened for the presence of BDV genomic RNA and antibody by RT-PCR and ELISA, respectively. 44.4% of the sera were detected positively, and one slowly grown sheep was analyzed to be pestivirus RNA positive and antibody-negative. The sheep kept virus positive and antibody negative in the next 6 months of whole fattening period, and was defined as persistent infection (PI). The virus was isolated in MDBK cells without cytopathic effect (CPE) and named as JSLS12-01. Near-full-length genome sequenced was 12,227 nucleotides (nt). Phylogenetic analysis based on 5'-UTR and N(pro) fragments showed that the strain belonged to genotype 3, and shared varied homology with the other 3 BDV strains previously isolated from Chinese goats. The genome sequence of JSLS12-01 also had the highest homology with genotype BDV-3 (the strain Gifhorn). Experimental infections of sheep had mild clinical signs as depression and short-period mild fever (5 days). Viremia was detected in 1-7 days post-infection (dpi), and seroconversion began after 14 dpi.

CONCLUSIONS

This study reported the genomic and pathogenesis characterizations of one sheep BDV strain, which confirmed the occurrence of BDV infection in Chinese sheep. This sheep derived BDV strain was classified as BDV-3, together with the goat derived strains in China. These results might be helpful for further understanding of BDV infection in China and useful for prevention and control of BDV infections in the future.

Two different epidemiological scenarios of border disease in the populations of Pyrenean chamois (Rupicapra p. pyrenaica) after the first disease outbreaks

Since 2001 several outbreaks of a new disease associated with Border disease virus (BDV) infection have caused important declines in Pyrenean chamois (Rupicapra pyrenaica) populations in the Pyrenees. The goal of this study was to analyze the post-outbreak BDV epidemiology in the first two areas affected by disease with the aim to establish if the infection has become endemic. We also investigated if BDV infected wild and domestic ruminants sharing habitat with chamois. Unexpectedly, we found different epidemiological scenarios in each population. Since the disease outbreaks, some chamois populations recuperated quickly, while others did not recover as expected. In chamois from the first areas, prevalence was high (73.47%) and constant throughout the whole study period and did not differ between chamois born before and after the BDV outbreak; in all, BDV was detected by RT-PCR in six chamois. In the other areas, prevalence was lower (52.79%) and decreased during the study period; as well, prevalence was significantly lower in chamois born after the disease outbreak. No BDV were detected in this population. A comparative virus neutralisation test performed with four BDV strains and one Bovine viral diarrhoea virus (BVDV) strain showed that all the chamois had BDV-specific antibodies. Pestivirus antibodies were detected in all the rest of analyzed species, with low prevalence values in wild ruminants and moderate values in domestic ruminants. No viruses were detected in these species. These results confirm the hypothesis that outbreaks of BDV infection only affect the Pyrenean chamois, although other wild ruminants can occasionally be infected. In conclusion, two different scenarios have appeared since the first border disease outbreaks in Pyrenean chamois: on the one hand frequent BDV circulation with possible negative impact on population dynamics in some areas and on the other, lack of virus circulation and quick recovery of the chamois population.

Seroprevalence of antibodies against pestiviruses in small ruminants in The Netherlands

In this study, a serological survey was performed to determine the prevalence of pestivirus (bovine viral diarrhea virus (BVDV) and border disease virus (BDV)) infected small ruminants herds in the Netherlands. After random selection of sheep farms, a sample size was determined to detect a 5% herd prevalence. 13 out of 29 farms were tested seropositive using an ELISA which detects antibodies directed against the non structural protein 3 (NS3) of pestiviruses. This resulted in a seroprevalence for the Netherlands of 45% [0.36; 0.54]. The within farm prevalence ranged from 4 till 65%. Using a virus neutralization assay, specific anti-BDV antibodies could be detected on two farms, while on one other farm anti-BVDV antibodies were present. On four farms antibodies to both viruses could be detected, on three of these farms antibodies against both viruses were equally present. At five farms that tested positive in the NS3-ELISA we were unable to detect pestivirus neutralizing antibodies in all sera using the VN test. This resulted in an estimated prevalence using the VN for the Netherlands of 28% [0.20; 0.60]. An additional survey in sera from dairy goats revealed that 34 out of 126 farms were serological positive resulting in a seroprevalence of 27% [0.23; 0.31], with a herd prevalence of 32% ranging from 1-100%.

Epidemiological study of border disease virus infection in Southern chamois (Rupicapra pyrenaica) after an outbreak of disease in the Pyrenees (NE Spain)

In 2001 and 2002, an outbreak of a previously unreported disease, associated with a border disease virus (BDV), caused high mortality in the Southern chamois (Rupicapra pyrenaica) population in the Alt Pallars-Aran National Hunting Reserve in the Catalan Pyrenees (NE Spain). Between 2002 and 2006, sera and/or tissue samples taken from 116 healthy chamois shot during the hunting season, plus 42 from chamois affected by different diseases, were studied. A blocking enzyme-immunosorbent assay (ELISA) was used to study pestivirus seroprevalence in 114 healthy hunted and 31 diseased chamois, yielding positive results in 73.7 and 22.6% of the chamois, respectively. Comparative virus neutralization tests (VNT) performed on 42 seropositive samples with 6 pestivirus strains yielded statistically higher titres to BDV Spain 97, followed by BDV chamois, BDV 137/4, BDV Moredun, Bovine Diarrhoea virus-1 (BVDV-1) NADL and BVDV-2 atypical. Virological investigations for pestivirus detection were performed using an antigen ELISA test in 82 healthy and 18 diseased chamois, RT-PCR in 16 healthy and in all diseased chamois, and virus isolation in 14 diseased chamois. No viral antigen was detected in any of the healthy animals. A pestivirus, characterized as BDV by monoclonal antibodies, was detected in the 10 chamois showing clinical signs consistent with BDV infection. Sequence analysis in the 5' untranslated region (5'-UTR) revealed that they were grouped into the BDV-4 genotype. In the remaining chamois, infectious keratoconjunctivitis, pneumonia, trauma and contagious ecthyma were diagnosed. The cause of death was unknown in five chamois. The results suggest that the infection has become endemic in the population and that it could have a significant impact on chamois population dynamics.

Influence of Communal Alpine Pasturing on the Spread of Pestiviruses among Sheep and Goats in Austria: First Identification of Border Disease Virus in Austria

The purpose of this investigation was to determine the influence of communal Alpine pasturing on the spread of pestivirus infections among sheep and goats. The study included 481 sheep from 23 farms and 131 goats from 26 farms pastured on separated Alpine meadows in the western part of Austria. At the starting of pasturing on the sheep meadow, 325 (67.6%) animals were seropositive, on the goat meadows in 16 (12.2%) samples antibodies to pestiviruses were detected. At the end of pasturing, 74 seronegative sheep and two seronegative goats had seroconverted. Between the beginning and the end of pasturing the seroprevalence in sheep increased significantly from 67.6% to 83% (P<0.05). Moreover, in the peripheral blood mononuclear cells of four sheep, pestivirus-specific RNA was detected before as well as after pasturing; these animals remained serologically negative throughout the investigation. They were, therefore, identified as persistently infected. Sequence analysis in the N(pro) region revealed that the detected pestiviruses were the same at genetic level and they were grouped into the Border disease virus (BDV)-3 genotype. No pestivirus RNA was found in goat samples. The results of this survey indicate that communal Alpine pasturing does play a key role in the spread of BDV. Moreover, BDV has been identified and characterized for the first time in sheep in Austria, which until then had been regarded as being free from BD.

Serological survey for antibodies against pestiviruses in sheep in Austria

The prevalence of antibodies to pestiviruses was investigated in 4931 sheep, in 377 flocks, in four federal states of Austria, by means of an indirect elisa that detected antibodies to Border disease virus (BDV) and bovine viral diarrhoea virus (BVDV). The mean flock prevalence was 62.9 per cent and the mean individual prevalence was 29.4 per cent. Comparative neutralisation studies on the elisa-positive samples with BVDV type 1 (BVDV-1), BVDV type 2 (BVDV-2) and BDV recorded 336 samples with higher titres (more than four times average) to BVDV-1, three samples with higher titres to BVDV-2 and 55 samples with higher titres to BDV. The other samples did not show clear differences in antibody titres against the strains of pestivirus tested because of cross-reactions. The seroprevalence of pestiviruses in sheep was significantly higher on farms with cattle. There were significant regional differences between the prevalences in flocks and individual sheep, the highest prevalences being in the region of Austria where communal alpine pasturing of sheep, goats and cattle is an important part of farming.

Severe outbreak of disease in the southern chamois (Rupicapra pyrenaica) associated with border disease virus infection

An outbreak of a previously unreported disease affecting southern chamois (Rupicapra pyrenaica) in the central Pyrenees (NE Spain) was recorded in 2001 and 2002. There was a marked temporal distribution, most animals being found between February and June. After the outbreak, the population was found to have decreased by about 42%, most probably due to the disease. We examined 20 affected chamois. Clinical manifestations included depression, weakness and movement difficulties in all cases. Three chamois presented abnormal behaviour, with absence of flight reaction, and 16 showed different degrees of alopecia with skin hyperpigmentation. At necropsy cachexia was observed in all animals, four chamois had abscesses in different parts of the body, four had pneumonia, one had an extensive subcutaneous infection on the head and neck and one had severe orchitis. Microscopic lesions were found in the brain, mainly edema, gliosis, espongiosis, cariorrexis and neuronal multifocal necrosis. A perivascular mononuclear inflammatory infiltrate was present in three of them. Skin lesions included marked follicular atrophy, mild to moderate epidermal hyperplasia with orthokeratotic hyperkeratosis and follicular hyperkeratosis, and hypermelanosis. In 13 chamois there were haemosiderin deposits in the spleen, and in three individuals kidney "cloissone" was observed. Intraeritrocitic parasites were detected either by direct observation or PCR in 8 of 17 chamois. A pestivirus was isolated and detected by RT-PCR from 12 of 13 affected chamois and antigenic characterized as border disease virus by monoclonal antibodies. This is the first time a border disease virus has been associated with an outbreak of a high-mortality disease in a wild species.

Flock-prevalence of border disease virus infection in Basque dairy-sheep estimated by bulk-tank milk analysis

Bulk-tank milk (BTM) samples from 154 sheep flocks were used to estimate BDV prevalence in the Basque Country in Spain using an ELISA and a RT-PCR test. The proportion of antibody-positive flocks was 68% but varied significantly between provinces and was 93% in Araba and 54-55% in Bizkaia and Gipuzkoa. Most ELISA-positive flocks had very low antibody inhibition percentage (AIP) indicating high seroprevalence and recent BDV exposure. However, only 9% flocks were PCR-positive suggesting few infected ewes were being milked at the time of sampling. Phylogenetic analysis of the 5' NCR sequences of BDV from seven infected flocks showed that all except one clustered within the group formed by BDV type C strains from a previous study in the region, whereas the remaining isolate was closest to BDV type A. These results suggest that BDV strains in most Basque flocks have a common origin and differences in prevalence between provinces are associated to recent events affecting BDV spread such as use of communal pastures and sheep trading. The widespread distribution of BDV in the region, advocates for the implementation of BDV control strategies and highlights the potential risk of sheep as a pestivirus reservoir for other species.

Genetic typing and prevalence of Border disease virus (BDV) in small ruminant flocks in Spain

Between 2001 and 2002, samples from 1,413 animals in 21 Spanish small ruminant flocks, most of them with animals showing clinical signs compatible with Border disease (BD), were screened for the presence of Pestivirus antigen and antibodies by an indirect peroxidase monolayer assay (IPMA) and the virus neutralization test (VNT), respectively. Although all flocks harboured seropositive animals, virus could only be isolated from animals in five of the flocks. Between 4 and 11 months later all animals older than 6 months in three of the flocks were resampled. At this time, 51-83% of them had neutralizing antibodies. The prevalence of persistently infected (PI) animals within two of the flocks was 0.3 and 0.6%, respectively. The third flock presumably had eliminated all the PI animals. Fourteen virus isolates were obtained. The 5' untranslated region (5'UTR) was amplified by RT-PCR and directly sequenced. Phylogenetic analyses classified them as a group of Border disease viruses (BDV), separated from BDV-1, but showing a relatively low bootstrap value. Three of the 14 isolates were in the same subgroup as a set of formerly characterised Spanish isolates from the Basque Country, which were allocated to subgroup BDV-C. In addition, they were in the group with an isolate from chamois, which is currently allocated in group BDV-4. Because of its close relation to the chamois isolate, these isolates were tentatively reallocated in a subgroup BDV-4a. The remaining isolates generated a new subgroup, related but not in the same cluster as the chamois isolate, and was therefore tentatively assigned to a new subgroup BDV-4b. Our results show that classification and nomenclature of BDV needs to be harmonised.

[Seroepidemiological survey of sheep in Carinthia for the dissemination of ruminant pestiviruses]

In this study serological investigations were performed to determine the prevalence of pestiviral infections in sheep in one Federal State of Austria, namely Carinthia. 1527 blood samples from sheep in 147 flocks were collected and tested by Enzyme-linked immunosorbent assay and virus-neutralisation tests for antibodies to ruminant pestiviruses. The estimated flock prevalence was 47.6%, the individual prevalence 16.3%. Significant geographical variations in the flock as well in the individual prevalence were found. The highest prevalence in sheep and in sheep flocks was established in the region Spittal/Drau with 25.9% and 69.7%.The individual and the flock prevalence was significantly higher on farms where cattle or sheep from other farms were present than on farms with no cattle (p < 0.017). All Enzyme-linked immunosorbent assay positive sera were tested for Bovine viral diarrhea virus-1 (strain NADL), Bovine viral diarrhea virus-2 (strain 125) and for Border disease virus (strain MOREDUN) by virus neutralisation tests. Seventy out of 249 positive samples revealed the highest titres (> or = two-fold) to Bovine viral diarrhea virus-1 and 25 to Border disease virus. The remaining positive samples did not show clear results because of cross reactions.

Genetic Characterization of a Caprine Pestivirus as the First Member of a Putative Novel Pestivirus Subgroup

Currently, the genus Pestivirus comprises four approved species, namely bovine viral diarrhoea viruses 1 and 2 (BVDV-1, BVDV-2), classical swine fever virus and border disease virus (BDV). Recently, three major genotypes have been identified within the species BDV and termed as subgroups BDV-1, BDV-2 and BDV-3. Here, an isolate from animals in a herd showing BD-like syndromes, which occurred in central Italy was analysed. A reverse transcriptase polymerase chain reaction was performed using primers that specifically amplify a fragment of the 5'-non-coding region (5'-NCR) from BDV. Both the 5'-NCR fragment and the entire Npro gene were sequenced and used for genetic typing. The 5'-NCR sequence revealed that the newly isolated Pestivirus could be allocated to the BDV species. Interestingly, the Npro sequence of this virus isolate significantly differed from all the ovine pestiviruses previously described, providing evidence for the presence of an additional subgroup within the species BDV.

Age-specific seroprevalence of Border disease virus and presence of persistently infected sheep in Basque dairy-sheep flocks

Using p125/p80 antibody and antigen-ELISA tests, age-specific seroprevalence and presence of persistently infected (PI) sheep were investigated in six commercial latxa dairy-flocks, housed for variable periods. The flocks all had a recent history of Border disease (BD). Every flock included seropositive sheep and seven 0.5-3-year-old PI sheep were detected in two of four flocks tested. Age-specific antibody patterns differed according to the presence or absence of PI sheep in the flock. In flocks free of PI sheep, seroprevalence was 6-13% in 1-year-old sheep and 42-93% in older sheep. In contrast, seroprevalence was 67-99% in sheep raised with PI sheep for at least 1 year and 29-33% in replacement 0.5-0.6-year-old sheep (including a PI sheep) indicating that Border disease virus (BDV) transmission in Basque dairy-flocks can be relatively slow. Moderate seroprevalence in young replacement sheep should not discourage further testing to detect PI sheep, and our results highlight the risk of failing to achieve "natural vaccination" prior to pregnancy by mixing PI sheep with BDV-unexposed ewes.

Pestivirus Exposure in Free-living and Captive Deer in Austria

During the hunting season of 2001-02, blood and spleen samples from 59 red deer (Cervus elaphus), 77 roe deer (Capreolus capreolus), four fallow deer (Dama dama), and five chamois (Rupicapra rupicapra) were collected from nine hunting districts (n = 133) and one deer farm (n = 12) in southern Austria. Sera were tested for antibodies against bovine viral diarrhea virus (BVDV) with an enzyme-linked immunosorbent assay (ELISA) and virus neutralization tests against three BVDVs and one border disease virus strain. Reverse transcriptase polymerase chain reaction was used for detection of pestivirus-specific RNA in spleen samples. Antibodies were detected in one serum sample when using ELISA and virus neutralization tests. Results of the virus neutralization tests of this sample provided strong evidence for the exposure to the BVDV-1 genotype. The spleen samples were negative for pestivirus-specific RNA.

Molecular Identification of a New Pestivirus Associated with Increased Mortality in the Pyrenean Chamois (Rupicapra pyrenaica pyrenaica) in Spain

Pestivirus infection was identified in 16 of 17 chamois during an outbreak of a previously unreported disease in Pyrenean chamois (Rupicapra pyrenaica pyrenaica) in northeastern Spain in 2001-02. By analysis of the 5' noncoding regions of the virus, we assigned it to the border disease virus cluster with pairwise similarity values ranging from 82.1% to 88.1%. It will be important to investigate the association of this pestivirus with disease in Pyrenean chamois.

[Border disease in a flock of sheep]

This report describes border disease in a flock of sheep in Switzerland. In April 2001, three ewes in a flock of 41 sheep gave birth to lambs that had generalized tremors and excessively hairy fleece. One of these, a three-week-old female lamb, was referred to our clinic for further diagnostic work-up. The lamb was very nervous, bleated constantly and had generalized muscle tremors, which were more pronounced in the head region. Hind end ataxia was observed, and the lamb was slow to correct its posture when the hind limbs were abducted, adducted or crossed. Blood samples were collected every six weeks to determine antibody titres to pestivirus and for virus isolation via cell culture. A skin biopsy sample was also collected and examined immunohistochemically for pestivirus antigen. Antibody titres in the first tests were suspicious and those of the second were negative. Pestivirus was identified in cell culture, and the skin biopsy sample was positive for pestivirus antigen. Blood samples were collected from all of the ewes and lambs and the buck for virus isolation via cell culture and determination of pestivirus antibody titres. Thirty-one animals were seropositive, six had borderline antibody titres and four were seronegative. Pestivirus was isolated from eight animals, which included the lamb described in this report. Of the virus-positive animals, three were seronegative, three others had borderline titres and two were seropositive. Six of the eight viruses isolated from cell culture were further characterized genetically via retrotranscription and polymerase chain reaction and subsequent sequencing. The phylogenetic analysis revealed that the causative agent was border disease virus. This is the first time that border disease virus has been isolated in Switzerland. The lamb referred to our clinic was observed for three months; it was then euthanatised and a postmortem examination was performed. Immunohistochemical examination of numerous organs revealed pestivirus antigen. The source of infection was though to be infected sheep from another flock, which shared a pasture. All antigen-positive animals were slaughtered.

Experimental model of Border Disease Virus infection in lambs: comparative pathogenicity of pestiviruses isolated in France and Tunisia

Pestiviruses have been isolated from live sheep pox Tunisian vaccines. Vaccination with these vaccines caused outbreaks of Border Disease in Tunisia. In order to study more precisely the pathogenicity of these isolates, three groups of eight four month old lambs from a pestivirus-free flock were infected by the intratracheal route with a French strain (AV) and two Tunisian isolates (SN3G and Lot21). Clinical, hematological, immunological and virological parameters were evaluated. The three groups developed mild fever and leucopaenia by day 3 to 6 post infection (pi). The differences in the weight curves were not significant. Viruses were isolated from the peripheral blood buffy coat cells by day 4 to 9 pi. Antibodies were present on day 16 pi following infection by the French strain and on day 21 pi with the Tunisian isolates. The results demonstrated that SN3G and Lot21 are almost similar to the French strain used as the reference strain. In field conditions, they could induce economical losses in naive flocks, alone or in association with other pathogens.

[Differential diagnosis of classical swine fever and border disease: seroepidemiological investigation of a pestivirus infection on a mixed sheep and swine farm]

During recent years neutralizing antibodies against Border Disease Virus (BDV) were found repeatedly in German pig herds. Consequently there was a demand for a differential diagnostic system. A permanent sheep cell line and BDV reference strain Moredun were chosen and were applied in a could be used case study. A pestivirus could be isolated from piglets on a mixed farm and was characterised as 'non-Classical Swine Fever' (CSF) by using monoclonal antibodies. Due to a CSF suspicion the pig herd was destroyed immediately. Serum samples of sheep from the same farm were used for further characterisation of the new virus isolate. A neutralization test of the sheep sera was performed against different pestiviruses and the new isolate. Neutralizing antibody titres against the new virus pig isolate were significantly higher than against all other pestiviruses. BDV strain Moredun recognised the antibodies clearly, whereas CSF viral strain Alfort 187 and several isolates of bovine viral diarrhoea virus (BVDV) strains scored the lowest cross reaction.

[Seroprevalence of maedi-visna and border disease in Switzerland]

3866 sheep from 226 flocks of breeding associations and 1218 sheep from 15 independent sheep owners were tested for the presence of serum antibodies against Maedi-Visna and Border Disease viruses. The flocks were randomly selected based on the relative proportion and the geographical distribution of the 4 predominant Swiss sheep breeds (Braunköpfiges Fleischschaf, Schwarzbraunes Berg- und Juraschaf, Walliser Schwarznasenschaf, Weisses Alpenschaf). Additionally two smaller breeds were included in the study (Charollais Suisse, Milchschafe). Sera of all sheep older than 1 year were collected together with data characterizing host and management factors. The sera were tested using established ELISAs for detection of antibodies to Maedi-Visna and Bovine Virus Diarrhea/Border Disease viruses. ELISA results of Maedi-Visna serology were confirmed by immunoblotting. 9% of the sheep of breeding associations were antibody-positive for Maedi-Visna virus. The results of the different breeds varied between 0.4% and 36%. A multiple logistic regression procedure identified breed, age, airing in barns, herd size, pasturing on alps and way of keeping the animals during winter as associated factors with individual serostatus. The prevalence of antibodies to Border Disease was 20% in sheep of breeding associations and 65% in those of independent sheep owners.

Seroprevalence of Border Disease in Danish sheep and goat herds

A study was conducted in 1994-96 with the aim of assessing the serological prevalence of Border Disease (BD) among sheep and goats in Denmark and to investigate possible relations to herd factors. From each of 1000 herds, 2 blood samples were obtained from animals older than 1 year. The examination for antibodies was performed using a blocking ELISA detecting antibodies to pestivirus. Data from 815 herds were analysed statistically by the maximum likelihood method in a multinomial model. The estimated herd prevalence was 0.083 and the estimated individual prevalence within the positive herds was 0.50. There was no difference between the prevalence in sheep and goat herds. Records for well over half of the herds could be combined with data from the Danish Central Husbandry Register. No association between occurrence of BD and herd size was found. Cattle were registered as contemporarily present on 135 out of 521 herds which was shown to be strongly associated to BD. The estimated herd prevalences of BD among farms with and without contemporary cattle were 0.24 and 0.042, respectively.

Associations of veterinary services and farmer characteristics with the prevalences of brucellosis and border disease in small ruminants in Spain

We investigated the farm factors associated with the prevalences of brucellosis and border disease (BD) in small-ruminant herds in the Madrid region of Spain. These infections were used as models of diseases of well-known and totally unknown distribution, respectively, to assess the association between the perception of the importance of a given disease on the relative contributions of veterinary services and the farmer's attitudes to its prevention. Sera, farming-management information and data concerning veterinary assistance and farmer characteristics were collected from 60 sheep or goat herds. The overall sero-prevalence of brucellosis was 5.7% (complement fixation) and for BD was 17.9% (ELISA test). The relationship between sero-positivity and the variables in the questionnaire was assessed by multivariable analysis using random-effects logistic-normal regression. 'Availability of veterinary services' was a major protective factor for brucellosis. In contrast, no association with veterinary services was observed for BD, whereas 'membership in a farmers' organization' (a variable associated with good farming practice and animal care) was a protective factor. 'Membership of a farmers' organisation' and two other farmer variables indicative of good husbandry ('youth' and 'schooling') were associated with a lower sero-prevalence of brucellosis in univariable analysis but they did not remain significant in the multivariable model. Our observations suggest that veterinary-activity variables predominate over non-specific protective farm factors related to good husbandry in the case the disease is subject to disease surveillance. This underscores the importance of organized control programs for veterinary services to be effective in terms of animal disease prevention.

Prevalence of antibodies to bovine viral diarrhoea virus and/or border disease virus in domestic ruminants

A total of 62 sera collected from cattle, buffalo, sheep, goats and camels were investigated for the presence of antibodies to bovine viral diarrhoea (BVD) virus. The prevalence of neutralizing antibodies to BVD virus was 49.2, 52.0, 27.5, 31.4 and 52.5% in cattle, buffalo, sheep, goats and camels, respectively. The positive sera were titrated against BVD virus (BVDV) strains NADL and Oregon C24V; the latter is closely related to border disease (BD) virus. The frequency distributions of the antibody titres to both strains are presented. The statistical analysis shows no significant difference between the antibody titres to BVDV strains NADL and Oregon C24V in cattle, buffalo, sheep, goats and camels. On the other hand antibody titres to BVDV were significantly higher (P < 0.05) in cattle and buffalo in comparison with sheep, goats and camels. The cell-bound immunoassay (CBIA) is a serological rest established for the detection and titration of antibodies to BVD virus and BD virus. The percentage of agreement between the CBIA and the neutralizing peroxidase-linked antibody (NPLA) test was 96.1 and 95.3% in cattle and buffalo, respectively. The sensitivity of the CBIA in comparison with the NPLA was 100% while the specificity was 92.3 and 90.3% when testing the sera of cattle and buffalo, respectively. The method is easy to perform, cheap and suitable for the conditions in Egypt.

[Pestivirus as causative agent of abortion and perinatal mortality in cattle and sheep in Switzerland]

The causal involvement of bovine viral diarrhoea virus (BVDV) and border disease virus (BDV) infection in bovine and ovine abortion and perinatal mortality remain unclear. From 1992 until 1994, 213 bovine and 31 ovine foetuses as well as 36 calves and 25 lambs which had died perinatally were investigated. Tissue samples were tested for the presence of pestiviruses and serum or fluid from the body cavities were analysed for the presence of pestivirus antibodies. Detection of pestiviruses was performed by (i) cell culture isolation, (ii) antigen ELISA and (iii) immunohistochemical staining for viral antigen. For antibody-testing an indirect ELISA was used. In nine bovine foetuses and in two calves BVDV was isolated. Pestiviruses, most likely BDV were detected in one ovine foetus and three lambs. In 6% of the bovine and 11% of the ovine foetuses anti-pestivirus antibodies were detected. However, clinical features and history of bovine cases did not show a correlation with the diagnostic results, In contrast, the presence of central nervous system signs in neonatal lambs and the detection of BDV was correlated.

Border disease in sheep

The current knowledge on border disease in sheep is reviewed. This is a congenital and teratogenic disorder induced by pestivirus. The history, etiology, epidemiology, clinical aspects, and pathologic lesions at postnatal and intrauterine infections (as well as in congenitally affected animals), pathogenesis, immunity, diagnosis, and control and prevention of the syndrome are discussed.

Persistent pestivirus infection in sheep in Apulia (southern Italy)

A study in a flock of 100 sheep was carried out to detect animals persistently infected with Border Disease Virus (BDV). From buffy coats of animals without neutralizing antipestivirus antibodies, 6 non cytopathic pestiviruses were isolated in cell cultures. Using 3 monoclonal antibodies, the 6 viruses were initially characterized as BDV strains.

Border disease virus transmitted to sheep and cattle by a persistently infected ewe: epidemiology and control

In a Swedish sheep flock comprising 202 ewes and 13 rams, a pair of twin lambs born in the spring of 1990 demonstrated signs of border disease (BD) and were persistently infected (PI) with border disease virus (BDV). Investigation showed that BDV had been introduced in the preceding tupping period 5-6 months earlier by a bought-in ewe which, on the basis of immunoperoxidase- and polymerase chain reaction techniques, was shown to be PI with BDV. Only 7 of the ewes, all of which had been in close contact with the PI ewe, seroconverted during the subsequent gestation. Apart from the PI twin lambs the losses caused by BDV were restricted to 2 barren ewes. The twin lambs, the PI ewe and lambs from the other 4 ewes that seroconverted were removed from the flock. The flock was thereafter free from an ongoing infection with BDV as shown by the absence of seroconversion. In addition, 5 heifers in late pregnancy most probably seroconverted to bovine virus diarrhoea virus (BVDV) when kept in close contact with the same PI ewe during the winter of 1989-90. When these heifers were reintroduced to the BVDV-free dairy herd from which they originated, their serum antibody titres ranged between 1:250 and 1:1250. Neither these heifers--not their calves--caused any spread of the infection in the herd, as indicated by the absence of seroconversion in 70 cows. The present investigation shows that in the control of both BDV in sheep and BVDV in cattle, it is important to ensure that the risk of transmission of pestivirus between the 2 species is minimized.

The nucleotide sequence of the 5'-untranslated region of bovine viral diarrhoea virus: its use as a probe in rapid detection of bovine viral diarrhoea viruses and border disease viruses

A 289 bp cDNA fragment from the 5'-untranslated region (UTR) of 16 bovine viral diarrhoea virus (BVDV) isolates was amplified by reverse transcription and polymerase chain reaction, and sequenced by dideoxy DNA sequencing. The sequence showed greater than 90% homology between the isolates and BVDV NADL in this region, and greater than 97% homology within a 72 base sub-region (nt 314-386). The 289 bp fragment was then used as a probe for rapid detection of BVDV and border disease virus (BDV) from cell culture samples by dot-blot hybridization. This probe hybridized to 100% of BVDV isolates (n = 78) and 100% of BDV isolates (n = 9), but not to the uninfected BT cells or other bovine infectious agents. A shorter probe from the more conserved sub-region also was tested for hybridization with some of the isolates, and the results were similar to those using the longer probe. These results suggest that the 5'-UTR is highly conserved among BVDV and BDV isolates, and may be used as a potential probe for rapid detection of BVDV and BDV in clinical and cell culture samples from cattle and sheep.

Pestivirus infections in ruminants in Norway

Serological surveys in Norway have demonstrated neutralising antibodies against bovine virus diarrhoea (BVD) virus in cattle, sheep and goats. The prevalences were 18.5%, 4.5% and 3.6%, respectively. Occurrence of pestivirus-induced disease in Norway is described. Outbreaks of reproductive failure and mucosal disease have been reported, and the number of persistently-infected animals detected has increased considerably in recent years. Acute BVD occurs rarely. Border disease (BD) in sheep, first diagnosed in 1981, has subsequently been demonstrated sporadically. In goats, typical BD was diagnosed in 1982, with three later occurrences of reproductive failure. Experimental infections in pregnant goats induced a high rate of severe foetopathogenic effect. Signs and lesions in offspring were comparable to ovine BD. Similar findings were demonstrated in goats given a pestivirus-contaminated vaccine. In newborn kids, experimental infection had an adverse influence on growth and health. Persistent infection in goats is probably rare.

Bovine virus diarrhoea-mucosal disease and border disease in Egypt

In Egypt, bovine virus diarrhoea-mucosal disease (BVD-MD) was initially detected as the result of a serological survey of cattle and sheep, using the serum neutralisation test. In 1970, the causal pestivirus was isolated from bovine calves and buffalo calves with pneumonia and enteritis. Mixed viral infections were also prevalent. Cases of immune tolerance were identified. The Egyptian industry had complained of unthrifty cattle and high death rates of bovine calves and buffalo calves. A rinderpest outbreak in 1982 involved some cattle and buffalo which had been vaccinated against the disease, and such animals were positive to the gel diffusion test for BVD-MD pestivirus. Extensive immunosuppression due to BVD MD virus was suspected, because the attenuated cell-culture vaccine against rinderpest, issued in Egypt since 1965, had not been tested for freedom from non-cytopathic BVD-MD virus. Experimental infection of susceptible sheep with BVD-MD virus resulted in symptoms of Border disease. Innocuity of the attenuated C24V bovine pestivirus vaccine for animal tissues and the immune system of calves was confirmed.

Border disease of sheep: the disease in the newborn, adolescent and adult

Border disease (BD) is a condition of newborn sheep that results from congenital infection by a non-cytopathic pestivirus occurring during the first half of gestation. The expression of the virus is largely determined by the age of the fetus at the time of infection, producing four distinct disease syndromes: (1) early embryonic death, (2) abortion and stillbirth, (3) birth of lambs with malformations, and (4) birth of small, weak lambs, lacking characteristic clinical signs, but bearing features of immunosuppression. The effects of the virus infection during the developmental stages of the fetus are most apparent as distinctive clinical signs at the time of birth but a state of specific immuno-tolerance with associated virus persistence remains for the lifetime of the sheep. Although the clinical signs disappear with time, some effects of virus persistence may continue into adolescence and often into adulthood. Characteristic lesions are found in the nervous, endocrine, skeletal and integumentary, and immune systems.

Toxoplasmosis and border disease in 54 Swedish sheep flocks. Seroprevalence and incidence during one gestation period

Serum samples from 704 animals from 54 Swedish sheep flocks were analysed by ELISA twice during 1 breeding season for antibodies to Toxoplasma gondii and border disease virus (BDV). An ELISA, originally developed for the detection of antibodies to bovine viral diarrhoea virus (BVDV) in cattle, was assessed on sheep sera and the results were compared with those obtained in a virus neutralization test. The correlation between the 2 assays proved good. Before breeding, 132 (19%) sheep in 42 flocks had antibodies to T. gondii and 7 (1%) sheep in 5 flocks were seropositive to BDV. During the observation period 4 sheep seroconverted to T. gondii and 13 to BDV, giving an incidence rate of 0.7% and 1.9% respectively. No clinical signs due to the infections were observed. In 5 flocks the frequency of barrenness, abortion or stillbirths exceeded 5%, 5% and 8%, respectively, but there was no evidence that this was attributable to the agents studied. The proportion of BDV-positive flocks was significantly higher among flocks that had been in contact with cattle than among those that had not.

Border disease in sheep caused by transmission of virus from cattle persistently infected with bovine virus diarrhoea virus

Two outbreaks of border disease occurred on farms with sheep flocks and breeding cattle. The infection of the pregnant sheep was probably caused by transmission of virus from calves persistently infected with non-cytopathic bovine virus diarrhoea virus (BVDV) which were kept in close confinement with the ewes during mid-pregnancy. Border disease was also induced experimentally in eight lambs by exposing their dams at 38 to 78 days of gestation to a heifer persistently infected with BVDV. Both the natural and the experimental infections were characterised by typical signs such as 'hairy-shaker' lambs and high lamb mortality. The diagnosis was confirmed by virus isolations from live-born lambs, seroconversion and pathology. The study supports the assertion that cattle persistently infected with BVDV and in close contact with pregnant sheep, are an important source of strains of virus capable of causing border disease.

Border disease of sheep--aspects for diagnostic and epidemiologic consideration

Border Disease (BD) is a condition of newborn sheep that results from congenital infection by a non-cytopathic pestivirus, occurring during the first half of gestation. The variations in expression of the virus directly relate to the age of the fetus at the time of infection. There are four distinct disease syndromes: (1) early embryonic death, (2) abortion and stillbirth, (3) birth of lambs with malformations, and (4) birth of small, weak lambs, lacking characteristic clinical signs, but bearing features of immunosuppression. In the newborn, the BD virus may be recovered from all tissues and teratogenic lesions are found in the endocrine, nervous, skeletal, integumentary and immune systems. These effects of virus infection are manifest in the clinical signs characteristic of the disease, such as tremors, ataxia, hairy birthcoat, low birth weight, facial bone malformations, short-boxy stature, and eye abnormalities. The consequences of the BD compromised immune system is an increased susceptibility to infection, a failure to produce specific antibody to BD virus, and an inability to clear the virus; features characteristic of the immuno-tolerant state. The lifelong shedding and persistence of virus is of epidemiologic importance. The persistently infected BD ewe remains a source of infection for the flock both through horizontal transmission (virus shedding) and congenital transmission (a persistently infected ewe will always bear a BD lamb). Detection of persistently infected individuals within a flock is difficult: clinical signs abate with time and most frequently no antibody to BD is produced.

Pestivirus infections in Norway. Epidemiological studies in goats

During one breeding season, 2335 female goats in 39 herds in different parts of Norway were examined for pestivirus infection and for reproductive performance. Before breeding, all animals were examined for neutralizing antibodies against the NADL strain of pestivirus, 83 (3.6 per cent) positive animals in 12 herds being demonstrated. The herd prevalences ranged from 1 to 63 per cent. Antibody titres varied from 1 in 4 to 1 in 2048. Of 1816 females in 30 herds for which post-breeding information was available, a total of 178 (9.8 per cent) animals in 25 of the herds demonstrated gestation failure. Three of these goats began to produce antibodies against the NADL strain during gestation. Sera from the 83 animals with NADL antibodies were titrated for neutralizing antibodies against three additional strains of pestivirus, the highest geometrical mean titre being found for antibodies against a Norwegian bovine strain.

Border disease without nervous signs or fleece changes

A natural infection with border disease virus occurred in a flock on low ground in Argyll in the spring of 1984. The outbreak was unusual in that the typical clinical signs of border disease, ie, tremor and, or, fleece changes were not present; manifestations of disease were restricted to abortion and the birth of small weak lambs. The disease was shown to have been introduced to the flock by four healthy ewes persistently infected with border disease virus among a group of 39 purchased in October 1983. Further investigations in late August 1984 detected viraemia in six of seven ill-thriven lambs and four of 24 apparently healthy lambs. Attempted 'natural vaccination' of susceptible sheep by mixing them at grass for three months with groups of ewes and lambs known to contain virus excretors was largely unsuccessful as only four of 22 'sentinel' sheep seroconverted. In October 1984 the persistently infected purchased animals and all that year's lamb crop were removed from the farm. No disease occurred in 1985 when the lambing percentage was 129 per cent compared with 100 per cent in 1984. Two of the four persistently infected purchased ewes were mated at Moredun Research Institute in December 1984 and both produced healthy but persistently infected lambs.

Border disease in a flock of sheep: epidemiologic, laboratory, and clinical findings

A flock of sheep in which border disease (BD) was enzootic was studied through a breeding season. At the beginning of the study (August 1981), 125 (82%) of 152 ewes were seropositive to the cross-reacting bovine viral diarrhea virus. Within 7 months, 3 (18%) of 17 seropositive ewes retested had reverted to seronegative. Of the remaining 21 ewes identified as seronegative, 7 (33%) converted to seropositive by the end of the study. Triplet lambs were born, 2 of which exhibited clinical signs of BD. The virus was isolated from blood lymphocytes from both of the affected lambs. The most severely affected lamb shed virus into the urine, saliva, and feces through 10 weeks of age. Lymphocyte stimulation tests indicated that the lymphocytes from the affected lambs had decreased function in months 4 through 7, but returned to normal function by the eighth month. Transmission of BD virus was investigated by exposing 5 seronegative ewes to the BD-infected lambs. Two of the contact ewes developed viremia and 3 converted to seropositive within the 13-week exposure period. Evidence from this and other studies supports a model of BD in gravid, nongravid, and persistently infected adult sheep.

A survey of hairy shaker disease (border disease, hypomyelinogenesis congenita) in sheep

A survey by mail in 1979 of 995 sheep farmers in Victoria enquiring as to the occurrence of hairy shaker disease (HSD) in lambs on their farms resulted in a 48% response. A total of 17 farms reported the presence of HSD. One hundred and eleven ewes produced lambs with HSD representing a small proportion only of the ewes (0.8%) on these farms and an even smaller percentage of the total ewes (0.03%) in the survey. Abortions were not prevalent on the majority of farms reporting HSD. There was no evidence that HSD was more common in any particular area in Victoria. As was anticipated mucosal disease virus/bovine virus diarrhoea (MDV) antibody was often present in serums from affected sheep. It was concluded that at present, the hairy shaker form of border disease did not appear to be an economically important problem in Victoria.