Clinical and laboratorial findings in pregnant ewes and their progeny infected with Border disease virus (BDV-4 genotype)

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.

Pathological lesions of lambs infected in utero with bovine viral diarrhoea virus type 1c (BVDV-1c)

BACKGROUND

Acute bovine viral diarrhoea virus (BVDV) infections in sheep are largely sub-clinical although infections of pregnant ewes have shown to result in significant fetal losses and persistently infected lambs. However, the extent and severity of abnormalities in lambs infected with BVDV in utero is still largely unknown.

METHODS

Twenty-two ewes were experimentally infected with BVDV-1c between 59 and 69 days of gestation. Fifteen lambs were submitted for pathological examination and the abnormalities observed in lambs and fetuses characterised.

RESULTS

Six lambs were identified as BVDV negative, and nine were identified as BVDV positive. Anasarca and cholestatic hepatopathy was observed in four BVDV positive lambs and associated with ewes with early seroconversion. One BVDV positive lamb was born with muscular tremors and a hairy coat associated with primary follicular dysplasia, a developmental abnormality normally associated with border disease infected lambs.

CONCLUSION

If similar lambing outcomes are identified in a commercial setting then BVDV should be considered, particularly in areas where sheep regularly come in to contact with cattle. In addition, as far as the authors are aware, this is the first reported case of a 'hairy shaker' lamb born as a result of an infection with BVDV-1c in Australia.

The Outcome of Porcine Foetal Infection with Bungowannah Virus Is Dependent on the Stage of Gestation at Which Infection Occurs. Part 2: Clinical Signs and Gross Pathology

Bungowannah virus is a novel pestivirus identified from a disease outbreak in a piggery in Australia in June 2003. The aim of this study was to determine whether infection of pregnant pigs with Bungowannah virus induces the clinical signs and gross pathology observed during the initial outbreak and how this correlates with the time of infection. Twenty-four pregnant pigs were infected at one of four stages of gestation (approximately 35, 55, 75 or 90 days). The number of progeny born alive, stillborn or mummified, and signs of disease were recorded. Some surviving piglets were euthanased at weaning and others at ages up to 11 months. All piglets were subjected to a detailed necropsy. The greatest effects were observed following infection at 35 or 90 days of gestation. Infection at 35 days resulted in a significant reduction in the number of pigs born alive and an increased number of mummified foetuses (18%) and preweaning mortalities (70%). Preweaning losses were higher following infection at 90 days of gestation (29%) and were associated with sudden death and cardiorespiratory signs. Stunting occurred in chronically and persistently infected animals. This study reproduced the clinical signs and gross pathology of the porcine myocarditis syndrome and characterised the association between the time of infection and the clinical outcome.

Decrypting the Origin and Pathogenesis in Pregnant Ewes of a New Ovine Pestivirus Closely Related to Classical Swine Fever Virus

This study shows the origin and the pathogenic role of a novel ovine pestivirus (OVPV) isolated in 2017 in Italy, as a pathogenic agent causing severe abortions after infection in pregnant ewes and high capacity for virus trans-placental transmission as well as the birth of lambs suffering OVPV-persistent infection. The OVPV infection induced early antibody response detected by the specific ELISA against classical swine fever virus (CSFV), another important virus affecting swine. The neutralizing antibody response were similar against CSFV strains from genotype 2 and the OVPV. These viruses showed high identity in the B/C domain of the E2-glycoprotein. Close molecular diagnostics cross-reactivity between CSFV and OVPV was found and a new OVPV molecular assay was developed. The phylodynamic analysis showed that CSFV seems to have emerged as the result of an inter-species jump of Tunisian sheep virus (TSV) from sheep to pigs. The OVPV and the CSFV share the TSV as a common ancestor, emerging around 300 years ago. This suggests that the differentiation of TSV into two dangerous new viruses for animal health (CSFV and OVPV) was likely favored by human intervention for the close housing of multiple species for intensive livestock production.

The Outcome of Porcine Foetal Infection with Bungowannah Virus is Dependent on the Stage of Gestation at Which Infection Occurs. Part 1: Serology and Virology

Bungowannah virus is a novel porcine pestivirus identified in a disease outbreak in Australia in 2003. The aim of this study was to determine the outcome of infection of the pregnant pig with this virus. Twenty-four pregnant pigs were infected at days 35, 55, 75 or 90 of gestation. Blood, tonsillar and rectal swabs were collected from each pig at birth and then weekly until euthanasia or death. Tissues were sampled at necropsy. Viral load was measured by real-time reverse-transcription polymerase chain reaction (qRT-PCR) and antibody levels in serum by peroxidase-linked immunoassay. Bungowannah virus was detected in the serum and excretions of all infected pigs at birth regardless of the stage of gestation at which infection occurred. Persistent infections occurred following infection prior to the development of foetal immunocompetence. Unexpectedly some animals infected at day 55 of gestation later cleared the virus and seroconverted. Viraemia and viral shedding resolved quickest following infection in late gestation.

Characterization of internal ribosome entry sites according to secondary structure analysis to classify border disease virus strains

Applying palindromic nucleotide substitutions (PNS) method, variable loci of the internal ribosome entry site (IRES) secondary structure in the 5' untranslated region (UTR) of Border disease virus sequences were analysed allowing their allocation into ten IRES classes within the species. Sequence characteristics of Turkish and Chinese strains were highly divergent from other genogroups, indicating geographic segregation and micro-evolutive steps within the species. Observed heterogeneity in the BDV species has to be considered for potential implications on diagnostic tests, control and preventive measures.

Experimental infection with high- and low-virulence strains of border disease virus (BDV) in Pyrenean chamois (Rupicapra p. pyrenaica) sheds light on the epidemiological diversity of the disease

Since 2001, Pyrenean chamois (Rupicapra pyrenaica pyrenaica) populations have been affected by border disease virus (BDV) causing mortalities of more than 80% in some areas. Field studies carried out in France, Andorra, and Spain have shown different epidemiological scenarios in chamois populations. This study was designed to confirm the presence of BDV strains of a high and low virulence in free-ranging chamois populations from Pyrenees and to understand the implications of these findings to the diverse epidemiological scenarios. An experimental infection of Pyrenean chamois with a high-virulence (Cadí-6) and low-virulence (Freser-5) BDV strains was performed. Pregnant and non-pregnant animals with and without antibodies against BDV were included in each group. Cadí-6 BDV strain was confirmed to be of high virulence for seronegative adults and their foetuses. The antibody negative chamois infected with Freser-5 BDV strain did not show symptoms, presented less viral distribution and RNA load in tissues than Cadí-6 group, and cleared the virus from the serum. However, foetuses died before the end of the experiment and RNA virus was detected in sera and tissues although with lower RNA load than the Cadí-6 group. Chamois from both groups presented lesions in brain but the ones infected with the low-virulence Freser-5 BDV strain were mild and most likely transient. In both groups, seropositive pregnant females and all but one of their foetuses did not present viraemia or viral RNA in tissues. The existence of a low-virulence strain has been confirmed experimentally and related to chamois population infection dynamics in the area where it was isolated. Such strain may persist in the chamois population through PI animals and may induce cross-protection in chamois against high-virulence strains. This study demonstrates that viral strain diversity is a significant factor in the heterogeneity of epidemiological scenarios in Pyrenean chamois populations.

Border disease in cattle

Within the family Flaviviridae, viruses within the genus Pestivirus, such as Border disease virus (BDV) of sheep, can cause great economic losses in farm animals. Originally, the taxonomic classification of pestiviruses was based on the host species they were isolated from, but today, it is known that many pestiviruses exhibit a broad species tropism. This review provides an overview of BDV infection in cattle. The clinical, hematological and pathological-anatomical findings in bovines that were transiently or persistently infected with BDV largely resemble those in cattle infected with the closely related pestivirus bovine viral diarrhoea virus (BVDV). Accordingly, the diagnosis of BDV infection can be challenging, as it must be differentiated from various pestiviruses in cattle. The latter is very relevant in countries with control programs to eradicate BVDV in Bovidae, as in most circumstances, pestivirus infections in sheep, which act as reservoir for BDV, are not included in the eradication scheme. Interspecies transmission of BDV between sheep and cattle occurs regularly, but BDV in cattle appears to be of minor general importance. Nevertheless, BDV outbreaks at farm or local level can be very costly.

Insemination with border disease virus-infected semen results in seroconversion in cows but not persistent infection in fetuses

BACKGROUND

This study examined various health variables in cows after artificial insemination with Border disease virus (BDV)-infected semen and the occurrence of persistent infection in ensuing fetuses. Five cows were inseminated (day 0) with BDV-infected semen as well as with semen from a fertile Eringer bull. One cow, inseminated with virus-free semen only, served as a control. Clinical examination, assessment of eating and rumination activities, measurement of intraruminal temperature and leukocyte count were used to monitor the health of the cows. Blood samples were collected at regular intervals for the detection of viral RNA and antibodies against BDV, and the cows were slaughtered on day 56. The uteri, placentae and fetuses were examined macroscopically, histologically, immunohistochemically and by means of molecular methods for the presence of pestiviruses.

RESULTS

The demeanour, eating and rumination activities and intraruminal temperature were not affected by insemination with BDV-infected semen, whereas the total leukocyte and lymphocyte counts dropped transiently and were significantly lower on day 6 than on day 0. Seroconversion occurred by day 28 in the five infected cows but not in the control cow. The uteri, placentae and fetuses had no macroscopic or histological lesions, and immunohistochemical examination and RT-PCR were negative for pestiviruses.

CONCLUSIONS

The findings showed that cows inseminated with BDV-infected semen seroconverted and fetuses thus produced were not persistently infected. Transmission of BDV to cattle through infected semen, therefore, seems to be of minor importance.

Influence of border disease virus (BDV) on serological surveillance within the bovine virus diarrhea (BVD) eradication program in Switzerland

BACKGROUND

In 2008, a program to eradicate bovine virus diarrhea (BVD) in cattle in Switzerland was initiated. After targeted elimination of persistently infected animals that represent the main virus reservoir, the absence of BVD is surveilled serologically since 2012. In view of steadily decreasing pestivirus seroprevalence in the cattle population, the susceptibility for (re-) infection by border disease (BD) virus mainly from small ruminants increases. Due to serological cross-reactivity of pestiviruses, serological surveillance of BVD by ELISA does not distinguish between BVD and BD virus as source of infection.

RESULTS

In this work the cross-serum neutralisation test (SNT) procedure was adapted to the epidemiological situation in Switzerland by the use of three pestiviruses, i.e., strains representing the subgenotype BVDV-1a, BVDV-1h and BDSwiss-a, for adequate differentiation between BVDV and BDV. Thereby the BDV-seroprevalence in seropositive cattle in Switzerland was determined for the first time. Out of 1,555 seropositive blood samples taken from cattle in the frame of the surveillance program, a total of 104 samples (6.7%) reacted with significantly higher titers against BDV than BVDV. These samples originated from 65 farms and encompassed 15 different cantons with the highest BDV-seroprevalence found in Central Switzerland. On the base of epidemiological information collected by questionnaire in case- and control farms, common housing of cattle and sheep was identified as the most significant risk factor for BDV infection in cattle by logistic regression.

CONCLUSION

This indicates that pestiviruses from sheep should be considered as a source of infection of domestic cattle and might well impede serological BVD surveillance.

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.

Genome Sequence of Border Disease Virus Strain JSLS12-01, Isolated from Sheep in China

Border disease virus (BDV) is a recognized virus in the genus Pestivirus and causes border disease (BD) in sheep and goats. Here, a novel BDV strain, JSLS12-01, was identified from sheep in Jiangsu Province, China. The complete coding sequence (CDS) was finished, which provides a better understanding of the molecular evolution of BDV isolates.

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.

Haematology and serum chemistry of Pyrenean chamois (Rupicapra pyrenaica) naturally infected with a border disease virus

In 2005 and 2006 an outbreak of disease associated with border disease virus (BDV) infection caused high mortality in the Pyrenean chamois (Rupicapra pyrenaica) in the Catalan Pyrenees (NE Spain). The aim of this study was to determine values for different haematological and serum biochemical analytes in 32 free-ranging Pyrenean chamois affected by the disease and to compare them with those obtained from healthy chamois. In the affected chamois red blood cell counts, haemoglobin concentrations, packed cell volumes, mean corpuscular volumes and lymphocyte counts were all lower, while the neutrophil and platelet counts were higher. Glucose, lactate, triglycerides, creatinine, total protein concentrations and alkaline phosphatase activity were also lower, in contrast to the concentrations of total bilirubin, urea and aspartate aminotransferase activity, which were higher. Most of the observed changes could be associated with cachexia and inflammation in the affected chamois. Lymphopenia could be directly related to the BDV, which would lead to immunosuppression and explain the high rate of secondary infection observed in these animals.

Neuropathologic Study of Border Disease Virus in Naturally Infected Fetal and Neonatal Small Ruminants and Its Association With Apoptosis

The present study describes the pathologic changes and cellular apoptosis in the central nervous system (CNS) of fetal and neonatal small ruminants infected with border disease virus (BDV), as demonstrated by immunohistochemistry and in situ hybridization. Abortions of ewes and goats were observed, as were births of lambs and kids with poor survival rates and nervous signs. Lesions included cerebellar hypoplasia, porencephaly, hydranencephaly, and nonsuppurative meningoencephalomyelitis with hypomyelinogenesis. Viral antigens and RNA were present in neuropil, glial, and neuronal cells, especially in periventricular areas, cerebellum, and brainstem. TUNEL positivity and labeling of anti-bax and anti-caspases 3, 8, and 9 were detected in BDV-infected CNSs, especially in glial and neuronal cells. The double immunostaining and TUNEL assay revealed that in BDV-infected animals, not only were BDV-infected glial and neuronal cells undergoing apoptosis, but so were uninfected cells in close vicinity of BDV-infected cells. The expression of activated caspases 3, 8, 9; bax; and TUNEL in glial and neuronal cells of the infected fetal and neonatal kids were significantly ( P < .05) higher than those of the infected fetal and neonatal lambs. Yet, the expression of bcl-2 in the CNSs of the infected fetal and neonatal lambs was higher ( P < .05) in neuronal and glial cells than in those of the infected fetal and neonatal kids. The results suggest that cell death in the BDV-infected CNS is induced by intrinsic and extrinsic cascades of apoptotic pathways.

Detection and quantification of pestivirus in experimentally infected pregnant ewes and their progeny

Background

Border disease virus (BDV) causes important reproductive losses, and eradication strategies focus on the identification and removal of persistently infected animals arising after in uterine infection. BDV infection dynamics were studied in 13 ewes experimentally infected with BDV-4 genotype at 3 phases of pregnancy [days 108 (group A), 76 (group B) and 55 (group C)] by quantification of viral RNA in blood collected on days -1 to parturition using quantitative real-time RT-PCR (qRT-PCR). Viral RNA loads were also measured in blood/foetal fluid and tissue samples from their offspring at lambing (3 foetuses, 7 stillborns, 15 lambs). qRT-PCR results were compared with those obtained by conventional RT-PCR and used to predict persistent infections.

Results

Viral RNA was detected in the ewes between days 2-15 p.i. The viraemia reached its highest peak between days 6-7 p.i. with a second peak at days 11-12 p.i. qRT-PCR was significantly faster to perform (less than 1 h) than conventional RT-PCR and detected BDV RNA in more ewes, being detection more continuous and prolonged in time. The virus was detected in peripheral blood in a higher percentage of lambs than in tissues, where differences in viral genome copies were more marked. Skin and cerebral cortex showed the highest viral RNA loads, and spleen and spinal cord the lowest. High viral RNA loads were observed in several animals in group B and all in group C, infected during middle and early foetal development, respectively, but also in one lamb from group A, infected during late foetal development. Serology and viral genome copy number estimates in blood and tissues were used to establish a quantitative cut-off threshold for transient viraemia.

Conclusion

Viral RNA quantification showed potential for the discrimination between persistent infections and transient viraemia using single-time point blood sampling and raised questions regarding foetal immune system development and the occurrence of persistent infections.

Detection of Border Disease Virus in Fetuses, Stillbirths, and Newborn Lambs from Natural and Experimental Infections

The purpose of the present study was to evaluate the use of enzyme-linked immunosorbent assay (ELISA) antigen detection in blood or fetal fluids and reverse transcription polymerase chain reaction (RT-PCR) amplification in tissues for routine laboratory diagnosis of Border disease virus (BDV) infection. Samples from 67 fetuses, 6 stillbirths, and 11 lambs from 25 commercial flocks with suspicion of BDV abortion and 3 fetuses, 7 stillbirths, and 15 lambs obtained from an experimental infection with a local isolate (BDV genotype 4) were investigated. Presence of BDV was detected by RT-PCR in 7.9% of fetuses, 50% of stillbirths, and 50% of lambs from the commercial flocks analyzed, corresponding to 8 of the 25 farms (32%). A similar percentage of the lambs and stillbirths from the experimental infection were positive by RT-PCR of tissue samples (54.5%), and the highest positivity was detected in lymph node, thyroid gland, and kidney. The current study revealed that RT-PCR analysis of stillbirths and lambs with clinical symptoms is more suitable than the analysis of fetuses to confirm the presence of BDV in a flock. Pestiviral antigen was detected by antigen ELISA in a high proportion of fetuses (24/58) and stillbirths (3/4) from commercial flocks, but in lambs, the presence of colostral antibodies masked the detection of the antigen by ELISA. Nevertheless, in lambs from the experimental infection that were not fed colostrum, antigen ELISA was less efficient than RT-PCR in detecting viral presence in stillbirths and lambs. Antigen ELISA is therefore recommended for fetuses with advanced autolysis that can adversely affect RNA integrity.