Pestiviruses

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.

Low CD4/CD8 ratio in classical swine fever postnatal persistent infection generated at 3 weeks after birth

Classical swine fever virus (CSFV) is one of the most important pathogens affecting swine. After infection with a moderate virulence strain at 8 hours after birth, CSFV is able to induce viral persistence. These animals may appear clinically healthy or showed unspecific clinical signs despite the permanent viremia and high viral shedding, in absence of immune response to the virus. Given the role played by this infection in disease control, we aimed to evaluate the capacity of CSFV to induce postnatal persistent infection at 3 weeks after birth. Nine pigs were CSFV infected and sampled weekly during 6 weeks and viral, clinical, pathological and immunological tests were carried out. Also, the CD4/CD8 ratio was calculated with the purpose to relate this marker with the CSFV persistent infection. The IFN‐α response was detected mainly 1 week after infection, being similar in all the infected animals. However, 44.4% of animals were CSFV persistently infected, 33.3% died and 22.2% developed specific antibody response. Interestingly, in persistently infected pigs, the T‐CD8 population was increased, the T‐CD4 subset was decreased and lower CD4/CD8 ratios were detected. This is the first report of CSFV capacity to confer postnatal persistent infection in pigs infected at 3 weeks after birth, an age in which the weaning could be carried out in some swine production systems. This type of infected animals shed high amounts of virus and are difficult to evaluate from the clinical and anatomopathological point of view. Therefore, the detection of this type of infection and its elimination in endemic areas will be relevant for global CSF eradication. Finally, the low CD4/CD8 ratios found in persistently infected animals may be implicated in maintaining high CSFV replication during persistence and further studies will be performed to decipher the role of these cells in CSFV immunopathogenesis.

Traces of history conserved over 600 years in the geographic distribution of genetic variants of an RNA virus: Bovine viral diarrhea virus in Switzerland

The first records of smallpox and rabies date back thousands of years and foot-and-mouth disease in cattle was described in the 16th century. These diseases stood out by their distinct signs, dramatic way of transmission from rabid dogs to humans, and sudden appearance in cattle herds. By contrast, infectious diseases that show variable signs and affect few individuals were identified only much later. Bovine viral diarrhea (BVD), endemic in cattle worldwide, was first described in 1946, together with the eponymous RNA virus as its cause. There is general agreement that BVD was not newly emerging at that time, but its history remains unknown. A search for associations between the nucleotide sequences of over 7,000 BVD viral strains obtained during a national campaign to eradicate BVD and features common to the hosts of these strains enabled us to trace back in time the presence of BVD in the Swiss cattle population. We found that animals of the two major traditional cattle breeds, Fleckvieh and Swiss Brown, were infected with strains of only four different subgenotypes of BVDV-1. The history of these cattle breeds and the events that determined the current distribution of the two populations are well documented. Specifically, Fleckvieh originates from the Bernese and Swiss Brown from the central Alps. The spread to their current geographic distribution was determined by historic events during a major expansion of the Swiss Confederation during the 15th and 16th centuries. The association of the two cattle populations with different BVD viral subgenotypes may have been preserved by a lack of cattle imports, trade barriers within the country, and unique virus-host interactions. The congruent traces of history in the distribution of the two cattle breeds and distinct viral subgenotypes suggests that BVD may have been endemic in Switzerland for at least 600 years.

Global knowledge gaps in the prevention and control of bovine viral diarrhoea (BVD) virus

The significant economic impacts of bovine viral diarrhoea (BVD) virus have prompted many countries worldwide to embark on regional or national BVD eradication programmes. Unlike other infectious diseases, BVD control is highly feasible in cattle production systems because the pathogenesis is well understood and there are effective tools to break the disease transmission cycle at the farm and industry levels. Coordinated control approaches typically involve directly testing populations for virus or serological screening of cattle herds to identify those with recent exposure to BVD, testing individual animals within affected herds to identify and eliminate persistently infected (PI) cattle, and implementing biosecurity measures such as double-fencing shared farm boundaries, vaccinating susceptible breeding cattle, improving visitor and equipment hygiene practices, and maintaining closed herds to prevent further disease transmission. As highlighted by the recent DISCONTOOLS review conducted by a panel of internationally recognized experts, knowledge gaps in the control measures are primarily centred around the practical application of existing tools rather than the need for creation of new tools. Further research is required to: (a) determine the most cost effective and socially acceptable means of applying BVD control measures in different cattle production systems; (b) identify the most effective ways to build widespread support for implementing BVD control measures from the bottom-up through farmer engagement and from the top-down through national policy; and (c) to develop strategies to prevent the reintroduction of BVD into disease-free regions by managing the risks associated with the movements of animals, personnel and equipment. Stronger collaboration between epidemiologists, economists and social scientists will be essential for progressing efforts to eradicate BVD from more countries worldwide.

An emerging novel virus: Atypical porcine pestivirus (APPV)

Emerging porcine pestivirus diseases frequently challenge prevention and control strategies in the swine industry. Over the past decade, a few novel pestiviruses have been identified in pigs. This article focuses on the recently emerging atypical porcine pestivirus (APPV) that potentially threatens global swine herd health security. The virus was first identified in 2016, in the United States and thereafter, accumulated evidence shows that it is currently distributed in three continents. The clinical presentation of APPV-infected pigs is characterized by congenital tremor (CT) type A-II in piglets, while adult pigs may become persistent carriers and shedders. Here, a literature review is conducted to summarize the published findings in the virus genomic biology, transmission, epidemiology, pathogenesis, and diagnosis, which would shed light on acceleration of development of anti-APPV strategies.

The Small-Compound Inhibitor K22 Displays Broad Antiviral Activity against Different Members of the Family Flaviviridae and Offers Potential as a Panviral Inhibitor

The virus family Flaviviridae encompasses several viruses, including (re)emerging viruses which cause widespread morbidity and mortality throughout the world. Members of this virus family are positive-strand RNA viruses and replicate their genome in close association with reorganized intracellular host cell membrane compartments. This evolutionarily conserved strategy facilitates efficient viral genome replication and contributes to evasion from host cell cytosolic defense mechanisms. We have previously described the identification of a small-compound inhibitor, K22, which exerts a potent antiviral activity against a broad range of coronaviruses by targeting membrane-bound viral RNA replication. To analyze the antiviral spectrum of this inhibitor, we assessed the inhibitory potential of K22 against several members of the Flaviviridae family, including the reemerging Zika virus (ZIKV). We show that ZIKV is strongly affected by K22. Time-of-addition experiments revealed that K22 acts during a postentry phase of the ZIKV life cycle, and combination regimens of K22 together with ribavirin (RBV) or interferon alpha (IFN-α) further increased the extent of viral inhibition. Ultrastructural electron microscopy studies revealed severe alterations of ZIKV-induced intracellular replication compartments upon infection of K22-treated cells. Importantly, the antiviral activity of K22 was demonstrated against several other members of the Flaviviridae family. It is tempting to speculate that K22 exerts its broad antiviral activity against several positive-strand RNA viruses via a similar mechanism and thereby represents an attractive candidate for development as a panviral inhibitor.

Bovine viral diarrhea virus subgenotype 1b in water buffalos (Bubalus bubalis) from Brazil

Serological studies have characterized the presence of the bovine viral diarrhea virus (BVDV) infection in water buffalo herds worldwide. However, the molecular characterization of BVDV strains circulating in this animal species is uncommon. The aim of this study was to identify young water buffalo with acute infection and characterize the subgenotype of the infecting wild-type BVDV strain. Two dairy water buffalo herds from Northeastern Brazil were selected based on the results of virus neutralization test which showed high titers of anti-BVDV antibodies. To identify viremic animals, the BVDV RNA was assessed by RT-PCR assay in serum samples from 44 asymptomatic young water buffalos, where 31 serum samples from herd A and 13 from herd B. Amplicons with 288 bp of BVDV 5'UTR region were obtained in 7 (15.9%) serum samples (herd A, n = 5; herd B, n = 2). One good-quality amplicon from each herd was selected for nucleotide sequencing. The phylogenetic analysis demonstrated that the two BVDV wild-type strains clustered with BVDV strains of the subgenotype 1b. This study identified for the first time the active infection by BVDV subgenotype 1b in two dairy water buffalo herds from Brazil. These results highlight the importance of that, as well as in cattle herds, also in water buffalo herds prophylaxis measures to control BVDV infection should be intensified, mainly because these species clearly coexist in buffalo farms within Brazil.

Homodimerisation-independent cleavage of dsRNA by a pestiviral nicking endoribonuclease

The glycoprotein E^rns plays a central role in the biology of the pestivirus bovine viral diarrhea virus (BVDV). This soluble endonuclease mediates the escape from an interferon (IFN) response in the infected fetus, thereby permitting the establishment of persistent infection. Viral single-stranded (ss) and double-stranded (ds) RNA act as potent IFN inducing signals and we previously showed that E^rns efficiently cleaves these substrates, thereby inhibiting an IFN response that is crucial for successful fetal infection. Considering that a large variety of RNases and DNases require dimerisation to cleave double-stranded substrates, the activity of E^rns against dsRNA was postulated to depend on homodimer formation mediated by disulfide bonds involving residue Cys171. Here, we show that monomeric E^rns is equally able to cleave dsRNA and to inhibit dsRNA-induced IFN synthesis as the wild-type form. Furthermore, both forms were able to degrade RNA within a DNA/RNA- as well as within a methylated RNA/RNA-hybrid, with the DNA and the methylated RNA strand being resistant to degradation. These results support our model that E^rns acts as 'nicking endoribonuclease' degrading ssRNA within double-stranded substrates. This efficiently prevents the activation of IFN and helps to maintain a state of innate immunotolerance in persistently infected animals.

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.

Serological survey for antibodies against pestiviruses in Wyoming domestic sheep

Pestiviruses including Bovine viral diarrhea virus type 1 (BVDV-1), BVDV-2 and Border disease virus (BDV) have been reported in both sheep and cattle populations, together with the HoBi-like, an emerging group of pestiviruses. Pestivirus control programs in the United States have focused on the control of BVDV-1 and 2. The incidence of pestivirus infection in sheep in the United States and the risk of transmission between cattle and sheep populations are unknown. The aim of this study was to perform serological surveillance for pestivirus exposure in sheep from an important sheep producing state in the Unites States, Wyoming. For this, sera from 500 sheep, collected across the state of Wyoming (US) in 2015-2016, were examined by comparative virus neutralization assay against four species/proposed species of pestiviruses: BVDV-1, BVDV-2, BDV and HoBi-like virus. Rates of exposure varied between geographic regions within the state. The overall pestivirus prevalence of antibodies was 5.6%. Antibodies were most frequently detected against BVDV-1 (4%), and the highest antibody titers were also against BVDV-1. Data from this study highlights understanding of the dynamics of sheep pestivirus exposure, consideration of reference strains used for VN assays, transmission patterns, and potential vaccination history should be taken into account in implementation of control measures against pestiviruses in sheep and for successful BVDV control programs in cattle.

Complete Genome Sequence of Bovine Viral Diarrhea Virus Subgenotype 2a Strain CN10.2015.821, Isolated in Piedmont, Italy

We sequenced the complete genome of noncytopathic bovine viral diarrhea virus (BVDV) type 2 strain CN10.2015.821. It belongs to the subgenotype 2a, and it was isolated from an immunotolerant and persistently infected calf identified during a serological investigation. The complete genome is composed of 12,273 nucleotides, organized as one open reading frame encoding 3,897 amino acids.

Factors associated with the bovine viral diarrhoea (BVD) status in cattle herds in Northwest Germany

In Germany, all calves are tested for the presence of bovine viral diarrhoea/mucosal disease virus (BVDV) virus since January 1, 2011. The basis for this compulsory investigation is the BVDV Federal Regulation (BVDVV), which demands testing of calves before the age of six months and according to the new regulation of June 2016 within four weeks or before entering another stock. In 2012, a questionnaire was sent to 7250 Lower Saxony cattle farmers to identify potential factors associated with the presence of BVDV. Completed questionnaires were received from 2542 farms for further analysis. For BVD status determination of these farms, the diagnostic results of 425,911 ear notch samples of calves as part of the BVD eradication period from June 2010 to December 2013 were used. For the analysis of the completed questionnaires, a univariable analysis was performed by the chi-square or Wilcoxon test for each variable studied. In addition, a multivariable logistic model was performed. Four potential risk factors remained after a backward selection in the final logistic regression model: the dairy production compared to the suckling and other types of production, the herd size, the purchase of animals and the location in western region in comparison with the central and eastern regions. In summary, according to the results of this study, the farm with the highest probability of a BVDV infection in Lower Saxony is a large dairy farm that purchases cattle and is located in a cattle-dense region. When the complete eradication of the virus will be achieved, the results of the present study may help to conduct a risk-oriented monitoring programme.

Border Disease Virus Infection of Bovine Placentas

Subsequent to a previous study of border disease virus (BDV) horizontal transmission from a persistently BDV-infected calf to 6 seronegative pregnant heifers, the heifers were slaughtered 60 days after exposure to the infected calf, and their fetuses and placentas were examined. Immunohistochemical examination of fetal organs and placenta showed positive labeling of moderate intensity for pestivirus antigen in 3 of 6 heifers. BDV infection in these 3 animals was confirmed by the detection of BDV RNA in different organs using reverse transcription quantitative polymerase chain reaction. In the placenta, the positive cells were visualized mostly on the fetal side. In those 3 heifers that harbored an infected fetus, the placental tissue in the placentome region showed a moderate to severe mononuclear and fibrosing placentitis and, in severe cases, necrotic areas. The inflammatory population was composed predominantly of T and B cells, a substantial number of macrophages, and, to a lesser extent, plasma cells. This is a novel report of placentitis in persistently BDV-infected fetuses from pregnant heifers that became acutely infected by cohousing with a calf persistently infected with BDV, which extends previous reports on bovine viral diarrhea virus-infected and BDV-infected cattle and sheep, respectively.

Mycoplasma bovis co-infection with bovine viral diarrhea virus in bovine macrophages

Several studies suggest that synergisms between Mycoplasma bovis and other microorganisms might exacerbate disease outcome of bovine mycoplasmosis. Screening several bovine cell types to assess their potential use as in vitro infection models for M. bovis, it was observed that a widely used cell line of bovine macrophages (Bomac cells) is in fact persistently infected with bovine viral diarrhea virus (BVDV). The cell line was first cured of this virus allowing comparative studies between both cell lines. Subsequently, uptake and co-culture of two M. bovis strains of different clonal complexes with Bomac cells contaminated with BVDV and in BVDV-free Bomac cells were assessed. Additionally, cell viability, cytotoxicity and induction of apoptosis after infection with M. bovis were evaluated. No differences in the levels of uptake and growth in co-culture were observed between the two Bomac cell types and both M. bovis strains. Cytotoxicity was increased after infection of BVDV-free cells with one of the two strains, while apoptotic cell death was slightly induced by this strain in both cell lines. Overall, the presence or absence of BVDV in Bomac cells did not grossly change the parameters tested upon infection with M. bovis. Nevertheless, this cell model is very useful when studying viral co-infections with bacteria and could also be used for multiple co-infections. Considering the broad contamination of cell cultures with BVDV, careful screening for this virus should routinely be performed as its presence might be relevant depending on the molecular mechanisms being investigated.

Pestivirus infection in cattle dairy farms: E2 glycoprotein ELISA reveals the presence of bovine viral diarrhea virus type 2 in northwestern Italy

Background

Bovine viral diarrhea virus (BVDV) types 1 and 2 are members of the Pestivirus genus of the Flaviviridae family. This genus also includes the HoBi-like virus, tentatively classified as BVDV type 3. BVDV-1 is widely distributed in Italy despite the extensive use of BVDV-1-based vaccines, while BVDV-2 and HoBi-like Pestivirus have been detected occasionally. Monitoring the occurrence of sporadic or atypical pestiviruses is a useful approach to evaluate the need for additional vaccine strains that can be used in BVDV control programs.

Results

In this study we developed a multiwell antibody ELISA based on the recombinant E2 protein of the three bovine pestiviruses. We evaluated the assay’s applicability for surveillance purposes using pooled milk samples, each prepared from a maximum of 35 lactating cows and collected from 176 dairy herds. As expected, the majority of the pooled samples reacted to a greater extent against the BVDV-1 E2 antigen. All three milk pools from a single farm reacted to the BVDV-2 antigen, however. Further analysis using spot tests, antigen detection, and sequence analysis of the 5′-UTR region confirmed the presence of five persistently infected calves carrying a BVDV-2a strain.

Conclusions

This study highlights for the first time that sporadic circulation of BVDV-2 can be predicted by immunoenzymatic methods in the absence of specific vaccination.

Electronic supplementary material

The online version of this article (10.1186/s12917-017-1305-z) contains supplementary material, which is available to authorized users.

Complete Genome Sequences of Three Border Disease Virus Strains of the Same Subgenotype, BDSwiss, Isolated from Sheep, Cattle, and Pigs in Switzerland

We report here the complete genome sequences of three border disease virus (BDV) strains of the same subgenotype isolated in Switzerland from a sheep, a cow, and a pig, respectively. This is the first report of full-length sequences of a tentatively new subgenotype isolated from three different species of cloven-hoofed farm animals.

Akabane, Aino and Schmallenberg virus-where do we stand and what do we know about the role of domestic ruminant hosts and Culicoides vectors in virus transmission and overwintering?

Akabane, Aino and Schmallenberg virus belong to the Simbu serogroup of Orthobunyaviruses and depend on Culicoides vectors for their spread between ruminant hosts. Infections of adults are mostly asymptomatic or associated with only mild symptoms, while transplacental crossing of these viruses to the developing fetus can have important teratogenic effects. Research mainly focused on congenital malformations has established a correlation between the developmental stage at which a fetus is infected and the outcome of an Akabane virus infection. Available data suggest that a similar correlation also applies to Schmallenberg virus infections but is not yet entirely conclusive. Experimental and field data furthermore suggest that Akabane virus is more efficient in inducing congenital malformations than Aino and Schmallenberg virus, certainly in cattle. The mechanism by which these Simbu viruses cross-pass yearly periods of very low vector abundance in temperate climate zones remains undefined. Yearly wind-borne reintroductions of infected midges from tropical endemic regions with year-round vector activity have been proposed, just as overwintering in long-lived adult midges. Experimental and field data however indicate that a role of vertical virus transmission in the ruminant host currently cannot be excluded as an overwintering mechanism. More studies on Culicoides biology and specific groups of transplacentally infected newborn ruminants without gross malformations are needed to shed light on this matter.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): Border disease

Border disease has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of Border disease to be listed, Article 9 for the categorisation of Border disease according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species concerned by Border disease. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, Border disease can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria as in Sections 3, 4 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (c), (d) and (e) of Article 9(1). The animal species to be listed for Border disease according to Article 8(3) criteria are mainly sheep and other species of the family Bovidae as susceptible and reservoirs.

First report of the novel atypical porcine pestivirus in Spain and a retrospective study

This study aimed to provide information regarding viral pathogenesis and molecular epidemiology linked with recently reported atypical porcine pestivirus (APPV) strains and to determine the circulation of APPV in Spain from 1997 to 2016. Two-day-old piglets with moderate-severe congenital tremor (CT) from a Spanish farm were received for diagnostic purposes. Sera, nasal and rectal swabs and tissue samples were collected. qRT-PCR was performed in these samples, and a retrospective study to detect APPV RNA was carried out using a serum collection from 1997 to 2016. APPV genome was identified with high and moderate RNA loads in different tissues of the CT affected pigs. High APPV RNA load was detected in lymphoid organs, suggesting that these constitute a target for APPV replication. In 89 of the 642 retrospectively analysed samples (13.9%), APPV genome was detected. CT cases were related to the presence of APPV in viraemic piglets below 1 week of age, in which the viral RNA load was the highest. A considerable number of animals between 4 and 14 weeks of age and some 1-week-old piglets were viraemic in the absence of CT, which can act as carriers of the virus. The relative risk of APPV and CT was 8.5 (CI 95% 5.8-12.5). Thus, our data show that APPV infection is epidemiologically related to CT. Phylogenetic analysis from 1615 NS2-3 nucleotides showed only one defined APPV clade, grouping the most phylogenetically related strains from Europe and China. Of this clade, there are other strains from Europe, USA and China. This data confirm the high APPV genetic diversity, not being able to cluster this virus according to the geographic area. Our result showed that APPV has been circulating in Spain at least since 1997, being the earliest date of detection of this virus worldwide and suggesting that APPV may be widespread.

Evaluation of 16 commercial antibody ELISAs for the detection of bovine viral diarrhea virus–specific antibodies in serum and milk using well-characterized sample panels

We performed a thorough fit-for-purpose evaluation of commercial ELISAs for the detection of bovine viral diarrhea virus (BVDV)-specific antibodies in serum and in milk by testing 2 panels of well-characterized serum and milk samples. Sixteen ELISAs from 9 different manufacturers, available on the Belgian market at the time of our study, were assessed for their diagnostic and analytical sensitivity (DSe and ASe, respectively), diagnostic specificity (DSp), and repeatability relative to the virus neutralization (VN) test considered to be the gold standard assay. Using serum as a matrix, DSe was much lower for competitive (c)ELISAs (min. 45%, max. 65%) than for indirect (i)ELISAs (min. 85%, max. 100%), partly because of the lower detection of positive samples from vaccinated animals included in the panel. ASe was also better for iELISAs; DSp was >95% for all but 2 ELISAs. Repeatability, expressed as coefficients of variation (CV) of optical densities, was generally good, although 3 ELISAs had a mean CV >10%. With milk samples, as observed for serum, DSe was lower for cELISAs (min. 57%, max. 75%) than for iELISAs (min. 61%, max. 89%), and DSp was high for all ELISAs (min. 94%, max. 100%). Both DSe and ASe were lower when testing milk samples compared to serum samples. These results confirm that serologic monitoring of BVDV-free herds should be performed using serum samples of unvaccinated animals to avoid interference of vaccination and to maximize the chance of detecting seroconversion linked to BVDV infection. Further investigations using a larger collection of field samples are recommended.

Host-derived apolipoproteins play comparable roles with viral secretory proteins Erns and NS1 in the infectious particle formation of Flaviviridae

Amphipathic α-helices of exchangeable apolipoproteins have shown to play crucial roles in the formation of infectious hepatitis C virus (HCV) particles through the interaction with viral particles. Among the Flaviviridae members, pestivirus and flavivirus possess a viral structural protein E^rns or a non-structural protein 1 (NS1) as secretory glycoproteins, respectively, while Hepacivirus including HCV has no secretory glycoprotein. In case of pestivirus replication, the C-terminal long amphipathic α-helices of E^rns are important for anchoring to viral membrane. Here we show that host-derived apolipoproteins play functional roles similar to those of virally encoded E^rns and NS1 in the formation of infectious particles. We examined whether E^rns and NS1 could compensate for the role of apolipoproteins in particle formation of HCV in apolipoprotein B (ApoB) and ApoE double-knockout Huh7 (BE-KO), and non-hepatic 293T cells. We found that exogenous expression of either E^rns or NS1 rescued infectious particle formation of HCV in the BE-KO and 293T cells. In addition, expression of apolipoproteins or NS1 partially rescued the production of infectious pestivirus particles in cells upon electroporation with an E^rns-deleted non-infectious RNA. As with exchangeable apolipoproteins, the C-terminal amphipathic α-helices of E^rns play the functional roles in the formation of infectious HCV or pestivirus particles. These results strongly suggest that the host- and virus-derived secretory glycoproteins have overlapping roles in the viral life cycle of Flaviviridae, especially in the maturation of infectious particles, while E^rns and NS1 also participate in replication complex formation and viral entry, respectively. Considering the abundant hepatic expression and liver-specific propagation of these apolipoproteins, HCV might have evolved to utilize them in the formation of infectious particles through deletion of a secretory viral glycoprotein gene.

The family Flaviviridae consists of 4 genera, namely Flavivirus, Pestivirus, Pegivirus, and Hepacivirus. Flaviviruses and pestiviruses can infect various species and tissues; however, infection of pegivirus and hepacivirus is observed in a strikingly restricted range of tissue and hosts. Although all the Flaviviridae viruses possess a similar genome structure, hepatitis C virus (HCV) from Hepacivirus encodes no secretory glycoprotein, such as E^rns of pestivirus and NS1 of flavivirus. The apolipoproteins, one of the host secretory glycoproteins, play important roles in the formation of infectious HCV particles through the interaction with viral particles. The data presented here show that the host-derived apolipoproteins and viral-derived E^rns and NS1 have overlapping roles in the maturation of infectious particles of Flaviviridae. Considering an abundant expression of apolipoproteins in the liver and their liver-specific propagation, HCV might have evolved to utilize the apolipoproteins in the formation of infectious particles through deletion of a gene encoding a secretory viral glycoprotein. The data of this manuscript also suggest that utilization of host factors in the viral life cycle is closely associated with the tissue- and species-specificities and evolution among Flaviviridae viruses.

Complete Genome Sequence of a Bovine Viral Diarrhea Virus Subgenotype 1g Strain Isolated in Italy

We report here the full-length sequence of the bovine viral diarrhea virus (BVDV) strain UM/103/04, isolated from a persistently infected cow in Italy. It belongs to the subgenotype 1g, which is described as a sporadic subgenotype in Italy. This is the first report of a complete genome sequence of BVDV-1g.

The core protein of a pestivirus protects the incoming virus against IFN-induced effectors

A multitude of viral factors - either inhibiting the induction of the IFN-system or its effectors – have been described to date. However, little is known about the role of structural components of the incoming virus particle in protecting against IFN-induced antiviral factors during or immediately after entry. In this study, we take advantage of the previously reported property of Classical swine fever virus (family Flaviviridae, genus Pestivirus) to tolerate a deletion of the core protein if a compensatory mutation is present in the NS3-helicase-domain (Vp447_∆c). In contrast to the parental virus (Vp447), which causes a hemorrhagic-fever-like disease in pigs, Vp447_∆c is avirulent in vivo. In comparison to Vp447, growth of Vp447_∆c in primary porcine cells and IFN-treated porcine cell lines was reduced >20-fold. Also, primary porcine endothelial cells and IFN-pretreated porcine cell lines were 8–24 times less susceptible to Vp447_∆c. This reduction of susceptibility could be partially reversed by loading Vp447_∆c particles with different levels of core protein. In contrast, expression of core protein in the recipient cell did not have any beneficial effect. Therefore, a protective effect of core protein in the incoming virus particle against the products of IFN-stimulated genes could be demonstrated.

Complete Genome Sequence of a Bovine Viral Diarrhea Virus Subgenotype 1h Strain Isolated in Italy

We sequenced the complete genome of bovine viral diarrhea virus (BVDV) strain UM/126/07. It belongs to subgenotype 1h. The complete genome is composed of 12,196 nucleotides organized as one open reading frame encoding 3,898 amino acids. This is the first report of a full-length sequence of BVDV-1h.

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.

Complete Genome Sequence of a Bovine Viral Diarrhea Virus Subgenotype 1e Strain, SLO/2407/2006, Isolated in Slovenia

Bovine viral diarrhea virus (BVDV) subgenotype 1e was isolated for the first time in Slovenia in 2006. Here, we report the complete genome sequence of BVDV-1e, strain SLO/2407/2006. The published genome will increase our understanding of the molecular characteristics of the BVDV-1e strains circulating in Europe.

What can pestiviral endonucleases teach us about innate immunotolerance?

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In this review, we describe the identification of the PRRs involved in the recognition of pestiviruses, and the mechanisms of these viruses to prevent the activation of host’s innate immune response with special emphasis on viral RNases.

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Most importantly, we extend these data and present our model of innate immunotolerance requiring continuous prevention of detection of immunostimulatory self nucleic acids, in contrast to the well-known long-term tolerance of the adaptive immune system targeted predominantly against proteins.

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This hypothesis is very likely relevant beyond the bovine species and might answer more fundamental questions on the discrimination between “self” and “viral nonself RNA”, which are relevant also for the prevention and treatment of chronic IFN induction and autoimmunity induced by “self-RNAs”.

Pestiviruses including bovine viral diarrhea virus (BVDV), border disease virus (BDV) and classical swine fever virus (CSFV), occur worldwide and are important pathogens of livestock. A large part of their success can be attributed to the induction of central immunotolerance including B- and T-cells upon fetal infection leading to the generation of persistently infected (PI) animals. In the past few years, it became evident that evasion of innate immunity is a central element to induce and maintain persistent infection. Hence, the viral non-structural protease N^pro heads the transcription factor IRF-3 for proteasomal degradation, whereas an extracellularly secreted, soluble form of the envelope glycoprotein E^rns degrades immunostimulatory viral single- and double-stranded RNA, which makes this RNase unique among viral endoribonucleases. We propose that these pestiviral interferon (IFN) antagonists maintain a state of innate immunotolerance mainly pertaining its viral nucleic acids, in contrast to the well-established immunotolerance of the adaptive immune system, which is mainly targeted at proteins. In particular, the unique extension of ‘self’ to include the viral genome by degrading immunostimulatory viral RNA by E^rns is reminiscent of various host nucleases that are important to prevent inappropriate IFN activation by the host’s own nucleic acids in autoimmune diseases such as Aicardi-Goutières syndrome or systemic lupus erythematosus. This mechanism of “innate tolerance” might thus provide a new facet to the role of extracellular RNases in the sustained prevention of the body’s own immunostimulatory RNA to act as a danger-associated molecular pattern that is relevant across various species.

Classical Swine Fever Virus vs. Classical Swine Fever Virus: The Superinfection Exclusion Phenomenon in Experimentally Infected Wild Boar

Two groups with three wild boars each were used: Group A (animals 1 to 3) served as the control, and Group B (animals 4 to 6) was postnatally persistently infected with the Cat01 strain of CSFV (primary virus). The animals, six weeks old and clinically healthy, were inoculated with the virulent strain Margarita (secondary virus). For exclusive detection of the Margarita strain, a specific qRT-PCR assay was designed, which proved not to have cross-reactivity with the Cat01 strain. The wild boars persistently infected with CSFV were protected from superinfection by the virulent CSFV Margarita strain, as evidenced by the absence of clinical signs and the absence of Margarita RNA detection in serum, swabs and tissue samples. Additionally, in PBMCs, a well-known target for CSFV viral replication, only the primary infecting virus RNA (Cat01 strain) could be detected, even after the isolation in ST cells, demonstrating SIE at the tissue level in vivo. Furthermore, the data analysis of the Margarita qRT-PCR, by means of calculated ΔCt values, supported that PBMCs from persistently infected animals were substantially protected from superinfection after in vitro inoculation with the Margarita virus strain, while this virus was able to infect naive PBMCs efficiently. In parallel, IFN-α values were undetectable in the sera from animals in Group B after inoculation with the CSFV Margarita strain. Furthermore, these animals were unable to elicit adaptive humoral (no E2-specific or neutralising antibodies) or cellular immune responses (in terms of IFN-γ-producing cells) after inoculation with the second virus. Finally, a sequence analysis could not detect CSFV Margarita RNA in the samples tested from Group B. Our results suggested that the SIE phenomenon might be involved in the evolution and phylogeny of the virus, as well as in CSFV control by vaccination. To the best of our knowledge, this study was one of the first showing efficient suppression of superinfection in animals, especially in the absence of IFN-α, which might be associated with the lack of innate immune mechanisms.

Absence of circulation of Pestivirus between wild and domestic ruminants in southern Spain

Ruminant pestiviruses (family Flaviviridae) affect both wild and domestic ruminants worldwide, causing reproductive disorders and severe economic losses. Wild (n=1442) and domestic (n=373) ruminants from southern Spain were tested for the presence of antibodies to pestiviruses. Seropositivity was detected by both ELISA and virus neutralisation test in 1/892 (0.1 per cent) red deer, 29/125 (23.2 per cent) cattle and 17/157 (10.8 per cent) sheep. Pestivirus-specific antibodies to bovine viral diarrhoea virus (BVDV) and border disease virus (BDV) genotypes 1, 4 and 5 were detected. Significantly higher antibody titres to BDV-4 compared with BVDV-NADL were found in one cattle farm. Results indicate that wild ruminants may act as spillover hosts from domestic ruminants, and therefore they do not represent a risk for domestic ruminants in southern Spain. The wide distribution of pestiviruses among sheep and cattle suggests that transmission between these species may occur.

Border Disease Virus: An Exceptional Driver of Chamois Populations Among Other Threats

Though it is accepted that emerging infectious diseases are a threat to planet biodiversity, little information exists about their role as drivers of species extinction. Populations are also affected by natural catastrophes and other pathogens, making it difficult to estimate the particular impact of emerging infectious diseases. Border disease virus genogroup 4 (BDV-4) caused a previously unreported decrease in populations of Pyrenean chamois (Rupicapra pyrenaica pyrenaica) in Spain. Using a population viability analysis, we compared probabilities of extinction of a virtual chamois population affected by winter conditions, density dependence, keratoconjunctivitis, sarcoptic mange, and BD outbreaks. BD-affected populations showed double risk of becoming extinct in 50 years, confirming the exceptional ability of this virus to drive chamois populations.

A nationwide database linking information on the hosts with sequence data of their virus strains: A useful tool for the eradication of bovine viral diarrhea (BVD) in Switzerland

Pestiviruses infect a wide variety of animals of the order Artiodactyla, with bovine viral diarrhea virus (BVDV) being an economically important pathogen of livestock globally. BVDV is maintained in the cattle population by infecting fetuses early in gestation and, thus, by generating persistently infected (PI) animals that efficiently transmit the virus throughout their lifetime. In 2008, Switzerland started a national control campaign with the aim to eradicate BVDV from all bovines in the country by searching for and eliminating every PI cattle. Different from previous eradication programs, all animals of the entire population were tested for virus within one year, followed by testing each newborn calf in the subsequent four years. Overall, 3,855,814 animals were tested from 2008 through 2011, 20,553 of which returned an initial BVDV-positive result. We were able to obtain samples from at least 36% of all initially positive tested animals. We sequenced the 5' untranslated region (UTR) of more than 7400 pestiviral strains and compiled the sequence data in a database together with an array of information on the PI animals, among others, the location of the farm in which they were born, their dams, and the locations where the animals had lived. To our knowledge, this is the largest database combining viral sequences with animal data of an endemic viral disease. Using unique identification tags, the different datasets within the database were connected to run diverse molecular epidemiological analyses. The large sets of animal and sequence data made it possible to run analyses in both directions, i.e., starting from a likely epidemiological link, or starting from related sequences. We present the results of three epidemiological investigations in detail and a compilation of 122 individual investigations that show the usefulness of such a database in a country-wide BVD eradication program.

Complete Genome Sequence of a Bovine Viral Diarrhea Virus Subgenotype 1e Strain Isolated in Switzerland

We sequenced the complete genome of the bovine viral diarrhea virus (BVDV) strain Carlito. It belongs to the subgenotype 1e that is described in Europe only and represents the second most prevalent subgenotype in Switzerland. This is the first report of a full-length sequence of BVDV-1e.

Immune Responses Against Classical Swine Fever Virus: Between Ignorance and Lunacy

Classical swine fever virus infection of pigs causes disease courses from life-threatening to asymptomatic, depending on the virulence of the virus strain and the immunocompetence of the host. The virus targets immune cells, which are central in orchestrating innate and adaptive immune responses such as macrophages and conventional and plasmacytoid dendritic cells. Here, we review current knowledge and concepts aiming to explain the immunopathogenesis of the disease at both the host and the cellular level. We propose that the interferon type I system and in particular the interaction of the virus with plasmacytoid dendritic cells and macrophages is crucial to understand elements governing the induction of protective rather than pathogenic immune responses. The review also concludes that despite the knowledge available many aspects of classical swine fever immunopathogenesis are still puzzling.

Pestiviral E(rns) blocks TLR-3-dependent IFN synthesis by LL37 complexed RNA

The ribonuclease activity of the soluble glycoprotein E(rns) of pestiviruses represents a unique mechanism to circumvent the host's innate immune system by blocking interferon type-I synthesis in response to extracellularly added single- (ss) and double-stranded (ds) RNA. However, the reason why pestiviruses encode a ribonuclease in addition to the abundant serum RNases remained elusive. Here, we show that the 5' UTR and NS5B regions of various strains of the RNA genome of the pestivirus bovine viral diarrhea virus (BVDV) are resistant to serum RNases and are potent TLR-3 agonists. Inhibitory activity of E(rns) was restricted to cleavable RNA products, and did not extend to the synthetic TLR-7/8 agonist R-848. RNA complexed with the antimicrobial peptide LL37 was protected from degradation by E(rns)in vitro but was fully inhibited by E(rns) in its ability to induce IFN in cell cultures, suggesting that the viral protein is mainly active in cleaving RNA in an intracellular compartment. We propose that secreted E(rns) represents a potent IFN antagonist, which degrades viral RNA that is resistant to the ubiquitous host RNases in the extracellular space. Thus, the viral RNase prevents its own pathogen-associated molecular pattern (PAMP) to inadvertently activate the IFN response that might break innate immunotolerance required for persistent pestivirus infections.

Complete Genome Sequence of Bovine Pestivirus Strain PG-2, a Second Member of the Tentative Pestivirus Species Giraffe

We report the complete genome sequence of bovine pestivirus strain PG-2. The sequence data from this virus showed that PG-2 is closely related to the giraffe pestivirus strain H138. PG-2 and H138 belong to one pestivirus species that should be considered an approved member of the genus Pestivirus.

Prolonged activity of the pestiviral RNase Erns as an interferon antagonist after uptake by clathrin-mediated endocytosis

The RNase activity of the envelope glycoprotein E(rns) of the pestivirus bovine viral diarrhea virus (BVDV) is required to block type I interferon (IFN) synthesis induced by single-stranded RNA (ssRNA) and double-stranded RNA (dsRNA) in bovine cells. Due to the presence of an unusual membrane anchor at its C terminus, a significant portion of E(rns) is also secreted. In addition, a binding site for cell surface glycosaminoglycans is located within the C-terminal region of E(rns). Here, we show that the activity of soluble E(rns) as an IFN antagonist is not restricted to bovine cells. Extracellularly applied E(rns) protein bound to cell surface glycosaminoglycans and was internalized into the cells within 1 h of incubation by an energy-dependent mechanism that could be blocked by inhibitors of clathrin-dependent endocytosis. E(rns) mutants that lacked the C-terminal membrane anchor retained RNase activity but lost most of their intracellular activity as an IFN antagonist. Surprisingly, once taken up into the cells, E(rns) remained active and blocked dsRNA-induced IFN synthesis for several days. Thus, we propose that E(rns) acts as an enzymatically active decoy receptor that degrades extracellularly added viral RNA mainly in endolysosomal compartments that might otherwise activate intracellular pattern recognition receptors (PRRs) in order to maintain a state of innate immunotolerance.

IMPORTANCE

The pestiviral RNase E(rns) was previously shown to inhibit viral ssRNA- and dsRNA-induced interferon (IFN) synthesis. However, the localization of E(rns) at or inside the cells, its species specificity, and its mechanism of interaction with cell membranes in order to block the host's innate immune response are still largely unknown. Here, we provide strong evidence that the pestiviral RNase E(rns) is taken up within minutes by clathrin-mediated endocytosis and that this uptake is mostly dependent on the glycosaminoglycan binding site located within the C-terminal end of the protein. Remarkably, the inhibitory activity of E(rns) remains for several days, indicating the very potent and prolonged effect of a viral IFN antagonist. This novel mechanism of an enzymatically active decoy receptor that degrades a major viral pathogen-associated molecular pattern (PAMP) might be required to efficiently maintain innate and, thus, also adaptive immunotolerance, and it might well be relevant beyond the bovine species.