An experimental study of Bungowannah virus infection in weaner aged pigs

Comparative Analysis of Tunisian Sheep-like Virus, Bungowannah Virus and Border Disease Virus Infection in the Porcine Host

Apart from the established pestivirus species Pestivirus A to Pestivirus K novel species emerged. Pigs represent not only hosts for porcine pestiviruses, but are also susceptible to bovine viral diarrhea virus, border disease virus (BDV) and other ruminant pestiviruses. The present study focused on the characterization of the ovine Tunisian sheep-like virus (TSV) as well as Bungowannah virus (BuPV) and BDV strain Frijters, which were isolated from pigs. For this purpose, we performed genetic characterization based on complete coding sequences, studies on virus replication in cell culture and in domestic pigs, and cross-neutralization assays using experimentally derived sera. TSV forms a distinct phylogenetic group more closely related to Pestivirus C (classical swine fever virus, CSFV) than to Pestivirus D (BDV). In contrast to BDV and BuPV, TSV replicates by far more efficiently on ovine than on porcine cells. Nevertheless, pigs were susceptible to TSV. As a consequence of close antigenic relatedness of TSV to CSFV, cross-reactivity was detected in CSFV-specific antibody assays. In conclusion, TSV is genetically closely related to CSFV and can replicate in domestic pigs. Due to close antigenic relatedness, field infections of pigs with TSV and other ruminant pestiviruses can interfere with serological diagnosis of classical swine fever.

Prevalence of Linda Virus Neutralizing Antibodies in the Austrian Pig Population

A novel pestivirus species, termed Lateral-shaking Inducing Neuro-Degenerative Agent virus (LindaV), was discovered in a piglet-producing farm in Austria in 2015 related to severe congenital tremor cases. Since the initial outbreak LindaV has not been found anywhere else. In this study, we determined the seroprevalence of LindaV infections in the domestic pig population of Austria. A fluorophore labeled infectious cDNA clone of LindaV (mCherry-LindaV) was generated and used in serum virus neutralization (SVN) assays for the detection of LindaV specific neutralizing antibodies in porcine serum samples. In total, 637 sera from sows and gilts from five federal states of Austria, collected between the years 2015 and 2020, were analyzed. We identified a single serum showing a high neutralizing antibody titer, that originated from a farm (Farm S2) in the proximity of the initially affected farm. The analysis of 57 additional sera from Farm S2 revealed a wider spread of LindaV in this pig herd. Furthermore, a second LindaV strain originating from this farm could be isolated in cell culture and was further characterized at the genetic level. Possible transmission routes and virus reservoir hosts of this emerging porcine virus need to be addressed in future studies.

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.

Infection of Ruminants, Including Pregnant Cattle, with Bungowannah Virus

Bungowannah virus is a pestivirus known to cause reproductive losses in pigs. The virus has not been found in other species, nor is it known if it has the capacity to cause disease in other animals. Eight sheep, eight calves and seven pregnant cows were experimentally infected with Bungowannah virus. It was found that sheep and calves could be infected. Furthermore, it was shown that the virus is able to cross the bovine placenta and cause infection of the foetus. These findings demonstrate the potential for species other than pigs to become infected with Bungowannah virus and the need to prevent them from becoming infected.

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.

Seroprevalences of Newly Discovered Porcine Pestiviruses in German Pig Farms

Several novel porcine pestiviruses that are linked to disease outbreaks in commercial pig farms were discovered during recent years. Bungowannah pestivirus (BuPV; new species Pestivirus F) causes sudden death in young pigs, but has only ever been isolated in the Australian region Bungowannah. Atypical porcine pestivirus (APPV; new species Pestivirus K) on the other hand has been found in multiple countries worldwide and is potentially linked to congenital tremor, a disease that causes considerable production problems in pig farms. To assess the seroprevalences of both viruses in German commercial farms during the years 2009/10 and 2018, two approaches were selected. Antibodies against Pestivirus F were detected by a traditional in-house indirect immunofluorescence test against the culture-grown virus isolate, while for the detection of Pestivirus K-specific antibodies, a newly developed test system utilizing a chimeric construct of bovine viral diarrhea virus 1 (BVDV-1; species Pestivirus A) containing the E1 and E2 encoding sequences of APPV was established. A total of 1115 samples originating from 122 farms located in seven German federal states were investigated. Antibodies against Bungowannah virus could not be detected, confirming the absence of this virus in other regions than the initially affected Australian pig farm complex. In contrast, antibodies against APPV were highly prevalent throughout Germany at both investigated time points. The seroprevalence at the state level fluctuated to some degree, but the overall percentage remained stable, as is to be expected for an endemic pestivirus lacking any form of control measures.

Clinical and Serological Evaluation of LINDA Virus Infections in Post-Weaning Piglets

The novel pestivirus species known as lateral-shaking inducing neuro-degenerative agent (LINDA) virus emerged in 2015 in a piglet-producing farm in Austria. Affected piglets showed strong congenital tremor as a result of severe lesions in the central nervous system. Here, we report the results of a controlled animal infection experiment. Post-weaning piglets were infected with LINDA to determine the susceptibility of pigs, the clinical consequences of infection and the humoral immune response against LINDA. No clinically overt disease signs were observed in the piglets. Viremia was hardly detectable, but LINDA was present in the spleen and several lymphatic organs until the end of the experiment on day 28 post-infection. Oronasal virus shedding together with the infection of one sentinel animal provided additional evidence for the successful replication and spread of LINDA in the piglets. Starting on day 14 post-infection, all infected animals showed a strong humoral immune response with high titers of neutralizing antibodies against LINDA. No cross-neutralizing activity of these sera with other pestiviral species was observed. According to these data, following postnatal infection, LINDA is a rather benign virus that can be controlled by the pig’s immune system. However, further studies are needed to investigate the effects of LINDA on the fetus after intrauterine infection.

New Leaves in the Growing Tree of Pestiviruses

Pestiviruses are a group of viruses of veterinary importance infecting livestock animals like pigs, cattle, and sheep, and also wildlife animals like wild boar and different deer species. While for decades only four classical species (Classical swine fever virus, Bovine viral diarrhea virus types 1 and 2, Border disease virus), and a few so-called atypical pestiviruses were known (e.g., Giraffe virus, Pronghorn virus, HoBi virus), a series of novel pestiviruses was identified in the last years (Bungowannah virus, Bat pestivirus, Norway rat pestivirus, Atypical porcine pestivirus, LINDA virus). The Australian Bungowannah virus could be isolated and further characterized by classical sequencing, but all the other latest novel pestiviruses were identified by metagenomics using next-generation sequencing technologies. Here, we describe these new viruses and their discovery and characterization. Differentiation is made between the occurrence of classical pestiviruses in new species and novel viruses or virus types.

Bungowannah virus--a probable new species of pestivirus--what have we found in the last 10 years?

Bungowannah virus was discovered following an outbreak of stillbirths and sudden death in young pigs. Affected animals consistently showed a myocardopathy with signs of cardiac failure. After virus isolation and PCR investigations were unsuccessful, direct fetal inoculation was undertaken. Nucleic acid purified from serum from infected fetuses was subjected to sequence-independent single-primer amplification and nucleic acid sequencing. Sequences consistent with a pestivirus were obtained. The entire genome was identified but was genetically remote from the recognized pestivirus species. This virus was not recognized by pan-pestivirus reactive monoclonal antibodies but was subsequently detected in cell cultures by immunoperoxidase staining using convalescent sow serum. Experimental infections of sows at different stages of gestation reproduced the myocarditis syndrome. Pre-weaning losses of 70 and 29% were observed following infection at days 35 and 90, respectively. Piglets infected at day 35 were shown to be persistently infected, while chronic infections were observed after fetal infection at day 55. Chronically infected piglets showed growth retardation and were viremic for up to 7 months. Myocarditis was associated with infection in late gestation (day 90). Non-pregnant sheep and cattle have been experimentally infected but with no evidence of disease. Infection of pregnant cattle in early gestation resulted in both maternal and fetal infection, but all infected fetuses mounted an antibody response to the virus. Analysis of the nucleic acid sequence confirmed that Bungowannah has a number of changes not observed in other pestiviruses. Genes encoding some of the structural proteins remain fully functional when inserted into a bovine viral diarrhea virus (BVDV) backbone. Cell culture-based studies have shown that Bungowannah virus will grow in cells extending from humans to bats as well as farm animals.

Genetic and antigenic characterization of Bungowannah virus, a novel pestivirus

Bungowannah virus, a possible new species within the genus Pestivirus, has been associated with a disease syndrome in pigs characterized by myocarditis with a high incidence of stillbirths. The current analysis of the whole-genome and antigenic properties of this virus confirms its unique identity, and further suggests that this virus is both genetically and antigenically remote from previously recognized pestiviruses. There was no evidence of reactivity with monoclonal antibodies (mAbs) that are generally considered to be pan-reactive with other viruses in the genus, and there was little cross reactivity with polyclonal sera. Subsequently, a set of novel mAbs has been generated which allow detection of Bungowannah virus. The combined data provide convincing evidence that Bungowannah virus is a member of the genus Pestivirus and should be officially recognized as a novel virus species.