Deborah S. Finlaison

In 2022, piggeries in southeastern Australia experienced an increase in reproductive losses and occasional neurologic disease in neonates with up to 100% mortality in some litters. Molecular testing identified a genotype IV Japanese encephalitis virus (JEV) as the etiological agent, detected for the first time in Australia. Necropsy of 235 JEV-positive domestic piglets, mostly stillbirths with 30% mummified, revealed hydranencephaly-porencephaly impacting the dorsal cerebrum as the most common lesion. Microscopically, this was characterized by varying degrees of parenchymal collapse as a result of liquefactive necrosis, hypoplasia, and dysplasia, with nonsuppurative inflammation and mineralization. In the most severe cases, hydranencephaly reduced the cerebral parenchyma to a thin membrane enclosing dilated lateral ventricles. Histologically, the affected neuroparenchyma was largely devoid of mature neurons, axons, myelin, and oligodendrocytes. What remained was mostly a dense population of IBA-1-positive histiocytes and few CD3-positive T-lymphocytes, interspersed within a dense network of GFAP-positive astrocytic processes. Immunohistochemistry for flaviviral antigen showed colocalization of viral antigen-positive neurons and necrotic foci. In less severe cases, cerebral necrosis occurred in well-demarcated, locally extensive regions or isolated gyri, sometimes with a vascular distribution, resulting in porencephaly. In addition, vascular calcification was noted, although with unknown significance and pathogenesis. Arthrogryposis, scoliosis, and kyphosis were observed in a small subset of the cases, which had myelodysplasia. Myelodysplastic changes varied and included central canal duplication, dysplastic gray matter, and bifurcation of the ventral medial sulcus. Multifocal necrosis and inflammation were also observed in the spinal cord, although the extent was typically limited.

Arthropod‐borne orthobunyaviruses belonging to the Simbu serogroup can cause congenital and neurological disease in livestock. Across Australia, the National Arbovirus Monitoring Program (NAMP) conducts surveillance for veterinary‐important arboviruses. Our study complements this broader surveillance framework by investigating the virus‐specific transmission patterns of Simbu group viruses (SGVs) present in New South Wales (NSW). To describe the distribution of six SGVs: Akabane, Aino, Douglas, Peaton, Tinaroo, and a recently recognised Shamonda‐like virus, we examined 24 years of serological data (2000–2023) from NSW sentinel cattle. The transmission of a Simbu serogroup virus was detected during every monitoring period (October–July), progressing from north to south along the NSW coastline. Inland transmission west of the Great Dividing Range (GDR) was intermittent (2012–2013, 2020, and 2022), when SGV distribution extended across the mountain range or progressed down the western slopes from Queensland. From 2014, repeated seasonal SGV transmission extended to the far south coast of NSW. Peaton virus was the most frequently detected and widely distributed virus. Since testing for the newly detected Shamonda‐like virus started in 2019, this virus has been widely detected across coastal NSW and often in herds also infected with Douglas or Peaton viruses. Discrepancies between the ELISA and virus neutralisation test (VNT) results suggest that this virus could have been present in NSW as early as 2012. From 2017, Akabane virus has a sporadic distribution. The distribution for both Aino and Tinaroo viruses was sporadic (2005–2023). These findings highlight the importance of long‐term, virus‐specific surveillance in identifying emerging variants and detecting exotic incursions.

Border disease viruses (BDV) and bovine viral diarrhoea viruses (BVDV) are members of the Pestivirus genus in the family Flaviviridae . While BVDV is one of the most significant endemic viral infections of cattle in Australia, BDV infection is generally considered to be uncommon in Australian sheep. This study describes the widespread detection of BDV on two properties in southern New South Wales following an investigation into poor pregnancy rates, resorbing foetuses and stillborn lambs. Extensive cross‐sectional serological studies identified a high seroprevalence in some groups of sheep and low prevalence in others, demonstrating both the extent of infection and the number of susceptible breeding sheep remaining at risk. BDV‐specific qRT‐PCR confirmed BDV infection of stillborn lambs, and a large number of ‘hairy’ lambs were confirmed as BDV infected by use of a pestivirus antigen ELISA at marking. In a group of BDV persistently infected lambs that were monitored for 12 months, postweaning survival was low, with 21 of 120 still alive at 5 months of age and 14 still alive at 12 months of age. This study highlights the potential impact BDV can have on production and how management strategies, including breeding young primiparous ewes under intensive management conditions can result in large‐scale virus transmission and disease.

The emergence of Japanese encephalitis virus (JEV) in eastern Australia in 2022 caused extensive reproductive disease in pigs and is a threat to public health. Groups of weaned piglets were experimentally infected with the Australian outbreak strain of JEV (genotype 4). All pigs challenged at 5 weeks of age were infected after an intradermal injection of 1 × 10^5.5 (n = 4) or 1 × 10^4.5 TCID₅₀/pig (n = 5). Intranasal instillation was less effective at this age, infecting 3/4 pigs with the same higher dose and 1/5 with the lower dose. Intradermal injection using 1 × 10^5.0 TCID₅₀/pig also infected 9/9 pigs at 11 weeks of age. Infection in all cases was confirmed by qRT-PCR of blood samples, which identified a viremia peak at 3–4 days and detected JEV-specific antibodies as early as 5 days after the challenge. The detection of JEV in oral and nasal swabs and in saliva from chew ropes was less consistent. JEV was detected in the tonsils of 21/22 infected pigs and was isolated from the tonsils of 9/9 pigs sampled 19 days after the challenge at 11 weeks of age. The infected pigs showed no clinical signs other than pyrexia on Days 4–6. Histopathology consistent with JEV infection was evident in the nervous tissues of all but two pigs sampled 28 days after the challenge and was characterized by meningitis, encephalitis and gliosis throughout the brain. Serological studies showed extensive cross-reactivity between JEV and Murray Valley encephalitis virus using blocking ELISAs. However, the determination of limiting-dilution titres allowed for the identification of the infecting virus. This in vivo infection model will be useful in evaluating JEV vaccines and for comparative pathogenesis studies with other JEV genotypes.

Orthobunyaviruses (order Bunyavirales, family Peribunyaviridae) in the Simbu serogroup have been responsible for widespread epidemics of congenital disease in ruminants. Australia has a national program to monitor arboviruses of veterinary importance. While monitoring for Akabane virus, a novel orthobunyavirus was detected. To inform the priority that should be given to this detection, a scoping review was undertaken to (1) characterise the associated disease presentations and establish which of the Simbu group viruses are of veterinary importance; (2) examine the diagnostic assays that have undergone development and validation for this group of viruses; and (3) describe the methods used to monitor the distribution of these viruses. Two search strategies identified 224 peer-reviewed publications for 33 viruses in the serogroup. Viruses in this group may cause severe animal health impacts, but only those phylogenetically arranged in clade B are associated with animal disease. Six viruses (Akabane, Schmallenberg, Aino, Shuni, Peaton, and Shamonda) were associated with congenital malformations, neurological signs, and reproductive disease. Diagnostic test interpretation is complicated by cross-reactivity, the timing of foetal immunocompetence, and sample type. Serological testing in surveys remains a mainstay of the methods used to monitor the distribution of SGVs. Given significant differences in survey designs, only broad mean seroprevalence estimates could be provided. Further research is required to determine the disease risk posed by novel orthobunyaviruses and how they could challenge current diagnostic and surveillance capabilities.

Orthobunyaviruses (order Bunyavirales, family Peribunyaviridae) in the Simbu serogroup have been responsible for widespread epidemics of congenital disease in ruminants. Australia has a national program to monitor arboviruses of veterinary importance. While monitoring for Akabane virus, a novel orthobunyavirus was detected. To inform the priority that should be given to this detection, a scoping review was undertaken to 1) Characterise the associated disease presentations and establish which of the Simbu group viruses are of veterinary importance; 2) Examine the diagnostic assays that have undergone development and validation for this group of viruses, and 3) Describe the methods used to monitor the distribution of these viruses. Two search strategies identified 224 peer-reviewed publications for 33 viruses in the serogroup. Viruses in this group may cause severe animal health impacts, but only those phylogenetically arranged in clade B are associated with animal disease. Six viruses (Akabane, Schmallenberg, Aino, Shuni, Peaton, and Shamonda) were associated with congenital malformations, neurological signs, and reproductive disease. Diagnostic test interpretation is complicated by cross-reactivity, the timing of foetal immunocompetence and sample type. Serological testing in surveys remains a mainstay of the methods used to monitor the distribution of SGVs. Due to significant differences in survey designs, only broad mean seroprevalence estimates could be provided. Further research is required to characterise the SGV detected and determine the disease risk posed by novel orthobunyaviruses and how they could challenge current diagnostic and surveillance capabilities.

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.

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.

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.

Infection of bulls with bovine viral diarrhoea virus (BVDV) can result in the development of virus persistence, confined to the reproductive tract. These bulls develop a normal immune response with high neutralizing antibody titres. However, BVDV can be excreted in the semen for a prolonged period. Although relatively rare, in this study we describe six separate cases in bulls being prepared for admission to artificial breeding centres. Semen samples were tested in a pan-Pestivirus-reactive real-time PCR assay and viral RNA was detected in semen from five of the bulls for three to eight months after infection. In one bull, virus was detected at low levels for more than five years. This bull was found to have one small testis. When slaughtered, virus was only detected in the abnormal testis. The low levels of BVDV in the semen of these bulls were only intermittently detected by virus isolation in cell culture. This virus-contaminated semen presents a biosecurity risk and confirms the need to screen all batches of semen from bulls that have been previously infected with BVDV. The use of real-time PCR is recommended as the preferred laboratory assay for this purpose.