Bluetongue disease in sheep in New South Wales - April 2023

In 2016, bluetongue virus (BTV), serotype 16 (BTV-16), was detected in New South Wales (NSW) in sentinel cattle for the first time. Over the next 6 years, BTV-16 has been detected regularly and over an increasing area of the BTV zone in NSW. In April 2023, disease was reported in sheep on two farms on the Northern Tablelands of NSW. The consistent clinical signs included reduced exercise tolerance, facial swelling, serous nasal discharges with encrustation of the nasal plane, subcutaneous oedema of the neck and brisket and variable congestion of the coronary band. Affected sheep were mainly mature ewes and rams, with an estimated morbidity of 20% over a period of 6-8 weeks. Although there were several unexpected deaths, no veterinary examination was sought. Predominantly BTV-16 RNA was detected in sick sheep, with an incidence of infection of approximately 40% in a cross section of one flock. These events represent the first confirmation of disease due to bluetongue virus in NSW. As these cases occurred in a region with a high density of sheep, if there is ongoing transmission of BTV-16 during subsequent summers, further disease might be expected.

The potential for bluetongue virus serotype 16 to cause disease in sheep in New South Wales, Australia

BLUETONGUE VIRUS SEROTYPE 16 DETECTION IN NSW: In coastal New South Wales (NSW), bluetongue virus (BTV) serotypes 1 and 21 are endemic and transmitted in most years without evidence of disease. However, serotype 16 (BTV-16) infection was detected for the first time in NSW in November 2016 in cattle undergoing testing for export. Retrospective testing of blood samples collected from sentinel cattle as part of the National Arbovirus Monitoring Program (NAMP) established that the first detected transmission of BTV-16 in NSW occurred in April 2016 in sentinel cattle on the NSW North Coast. Subsequently, until 2022, BTV-16 has been transmitted in most years and was the predominant serotype in the 2018-2019 transmission season. The data available suggests that BTV-16 may have become endemic in NSW. EXPERIMENTAL STUDIES: During experimental infection studies with BTV-16, all sheep were febrile, with the peak of viremia occurring 6-10 days after inoculation. There was nasal and oral hyperaemia in most sheep with several animals developing a nasal discharge and nasal oedema. All sheep developed coronitis of varying severity, with most also developing haemorrhages along the coronary band. There was a high incidence of haemorrhage in the pulmonary artery, epicardial petechiae, extensive pericardial haemorrhages and moderate body cavity effusions including pericardial effusions. CONCLUSION: Overall, experimental pathogenicity findings suggest moderate disease may occur in sheep in the field. These findings, when combined with climatic variability that could result in an expansion of the range of Culicoides brevitarsis into major sheep-producing areas of the state, suggest that there is an increasing risk of bluetongue disease in NSW.

Expanding the range of the respiratory infectome in Australian feedlot cattle with and without respiratory disease using metatranscriptomics

BACKGROUND

Bovine respiratory disease (BRD) is one of the most common diseases in intensively managed cattle, often resulting in high morbidity and mortality. Although several pathogens have been isolated and extensively studied, the complete infectome of the respiratory complex consists of a more extensive range unrecognised species. Here, we used total RNA sequencing (i.e., metatranscriptomics) of nasal and nasopharyngeal swabs collected from animals with and without BRD from two cattle feedlots in Australia.

RESULTS

A high abundance of bovine nidovirus, influenza D, bovine rhinitis A and bovine coronavirus was found in the samples. Additionally, we obtained the complete or near-complete genome of bovine rhinitis B, enterovirus E1, bovine viral diarrhea virus (sub-genotypes 1a and 1c) and bovine respiratory syncytial virus, and partial sequences of other viruses. A new species of paramyxovirus was also identified. Overall, the most abundant RNA virus, was the bovine nidovirus. Characterisation of bacterial species from the transcriptome revealed a high abundance and diversity of Mollicutes in BRD cases and unaffected control animals. Of the non-Mollicutes species, Histophilus somni was detected, whereas there was a low abundance of Mannheimia haemolytica.

CONCLUSION

This study highlights the use of untargeted sequencing approaches to study the unrecognised range of microorganisms present in healthy or diseased animals and the need to study previously uncultured viral species that may have an important role in cattle respiratory disease. Video Abstract.

Multiplexed serotype-specific real time PCR assays - a valuable tool to support large scale surveillance for bluetongue virus infection

In the last decade, real time PCR has been increasingly adopted for bluetongue diagnosis with both broadly reactive and serotype-specific assays widely used. The use of these assays and nucleic acid sequencing technologies have enhanced bluetongue virus detection, resulting in the identification of a number of new serotypes. As a result, 27 different serotypes are officially recognised and at least 3 more are proposed. Rapid identification of the virus serotype is essential for matching of antigens used in vaccines and to undertake surveillance and epidemiological studies to assist risk management. However, it is not uncommon for multiple serotypes to circulate in a region either concurrently or in successive years. It is therefore necessary to have a large suite of assays available to ensure that the full spectrum of viruses is detected. Nevertheless, covering a large range of virus serotypes is demanding from both a time and resource perspective. To overcome these challenges, real time PCR assays were optimised to match local virus strains and then combined in a panel of quadriplex assays, resulting in 3 assays to detect 12 serotypes directly from blood samples from cattle and sheep. These multiplex assays have been used extensively for bluetongue surveillance in both sentinel animals and opportunistically collected samples. A protocol to adapt these assays to capture variations in local strains of bluetongue virus and to expand the panel is described. Collectively these assays provide powerful tools for surveillance and the rapid identification of bluetongue virus serotypes directly from animal blood samples. This article is protected by copyright. All rights reserved.

Prolonged Detection of Bovine Viral Diarrhoea Virus Infection in the Semen of Bulls

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.

Clinical and epidemiological features of West Nile virus equine encephalitis in New South Wales, Australia, 2011

BACKGROUND

Between February and June 2011, more than 300 horses with unexplained neurological disease were observed in New South Wales, Australia. A virulent strain of West Nile virus (WNV_NSW2011 ), of Australian origin, was shown to be the cause of many of these cases.

METHODS

We reviewed the clinical descriptions provided by veterinary practitioners and the associated laboratory results. Although there was a range of clinical signs described, ataxia was the only sign that was consistently described in laboratory-confirmed cases.

RESULTS

WNV was detected in brain samples by real-time reverse transcription PCR assay and virus isolation. For serological confirmation of clinical cases, an equine IgM ELISA specific for WNV was shown to be the most effective tool.

CONCLUSION

A state-wide serological survey undertaken after the outbreak indicated that, contrary to expectation, although infection had been widespread, the seroprevalence of antibodies to WNV was very low, suggesting that there could be a significant risk of future disease outbreaks.

Identification of a novel nidovirus as a potential cause of large scale mortalities in the endangered Bellinger River snapping turtle (Myuchelys georgesi)

In mid-February 2015, a large number of deaths were observed in the sole extant population of an endangered species of freshwater snapping turtle, Myuchelys georgesi, in a coastal river in New South Wales, Australia. Mortalities continued for approximately 7 weeks and affected mostly adult animals. More than 400 dead or dying animals were observed and population surveys conducted after the outbreak had ceased indicated that only a very small proportion of the population had survived, severely threatening the viability of the wild population. At necropsy, animals were in poor body condition, had bilateral swollen eyelids and some animals had tan foci on the skin of the ventral thighs. Histological examination revealed peri-orbital, splenic and nephric inflammation and necrosis. A virus was isolated in cell culture from a range of tissues. Nucleic acid sequencing of the virus isolate has identified the entire genome and indicates that this is a novel nidovirus that has a low level of nucleotide similarity to recognised nidoviruses. Its closest relatives are nidoviruses that have recently been described in pythons and lizards, usually in association with respiratory disease. In contrast, in the affected turtles, the most significant pathological changes were in the kidneys. Real time PCR assays developed to detect this virus demonstrated very high virus loads in affected tissues. In situ hybridisation studies confirmed the presence of viral nucleic acid in tissues in association with pathological changes. Collectively these data suggest that this virus is the likely cause of the mortalities that now threaten the survival of this species. Bellinger River Virus is the name proposed for this new virus.

Review: Risks of disease transmission through semen in cattle

The purpose of this paper is to review scientific evidence concerning pathogens that could potentially be transmitted via bovine semen. As a result of a careful analysis of the characteristics of infections that may cause transmission of disease through semen, effective control procedures can be identified that provide minimal constraint to the introduction of new bulls into herds for natural breeding and importation of valuable novel genetics through artificial insemination. The potential for transmission through bovine semen and corresponding effective control procedures are described for bovine herpesvirus 1, bovine viral diarrhea virus, bovine leukemia virus, lumpy skin disease virus, bluetongue virus, foot-and-mouth disease virus, and Schmallenberg virus. Brief consideration is also provided regarding the potential for transmission via semen of Tritrichomonas foetus, Campylobacter fetus venerealis, Brucella abortus, Leptospira spp., Histophilus somni, Ureaplasma diversum, Mycobacterium avium subsp. paratuberculosis, Chlamydiaceae, Mycobacterium bovis, Coxiella burnetii, Mycoplasma mycoides ssp. mycoides and Neospora caninum. Thoughtful and systematic control procedures can ensure the safety of introducing new bulls and cryopreserved semen into cattle production systems.

Application of an embryonated chicken egg model to assess the vector competence of Australian Culicoides midges for bluetongue viruses

Culicoides biting midges (Diptera: Ceratopogonidae) are vectors of a number of globally important arboviruses that affect livestock, including bluetongue virus (BTV), African horse sickness virus and the recently emerged Schmallenberg virus. In this study, a model using embryonated chicken eggs (ECEs) was utilized to undertake vector competence studies of Australian Culicoides spp. for 13 laboratory-adapted or wild-type virus strains of BTV. A total of 7393 Culicoides brevitarsis were reared from bovine dung, and 3364 Culicoides were induced to feed from ECEs infected with different strains of BTV. Of those, 911 (27%) survived the putative extrinsic incubation period of 9-12 days. In some trials, virus was also transmitted onward to uninfected ECEs, completing the transmission cycle. This model does not rely on the use of colonized midges and has the capacity to assess the vector competence of field-collected insects with strains of virus that have not previously been passaged in laboratory culture systems. There is also potential for this model to be used in investigations of the competence of Culicoides spp. for other arboviruses.

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

A specific concept of strain was developed in order to classify the BTV serotypes ever reported in Europe based on their properties of animal health impact: the genotype, morbidity, mortality, speed of spread, period and geographical area of occurrence were considered as classification parameters. According to this methodology the strain groups identified were (i) the BTV strains belonging to serotypes BTV‐1–24, (ii) some strains of serotypes BTV‐16 and (iii) small ruminant‐adapted strains belonging to serotypes BTV‐25, ‐27, ‐30. Those strain groups were assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7, Article 5 on the eligibility of bluetongue to be listed, Article 9 for the categorisation according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to bluetongue. The assessment has been performed following a methodology composed of information collection, expert judgement at individual and 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. The strain group BTV (1–24) can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL, while the strain group BTV‐25–30 and BTV‐16 cannot. The strain group BTV‐1–24 meets the criteria as in Sections 2 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (b) and (e) of Article 9(1) of the AHL. The animal species that can be considered to be listed for BTV‐1–24 according to Article 8(3) are several species of Bovidae, Cervidae and Camelidae as susceptible species; domestic cattle, sheep and red deer as reservoir hosts, midges insect of genus Culicoides spp. as vector species.

First reported outbreak of locally acquired hepatitis E virus infection in Australia

OBJECTIVE

To determine the source and extent of a locally acquired hepatitis E virus (HEV) infection outbreak.

DESIGN, SETTING AND PARTICIPANTS

A cluster of notified cases of HEV infection linked to a single restaurant (X) was identified in May 2014. People with laboratory-confirmed HEV infection in New South Wales between January 2013 and December 2014 were interviewed about potential risk factors for HEV infection. Co-diners at restaurant X and patients with suspected but unexplained viral hepatitis were retrospectively tested. Foods eaten by the infected persons were compared with those of seronegative co-diners. HEV RNA detected in sera from infected persons was sequenced and genotyped. Implicated foods were traced back to their sources.

MAIN OUTCOME MEASURES

Potential sources of infection, including overseas travel and foods eaten, and origin of implicated food products.

RESULTS

In 55 serologically confirmed cases of HEV infection, 24 people had not travelled overseas during their incubation periods. Of the 24, 17 reported having eaten at restaurant X, 15 of whom could be interviewed. All reported consuming pork liver pâté, compared with only four of seven uninfected co-diners (P < 0.05). The other seven people with locally acquired infections each reported consuming a pork product during their incubation periods. HEV RNA was detected in 16 of the 24 cases; all were of genotype 3. Sequencing indicated greater than 99% homology among restaurant X isolates. HEV RNA was isolated from pork sausages from a batch implicated in one of the locally acquired infections not linked with restaurant X. The pork livers used for pâté preparation by restaurant X were traced to a single Australian farm.

CONCLUSIONS

This is the first reported HEV outbreak in Australia. HEV should be considered in patients presenting with a compatible illness, even without a history of overseas travel. Pork products should be thoroughly cooked before consumption.

European interlaboratory comparison of Schmallenberg virus (SBV) real-time RT-PCR detection in experimental and field samples: The method of extraction is critical for SBV RNA detection in semen

Molecular methods for the detection of Schmallenberg virus (SBV) RNA were rapidly developed after the emergence of this novel orthobunyavirus in Europe. The SBV epizootic wave has declined, but infectious SBV in SBV RNA-positive semen remains a possible risk for the distribution of SBV. However, the abilities of SBV molecular detection methods used at European laboratories have not yet been assessed, to our knowledge. The performances of extraction and real-time reverse transcription polymerase chain reaction (RT-qPCR) methods used at 27 German and 17 other European laboratories for SBV RNA detection in the matrices of whole blood, serum, tissue homogenate, RNA eluates, and bovine semen were evaluated in 2 interlaboratory trials with special emphasis on semen extraction methods. For reliable detection of viral genome in bovine semen samples, highly effective extraction methods are essential to cope with the potential inhibitory effects of semen components on PCR results. All methods used by the 44 laboratories were sufficiently robust to detect SBV RNA with high diagnostic sensitivity (100%) and specificity (95.8%) in all matrices, except semen. The trials demonstrated that the published recommended semen extraction methods (Hoffmann et al. 2013) and a combination of TRIzol LS with an alternative extraction kit have a considerably higher diagnostic sensitivity to detect SBV RNA in semen up to a detection limit of Cq ≤35 compared to other extraction methods used. A thorough validation of extraction methods with standardized semen batches is essential before their use for SBV RNA detection in bovine semen.