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Virus can ‘open door’ to respiratory disease (Nov/Dec 23)

Research has revealed that bovine coronavirus is playing a critical role in causing respiratory disease in calves and cattle. But the good news is that there’s a vaccine that can help to keep a lid on it.


TEXT DAVID BUTLER



Since the global COVID-19 pandemic, medical practitioners have become more aware of the threat to human health posed by the family of coronaviruses. But new diagnostic data suggests coronavirus could also play a more important role when it comes to bovine respiratory disease (BRD) than previously thought.


Recent UK studies show that bovine coronavirus (BCoV) as being the most prevalent virus found in routine disease screening and nasal swab samples taken during a BRD outbreak.


According to Biobest Laboratories’ vet Paul Burr, the fact that BCoV is frequently isolated, alongside other perhaps more recognised respiratory disease pathogens such as BRSV, M haemolytica, PI3 and M bovis, suggests an interplay between these organisms.


“Research has already shown that BCoV infection disturbs the protective mucus lining of the thoracic tract,” he says. “So it could be that BCoV ‘opens the door’ for the other viral and bacterial pathogens to establish themselves and cause disease.”


The UK BCoV prevalence picture mirrors that seen in Europe. A recent 16-country European study found every dairy herd was seropositive for BCoV, and those with BCoV-seropositive calves had an increased risk of suffering from BRD.


“Work shows that calves shedding BCoV nasally are between 1.5 and 2.7 times more likely to have BRD than those that don’t shed the virus,” adds Dr Burr. “So it’s clear that this virus does play a role in calf/cattle pneumonia, it’s just that up until now we haven’t been looking for it and perhaps don’t fully understand its potential to cause disease.”


Nasal-swab samples


He believes BCoV hasn’t had the focus it deserves from the vet community, despite a growing body of evidence worldwide demonstrating both its presence and clinical importance when tackling BRD.


To help develop understanding, Dr Burr analysed more than 400 nasal-swab samples taken between 2020 and 2022 from BRD-affected cattle in UK herds.


BCoV was found in 39% of samples, making it the most frequently diagnosed virus of those included in the routine testing. “While the properties of BCoV infection, such as extended shedding, may increase the potential for its detection compared to other viruses, the results confirm that it is an important pathogen in the UK – consistent with other recent work in this country, in Europe and worldwide.”


The pathogen was found most frequently during the winter (December to February), but was also present year-round. There did appear to be some regional bias too, with BCoV being found most frequently in Northern Ireland, the West Midlands and the south-west region of the UK. Evidence of the UK-wide prevalence of BCoV is supported by a recent study in Scotland – carried out as an adjunct to the 16-country European research project – as well as routine BRD screening conducted by MSD Animal Health.


BCoV exposure


Working alongside the Clyde Veterinary Group, Katie Denholm, an academic clinician based at Glasgow University Veterinary School, enrolled 10 commercial dairy herds in central Scotland that all had a history of BRD. Nasal swabs, faecal samples and bloods were taken for testing from cattle on these units. The samples were taken from young pre-weaned calves, older calves and adult cattle. Bulk milk samples were also taken to test for BCoV antibodies.


“The serology results confirmed that almost all the cattle tested had been exposed to BCoV at some point in their lives because antibodies to the virus were present in their blood. But a few of the nasal swab and faecal samples also tested positive in some herds,” says Ms Denholm.


Further evidence of BCoV exposure in cattle in the UK can be found in 2021 to 2022 BRD screening surveillance data. Calf serology on 59 UK farms known to have had a history of BRD issues reported 91.5% of samples being positive for BCoV.


If vet diagnostics suggest bovine coronavirus is implicated in any pneumonia problem, a new vaccine, Bovilis Nasalgen-C, could help to improve BRD management on some UK dairy units.

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