How bovine coronavirus is linking pneumonia and calf scour
© Tim Scrivener Bovine coronavirus has been identified as the most prevalent virus associated with bovine respiratory disease outbreaks on UK farms, and the pathogen is likely to be present on most units.
Commonly referred to as pneumonia, bovine respiratory disease (BRD) is caused by a multitude of pathogens and it is likely bovine coronavirus (BCoV) has played a part in the complex for some time.
However, it is only recently that scientists have started to look for the virus in association with respiratory illness.
Dr Paul Burr, vet and director of Biobest Laboratories, analysed more than 400 nasal swab samples taken from BRD-affected cattle in the UK between 2020 and 2022.
BCoV was found in 39% of samples, making it the most frequently diagnosed virus.
See also: 4 ways to improve on 60-day calf mortality rate
Separate surveillance blood testing carried out on calves aged three to six months from 59 UK farms highlighted that 91.5% had been exposed to BCoV, as shown by the presence of antibodies.
Furthermore, testing on 10 Scottish dairy farms identified broad exposure across all ages of cattle, says Dr Katie Denholm, academic clinician at Glasgow University Veterinary School.
“We found that bovine coronavirus was more prevalent than we had anticipated, which fits with some more recent international literature that’s seeing a sort of shift and more coronavirus in respiratory samples from bovines,” she explains.
The bacterial pathogens Mannheimia haemolytica and Mycoplasma bovis remain the main bugs identified in a BRD outbreak (see table).
However, Kat Baxter-Smith, veterinary adviser at the drug manufacturer MSD, says it is likely that viruses such as BCoV come in first and damage the protective mucus layer of the respiratory tract, which normally acts to stop pathogens from invading cells.
“That means other pathogens can then get free access to the respiratory cells and infect them and cause more severe disease,” she adds.
The link with scour
Katie thinks it likely that farms that have scour linked to coronavirus could also have respiratory disease associated with the pathogen.
“You could definitely have diarrhoea and respiratory diseases at the same time caused by coronavirus on your farm. Usually, you’ll see respiratory disease first, but not always,” she says, adding that scour is usually caused by multiple pathogens, such as coronavirus and rotavirus.
It is possible that calves develop a respiratory infection, then cough and swallow, thus infecting the enteric tract. This does not necessarily mean calves develop scour.
Subclinical disease
There is a risk that animals are subclinically infected with BCoV and thus show no physical signs of disease, says Katie.
However, calves shedding BCoV nasally have been shown to be 1.5 to 2.7 times more likely to have BRD than those not shedding the virus.
“There can be other animals on the farm that are subclinically affected and are sort of reservoirs for infection,” she says.
“And they can have an initial respiratory amplification of the virus, which then transits to the gut, resulting in faecal shedding, which then further exacerbates the problem.”
Percentage of UK farms positive for pneumonia pathogens |
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|
|
Bovine coronavirus (BCoV) |
Bovine respiratory syncytial virus (BRSV) |
Bovine parainfluenza-3 virus (Pi3) |
Mannheimia haemolytica |
Mycoplasma bovis |
|
Surveillance* |
91.5% |
35.6% |
91.5% |
91.5% |
35.6% |
|
Outbreak** |
38.6% |
21.6% |
11.5% |
61.7% |
39.1% |
|
Notes: *Calf serology from 59 farms across UK which had a history of BRD (2021-22). **Nasal swab from 407 farms submitted to Biobest (2020-22) |
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Tips for identifying and preventing respiratory coronavirus
1. Test for pathogens
As all pneumonia pathogens present in a similar way, with coughing, laboured breathing and a high temperature, it is worthwhile testing to identify the specific cause.
When there is a disease outbreak, MSD veterinary adviser Kat Baxter-Smith advises taking nasal swabs from five calves, which can be pooled for more cost-effective testing.
Surveillance blood testing can also be carried out on calves aged three to six months to get an idea of what respiratory pathogens they have been exposed to.
This could be done at the end of block calving, or after winter housing in all-year-round calving herds. The data can be used to inform future preventative strategies.
Dr Katie Denholm at Glasgow University Veterinary School says not all labs currently test for coronavirus as a respiratory pathogen, and the decision as to whether to test for it, together with other pathogens, should lie with a vet.
This will be based on a farm’s individual history and risk.
2. Get better at identifying mild respiratory disease
Identifying and addressing early signs of respiratory disease is essential to stop issues from escalating.
Katie advises farmers to use a health scoring tool, such as the Wisconsin Madison Scoring system.
This is a free, online tool that assigns a respiratory score and faecal score to individual calves, based on observations. This allows low-grade, rumbling infection to be identified and calves can be monitored.
Katie advises:
- Separating calves with mild signs to reduce the risk of infection spread
- Treating mild infections promptly with non-steroidal anti-inflammatories
- Taking a holistic view of calf housing, ventilation and hygiene and making improvements.
3. Provide adequate colostrum
Colostrum management is the cornerstone of disease prevention, providing calves with their dam’s immunity.
Vaccination (see point 4) against specific diseases can help bolster the levels of immunoglobulins in colostrum, which can then be passed to the calf.
Feed only good-quality, clean colostrum, and deliver three litres in the first two hours of birth.
4. Manage scour to reduce infection pressure
Use calf-side scour testing kits, available through vets and registered animal health advisers (Ramas) to establish the cause of scour, advises Kat.
Even if coronavirus has been identified as a respiratory pathogen, a combination of pathogens could be causing scour.
Cows can be vaccinated against the scour pathogens coronavirus, rotavirus and E coli K99. Antibodies are then passed to the calf via colostrum.
This does not protect calves from the respiratory form of coronavirus. However, it protects the calf from scour and it reduces shedding and, therefore, pathogen load in the environment.
This could reduce the risk of calves being exposed to the virus.
5. Consider vaccinating against BCoV
A new intranasal BCoV vaccine has been developed to reduce the clinical signs of respiratory disease and nasal viral shedding of BCoV.
This will likely be available to UK farmers this year and can be used in cattle from birth. A vaccination programme should be designed in consultation with a vet.