Researchers at the Norwegian School of Veterinary Science are engaged in continuing research into infection dynamics and the potential for preventing infection with the bovine respiratory syncytial virus (BRSV), one of the main causes of respiratory disease in cattle.
Results of a recent study, published in Veterinary Record, indicate some potential for using surveillance and biosecurity to prevent BRSV outbreaks in herds.
The goals of the study were to
- Estimate the prevalence and geographical distribution of herds with BRSV circulating within the previous year in Norway.
- Shed new light on the dynamics of BRSV by repeating the study twice in the same herd six months apart, better defining temporal distribution of infection in herds.
- Compare distributions to factors, such as season and size of herds.
The researchers randomly selected 134 Norwegian dairy herds to participate in the study of infection dynamics of the BRSV virus. They tested five calves from each herd antibodies against BRSV and tested again six months later. They defined a herd as positive if at least one animal aged between 150-365 days was shown to have antibodies against the virus.
The researchers found 54 percent of the herds tested positive for exposure to BRSV during the study period, with wide variation between different parts of the country. However, they found several herds with negative test results located in close proximity to herds infected by the virus, and some herds remained free of the virus in spite of proximity to newly infected herds. Twenty-seven (33 per cent) of the 81 herds initially testing negative changed to positive, and 9 (33 per cent) of these 27 herds showed all animals positive on the second sampling. Fifteen (42 per cent) of the 36 herds initially being positive changed to negative, and 21 of them (58 per cent) remained positive on second sampling. Of the herds negative on first sampling, 54 (46 per cent) were also negative on the second.
The researcher team reached these conclusions:
- There is high variation in prevalence and pattern of infection dynamics within and between herds in the different regions.
- There are rapid shifts in infectious status at herd level.
- The rate of new infections at herd level does not vary with season.
- Negative herds were found in close proximity to positive herds.
- Combined with a high elimination rate in infected herds, it should be possible to lower the prevalence of BRSV by preventing the introduction of virus into herds throughout the year.
- A suitable strategy could be to employ close surveillance and focus on the negative herds followed by high biosecurity to avoid new introductions of virus in these herds.
Read more from Veterinary Record.