The two most costly infections in Norwegian cattle. Is it possible to control bovine respiratory syncytial virus and bovine coronavirus?

The primary objective of this project was to generate fundamental knowledge to reduce the occurrence of bovint respiratorisk syncytialvirus (BRSV) and bovint coronavirus (BCoV)which in the Norwegian cattle population. Secondary objectives were to: Generate knowledge of occurrence of both infections in Norway Evaluate the most important dispersal patterns of BRSV and BCoV: role of direct transmission (live animals, humans) role of indirect transmission (humans, utensils) Document consequences of the infections in Norway today Evaluate a new diagnostic test to detect antibodies in bulk tank milk Study risk factors for infection on herd level. Dissiminate the results to producers, veterinarians and advisors and motivate them to implement preventive measures Many Norwegian herds experience outbreak of infectious diseases each year. The two most important viruses causing such outbreaks are BRSV and BCoV, which result in respiratory disease and winter dysentry. The negative consequences of these infections are considered serious for animal welfare, productions and the use of antibiotics due to secundary infections. This led to the initiative to start this project in 2013. A national screening of bulk tank milk from dairy herds has been conducted, where this is analyzed for antibodies to BRSV and BCoV. 70 % of the herds were positive for antibodies to BRSV, and 78.5 % were positive for BCoV. A new diagnostic test was used, that was validated in the project by use of a so-called latent class analysis and compared with the traditionally used test, which provided basic information about the test performance. The national results showed considerable variation in occurrence between regions. Prevalence and spatial distribution was furter studied in some counties. Different transmission patterns and risk factors have then been assessed. For both viruses, both indirect transmission and direct transmission by live animal movements is important, but live animal movements more so for BCoV. The positive herds were clustered, which could only partly be explained by geography, herd size and live animal trade. Direct spread of BCoV from calves and indirect via humans and utensils was evaluated in a live animal experiment. This showed that virus is shed for a longer period than previously known. However, sentinel calves introduced three weeks after infection remained negative, indicating that the practical implication of this viral shedding might be less important. Further studies on indirect transmission potential from human nasal mucosa and equipment and clothes that have been exposed to virus indicated that utensils and clothes that are contaminated represent a risk also the day after use, while virus survival in human mucosa seems to be of less importance. The virus? ability to survive under different environmental conditions and on human skin was also studied, and supports that BCoV can survive for some time in the environment. This is of practical relevance; measures should be implemented to avoid indirect transmission between herds. Genetic analysis of virus isolates from the the calves in the experiment has been done to detect the natural mutation rate when BCoV is spread between animals. This is done by use of deep sequencing and extended genome sequencing. Relatively little diversity was detected. This knowledge will form the basis for molecular epidemiology studies to be performed on isolates from field outbreaks from different herds. If the basic mutation rate is known, one can use that to interpret the relationship between different outbreaks, which again can be used to trace the infection route (molecular epidemiology) Herds with clinical outbreak of winter dysenteria (BCoV) in 2011/2012 have been identified and used in a case/control-study on consequences of such outbreaks. The results show acute and long-term reduction in milk production on herd leve, and in addition reduced milk quality. This is the first time this is documented in a population. The results from the project has been communicated to the producers, veterinarians and collaborators. Knowledge gained in the project is the basis for 7-9 scientific papers and two PhDs. The collaboration with the cattle industry and the knowledge gained in the project has also lead to the launching of a national control program against BRSV and BCoV by a joint cattle industry in 2016, which is unique internationally. The project has therefore also led to action towards better animal velfare, production and increased sustainibility in the cattle industry.

The Norwegian cattle population is free of many infectious diseases; many due to eradication programs. The two most costly infections today is BRSV, causing contagious respiratory disease, and BCoV, causing diarrhea in calves and adults (winter dysentery) . BRSV is one of the most serious welfare problems and practically all outbreaks of respiratory disease are caused by BRSV in Norway. A recent outbreak of winter dysentery showed that the larger dairy herds lost NOK 100 000 each in reduced milk production . In addition both infections have detrimental effects on the cows' welfare, milk quality, growth rate, feed utilization, reproduction performance, and increases the use of antibiotics. Preliminary data shows serious and hitherto underestimated consequenc es on profitability and animal welfare of BRSV and BCoV. It is probably possible to limit the incidence of these infections. That requires documented knowledge on economic consequences, dispersal patterns, transmission modes between herds and preventive measures. The project's aim is to generate this knowledge and communicate the results. This is going to form the basis of an eventual control program of international significance. The project includes a screening of all dairy herds in Norway based on a ntibodies against BRSV and BCoV in bulk tank milk. Negative herds will be re-tested annually to identify recently infected herds. Together with information on preventive measures implemented and the purchase of live animals the effect on these measures an d trade with animals can be evaluated. The dissemination pattern will be analyzed by genetic analysis of virus strains from outbreaks. Experimental infections in calves will also be conducted to study transmission of virus via the airway mucosa of humans as well as equipment commonly brought from farm to farm by veterinarians. Finally the different preventive measures as well as a possible control program will be assessed by cost-benefit analysis.