Bovine Respiratory Disease Complex: Prevalence of the Main Respiratory Viruses Involved in Pneumonia in Spain

The most common cause of disease among cattle is Bovine Respiratory Disease, and its control has a great impact on the profitability of cattle farms. It is a multifactorial and polymicrobial complex, involving both bacteria and viruses. The objective of this study was to assess the prevalence of the most relevant bovine respiratory viruses (bovine viral diarrhoea, bovine herpesvirus type 1, and bovine respiratory syncytial viruses) due to their clinical relevance, and also their course over time to facilitate decision-making when designing vaccination programmes based on scientific evidence. Samples from animals with early symptoms of respiratory disease were taken using the BOVIRESPCHECK kit, enabling nasal swabs to be taken from four different animals within the same farm. The samples were analysed separately for each animal (not pooled) for the detection of the three viruses by real time polymerase chain reaction. Between 2016 and 2020, a total of 964 reports were created, from a total of 661 cattle farms distributed all over Spain. Each report corresponds to a farm that had an outbreak or respiratory problem at the time. The most frequently detected virus was bovine respiratory syncytial virus, present in 31.5% of the reports, followed by bovine viral diarrhoea virus detected in 23.94% of them. Both viruses were found in combination in 15.96% of cases, showing a significant positive correlation between them. The bovine herpesvirus type 1 was detected in 17.2% of reports; however, the prevalence reached a peak at 28.11% in 2020 with the restriction in use of multivalent (non-marker) vaccines in the country. These results underline the significance of implementing complete vaccination programmes that cover all the most important respiratory viruses. Vaccination against bovine respiratory syncytial and bovine viral diarrhoea viruses seems to be justifiable not only because of the high incidence of both pathogens, but also because of the positive correlation between them. The use of infectious bovine rhinotracheitis monovalent marker vaccines should be added to the above-mentioned vaccines, as their exclusion could be partly responsible for the increased incidence of the bovine herpesvirus type 1 and its associated pathology in 2020. There is a need for a multivalent vaccine including the most relevant viruses with an IBR-marker component to control BRD.