Infectious Bovine Rhinotracheitis (IBR) is a major concern for the global livestock industry due to its considerable economic consequences. Caused by Bovine herpesvirus 1 (BoHV-1), the disease manifests in a wide range of clinical outcomes. Beyond these direct effects, IBR also contributes to infertility, reduced milk yield, and immunosuppression, which together compromise productivity on cattle farms. Owing to these impacts, IBR is regarded as an economically significant disease, and active surveillance programs are in place across Europe.
One important pillar of many IBR eradication programs has been the application of DIVA vaccination with a gE deletion. However, the Animal Health Law, issued by the European Union, pushes to move from gE antibody detection to whole virus or gB antibody detection. After all, gB and whole virus antibody ELISAs are considered more sensitive and in certain ways also more specific as compared to gE ELISAs. In Belgium, farm statuses are in part based on the application of vaccination. Thus, registration of vaccination is obligatory. However, it is clear that a significant portion of the vaccinations are not registered when we observe the numbers of sold vaccines from the national stock of available DIVA vaccines while vaccination registrations remain low. Therefore, it is unclear which farms can be surveilled using gB or whole virus antibody ELISAs.
In 2022, bulk milk samples from all dairy farms participating in the June monitoring campaign were duplicated and analyzed at Sciensano using both gE and gB antibody ELISAs. Following a major and unexpected IBR outbreak in West-Vlaanderen in 2024, vaccine demand surged and national stocks were frequently depleted, although official registration rates remained low. Consequently, the vaccination ban deadline was postponed three times, and attitudes in the field shifted markedly in favor of vaccination. To assess the impact of this outbreak, the experiment was repeated in February 2025. Surprisingly, vaccination prevalence did not increase (38%) compared to 2022 (48%), although the outbreak likely slowed the expected decline in vaccinated herds. Additional analyses revealed patterns of regional and veterinary clustering, evidence of gE aspecificity, and an effect of milk freshness on gE test performance.
This data shows that a significant portion of the IBR surveillance of dairy farms in Belgium can shift towards whole virus antibody ELISA, which directly solves some of the gE antibody ELISA down sides, including the legal limits imposed by the Animal Health Law. Furthermore surveillance can be refined by taking in account the regional differences.
