Infectious Bovine Rhinotracheitis Post-Eradication Program in the Autonomous Province of Bolzano, Italy: A Retrospective Study on Potential Bovine Herpesvirus Type 2 Cross-Reactivity

SIMPLE SUMMARY: Infectious bovine rhinotracheitis is one of the diseases caused by bovine herpesvirus type 1; it affects cattle and can heavily damage the livestock industry. Several countries have adopted different prevention measures, and some of them have been declared free from infectious bovine rhinotracheitis. Our work is focused on data collected in the autonomous province of Bolzano (Italy). This province underwent an eradication program between 1991 and 2000. In 2000, the territory was declared IBR-free. Since 2001, a post-eradication program has been conducted, which includes annual milk testing. If a positive result is found, additional blood tests are performed. During the several years of the post-eradication program, positive results were detected in bulk milk and serum samples; our hypothesis is that these positive results are potentially caused by bovine herpesvirus type 2 cross-reactivity. ABSTRACT: Bovine alphaherpesviruses, BoAHV, can cause respiratory, genital and neurological disorders. In particular, bovine alphaherpesvirus type 1 (BoAHV1) is one of the most significant ruminant pathogens worldwide and it can heavily damage the livestock industry. BoAHV1 can cause infectious bovine rhinotracheitis (IBR) along with fertility disorders. Bovine alphaherpesvirus type 2 (BoAHV2) can cause two different conditions as well: pseudo-lumpy skin disease (PSLD) and bovine herpetic mammillitis (BHM). The autonomous province of Bolzano (Italy) has adopted several strategies to control and eradicate IBR, and it was declared in 2000 to be IBR-free by the European Commission. Since 2001, a post-eradication monitoring program has overseen the serological analysis of bulk milk and, in the presence of a positive result, a follow-up examination is performed on the individual blood serum of all bovines older than 24 months that belong to bulk milk-positive herds. Despite the detection of positives in both bulk milk and serum samples, South Tyrol has been declared IBR-free, as these positives have never been confirmed through seroneutralization. Between 2014 and 2022, approximately 41,000 bulk milk (averaging 4300 samples/year) and 3229 serum samples were tested for BoAHV1. The aim of this study was to evaluate the post-eradication program for IBR with a particular focus on the potential cross-reactivity with BoAHV2; for this reason, serum samples were also tested for BoAHV2 antibodies. This study could be of great importance for those countries that submit herds to an IBR monitoring and eradication program; performing further analyses to confirm and explain false positive outcomes would increase the reliability of the obtained results.