Bovine herpesvirus 2 (BHV-2) - geographical distribution and influence on IBR serology (2018) master thesis by Patricia Kulka

BHV-2 is the cause of bovine herpes mammillitis in cows. The disease affects the skin of the teats and udder and impairs the milkability for around 4 weeks. Also, milk production can decrease during illness.  Furthermore, BHV-2 antibodies (AB) have been discussed to cross-react with serological detection of BHV-1, the cause of the enzootic infectious rhinotracheitis (IBR). Previous analyses hinted at an overlap of regions with increased occurrence of IBR false-positive samples and regions with higher antibody titers for BHV-2. However, these data were based on a limited number of samples from specific regions of Switzerland.

The first goal of this master`s thesis was therefore to get a status on the distribution of BHV-2 antibodies in dairy cattle farms covering the full area of Switzerland. Bulk milk samples collected for milk quality control purposes provided an easy to get sample that reflects well the antibody status of the herd. In a second part, a possible cross sensitivity of BHV-2 antibodies in ELISA tests for IBR serology (BHV-1) was investigated.

We tested 380 randomly selected bulk milk samples for BHV-2-ABs in ELISA. The mean ELISA-values per region showed that Eastern Switzerland and Zurich had significantly higher antibody titres than the other regions. These regions have also a relatively high number of false-positive IBR-serology results. Interestingly, this “hotspot” for BHV-2 in the eastern parts of Switzerland seem to stretch out into western Austria, southern Germany and northern Italy, where BHV-2 (and false-positive IBR results) are also relatively frequent and covers mainly alpine areas.

For the second part, we tested 56 known IBR-ELISA-false-positive and the same number of geographically and temporary matched negative controls for the BHV-2 antibodies in ELISA and SNT. Chi-Square testing showed significantly more BHV-2-positive or indeterminate results in the IBR-ELISA false positive group than in the IBR-ELISA negative controls.  Quantitative statistics confirmed significantly higher BHV-2 ELISA values in the IBR-ELISA false-positive group than in the IBR-ELISA negative controls.

The finding of qualitatively and quantitatively significantly higher BHV-2 antibody contents in IBR-ELISA false positive sera than in their geographically matched IBR-ELISA negative controls supports the hypothesis that high BHV-2 antibody titers could be one of the factors that favor the occurrence of false positive IBR serology results.