Bovine Alphaherpesvirus 2 infections in Bavaria: an analysis of the current situation - several years after eradicating Bovine Alphaherpesvirus 1

Abstract

Background: Bavaria, a large federal state in Germany, has been declared free from infections with Bovine Alphaherpesvirus 1 (BoHV-1) in 2011. To maintain this status the cattle population is monitored for antibodies against BoHV-1 regularly. Several years ago, infrequent but recurrent problems in this sero-surveillance were statistically put into correlation with the presence of antibodies against Bovine Alphaherpesvirus 2 (BoHV-2). In Europe, BoHV-2 is primarily known as the agent causing bovine herpes mammillitis. However, very little information about BoHV-2 infections in Bavaria is available so far. Therefore, the aims of this study were to determine BoHV-2 seroprevalences and to detect virus genomes in potential clinical samples.

Results: 6801 blood sera of healthy cattle from all over Bavaria were tested for antibodies against BoHV-2, revealing an overall seroprevalence of 5.51%. Interestingly, seroprevalences markedly varied between the North and the South of Bavaria, namely from 0.42 to 11.17%. Concurrently, the previously reported relation between the epidemiologically inexplicable sero-reactivities in BoHV-1 ELISAs and the presence of BoHV-2 infections were statistically corroborated in this study. To detect BoHV-2 genomes a fast and sensitive real time PCR was established. Using a multiple PCR strategy, tissue samples from skin lesions at relevant localizations, corresponding lymph nodes, and trigeminal ganglia from 111 animals, as well as nasal swabs from 918 bovines with respiratory symptoms were tested. However, BoHV-2 genomes were not detected in any of these samples.

Conclusions: BoHV-2 antibodies were found in samples from bovines all over Bavaria, albeit with an explicit South-North-divide. BoHV-2 genomes, however, could not be detected in any of the analyzed samples, indicating that acute clinical cases as well as obvious virus reactivation are relatively rare. Consequently, the future spread of BoHV-2 infections throughout Bavaria, particularly, after eradicating BoHV-1, has to be further monitored.

Keywords: Bavaria; BoHV-1; BoHV-2; Bovine Alphaherpesvirus 1; Bovine Alphaherpesvirus 2; Bovine herpes mammillitis; Germany; Real time PCR; Seroprevalence.

Fig. 1

Correlation between BoHV-2 ELISA results and titers of neutralizing antibodies. Each symbol represents the results of one sample in both tests. The data for 128 samples are shown. ELISA results are indicated as S/P%-values. In case of duplicate analyses the mean S/P%-value per sample is given. Sera with ELISA values ≤90% are classified as negative by the manufacturer and are depicted as diamonds (♦) for S/P%-values ≤10%, circles (◯) for S/P%-values between 10 and 50%, or hexagons (⬡) for S/P values between 50 and 90% . Triangles (▲) indicate results classified as doubtful by ELISA (90% < S/P% < 110%). ELISA-positive sera are indicated by rectangles (■)

Fig. 2

BoHV-2 seroprevalences in Bavaria divided into administrative regions. Seroprevalences calculated for 406 holdings are shown as black diamonds (♦), and those calculated for 6801 individual animals, irrespective of the correspondent farm, as open diamonds (◇). A holding is rated as “BoHV-2 seropositive” if at least one seropositive bovine animal is kept. Confidence intervals covering the true seroprevalence with a certainty of 95% are given

Fig. 3

Map of Bavaria indicating the geographical distribution of BoHV-2 seropositive results. The seven administrative regions are shown. Swabia, Upper, and Lower Bavaria represent South Bavaria whereas Upper, Middle, and Lower Franconia as well as Upper Palatinate are addressed as North Bavaria in this study. Black triangles (▲) indicate postal code areas where at least one BoHV-2 antibody positive animal was detected. The data is not quantitative as 561 positive samples were categorized into 100 postal code areas. The map was generated using the software GfK Regiograph Analysis and Adobe Illustrator

Fig. 4

BoHV-2 intra-herd seroprevalences calculated for farms keeping at least one BoHV-2 seropositive animal. BoHV-2 antibodies were determined by ELISA and in case of doubtful or increased reactivities, were confirmed by SNT. One diamond is attributed to one farm. White diamonds (♢) represent farms with one to ten animals tested (n = 20), grey ones () farms with eleven to 50 animals tested (n = 54), and black ones (♦) farms with more than 50 animals tested (n = 4). Solid horizontal lines indicate the median seroprevalence for the respective region. Dotted lines represent the median of intra-herd BoHV-2 seroprevalences calculated for all of Bavaria

Fig. 5

BoHV-2 seroprevalences in relation to BoHV-1 ELISA results. Black diamonds (♦) indicate results when interpreted for holdings, open diamonds (♢) when individual animals are considered. Farms where at least one BoHV-2 seropositive animal is kept are classified “BoHV-2 seropositive”. With respect to results in the BoHV-1 ELISAs, holdings are categorized as follows: “BoHV-1 ELISA negative” (Trachitest negative), “Trachitest-positive” (Trachitest positive but gB-ELISA negative), “non-negative” (Trachitest and gB-ELISA positive or suspect, but gE-ELISA negative). The mean data for 406 holdings and 6801 cattle is given as “total”