Analysis of BVDV isolates and factors contributing to virus transmission in the final stage of a BVDV eradication program in lower Austria.

The BVDV eradication program in Lower Austria according to the Swedish model started in 1997 as a voluntary strategy and became obligatory for all herd owners in 2004. In this paper we analyse BVDV isolates found in PI animals of the last infected cattle farms at the genetic level and describe possible risk factors for virus transmission in the final stage of the BVDV eradication program in Lower Austria, where only five infected herds were identified in 2010. Viral isolates from 23 farms on which PI animals had been detected in 2009 (n = 10), 2010 (n = 5), 2008 (n = 5) and in 2006 (n = 3) were analysed at a genetic level at the 5'-UTR. All isolates analysed by phylogenetic analysis fall into five BVDV-1 subgenotypes, i.e., b, e, f, g, and h. No new subgenotypes were identified when compared to isolates analysed at the beginning of the BVDV eradication program. The phylogenetic analysis also revealed three groups of herds with genetically identical isolates; the first group comprised two herds, the second seven herds and the third four herds. Analysis of several factors such as distance between herds, purchase of cattle, work of farmers, veterinarians, assistants of milk recording associations and animal carriers indicated the latter as the most critical factor for transmitting the same viruses. Seven herds of two groups of identical BVDV isolates were served by the same cattle carrier, six herds shared the veterinarian and five herds had the same assistant of the milk recording association who could be the risk factor for the introduction of BVDV into the herd. The analysis helped to stop virus transmission. Therefore, from early 2012 up to now, no new infection has occurred in Lower Austria. The results indicated that biosecurity is a very important factor to prevent the spreading of viruses in the final stage of the BVDV eradication program.