Bluetongue virus serotypes 1 and 4 in Sardinia during autumn 2012: New incursions or re-infection with old strains?

Since 2000 several bluetongue virus (BTV) incursions have occurred in Sardinia (Italy) involving serotypes 1, 2, 4, 8 and 16. In October 2012, new BT outbreaks caused by BTV-1 and BTV-4 were reported. Nearly 500 flocks were infected and 9238 sheep died because of the infection. When sequenced, Seg-10 of both strains shared 99% similarity at nucleotide level with BTV strains that have circulated in the Mediterranean basin in the last few years. Similarly, Seg-5 sequences of BTV-1 and BTV-4 newly isolated Sardinian strains are identical and cluster together with recent BTV-1 circulating in the Mediterranean Basin and the BTV-4 strains isolated in Tunisia in 2007 and 2009. These BTV-4 strains differ from the ones that circulated in Europe from 2003 to 2005 and appear to be reassortant strains.