Analysis of bluetongue serotype 3 spread in Tunisia and discovery of a novel strain related to the bluetongue virus isolated from a commercial sheep pox vaccine.

Bluetongue (BT), is one of the OIE-listed major diseases of ruminants. Following the official report of BT virus serotype 3 (BTV-3) in a sheep in Cap Bon (Tunisia), blood and serum samples of ruminants were collected from some areas of Tunisia to further investigate the presence of this virus in the country. A quantitative real time RT-PCR has been first developed for the detection and quantitation of BTV-3 RNA from field specimens. Out of 62 collected blood samples, 23 were shown to be positive for BTV-3 RNA. Isolation on cell cultures was also possible from six samples. Genome sequencing revealed the circulation of two unrelated western strains of BTV-3, one circulating in Cap Bon and neighboring areas, and the other circulating nearby the border with Libya. The presence of a putative novel BTV serotype (BTV-Y TUN2017) in sheep introduced from Libya to Tunisia, genomically related to the BTV strain contaminating a commercially-available sheep pox vaccine and to BTV-26, has been also demonstrated. This finding highlights the pressing need for a prompt production and release of a novel inactivated BTV-3 vaccine to be used in case of emergence or proactively in the areas of Southern Europe at major risk of BTV introduction. The assessment of a novel vaccine will certainly exalt the role and importance of surveillance activities and collaboration with Northern African countries.