Bluetongue virus (BTV), genus Orbivirus - family Reoviridae, causes the bluetongue (BT) disease, one of the OIE - listed major diseases of ruminants. BT has a global distribution normally coinciding with that of the corresponding competent Culicoides midges, vectors of the virus.

BTV exists into multiple serotypes and two major geographic groups of BTVs have been identified and designated as eastern (e) or western (w) topotypes. They include viruses from Australia and the Middle/Far East, or Africa and the Americas, respectively (Maan et al., 2008).

Since 1998, southern Europe has experienced multiple incursions of different serotypes and topotypes of BTV. Predominantly, BTV incursions have entered southern Europe via two distinct routes. Strains of BTV-1e, BTV-4w, BTV-9e and BTV-16e have all entered the eastern Mediterranean region. BTV-1w, BTV-2w and BTV-4w have entered Europe most likely as a result of wind-blown dissemination of infected midges from Northern Africa. Specifically, the virus had been likely introduced to Europe from Northern Africa via two major gateways: (i) from Morocco to Spain through the Straits of Gibraltar, (ii) from Tunisia to Italy through Sicily or Sardinia (Wilson and Mellor, 2008).

The introduction of BTV from Tunisia to Italy was reported the first time in 2000, when the first BT incursion in Sardinia, was immediately linked with BTV-2w circulation in the northeastern part of Tunisia in 1999 (Calistri et al., 2004). In 2012, a novel reassortant strain of BTV-4w was identified in Sardinia together with BTV-1w (Lorusso et al., 2013). This reassortant BTV-4w was shown to be closely related to BTV-4w isolated in Tunisia in 2007 and 2009. Likewise, BTV-1w Sardinian strain originated from a strain closely related to a BTV-1w isolated in Tunisia in 2011 (Lorusso et al., 2014).

On November 1^st 2016, an eight years old red-head Barbarine ewe, located in the Gouvernorat de Nabeul, delegation Beni Khalled, Imada Hannous (36°37059.04″N-10°42039.52″E), in the north-eastern part of Tunisia, in the central area of Cap Bon, showed clinical signs consistent with BTV infection. The animal belonged to a flock composed by 46 sheep, seven goats and eight cattle. The newly identified BTV was typed as western BTV-3 with a clear African origin (NCBI, KY432369-KY432378; Lorusso et al., 2017). Further surveillance activities conducted in collaboration between the Tunisian and Italian authorities, revealed the presence of BTV-3 RNA and antibodies in sheep of some Tunisian regions. Moreover, an additional western BTV-3 strain, named BTV 3 TUN2016/Zarzis (NCBI, MF124292 MF124301) was identified nearby the border with Libya. The two viruses are different by comparative analysis of the genome constellations (Lorusso et al., 2018).

In November 2017, a 3 years old female crossbred sheep belonging to a flock of nearly 400 animals located in the surroundings of Trapani (Western part of the island of Sicily, facing the peninsula of Cap Bon) showed clinical signs consistent with BT infection. Symptoms included fever, oedema of the head, nasal discharge, and depression. The veterinary services of local health unit (ASL) visited the entire flock and collected EDTA-blood and serum samples from the symptomatic sheep. The Seg 2 of BTV-3 identified in Sicily was identical to that of BTV-3 TUN2016, first detected in Cap Bon in November 2016 (Lorusso et al., 2017) (figure 1). On December the 4^th, the Italian Ministry of Health notified the outbreak to the OIE and a restriction zone of 150 km around the outbreak was established in accordance with the national and EU legislation. The Italian Ministry of Health requested ad hoc surveillance activities in order to understand the spread of the infection. Sixty cattle and sheep holdings were recruited in a 20 km radius from the infected farm for serological (ELISA and serum-neutralization, SN) and molecular screening. This analysis revealed an additional sheep, in the same first infected farm, tested positive for BTV-3 antibodies by ELISA/SN but negative for BTV-3 RNA.

BTV-3 circulation in Sicily is of great concern for the Italian and European livestock industry due to the unavailability of inactivated vaccines for this serotype. Only a modified live-attenuated vaccine (MLV) for BTV-3 exists and it is produced (in combination with other serotypes) by the Onderstepoort Biological Product (Pretoria-Republic of South Africa), but the use of MLVs in the EU has been discontinued. As past BT epidemics have generally occurred through a limited diffusion in the first vector season, while a widely spread and extensive damage were reported in the following years (Meroc et al., 2009), novel BTV-3 outbreaks may occur in the forthcoming warm season, with severe consequences for the livestock industry.

BTV 3 in Sicily emphasizes the importance for the EU of having in place robust collaborations and surveillance activities with Northern African authorities on public and animal health for early warning systems and the assessment of proper preventive measures.

On December the 4^th, the Italian Ministry of Health notified the outbreak to the OIE and a restriction zone of 150 km around the outbreak was established in accordance with the national and EU legislation. The Italian Ministry of Health requested ad hoc surveillance activities in order to understand the spread of the infection. Sixty cattle and sheep holdings were recruited in a 20 km radius from the infected farm for serological (ELISA and serum-neutralization, SN) and molecular screening. This analysis revealed an additional sheep, in the same first infected farm, tested positive for BTV-3 antibodies by ELISA/SN but negative for BTV-3 RNA.

BTV-3 circulation in Sicily is of great concern for the Italian and European livestock industry due to the unavailability of inactivated vaccines for this serotype. Only a modified live-attenuated vaccine (MLV) for BTV-3 exists and it is produced (in combination with other serotypes) by the Onderstepoort Biological Product (Pretoria-Republic of South Africa), but the use of MLVs in the EU has been discontinued. As past BT epidemics have generally occurred through a limited diffusion in the first vector season, while a widely spread and extensive damage were reported in the following years (Meroc et al., 2009), novel BTV-3 outbreaks may occur in the forthcoming warm season, with severe consequences for the livestock industry.

BTV 3 in Sicily emphasizes the importance for the EU of having in place robust collaborations and surveillance activities with Northern African authorities on public and animal health for early warning systems and the assessment of proper preventive measures.

1. Calistri, P., Giovannini, A., Conte, A., Nannini, D., Santucci, U., Patta, C., Rolesu, S., Caporale, V., 2004. Bluetongue in Italy: part I. Vet. Ital. 40 (3), 243–251

2. Lorusso, A., Sghaier, S., Carvelli, A., Di Gennaro, A., Leone, A., Marini, V., Pelini, S., Marcacci, M., Rocchigiani, A.M., Puggioni, G., Savini, G., 2013. Bluetongue virus serotypes 1 and 4 in Sardinia during autumn 2012: new incursions or re-infection with old strains? Infect. Genet. Evol. 19, 81–87.

3. Lorusso, A., Guercio, A., Purpari, G., Cammà, C., Calistri, P., D'Alterio, N., Hammami, S., Sghaier, S., Savini, G. Bluetongue virus serotype 3 in Western Sicily, November 2017. Vet Ital. 2017 Dec 29;53(4):273-275. doi: 10.12834/VetIt.251.520.178

4. Lorusso, A., Sghaier, S., Di Domenico, M., Barbria ME., Zaccaria, G., Megdich A., Portanti, O., Seliman, IB., Spedicato, M., Pizzurro, F., Carmine, I., Teodori, L., Mahjoub, M., Mangone, I., Leone, A., Hammami, S., Marcacci, M., Savini, G. 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. Infect Genet Evol. 2018 Apr;59:63-71. doi: 10.1016/j.meegid.2018.01.025. Epub 2018 Jan 31

5. Lorusso, A., Guercio, A., Purpari, G., Cammà, C., Calistri P., D'Alterio N., Hammami, S., Sghaier S., Savini, G. Bluetongue virus serotype 3 in Western Sicily, November 2017. Vet Ital. 2017 Dec 29;53(4):273-275. doi: 10.12834/VetIt.251.520.178. PMID: 29307120

6. Maan, S., Maan, N.S., Ross-smith, N., Batten, C.A., Shaw, A.E., Anthony, S.J., Mertens, P.P.C., 2008. Sequence analysis of bluetongue virus serotype 8 from the Netherlands 2006 and comparison to other European strains. Virology 377 (2), 308–318. http:// dx.doi.org/10.1016/j.virol.2008.04.028

7. Meroc, E., Herr, C., Verheyden, B., Hooyberghs, J., Houdart, P., Raemaekers, M., Minties, K. (2009). Bluetongue in Belgium: Episode II. Transboundary and Emerging Diseases, 56, 39–48

8. Wilson, A., Mellor, P., 2008. Bluetongue in Europe: vectors, epidemiology and climate change. Parasitol. Res. 103, 69–77.