Nairoviruses are small, enveloped RNA viruses in which the genome consists of three segments of single stranded, negative sense RNA, designated Large (L), Medium (M) and Small (S) [10] . The S, M and L segments encode, respectively, the nucleocapsid protein (N), at least two envelope glyoproteins (Gn and Gc) and the viral RNA-dependent RNA-polymerase (L). The L segment is unusual among bunyaviruses, being extremely long (.12 kb), encoding a single protein of .450 kDa. The carboxyterminal half of this protein contains most of the polymerase motifs, while the amino-terminal part is largely of unknown function. The genus contains more than 30 different virus isolates, loosely grouped based on serum cross-reactivity and hemagglutination inhibition [11] , since sequence data on all but a few of these viruses has been limited or missing until recently. The most important serogroups are the NSDV serogroup, which also includes Dugbe virus (DUGV) and Kupe virus, and the Crimean Congo hemorrhagic fever virus (CCHFV) serogroup, which contains CCHFV and Hazara virus, both human pathogens. CCHFV causes a severe disease in human beings, with a reported mortality rate of 3-30% [12] . The disease is very similar to that caused in sheep by NSDV infection and is characterised by haemorrhage, myalgia, and fever.