In order to study the pathological effects of the infection in the organs where BTV replicates, histological analysis were performed on material of several organs extracted from BTV infected and uninfected IFNAR(−/−) mice at 48 h.p.i. Gross pathological alterations were characterized by widespread oedema, haemorrhages especially in spleen and lungs, and enlarged spleen and lymph nodes. This evidence concerns the gene IFNAR1 and infection.