Animal experiments were carried out at the ''Istituto G. Caporale'' (Teramo, Italy) following local and national approved protocols regulating animal experimental use. Study 1. Litters of 3-day old NIH-Swiss mice (n = 8-12), were inoculated intra-cerebrally with 10 3 TCID 50 of either BTV-1, (2/2) 129/Sv], were inoculated intraperitoneally with 100 PFU of either BTV-1, BTV-8, BTV-1DNS4 or BTV-8DNS4. For each virus, two groups (n = 5) of mice were inoculated using two different virus preparations. Survival plots were constructed using data collected from two experimental groups (n = 10) with the exception of a mock infected group that was constituted by a single group of 6 mice. Formalin-fixed and paraffin-embedded brains tissue sections from inoculated (and mock inoculated) mice were used in immunohistochemistry. Sections (4-6 mm) were examined for the presence of BTV NS4 using a polyclonal NS4 antiserum and the EnVision (DAKO) detection system.