GROWTH OF A NEUROINVASIVE STRAIN OF BLUETONGUE VIRUS IN SUCKLING MICE

Some strains of bluetongue virus cause congenital brain damage in bovi ne and ovine fetuses, as well as in neonatal mice. Two strains of blue tongue virus serotype 11 (UC-2 and UC-8) which differ in neuroinvasive ness were used to determine the biological basis for this difference. UC-2 and UC-8 were inoculated subcutaneously into newborn mice and vir us was titrated from blood, plasma and brain tissues over 14 days. For the invasive UC-8 strain, 50-175 plaque forming units of virus per ml was found associated with the blood cells and no virus was detected i n the plasma. The virus was detected in the brain at day one post inoc ulation, and again at day 7, increasing to day 11. The results indicat e that UC-8 was able to reach the brain soon after inoculation and to replicate and/or remain in the blood circulation better than UC-2. Imm unohistochemical examination of frozen brain sections revealed a sudde n, multifocal appearance of UC-8 at day 9, with more viral antigen see n at days 11 and 13, which was barely detected by day 15. Viral antige n was not associated with blood vessels in the brain, indicating that the viral invasion was not from infected vascular endothelium. No viru s was detected in the mice infected with strain UC-2.