Neurovirulence of the UC-2 and UC-8 strains of bluetongue virus serotype 11 in newborn mice.

In vivo and in vitro experiments were done to investigate whether the difference in neurovirulence between the two strains of bluetongue virus 11, UC-2 and UC-8, is based on a different capability to gain access to the brain from the subcutaneous inoculation site or on a different tropism for neural cells. In newborn Balb/c mice subcutaneous inoculation of UC-8 at doses between 10(-0.2) plaque forming units (PFU) and 10(4.8) PFU caused a severe necrotizing encephalitis whereas UC-2 at doses of up to 10(4.4) PFU did not affect newborn Balb/c mice. However, intracranial inoculation of 10(2.4) PFU of either virus strain produced severe necrotizing encephalitis. In vitro both virus strains infected dissociated brain cell cultures similarly. Double labelling immunofluorescent staining with markers specific for neural cells did not reveal differences in the target cells for the two viruses. The difference in neurovirulence between UC-2 and UC-8, therefore, appears to be determined by the ability of UC-8 to infect the brain from a subcutaneous inoculation site.