Vaccination against louping Ill virus protects goats from experimental challenge with Spanish goat encephalitis virus

Spanish goat encephalitis virus (SGEV) is a recently described member of the genus Flavivirus belonging to the tick-borne encephalitis group of viruses, and is closely related to louping ill virus (LIV). Naturally acquired disease in goats results in severe, acute encephalitis and 100% mortality. Eighteen goats were challenged subcutaneously with SGEV; nine were vaccinated previously against LIV and nine were not. None of the vaccinated goats showed any clinical signs of disease or histological lesions, but all of the non-vaccinated goats developed pyrexia and 5/9 developed neurological clinical signs, primarily tremors in the neck and ataxia. All non-vaccinated animals developed histological lesions restricted to the central nervous system and consistent with a lymphocytic meningomyeloencephalitis. Vaccinated goats had significantly (P <0.003) greater concentrations of serum IgG and lower levels of IgM (P <0.0001) compared with unvaccinated animals. SGEV RNA levels were below detectable limits in the vaccinated goats throughout the experiment, but increased rapidly and were significantly (P <0.0001) greater 2–10 days post challenge in the non-vaccinated group. In conclusion, vaccination of goats against LIV confers highly effective protection against SGEV; this is probably mediated by IgG and prevents an increase in viral RNA load in serum such that vaccinated animals would not be an effective reservoir of the virus.This work was supported by a grant from Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), reference number E-RTA2013-00013-C04-04 (FEDER co-funded) and the Rural and Environment Science and Analytical Services (RESAS) division of the Scottish Government.Peer Reviewe