Clinical infection of Cantabrian chamois (Rupicapra pyrenaica parva) by louping ill virus: new concern for mountain ungulate conservation?

Louping ill virus (LIV) was recently involved in an outbreak of encephalitis in domestic goats from Asturias region, northwestern Spain. Since livestock and wildlife in Asturias are frequently in close contact, we designed a retrospective survey for LIV antibody prevalence in wild ungulates by testing sera from 51 red deer (Cervus elaphus), 19 Cantabrian chamois (Rupicapra pyrenaica parva) and 8 roe deer (Capreolus capreolus) by the haemagglutination inhibition (HI) test. Only two Cantabrian chamois out of the 78 tested (2.6 ± 3.5 %) gave positive results. Seroprevalence in chamois was 10.5 ± 13.8 %. One of these chamois was found dead after falling down a cliff and the other one was found alive but with neurological signs. Histological examination of brain samples revealed that both animals showed severe inflammatory lesions compatible with a viral encephalitis caused by LIV, but LIV antigen was not detectable by specific immunohistochemistry. Real time RT-PCR was performed on formalin-fixed paraffin embedded sections of brain but was unable to confirm the presence of LIV RNA due to poor sample quality. By testing one of two HI positive sera from chamois by virus neutralization test and plaque reduction neutralization test against West Nile virus, Bagaza virus, Usutu virus, LIV and tick-borne encephalitis virus, we confirmed the presence of high antibody titres (1:10240) against LIV in the absence of antibodies to another Flavivirus. This work describes the first association between LIV and clinical encephalitis in chamois, which suggests that special attention should be paid to the impact on chamois conservation and management in Asturias, and perhaps in other European regions.