Louping ill is a tick-borne, zoonotic, viral disease that is most important in sheep and red grouse. Severe clinical signs can be seen in naive sheep flocks moved into endemic areas. Many animals may develop neurological disease, and up to 60% of the flock can die. In endemic areas, most losses occur among unvaccinated younger sheep that are no longer protected by maternal antibodies. Louping ill is a serious problem in red grouse populations; few chicks may survive in some endemic areas. The mortality rate can be as high as 80% in experimentally infected birds. Cases of louping ill are also reported occasionally in other species including goats, llamas, alpacas, swine, horses and deer. Humans can develop flu-like symptoms or neurological signs after exposure, but the illness is rarely fatal.