Louping-ill (/ˈlaʊpɪŋɪl/) is an acute viral disease primarily of sheep that is characterized by a biphasic fever, depression, ataxia, muscular incoordination, tremors, posterior paralysis, coma, and death.

Louping-ill is a tick-transmitted disease whose occurrence is closely related to the distribution of the primary vector, the sheep tick Ixodes ricinus.

[citation needed] According to a ProMED article,[4] disease in sheep has been controlled in the UK by a vaccine (ATCvet code: QI04AA01), originally developed by Scotland's Moredun Research Institute by Prof John Russell Greig.

[6] The clinical symptoms in humans include influenza-like illness (fever, headache, and muscle stiffness), biphasic encephalitis (initial flu-like symptoms followed by neurological signs such as severe headache, vomiting, and neck stiffness), poliomyelitis-like illness (paralysis ranging from mild to severe), and in rare cases hemorrhagic fever.

These include laboratory personnel working with the virus, farmers, shepherds, or butchers handling infected sheep or animal tissues, as well as individuals exposed to tick bites in endemic areas.