Louping ill virus (LIV) is an arboviral flavivirus (enveloped, positive-sense single-stranded RNA) that is of most significance to sheep and red grouse (Lagopus lagopus scoticus). However, this virus has been shown to infect many species, and while wildlife are not believed to develop severe clinical signs secondary to infection, they likely play a role in disease persistence by acting as maintenance hosts. LIV is composed of multiple subtypes that tend to cluster geographically (e.g., Spanish, Turkish, British, Irish). LIV is closely related to tickborne encephalitis virus (TBEV), from which it is often clinically indistinguishable due to similarities in disease presentation. LIV is a zoonotic agent, although disease is less severe in humans.