Abstract
Severe Combined Immunodeficient (SCID) mice lack both T and B lymphocytes which makes them highly susceptible to infectious agents. In the present communication, we describe an outbreak of Theiler's encephalomyelitis in a colony of SCID mice which was characterized by an unusually high prevalence of clinically overt cases. Diagnosis was based on the clinical signs, histological lesions and presence of antibodies in contemporaneous immunocompetent mice. This is the first report of this disease in SCID mice and, to our knowledge, also the first reported outbreak of Theiler's encephalomyelitis in the UK.