Mouse Poliomyelitis or Theiler's Mouse Encephalomyelitis1

Abstract

The virus is found in the small intestine of most laboratory white mice, especially in mice 1-12 months old; it also grows in the chick embryo. The virus is 9-13 m[mu] in size, and is susceptible to 55[degree]C for 30 minutes. The incubation period of the disease is 7-30 days after which flaccid paralysis in the hind legs develops due to necrosis of the anterior horn cells. All strains infect when injected intracerebrally but only the most virulent strains infect by the intranasal or intraperitoneal route. Diagnosis is made by observing symptoms, and obtaining positive intracerebral transfer and cross-immunity tests. Old mice acquire a natural immunity.