Murine encephalitozoonosis: the effect of age and mode of transmission on occurrence of infection.

Experiments were conducted to determine whether neonatal mice are more susceptible to E. cuniculi than adult mice, and whether vertical and/or horizontal transmission occur in murine encephalitozoonosis. E. cuniculi infection in neonates did not cause mortality or clinical signs, but did result in chronic infection. Despite initial age-related immunodeficiency, mice infected as neonates eventually developed humoral and cell-mediated immune responses against the parasite comparable to those seen in adult mice. The results suggested that neonatal mice are not more susceptible to E. cuniculi than adult mice. Pups from either infected or normal parents did not differ in humoral and cell-mediated immune responses after challenge, suggesting that pups from infected parents were not infected with E. cuniculi during gestation. In contrast, mice became infected by caging with infected mice demonstrating that horizontal infection does occur.