The effect of age on the infection and immunoresponsiveness of mice to Babesia microti.

5he effect of age on the immunological responses to Babesia microti infection in the mouse was investigated. Aged mice experienced reduced and delayed peak parasitemias compared to younger animals; however, the old mice failed to clear the parasites from the blood and experienced fluctuating parasitemias until death. Babesiosis produced suppression of responses to nonspecific B and T cell mitogens concomitant with rising autoantibody plaque forming cells reactive with untreated and bromelain modified mouse erythrocytes. Similar observations of increased susceptibility to babesiosis with age and immunosuppression have been made in human babesiosis. Thus, the murine model for this hemoprotozoan infection is faithful to the human immunological responses.