Trypanosoma cruzi: constancy of clone pathogenicity for inbred mice during long-term in vitro maintenance

The reproducibility of infection of C3H/He mice with T. cruzi clones Sylvio-X10/4 and Sylvio-X10/7 maintained in the laboratory for 946 and 496 days respectively was assayed. Clone X10/7 from 15 different in vitro passages consistently induced an acute lethal infection (94.3% mortality) and constant survival time (Mean = 24.6 d.p.i.). Female mice survived significantly longer than males and mice older than 30 days at the time of infection survived significantly longer than younger mice. The mortality of mice infected with clone X10/4 from 23 different in vitro passages was lower (5.1%) and their survival longer (Mean = 42.7 d.p.i.) than mice infected with clone X10/7. High anti-T. cruzi IgG titres were detected in the plasma of all mice killed after 30 d.p.i. Histologically, the heart, skeletal muscles and/or large intestine contained intracellular parasites in 59% of the mice; parasites were found in mice of all groups tested. The hearts of all mice were comparably inflammed regardless of parasite passage number or duration of infection. These data demonstrate that the presentation and course of infection of inbred mice with two T. cruzi clones is not changed by either the duration or protocol used for in vitro maintenance; the reported loss or change in virulence of T. cruzi strains during long-term in vitro maintenance did not occur. Consequently, T. cruzi clones and inbred mice provide a dependable and reproducible means to study host-parasite interactions.