Tritrichomonas foetus: comparison of isolate virulence in an estrogenized mouse model.

Previous studies indicated that Tritrichomonas foetus isolate ATCC 30003 was capable of maintaining only short-term genital infection in estrogenized BALB/c mice. In the present study, the ability of eight T. foetus isolates to establish and maintain infections in intravaginally inoculated estrogenized BALB/c mice was examined. All isolates were found to be equally capable of establishing genital infections but varied greatly in ability to maintain infections. One isolate maintained infection for less than 7 weeks, four isolates maintained intermediate infections lasting less than 13 weeks, and three isolates maintained chronic infections of greater than 26 weeks. Varying the number of trophozoites inoculated intravaginally decreased the ability of isolates to establish infection but did not affect maintenance of infection. Prolonged passage of T. foetus isolates either in vivo in an estrogenized nu/nu BALB/c mouse or by in vitro culture failed to affect their ability to maintain infection, suggesting that virulence was parasite-dependent and not related to environment-induced changes. Co-infection of estrogenized mice with isolates ATCC 30003 and MU Y32 failed to increase the length of ATCC 30003 infections or decrease the length of isolate MU Y32 infections. Taken together these results indicate that T. foetus isolates vary greatly in virulence in estrogenized BALB/c mice and provide evidence suggesting that maintenance of infection is a parasite-controlled factor.