Experimental model of progressive disseminated trichosporonosis in mice with latent trichosporonemia.

Trichosporon asahii and Trichosporon mucoides are the most common strains of fungi that cause disseminated trichosporonosis, a severe opportunistic infection in immunocompromised hosts. We have previously established a nested PCR assay using serum samples for detection of both strains. Here we describe a new experimental animal model for investigating the underlying mechanisms of disseminated trichosporonosis. T. asahii (OMU239, a clinical isolate from a patient with acute myelogenous leukemia) and 8-week-old ICR male mice were used in all experiments. A suspension of T. asahii (3 x 10(6) CFU/animal) was injected into the caudal vein of each mouse after immunosuppression with cyclophosphamide (200 mg/kg of body weight/day for 2 days) and prednisolone (30 mg/kg/day for 1 day). Mice were then divided into four subgroups (R0, R1, R2, and R3) based on the time of reimmunosuppression. The latter was performed using the same drugs 1 week (group R1), 2 weeks (group R2), and 3 weeks (group R3) after fungal infection. Reimmunosuppression was not performed in group R0. The 5-week-survival rates of mice after T. asahii infection were 0% for group R1, 50% for group R2, 80% for group R3, and 80% for group R0. There was a significant difference in the survival rates between group R1 and either group R0 or R3 (P < 0.05). Fungal clearance in peripheral blood and various organs of group R1 and R2 was delayed relative to that of group R0 but was similar to the control in group R3 in spite of reimmunosuppression. Our results suggest that the critical period for the development of disseminated trichosporonosis in our model is shorter than 3 weeks after T. asahii infection. We concluded that mice during this critical period were in a state of latent trichosporonemia. Comparison of the survival rates suggests that the nested PCR assay was more useful than blood culture and glucuronoxylomannan antigen assay in the detection of this latent trichosporonemia.