Variants of Sporothrix schenckii with attenuated virulence for mice.

Strains of Sporothrix schenckii preserved under mineral oil were examined for virulence in BALB/c mice. The mice were inoculated with S. schenckii conidia and development of cutaneous lesions, signs of inactivity, weight loss, survival rates, number of viable yeast cells in lung and spleen, splenomegaly and organ lesions were evaluated. After intravenous injection of 7.5 x 10(6) conidia, two of five S. schenckii strains were unable to induce systemic disease and to kill the mice, only producing cord-like lesions on the tail that regressed with mouse maturation. Very small numbers of viable cells isolated from the spleen confirmed the lower invasive ability of these strains when compared with other strains studied here. These results suggest a relationship between the attenuation of virulence and the storage method under mineral oil after long periods of time.