Experimental infections in rabbits and humans with Pityrosporum orbiculare and P. ovale.

The purpose of this investigation was to produce experimental tinea versicolor in rabbits and humans with Pityrosporum orbiculare and P. ovale. P. orbiculare and P. ovale were inoculated, with and without occlusion, on the inside of the ear in 10 male rabbits and on the upper arm in 10 patients with a history of tinea versicolor, and in 3 healthy volunteers. After 1 week tinea versicolor-like lesions were produced with both P. orbiculare and P. ovale in 8 of 10 rabbits. Likewise experimental infections, similar to those found clinically in tinea versicolor, were seen, after 1 week, in 5 patients with a history of tinea versicolor and in the 3 healthy volunteers. Two of 5 patients inoculated for only 4 days showed identical but less pronounced lesions. Experimental infections could only be produced with occlusion. Microscopically short hyphae and transformation between round and oval forms were seen in both P. orbiculare and P. ovale. This investigation adds to the identity of P. orbiculare and P. ovale and also to the identity of these 2 fungi and the fungus seen in tinea versicolor. Spontaneous healing and the fact that experimental infections were produced only under occlusion illustrates the importance of predisposing factors in tinea versicolor.