Dermal sensitivity to Coccidioides immitis. A comparison of responses elicited in man by spherulin and coccidioidin.

Spherulin, a new reagent prepared from the spherule form of Coccidioides immitis, was compared with classic mycelium-derived coccidioidin in delayed dermal sensitivity reactions of man. Among 243 residents of a region of Mexico endemic for coccidioidomycosis, the reactor ratio was 64 per cent with spherulin (2.8 op.g) compared to 41 per cent with coccidioidin (1:100; 26.0 p.g). All reactors to coc.cidioidin were reactive to spherulin; however, the coccidioidin reaction was nonreactive in 35 per cent of the reactors to spherulin. Also, spherulin elicited a strong reaction in a subject who had had disseminated coccidioidomycosis and in whom the coccidioidin test was nonreactive. Neither of the reagents elicited reactions in any of 86 subjects who had never entered an area of coccidioidal endemicity; nor was there evidence that either reagent produced false positive reactions in subjects reactive to histoplasmin or in those with a variety of other mycotic and nonmycotic diseases.