coccidioidin

noun

coc·​cid·​i·​oi·​din -ˈȯid-ᵊn, -ˈȯi-ˌdin 

: an antigen derived from a fungus of the genus Coccidioides (C. immitis) while in its mycelial phase and used to detect skin sensitivity to and, by inference, infection with this organism compare spherulin