Histopathologic changes seen in onychomycosis due to a Fusarium sp. of fungus. Fusarium sp. are pathogenic towards both humans and many plants. Some species may cause a range of opportunistic infections in humans. In humans with normal immune systems, fusarial infections may occur in the nails (onychomycosis) and in the cornea (keratomycosis or mycotic keratitis). In humans whose immune systems are weakened in a particular way, aggressive fusarial infections can penetrate the entire body and bloodstream (disseminated infections).