Nine cases of unusual infections in humans are presented. In each case, we present the clinical history, histopathologic changes (if indicated), morphologic features of the causative organism, diagnosis, discussion, differential diagnosis, therapy, and current literature. All of the cases are illustrated with pertinent photographs. The nine cases are as follows: (i) acanthocephaliasis, the first acquired human infection by Moniliformis moniliformis in the United States; (ii) dipylidiasis, an uncommon infection caused by the dog tapeworm, Dipylidium caninum; (iii) granulomatous amebic encephalitis, caused by the recently identified leptomyxid group of amebae; (iv) schistosomiasis, a dual infection of the urinary bladder with the rare presentation of both adult worms and eggs of Schistosoma haematobium and Schistosoma mansoni in tissue sections; (v) syphilitic gastritis, an uncommon presentation of Treponema pallidum infection, in a patient with an additional incidental infection by Helicobacter pylori; (vi) microsporidiosis, the only infection caused by a Pleistophora sp. in humans; (vii) sporotrichosis, a rare disseminated infection caused by Sporothrix schenckii with numerous yeast cells in the scrotum; (viii) angiostrongyliasis, the first and only infection caused by Angiostrongylus costaricensis acquired in either Puerto Rico or the United States; and (ix) botryomycosis of the skin and subcutaneous tissue, caused by gram-positive cocci with an unusually large number of granules.

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