Histoplasma capsulatum is a dimorphic fungus that is traditionally classified in three varieties: Hc var. capsulatum, Hc var. duboisii, and Hc var. farciminosum (HCF). Cytology, hematology, pathology, polymerase chain reaction (PCR), sequencing, and phylogenetic analyses were applied on samples collected from the blood and the eye of a horse with pustular lesions and ocular discharge. Physical examination and cytopathological tests showed H. capsulatum infection. Additionally, the results of two PCR tests confirmed H. capsulatum infection. The phylogenetic tree of the internal transcribed spacer sequence of Iranian H. capsulatum showed homology with the HCF variety. For the first time, H. capsulatum infection in the eye of a horse from Iran was detected and phylogenetically analyzed. This study revealed that H. capsulatum could establish infection in Iranian animals in addition to people, and indicated the role of soil enriched with bird dropping in the preparation of a favorable environment for H. capsulatum propagation. Further investigations are required to clarify the natural history and risk factors associated with histoplasmosis in Iran.

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