Rhinosporidiosis. Light micrograph of a section through a mucous membrane containing sporangia (circular) of Rhinosporidium seeberi, causative agent of rhinosporidiosis. The sporangia contain numerous reproductive structures called sporangiospores. Rhinosporidiosis causes polyps to form in the nasal cavity, which may cause bleeding or obstruction. Treatment is by surgical removal of the polyps. R. seeberi was once thought to be a fungus, however, research suggests it is a rare protist parasite of fish, which is transmitted to humans by swimming in lakes or rivers. Rhinosporidiosis is most common in India and Sri Lanka. Magnification: x360 when printed 10cm wide.