Schistosomes, or blood flukes, normally deposit their eggs in the small vessels of the gut and urinary bladder, from which they pass into the external environment via the feces or urine. Some eggs, however, may get into the general circulation and reach the CNS, where they become encapsulated. This condition has been noted in people and domestic animals.
Troglotrema acutum inhabits the frontal and ethmoidal sinuses of foxes and mustelids in Europe. Flukes live in pairs in cysts in these sinuses. These parasites cause decalcification and atrophy of the bony walls of the sinuses and eventually result in perforation into the cranial cavity. Microorganisms enter the cranial vault, leading to fatal, purulent meningitis. No treatment is available.