[4] Human cases of philophthalmosis are rare, but have been previously reported in Europe, Asia, and America (i.e., Yugoslavia, Sri Lanka, Japan, Israel, Mexico, and the United States).

Upon contact with a snail, the miracidium perforates the host epidermis with the aid of secretions and the anterior cilia.

Cercariae are released from the snail and encyst on aquatic vegetation or other solid objects in the water.

Excystment of the metacercariae occurs immediately upon reaching the mouth or crop of the bird and not in the stomach or intestine as in many other digenetic trematodes.

Within three to five hours after ingestion, immature worms may be found in the esophagus, nasal passages, the orbit and the lobes of the lacrimal gland.

Humans rarely serve as incidental hosts, but may do so when they ingest metacercariae on aquatic vegetation.

Infection may cause congestion and erosion of the conjunctivae,[7] conjunctivitis with persistent lacrimation,[8] and semilunar fold swelling[9] in chickens, ostriches, and humans, respectively.

[8] An outbreak of Philophthalmus gralli has been reported in 2005 in ostriches in Zimbabwe; 17 were found to be infected by this parasite.

They had swollen eyes, severe conjunctivitis, and constant lacrimation, accompanied by a purulent exudates.