Philophthalmus gralli

Philophthalmus gralli, commonly known as the oriental avian eye fluke, parasitises the conjunctival sac of the eyes of many species of birds, such as galliforms and anseriforms. In Brazil this parasite was reported in native anseriforms species. It was first discovered by Mathis and Leger in 1910 in domestic chickens from Hanoi, Vietnam. Birds are definitive hosts and freshwater snail species are intermediate hosts (e.g. Tarebia granifera and Melanoides tuberculata). 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). Philophthalmus gralli reaches sexual maturity in a bird and produces eggs. Fully embryonated eggs are shed into the water from the definitive host’s eyes. Miracidium is induced to hatch when ripe eggs are released from the worm into water. Upon contact with a snail, the miracidium perforates the host epidermis with the aid of secretions and the anterior cilia. It penetrates the snail far enough to release a single rediae. The mother redia localizes in the heart and produces daughter rediae, which migrate to digestive glands to continue its development and produce megalurous cercariae. Cercariae are released from the snail and encyst on aquatic vegetation or other solid objects in the water. The definitive host, which is usually an aquatic bird, becomes infected upon ingestion of metacercariae. 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. The P. gralli egg is nonoperculate and oval. The shell is thin and elastic and has an internal thickening at the small end.