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Avian Trematode Philophthalmus

2006; Elsevier BV; Volume: 113; Issue: 6 Linguagem: Inglês

10.1016/j.ophtha.2006.02.038

1549-4713

Samar Basak, Prashant Singhal, Tushar K. Hazra, David I. Gibson,

Coccidia and coccidiosis research

Philophthalmatids are digenean trematodes that primarily parasitize the eyes of birds. A variety of mammals, including humans, rarely serve as accidental hosts. Up to now, there have been only 7 reports of human ocular infection with Philophthalmus.1Lamothe-Argumedo R. Diaz-Camacho S.P. Nawa Y. The first human case in Mexico of conjunctivitis caused by an avian parasite Philophthalmus lacrimosus.J Parasitol. 2003; 89: 183-185Crossref PubMed Scopus (18) Google Scholar An 18-year-old male presented with redness and discomfort in the right eye for 2 months. He initially was treated elsewhere with topical steroids, which caused some relief in redness but recurred on stopping the medicine. He gave a history of a daily bath in a pond. On examination, he had unaided visual acuity of 6/6 in both eyes and an apparently normal left eye. On slit-lamp examination in the right eye, there was mild conjunctival chemosis, redness, and papillary reaction of the superior fornix. Close examination after retraction of the upper lid revealed a live worm of about 2 mm moving at the superior fornix (Fig 1 [available at http://aaojournal.org]). It was partly subconjunctival and partly on the surface. The anterior segment and the fundus were normal. Systemic examination was normal. On the same day, the patient was taken to the operating theater and the parasite was removed surgically under topical anesthesia. It was live and intact, and the movement of the worm was videophotographed under the operating microscope at a higher magnification (Fig 2 [available at http://aaojournal.org]). It was 4.5 to 5.0 mm long and <1 mm in diameter. The acetabulum and the contractile neck were evident at a higher magnification, which confirmed that it was a trematode. The patient was given a topical antibiotic 4 times daily for 1 week. The redness and discomfort in the right eye subsided shortly afterwards. After 4% formalin fixation, the parasite was greatly contracted and became oval (Fig 3 [available at http://aaojournal.org]). Morphological and anatomical features visible under light microscopy and its site in the eye clearly identified it as a trematode belonging to the genus Philophthalmus Looss, 1899. Scanning electron microscopy helped in confirming the diagnosis (Fig 4 [available at http://aaojournal.org]).Figure 4Scanning electron micrograph of the forebody of the worm. A = acetabulum; O = oral sucker.View Large Image Figure ViewerDownload (PPT) The first case of human ocular philophthalmosis was reported by Markovic from Yugoslavia in 1939.2Markovic A. Der erste Fall von Philophthalmose beim Menschen.Albrecht Von Graefes Arch Ophthalmol. 1939; 140: 515-526Crossref Scopus (13) Google Scholar Since then, there have been 6 further documented case reports of human Philophthalmus infections in the literature, and all 8 records (including the present one) to date have been single-worm infections. Normally, the sexually mature Philophthalmus species deposit eggs in the eyes of domesticated fowl (mainly chickens and ducks). The eggs hatch in freshwater to release larvae (miracidium), which find an aquatic gastropod snail as an intermediate host. Within the snail, the worm reproduces and releases hundreds of tailed larvae (cercariae) that leave the host and are encysted as the metacercarial stage. Birds, the natural hosts, usually acquire infection by ingesting these metacercariae, which then migrate from the esophagus to the nasal passages and ultimately to the eyes of the host, or by cercariae coming in direct contact with the eyes. Human infection may be possible by direct inoculation of cercariae or metacercariae into the eye or by ingestion of contaminated water. In this case, the patient had a habit of catching the snail during his pond bath. In animal experimental infections, both ingestion of cysts and their placement onto the eye have resulted in ocular philophthalmosis.3Howell M.J. Bearup A.J. The life histories of two bird trematodes of the family Philophthalmidae.Proc Linn Soc N S W. 1967; 92: 182-194Google Scholar The damage incurred to the human eye by this trematode is not severe, as its localization in all cases is superficial. From the literature, it is clear that ocular philophthalmosis causes no remarkable clinical manifestations in man, experimental animals, or its natural avian hosts. Therefore, the treatment poses no problem, and in most cases, removal of the parasite results in healing, without the need for any antiparasitic medicine. Species-specific diagnosis was not possible in this case, as the specimen initially was kept in formalin and was greatly contracted. Even if properly fixed, the conclusive species identification is only possible from identification of infected snails and completion of life history under laboratory condition,4Lang Y. Weiss Y. Garzozi H. et al.A first instance of human philophthalmosis in Israel.J Helminthol. 1993; 67: 107-111Crossref PubMed Scopus (24) Google Scholar but as it appeared ovigerous, it was a mature worm. However, the usual species present in domesticated fowl in India is P. gralli Mathis & Leger, 1910.5Ghosh R.K. Chakrabarti S. Review of the Indian species of the trematode genus Philophthalmus Looss, 1899 parasites in the conjunctiva of bird’s eye.Rec Zool Surv India. 2002; 100: 215-226Google Scholar