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Philophthalmiasis

[Philophthalmus spp.]

Causal Agents

Trematodes in the genus, Philophthalmus, the eye flukes. The three species recorded in humans are P. lacrymosus, P. gralli and P. palpebrarum.

Life Cycle

lifecycle

Fully-embryonated eggs are shed into the water from the definitive host’s eyes The number 1. Miracidia hatch almost immediately in water The number 2 and penetrate the snail intermediate host The number 3. Several snail genera may serve as intermediate hosts, including Thiara spp. and Melanoides spp. Inside the snail host, the miracidia (which contain a pre-formed redia) undergo a series of stages (The number 3a, The number 3b) and become cercariae. Cercariae are released from the snail The number 4 and encyst on aquatic vegetation or other solid objects in the water The number 5. The definitive host, which is usually an aquatic bird, becomes infected upon ingestion of metacercariae The number 6. Metacercariae excyst in the mouth and migrate to the eye where the adults reside The number 7. Humans rarely serve as incidental hosts, but may do so when they ingest metacercariae on aquatic vegetation The number 8.

Geographic Distribution

Presumed worldwide. The known human cases are from the United States, Central Europe, the Middle East and southeast Asia and Japan.

Clinical Presentation

There are two forms of ocular philophthalmiasis. One is an external form with follicular conjunctivitis and superficial keratitis. Patients with this form often have watery discharge from the palpebral conjunctiva of the upper and lower eyelids. The second is a sub-conjunctival form consisting of a mild edema with minimal cellular reaction.

Pentatrichomonas hominis trophozoites.

 

There is no known cyst stage for Pentatrichomonas hominis. Trophozoites are pyriform in shape, measuring 6-20 µm long. They possess five flagella: four directed anteriorly and a fifth directed posteriorly, that forms the outer edge of the undulating membrane and projects beyond the posterior as a free flagellum. The axostyle is slender and projects from the posterior end. The single nucleus is located at the anterior end and contains a small karyosome.

Figure A: Trophozoite of P. hominis in a stool specimen, stained with trichrome.

Figure B: Trophozoite of P. hominis in a stool specimen, stained with trichrome.

Figure C: Trophozoite of P. hominis in a stool specimen, stained with trichrome.

Figure D: Two trophozoites of P. hominis in a stool specimen, stained with trichrome.

Figure E: Trophozoites of P. hominis in a stool specimen, stained with trichrome.

Figure F: Trophozoite of P. hominis in a stool specimen, stained with iron hematoxylin.

Laboratory Diagnosis

Pentatrichomonas hominis is identified through the detection of trophozoites in stool specimens. Identification is best accomplished by direct wet mounts that reveal the characteristic, jerky movement of the organisms. They may also be identified in permanent stained smears, although their affinities for stain are inconsistent and with their small size are often overlooked.

Treatment Information

For information about treatment please contact CDC-INFO.

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.

  • Page last reviewed: December 30, 2017
  • Page last updated: December 30, 2017
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