page_title: Paragonimus westermani
section_title: Morphology
hierarchical_section_title: Paragonimus westermani / Morphology
context_page_description: Paragonimus westermani is the major species of lung fluke that infects humans, causing paragonimiasis. The species sometimes is called the Japanese lung fluke or oriental lung fluke. Human infections are most common in eastern Asia and in South America. Paragonimus westermani was discovered when two Bengal tigers died of paragonimiasis in zoos in Europe in 1878. Several years later, infections in humans were recognised in Formosa.
context_section_description: In size, shape, and color, Paragonimus westermani resembles a coffee bean when alive. Adult worms are 7.5 mm to 12 mm long and 4 mm to 6 mm wide. The thickness ranges from 3.5 mm to 5 mm. The skin of the worm (tegument) is thickly covered with scalelike spines. The oral and ventral suckers are similar in size, with the latter placed slightly pre-equatorially. The excretory bladder extends from the posterior end to the pharynx. The lobed testes are adjacent from each other located at the posterior end, and the lobed ovaries are off-centered near the center of the worm (slightly postacetabular). The uterus is located in a tight coil to the right of the acetabulum, which is connected to the vas deferens. The vitelline glands, which produce the yolk for the eggs, are widespread in the lateral field from the pharynx to the posterior end. Inspection of the tegumental spines and shape of the metacercariae may distinguish between the 30-odd species of Paragonimus spp. but the distinction is sufficiently difficult to justify suspicion that many of the described species are synonyms.
  Eggs: Paragonimus westermani eggs range from 80 to 120 µm long by 45 to 70 µm wide. They are yellow-brown, ovoid or elongate, with a thick shell, and often asymmetrical with one end slightly flattened. At the large end, the operculum is clearly visible. The opposite (abopercular) end is thickened. The eggs are unembryonated when passed in sputum or feces.
  Cercaria (not shown): Cercariae are often indistinguishable between species. There is a large posterior sucker, and the exterior is spined.
  Metacercaria: Metacercariae are usually encysted in tissue. The exterior is spined and has two suckers
  Adults: Adult flukes are typically reddish brown and ovoid, measuring 7 to 16 mm by 4 to 8 mm, similar in size and appearance to a coffee bean.They are hermaphroditic, with a lobed ovary located anterior to two branching testes. Like all members of the Trematoda, they possess oral and ventral suckers.
caption: Egg of Paragonimus westermani
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