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Bile-Duct Trematodes Found in the Lungs and Body Cavity of a Great Egret

Close-up of an eastern great egret in Osaka, Japan
Research · Disease, parasites & microbiology

A 2026 case report from South Korea documented an unusual infection in an eastern great egret (Ardea alba modesta). Multiple trematodes identified as Pegosomum bubulcum, a species that typically inhabits the bile ducts of birds, were found well outside their usual site — on the surface of the liver, in the coelomic cavity and in the lungs.

Parasites outside their usual location

When a parasite occurs in a tissue or organ other than its usual site, the condition is described as ectopic parasitism. In this egret, the finding was accompanied by severe coelomitis, an inflammation of the body cavity, and severe airsacculitis affecting the air sacs. The extrahepatic bile duct — the section carrying bile outside the liver — was also markedly dilated and fibrotic.

The bird was examined in a severely weakened condition. The case description reports hypothermia, dehydration and watery diarrhoea, signs that initially suggested bacterial enteritis. The trematodes were identified only during the post-mortem examination. This made the case diagnostically notable: the most conspicuous clinical signs did not reveal that a trematode normally associated with the biliary system was also present in the lungs and body cavity.

An unusual pathological finding, not a population estimate

The report documents the abnormal distribution of P. bubulcum and the substantial inflammatory and fibrotic changes present in the same bird. It does not, however, establish from a single case how common ectopic infection is in eastern great egrets, nor can one individual be used to estimate the parasite’s prevalence or its importance at population level.

The distinction is also important when interpreting cause and effect. The published report documents the ectopic trematodes alongside severe pathological changes, but a case report is primarily a detailed description of one affected animal. Its main new finding is therefore that P. bubulcum can occur far beyond the bile ducts in this host at the same time as extensive inflammatory and fibrotic changes.

The report was published electronically in the Journal of Wildlife Diseases on 29 June 2026. It adds a documented example of ectopic trematode infection in a great egret and highlights how necropsy can reveal infections that were not apparent from the animal’s clinical signs alone.

Sources and image credit

  1. Oh, B., Park, B.-K., Kim, M., Han, J.-I., Oh, S.-I., & Kim, B. (2026). Ectopic Parasitism of Pegosomum bubulcum in an Eastern Great Egret (Ardea alba modesta). Journal of Wildlife Diseases, 62(3), 727–730.Primary peer-reviewed case report. Multiple Pegosomum bubulcum trematodes, a species that typically inhabits avian bile ducts, were found on the liver surface, in the coelomic cavity and in the lungs of an eastern great egret in South Korea, alongside severe coelomitis, airsacculitis and a markedly dilated, fibrotic extrahepatic bile duct. Published electronically 29 June 2026.

Image: Laitche — wild eastern great egret (Ardea alba modesta) photographed at Tennōji Park, Osaka, Japan, 13 November 2016; Wikimedia Commons Featured Picture and Quality Image; representative exact-subspecies image, not the bird in the parasite case report · CC BY-SA 4.0 · Source

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