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Intestinal Capillariasis

[Capillaria philippinensis]

Causal Agent

The nematode (roundworm) Capillaria philippinensis causes human intestinal capillariasis.

Life Cycle

lifecycle

Typically,unembryonated eggs are passed in the human stool The number 1 and become embryonated in the external environment The number 2; after ingestion by freshwater fish, larvae hatch, penetrate theintestine, and migrate to the tissues The number 3. Ingestion of raw or undercooked fish results in infection of thehuman host. Humans are the only demonstrated hosts The number 4. The adults of Capillaria philippinensis (males: 2.3 to 3.2mm; females: 2.5 to 4.3 mm) reside in the human small intestine, where theyburrow in the mucosa The number 5. The females deposit unembryonated eggs. Some of thesebecome embryonated in the intestine, and release larvae that can causeautoinfection. This leads to hyperinfection (a massive number of adult worms) The number 6. Capillaria philippinesis is currently considered aparasite of fish eating birds, which seem to be the natural definitive host The number 7.

Geographic Distribution

Capillaria philippinensis is endemic in the Philippines and also occurs in Thailand. Rare cases have been reported from other Asian countries, the Middle East, and Colombia.

Clinical Presentation

Intestinal capillariasis (caused by C. philippinensis) manifests as abdominal pain and diarrhea, which, if untreated, may become severe because of autoinfection. A protein-losing enteropathy can develop which may result in cachexia and death.

Capillaria philippinensis eggs.

 

Capillaria philippinensis eggs are 35 to 45 µm in length by 20-25 µm in width. They have two inconspicuous polar prominences and a striated shell. Eggs are unembryonated when passed in feces.

Figure A: Egg of C. philippinensis in an unstained wet mount of stool.

Figure B: Egg of C. philippinensis in an unstained wet mount of stool.

Figure C: Egg of C. philippinensis in an unstained wet mount of stool.

Figure D: Egg of C. philippinensis in an unstained wet mount of stool.

Capillaria philippinensis adults.

 

Capillaria philippinensis adult males are 2.0-3.5 mm in length and females are 2.5-4.5 mm in length. Females may contain embryonated or unembryonated eggs in utero. Fish-eating birds are the usual definitive host, but humans may harbor adults after consuming larvae in undercooked or raw fish.

Figure A: Longitudinal section of an adult of C. philippinensis from an intestinal biopsy specimen stained with hematoxylin and eosin (H&E).

Figure B: Longitudinal section of an adult of C. philippinensis from an intestinal biopsy specimen stained with hematoxylin and eosin (H&E).

Figure C: Longitudinal section of an adult C. philippinensis from an intestinal biopsy specimen, stained with H&E.

Figure D: Higher magnification of Figure C, showing stichocytes within the adult worm.

Figure E: Cross-section of a gravid adult female C. philippinensis from an intestinal biopsy specimen, stained with H&E. Shown in this figure are a bacillary band (blue arrow), the intestine (red arrow) and uterus containing an egg in cross-section (black arrow).

Diagnostic Findings

The specific diagnosis of C. philippinensis is established by finding eggs, larvae and/or adult worms in the stool, or in intestinal biopsies. Unembryonated eggs are the typical stage found in the feces. In severe infections, embryonated eggs, larvae, and even adult worms can be found in the feces.

More on: Morphologic comparison with other intestinal parasites

Treatment Information

Treatment information for intestinal capillariasis can be found at: https://www.cdc.gov/parasites/capillaria/health_professionals/index.html

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 14, 2017
  • Page last updated: December 14, 2017
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