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Hepatic Capillariasis

[Capillaria hepatica]

Causal Agent

The nematode (roundworm) Capillaria hepatica causes hepatic capillariasis in humans.


Life Cycle

lifecycle

Capillaria hepatica has a direct life cycle that requires only one host.  Adult worms invade the liver of the host (usually rodents, but may also be pigs, carnivores and primates, including humans), and lay hundreds of eggs in the surrounding parenchyma The number 1.  The eggs are not passed in the feces of the host, and remain in the liver until the animal dies and decomposes The number 2, or is eaten by a predator or scavenger The number 3.  Eggs ingested by such an animal are unembryonated, are not infectious, and are passed in the feces, providing an efficient mechanism to release eggs into the environment The number 4.  Cannibalism has been reported as an important role in transmission among rodent populations.  Eggs embryonate in the environment The number 5, where they require air and damp soil to become infective.  Under optimal conditions, this takes about 30 days.  The cycle continues when embryonated eggs are eaten by a suitable mammalian host The number 6.  Infective eggs hatch in the intestine, releasing larvae.  The larvae migrate via the portal vein to the liver.  Larvae take about four weeks to mature into adults and mate.  Humans are usually infected after ingesting embryonated eggs in fecal-contaminated food, water, or soil The number 7.  Occasionally in humans, larvae will migrate to the lungs, kidneys, or other organs.  The presence of C. hepatica eggs in human stool during routine ova-and-parasite (O&P) examinations indicates spurious passage of ingested eggs, and not a true infection.  Diagnosis in humans is usually achieved by finding adults and eggs in biopsy or autopsy specimens.

Geographic Distribution

Rare cases of human infections with C. hepatica have been reported worldwide.

Clinical Presentation

Hepatic capillariasis (C. hepatica) manifests as an acute or subacute hepatitis with eosinophilia, with possible dissemination to other organs. It may be fatal.

Capillaria hepatica eggs.

 

Capillaria hepatica eggs are 50-70 µm long by 30-35 µm wide. They have a striated shell and shallow polar prominences. Eggs are unembryonated when seen in human feces (an indication of a spurious infection). Diagnosis is usually made by finding eggs in biopsy or autopsy specimens.
Figure A

Figure A: Eggs of C. hepatica in liver stained with hematoxylin and eosin (H&E).

Figure A

Figure A: Eggs of C. hepatica in liver stained with hematoxylin and eosin (H&E).

Figure D

Figure D: Eggs of C. hepatica in liver stained with H&E.

Figure C

Figure C: Eggs of C. hepatica in liver stained with H&E.

Capillaria hepatica adults.

 

Capillaria hepatica adults may reach up to 20mm in length but are rarely seen intact, as they mature and die in the parenchyma of the liver.
Figure A

Figure A: Cross section of a male C. hepatica in liver tissue, stained with hematoxylin and eosin (H&E). Note the presence of the intestine (blue arrow) and the coiled sections of the testes (black arrows).

Figure B

Figure B: Cross section of C. hepatica in liver tissue, stained with H&E. Note the presence of the intestine (blue arrow) and bacillary bands (black arrows).

Figure C

Figure C: Cross-section of C. hepatica in liver tissue, stained with H&E. Note the presence of a stichocyte (black arrow) and bacillary bands (blue arrows). Image taken at 200x magnification.

Diagnostic Findings

The specific diagnosis of C. hepatica infection is based on demonstrating the adult worms and/or eggs in liver tissue at biopsy or necropsy. (Note: identification of C. hepatica eggs in the stool is a spurious finding, which does not result from infection of the human host, but from ingestion by that host of livers from infected animals.)

More on: Morphologic comparison with other intestinal parasites

Treatment Information

Mebendazole*, is the drug of choice for adults, 200 mg orally twice a day for 20 days; the pediatric dosage is the same.

Alternative:

Albendazole*, adults, 400 mg orally once a day for 10 days; the pediatric dosage is the same.

(Note: Albendazole must be taken with food; a fatty meal increases oral bioavailability.)

Mebendazole

Mebendazole is available in the United States only through compounding pharmacies.

Mebendazole is in pregnancy category C. Data on the use of mebendazole in pregnant women are limited. The available evidence suggests no difference in congenital anomalies in the children of women who were treated with mebendazole during mass treatment programs compared with those who were not. In mass treatment programs for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO allows use of mebendazole in the 2nd and 3rd trimesters of pregnancy. The risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

Pregnancy Category C: Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal, or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus.

It is not known whether mebendazole is excreted in breast milk. The WHO classifies mebendazole as compatible with breastfeeding and allows the use of mebendazole in lactating women.

The safety of mebendazole in children has not been established. There is limited data in children age 2 years and younger. Mebendazole is listed as an intestinal antihelminthic medicine on the WHO Model List of Essential Medicines for Children, intended for the use of children up to 12 years of age.

Albendazole

Oral albendazole is available for human use in the United States.

Albendazole is pregnancy category C. Data on the use of albendazole in pregnant women are limited, though the available evidence suggests no difference in congenital abnormalities in the children of women who were accidentally treated with albendazole during mass prevention campaigns compared with those who were not. In mass prevention campaigns for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO allows use of albendazole in the 2nd and 3rd trimesters of pregnancy. However, the risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

Pregnancy Category C: Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal, or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus.

It is not known whether albendazole is excreted in human milk. Albendazole should be used with caution in breastfeeding women.

The safety of albendazole in children less than 6 years old is not certain. Studies of the use of albendazole in children as young as one year old suggest that its use is safe. According to WHO guidelines for mass prevention campaigns, albendazole can be used in children as young as 1 year old. Many children less than 6 years old have been treated in these campaigns with albendazole, albeit at a reduced dose.

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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: May 3, 2016
  • Page last updated: May 3, 2016
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