Capillariasis

A parasitic disease caused by infection with species of Capillaria.

Capillariasis Life Cycle

Pathogenic species

Capillariasis is a parasitic disease in humans caused by two different species of capillarids:

• Capillaria hepatica and Capillaria philippinensis - C. hepatica is transferred through the fecal matter of infected animals and can lead to hepatitis.
• C. philippinensis is transferred through ingesting infected small freshwater fish and can lead to diarrhea and emaciation.

Capillaria hepatica

Natural habitat

• Infection with C. hepatica is rare but has been reported worldwide.
• Infection with C. philippinensis is frequently found in the Philippines and Thailand. Some cases have been found in other Asian countries, the Middle East, and Colombia.

Cause

The nematode (roundworm) Capillaria philippinensis causes human intestinal capillariasis. Two other Capillaria species parasitize animals, with rare reported instances of human infections. They are C. hepatica, which causes in humans hepatic capillariasis, and C. aerophila, which causes in humans pulmonary capillariasis.

Capillaria Philippinensis - lifecycle

Capillaria infection in a 16 year old girl (Philippines)

• Typically, unembryonated, thick-shelled eggs are passed in the human stool and become embryonated in the external environment in 5—10 days;
• after ingestion by freshwater fish, larvae hatch, penetrate the intestine, and migrate to the tissues.
• Ingestion of raw or undercooked fish results in infection of the human host.  
• The adults of Capillaria philippinensis are very small (males: 2.3 to 3.2mm; females: 2.5 to 4.3 mm) and reside in the human small intestine, where they burrow in the mucosa.
• In addition to the unembryonated, shelled eggs which pass into the environment, the females can also produce eggs lacking shells (possessing only a vitelline membrane), which become embryonated within the female’s uterus or in the intestine.
• The released larvae can re-invade the intestinal mucosa and cause internal autoinfection.
• This process may lead to hyperinfection (a massive number of adult worms).
• Experimental trials have established heavy patent infections in several bird species (particularly herons, egrets, and bitterns), but extensive surveys of wild birds in endemic areas have largely failed to detect infection.
• Many species of freshwater fish appear susceptible to infection and act as intermediate hosts.

Capillaria hepatica - lifecycle

Capillaria hepatica eggs

• The nematode (roundworm) Capillaria hepatica (=Calodium hepaticum) causes hepatic capillariasis in humans.
• Capillaria hepatica has a direct life cycle, with no intermediate host. It can develop with only one definitive host, but likely requires two hosts to complete the life cycle.
• Adult worms are located deep within the liver parenchyma of the host, and lay hundreds of eggs in the surrounding parenchymal tissue.
• The eggs trapped in the parenchyma can not be passed in the feces of the host, and remain in the liver until the animal dies, or more likely, is eaten by a predator or scavenger.
• Eggs ingested by scavengers are unembryonated (not infectious) and are passed in through the digestive tract into and out in feces, providing an efficient mechanism to release eggs into the environment; this is ecologically the most likely primary route of transmission.
• Eggs embryonate in the environment, where they require air and damp soil to become infective. Under natural conditions, embryonation is slow and may take between 6 weeks and 5 months. The cycle continues when embryonated eggs are eaten by a suitable mammalian host.
• Infective eggs hatch in the intestine, releasing first stage larvae.
• The larvae penetrate the intestinal wall and migrate via the portal vein to the liver parenchyma within 3-4 days.
• Larvae take about 3-4 weeks to mature into adults and mate.
• Humans are usually infected after ingesting embryonated eggs in fecally-contaminated food, water, or soil  .
• Notably, 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.

Hosts

C. hepatica has a low host specificity, but rodents such as rats are generally believed to be the most typical host. Infections have also been identified in wild and domestic carnivores (e.g. foxes, dogs, cats), lagomorphs, swine, primates, and humans.

Geographic Distribution

C. hepatica has a broad global distribution in wildlife. Human cases have originated from all inhabited continents except for Australia, although there it exists in wildlife.

Diagnosis

• C. hepatica can be diagnosed by performing a liver biopsy, needle biopsy, or after death at autopsy.
• Analyzing stool samples for C. hepatica cannot be used to diagnose infection. C. philippinensis can be diagnosed by taking a biopsy of the tissue of the small intestine or by analyzing stool samples.

Human to human transmission

• C. hepatica can be transmitted human to human when eggs are deposited through human fecal matter into the soil.
• The eggs then become infective in the soil, and humans ingest infective soil directly by eating soil (pica) or indirectly through contaminated food or water.
• C. philippinensis cannot be transmitted human to human and requires the intermediate freshwater fish host.
• Adult C. philippinensis worms in humans can release eggs that hatch into larvae in the intestine and cause hyperinfection.

Capillaria hepatica eggs

Signs and symptoms

• When a human is infected with only one C. hepatica worm, there are often no signs or symptoms.
• With multiple worms and female worms that lay eggs continually, the clinical manifestations of C. hepatica include hepatitis, anemia, fever, hypereosinophilia, and even death.
• When a human is first infected with C. philippinensis, the signs and symptoms include general abdominal pain and diarrhea.
• Later on, nausea, vomiting, weight loss, and even death can occur.

Prevention

• In order to prevent both types of capillariasis, proper hygiene and disposal of fecal matter is important.
• Specific latrines should be used that are both out of reach from animals and will not let fecal matter seep into the water or around the food supply.
• Washing your hands with soap and warm water after touching or working with soil and before handling food.
• Teach children the importance of washing hands to prevent infection.
• Wash fruits and vegetables before eating them.
• Do not eat raw or undercooked fish.

Cooking

• Cook fish adequately (to an internal temperature of at least 145° F [~63° C]).
• Freezing
• At -4°F (-20°C) or below for 7 days (total time), or
• At -31°F (-35°C) or below until solid, and storing at -31°F (-35°C) or below for 15 hours, or
• At -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for 24 hours.

Treatment

• The medications used to treat C. hepatica include thiabendazole and albendazole. However, C. hepatica is a rare infection and clinical experience is limited.
• Steroids have been used to help control the inflammation of the liver.
• To treat C. philippinensis, medications that can be used include mebendazole (200 mg twice a day for 20 days), and albendazole (400 mg a day for 10 days).

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