Capillaria spp. – Tiny Worms
Dangerous Parasitic Nematodes of Humans and Animals
Capillaria hepatica lives in the liver; Capillaria philippinensis infests the intestine. Both are unusual but serious infections in humans.
Capillaria spp. are nematodes, or roundworms. There are many different species infecting a wide range of vertebrate hosts—a few occasionally infect human hosts causing serious parasitic disease. The best known of these are C. hepatica and C. philippinensis.
Capillaria hepatica
Capillaria hepatica is a tiny worm that commonly infects rodents worldwide, living in the liver. Its lifecycle is interesting:
- Female worms, about two centimetres long, produce eggs in the liver of the rodent host.
- When the host dies and decomposes, or is eaten by another animal, the eggs are liberated from the liver and dispersed in the environment. (When the original host is eaten, the eggs simply pass through the second animal’s intestine and are deposited back on the ground.)
- Eggs in soil develop and are soon infective to a new vertebrate host.
- When infective eggs of C. hepatica are swallowed in soil, larvae hatch in the intestine and travel to the liver where they mature to adult male and female worms and once again begin producing eggs. Thus, if a human accidentally swallows soil contaminated with the feces or remains of an infected animal, or eats food contaminated with the same material, he or she may soon harbour C. hepatica in the liver.
Capillaria hepatica is thought to be quite rare in humans; however, it may be more common than we think—a sample from the liver is required for recovery of the characteristic worms and eggs for identification and such samples are rarely collected. Symptoms of hepatic capillariasis mimic other more familiar diseases such as hepatitis, liver abscess, and Hodgkin’s disease. An infection involving many worms in the liver with the accumulation of many eggs can be fatal.
Capillaria philippinensis
Capillaria philippinensis was unknown in humans until the 1960s, when an outbreak of the parasite killed a number of people in Luzon, an island in the Philippines. Subsequently, it has been found in Indonesia, Japan and Taiwan, Southeast Asia and the Middle East, possibly spread to these locations by migrating birds.
Capillaria philippinensis is easier to diagnose that C. hepatica because the parasites can be recovered from stool:
- Adult male and female worms live in the intestine. Females produce both eggs and larvae. Unlike most intestinal nematodes, this parasite can multiply in the intestine, producing many parasites even though there may have been only a few initially.
- Adult worms, eggs, and larvae are passed in the stool.
- Infective eggs in water are eaten by fish. Hatching, the larvae mature in the fish intestine.
- Humans, and probably other hosts including other primates, rodents, and birds, get C. philippinensis when they swallow raw, whole fish that harbour the parasite.
A C. philippinensis infection can be serious because the parasite can multiply to huge numbers in the intestine, and the worms and larvae do extensive damage to the intestinal lining. Symptoms include diarrhea, abdominal pain, nutritional deficiency, and marked weight loss.
Fortunately, this parasitic disease is relatively rare in humans. It is also easily preventable: do not eat raw whole fish.
Read about other parasites that trouble humans:
Trichomonas vaginalis Parasite
Sources:
Beaver, Paul Chester, Rodney Clifton Jung, and Eddie Wayne Cupp. Clinical Parasitology 9th ed. Philadelphia: Lea and Febiger, 1984.
Garcia, Lynn S. and David A. Bruckner. Diagnostic Medical Parasitology 3rd ed. Washington: ASM Press, 1997.
Roberts, Larry S. and John Janovy Jr. Foundations of Parasitology 6th Ed. Boston: McGraw Hill, 2000.
