Capillaria Infection

Capillaria is a genus of parasitic nematodes (roundworms) that comprises over 300 species, most of which infect animal species. Four species (Capillaria aerophila, Capillaria hepatica, Capillaria philippinensis and Capillaria plica) have been reported to infect many mammals, includinf man. Capillaria hepatica (Capillary liver worm), a nematode as slender as human hair and measuring up to 4 inches in length, is found in the liver of most rats. It deposits its eggs in the liver tissue which serves as a source of nourishment for adult worms. If enough worms are present, the host may suffer liver failure and die from hepatic capillariasis. Often the disease is unsuspected and discovered only at autopsy. The species is common in rodents, but also occurs in dogs, cats, monkey, soil earthworms and may also infect man. The infection produces fever, enlarged liver, and abdominal swelling. No treatment has been developed yet.

Capillaria aerophila, also called Eucoelus aerophilus, is a 1-2 inches-long nematode that infects the nasal cavity, trachea, bronchi and bronchioles of dogs and cats. Eggs are coughed, swallowed and passed in the feces. The life cycle is direct, but earthworms may serve as a transport host. Most infections have no signs, but in severe cases coughing, nasal discharge, poor body condition, weight loss, difficulty breathing and fever can be seen and result in bronchitis and pneumonia (pulmonary capillariasis). Diagnosis is established by finding worm eggs in sputum.

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Capillaria plica resides in the urinary bladder, ureters and kidneys of various wild carnivores. Hunting can be a risk for this parasite infection in dogs because fox population represents a major source of infection for hunting dogs. Dogs infected with Capillaria plica may have disturbances in urination, cystitis and even kidney failure.

Capillaria philippinenisis is an extremely small nematode (1.5 -3.9 mm). Fish-eating birds are natural hosts. Humans become infected by eating poorly cooked fish. The disease is common in Philippines, Thailand and South China. Local eating habits include ingestion of raw animal organs and the use of intestinal animal juices to season rice and eating uncooked crabs. Infection with Capillaria philippinenisis always causes illness. Heavy infection with Capillaria philippinenisis (intestinal capillariasis) is manifest as watery diarrhea, gurgling stomach, abdominal cramps and malabsorption of fats and sugars and may lead to death if untreated.

Microscopic organism
A microscopic organism at 1000X magnification
Micrograph by Laura Johnston


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  2. Parasitic Diseases. M. Katz, D.D. Despommier, Robert Gwadz
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  4. Essentials of Veterinary Parasitology. Hany Elsheikha, Naveed Ahmed Khan
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