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Capillaria philippinensis is a nematode discovered in 1963 as a parasite of humans in the Philippines. In contrast to other Capillaria species, it is an intestinal parasite. Its appearance as a human pathogen was sudden and unexpected. One or two isolated cases were followed by an epidemic in Luzon in 1967 that killed several dozen people. It has now been reported from Thailand, Iran, Japan, and Egypt.
It is probably a zoonotic disease, but the original host remains unknown. Capillaria philippinensis has been transmitted experimentally to monkeys, gerbils, rats, and several species of migratory fish-eating birds. Some female worms bear living juveniles, and adults pass from the definitive host in feces. When feces reach water, eggs embryonate and are eaten by small fishes. After hatching in a fish’s intestine, juveniles develop for a few weeks until they become ineffective for a definitive host. Juveniles released by females in a definitive host’s intestine are autoinfective and massive populations can accumulate, causing severe pathology.
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The parasite is small; males measure 2.3 mm to 3.2 mm, and females measure 2.5 mm to 4.3 mm long. The male has small caudal alae and a spineless spicule sheath. The esophagus of females is about half as long as the body. Females produce Capillaria – type of eggs that lack pits.
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Intensive surveys of Philippine fauna have so far failed to identify any reservoir host, but fish-eating birds are prime suspects. Migratory birds are probably the means by which the infection has spread to other Asian countries and even to the Middle East. Because infective juveniles are in fish intestines, any region where people savor small, whole, raw fish may experience new cases.
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Worms repeatedly penetrate mucosa of the small intestine and reenter the lumen, especially jejunum, leading to progressive degeneration of mucosa and submucosa. Infected people usually experience diarrhea and abdominal pain, progressing to weight loss, weakness, malaise, anorexia, and emaciation. Protein and electrolytes, especially potassium, are lost, and there is malabsorption of fats and sugars. Patients die from loss of electrolytes, heart failure, and sometimes secondary bacterial infection.
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Diagnosis and Treatment
Adults and eggs, as well as juveniles, are abundant in feces of heavily infected people, and at least one of them is necessary for specific diagnosis. The only other intestinal nematode in humans in which juveniles pass in feces is Strogylodes stercorals, and presence of the easily distinguished eggs and adults of C. philippinensis differentiates these two.
Albendazole and mebendazole are effective in curing this disease. Control consists of persuading people to refrain from eating small raw fish whole.