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Worms/Helminths Note that many types of worms cause GI problems. Readers are encouraged to also check that section.
Angiostrongyliasis (Caribbean, Southeast Asia, Pacific Islands): Angiostrongyliasis includes several distinct nematode (roundworm) infections caused by Angiostrongylus sp. as follows. (1) Nematode (rat lungworm) infection with A. cantonensis that often is subclinical. Larvae migrate to the CNS and may cause eosinophilic meningoencephalitis. Symptoms may include severe headache (most common symptom), stiff neck, low grade fever, nausea, vomiting, abdominal discomfort, paresthesias of trunk and extremities, and other neurologic signs, including unilateral facial paralysis. The disease is usually self-limiting. Treatment is supportive, and includes corticosteroids, spinal taps, and analgesics. Antihelminthics are not used because of host reaction to dead worms in the CNS. (2) Nematode infection with A. costaricensis of the gastrointestinal tract with cutaneous, intestinal, and pulmonary manifestations (related to the nematode life cycle in the host body); and in some cases, hyperinfection syndrome. Cutaneous manifestations include edema, inflammation, and pruritis. Intestinal manifestations include abdominal and flank pain, fever, malaise, anorexia, nausea, vomiting, and weight loss. Pulmonary manifestations include cough, rales, wheezing, low grade fever, and hemoptysis. Hyperinfection syndrome includes severe pulmonary, cardiac, neurologic symptoms, progressing to septicemia and death. Treatment includes supportive therapy and glucocorticoids; and in some cases ivermectin or thiabendazole or albendazole.
Anisakiasis (Mexico, Central and South America, Japan): Anisakiasis is a nematode (roundworm) infection of the stomach or intestinal wall with Anisakis. Manifestions vary according to primary site of infection and improvement usually occurs within a few weeks. Acute gastric anisakiasis has an acute onset of progressive epigastric pain, nausea, and vomiting within hours of ingesting lavae. Acute intestinal manifests as low-grade fever, colicky lower (or diffuse) abdominal pain, nausea, vomiting, and diarrhea. Chronic anisakiasis produces chronic symptoms similar to gastritis, peptic ulcer disease, inflammatory bowel disease, and other GI disorders. Treatment is symptomatic, and in a few cases, surgical.
Ascariasis: See full discussion (Worldwide): Ascariasis is a nematode or roundworm infection with Ascaris lumbricoides causing transient respiratory symptoms initially and chronic gastrointestinal symptoms. The adult worms are more than 20 cm. in length, hence are easily seen in stool and may also emerge from the nose or mouth as a result of coughing or vomiting. Treatment is with albendazole single dose of 400 mg po (not FDA approved) or mebendazole or pyrantel pamoate.
Capillariasis, intestinal (Southeast Asia, especially Thailand and the Philippines): Capillariasis is a nematode (Capillaria philippinensis) infection resulting from ingestion of infected raw fish. Onset is insidious with abdominal pain and watery diarrhea. Progressive autoinfection may lead to enteropathy, protein loss, and severe malabsorption. Treatment is with mebendazole 200 mg bid po for 20 days or albendazole.
Cutaneous larva migrans (Worldwide, including Southeastern U.S.): Cutaneous larva migrans is a distinctive serpinginous dermatitis caused by hookworm larval penetration of the skin. See hookworm.
Dracunculiasis (Guinea worm disease) (Primarily West Africa [Nigeria] and Sudan; other areas of tropical Asia and Africa, Middle East, South America): Dracunculiasis is a tissue nematode infection with Dracunculus medinensis, the largest (up to one meter in length) filarial worm affecting humans. Infection occurs when small Cyclops (crustaceans) that contain larvae are ingested in contaminated fresh water such as that from large open wells. Infected persons are asymptomatic for approximately one year. Then, as the female worm reaches maturity, a papule, or in some cases, a sepinginous elevation of the skin develops - usually on a lower extremity. The papule progresses to a painful and pruritic blister, then an ulcer, and then the prolapsed uterus of the worm becomes visible and on contact with water releases larvae in a milky fluid. After repeated emptying, the worm dies and can then be slowly pulled forth and wound around a stick over a period of several weeks. Metronidazole 250 mg po tid for 10 days is used as an adjunct to mechanical removal. In most cases one to two worms emerge/year. Most people with dracunculiasis are incapacitated for about a month. Secondary bacterial infections are the most common complication.
Echinococcosis (Hydatid disease): See full discussion (Most of the world; endemic in South America, North Africa, Middle East, Southern Europe - especially in areas where sheep are raised). Echinococcosis or hydatid disease is a tapeworm infection that often is asymptomatic, especially in the lengthy early stages. Echinococcus embryos trapped in various organs (especially the liver or lung) develop into hydatid cyst(s), which grow and eventually cause dysfunction according to the function or area of the organ(s). Surgical excision of the cyst remains the treatment of choice. Albendazole is given pre and post-operatively. Drug treatment includes albendazole or mebendazole or praziquantel - all with poor cure rates.
Enterobiasis or Pinworm infection (Worldwide; most common helminthic infection in Western Europe and U.S.): Enterobiasis is a nematode infection of the intestinal tract caused by Enterobius vermicularis eggs which are ingested via contaminated food or soiled hands. Manifestations/associated problems include perianal pruritis, vulvovaginitis in prepubertal girls, and secondary enuresis and urinary tract infection. Treatment is with mebendazole single dose of 100 mg po, repeated in 2 weeks or albendazole single dose of 400 mg po, repeated in 2 weeks (Not FDA approved for this use).
Filariasis: See full discussion (Distribution given below). The filarial parasites are tissue-dwelling roundworms whose microfilarial (mf) larvae are transmitted by several species of mosquitos or flies. The most problematic forms of filariasis are (1) Bancroftian filariasis and Malayan filariasis (much of the tropical and subtropical world between the Tropics of Cancer and Capricorn) which involve the lymphatic system and result in elephantiasisis; (2) loiasis or loa loa (tropical Africa) in which worms live in subcutaneous tissue; and (3) Onchocerciasis (tropical Africa and to a lesser extent Central and South America) which causes river blindness and skin disorders. Treatment in most cases is effective only against the mf, hence the infection continues and repeated treatment (with ivermectin and/or DEC) may be necessary.
Gnathostomiasis (China, Japan, Southeast Asia, Pacific Islands): Gnathostomiasis is a tissue nematode (roundworm) infection with Gnathostoma spinigerum following ingestion of undercooked fish or fowl. Initial symptoms are nausea, vomiting, right upper quadrant abdominal pain, hepatomegaly, fever, and eosinophilia; followed 2-4 weeks later by diffuse painless, pruritic subcutaneous swelling which may migrate, wax and wane, or appear as serpiginous. Swelling is due to migration of the immature worm, and usually is found on an arm or leg, but may also occur in the eyelid (with associated ocular symptoms) or may also affect visceral organs. Eosinophilic myeloencephalitis occurs when the worm migrates along a large nerve trunk resulting in nerve root pain, paralysis, severe headache, and/or signs of cerebral hemorrhage. Treatment includes surgical removal + albendazole 400 mg po for 21 days (not FDA approved and not highly effective).
Hookworm: See full discussion (Most tropical and subtropical areas of the world). An important cause of anemia, hookworms are intestinal parasites (nematodes, including Ancylostoma duodenale, Unicinaria stenocephala, and Necator americanus) whose larvae are transmitted from soil through the skin. Incubation is 2-8 weeks. Most people (with small parasite loads) are asymptomatic. Entry points are sometimes pruritic. Higher loads result in anorexia or increased appetite, abdominal discomfort, weight loss, nausea and vomiting, diarrhea and/or constipation, and anemia. Respiratory symptoms occur in a few patients. Infants and children may experience severe anemia, protein deficiency, and developmental delays. Treatment is with mebendazole, albendazole, or pyrantel pamoate. None of these are safe in pregnancy and neither mebendazole nor albendazole should be given to children under 1 year of age. The anemia should be treated with ferrous sulfate.
Hydatid disease: See echinococcus or full discussion.
Hymenolepiasis (Americas, Mediterranean, Near East, India, Australia): Hymenolepsis nana is the smallest and most common tapeworm (cestode) parasitizing humans. H. nana is spread by the fecal-oral route and is especially common in institutions. Most infected persons are asymptomatic, but very high loads may produce anorexia, abdominal pain, and diarrhea. Treatment is with praziquantel 25 mg/kg in one po dose.
Loiasis or loa loa: See full discussion or summary of filariasis.
Onchocerciasis (tropical Africa and to a lesser extent Central and South America) which causes river blindness and skin disorders. Treatment in most cases is effective only against the mf, hence the infection continues and repeated treatment (with ivermectin and/or DEC) may be necessary. See full discussion of filariasis.
Strongylodiasis (Most of the tropical world): Strongylodiasis is a nematode (roundworm) infection by Strongyloides stercoralis following larval penetration of the skin. A minority of infected persons are asymptomatic. Cutaneous manifestions may occur at the site of penetration (often feet), and include inflammation, serpiginous or urticarial tracts, and pruritis. Intestinal manifestations follow cutaneous, and include abdominal pain, nausea, flatulence, and diarrhea. Larval migration to lungs results in a variety of pulmonary symptoms, ranging from cough to pneumonia, pleural effusion, and miliary abscesses. Hyperinfection syndrome causes life-threatening CNS, cardiac, and wide-ranging gastrointestinal problems. Treatment is with ivermectin 200 mcg/kg/day po for two days. Albendazole and thiabendazole have also been used.
Tapeworms and cysticercosis (Worldwide, but endemic in certain areas): Tapeworm or cestode infections result from the ingestion of Taeniasis sp. eggs, often found in undercooked meat or excreted proglottids (segments) of the adult tapeworm. Depending on the species, adult tapeworms reach a length of eight meters and live as long as 25 years. The beef tapeworm (Taeniasis saginata) usually causes gastrointestinal discomfort and weight loss. Awareness of infection often is through discovery of proglottids in the stool. Manifestations of intestinal infection with the pork tapeworm (Taeniasis solium) are similar to those of the beef tapeworm. However, ingestion of food that is fecally contaminated with T. solium eggs results in cysticercosis. The symptoms of cysticercosis are caused by the presence of cysticeri (encapsulated larvae) and the resulting inflammatory reaction or space-occupying lesions. The incubation period is as long as five years. Manifestions are most commonly varied neurologic problems, including fever, headache, CVA, hydrocephalus, seizures, and other symptoms of increased intracranial pressure. Visual manifestations may be from increased intracranial pressure or a cyst in the eye. Cysts are also found in subcutaneous and muscle tissue. Treatment of intestinal tapeworms is with a single dose of praziquantel 5-10 mg/kg. Treatment of cysticercosis is with albendazole 5 mg/kg po tid for 8-30 days or praziquantel 20 mg/kg po tid for 14 days. Therapy may increase symptoms, in which case dexamethasone helps reduce distress. Also see echinococcosis and hymenolepiasis.
Toxocariasis (Worldwide): Toxocariasis is the most common visceral larva migrans and is due to infection with the tissue nematode (roundworm) toxocara canis or T. cati. Toxocariasis is most common among children who eat feces-contaminated dirt. Most infections are small load and asymptomatic except for mild eosinophilia. Heavy worm loads, decreased immune competence, and other factors may lead to malaise, fever, cough and wheezing, hepatomegaly, anorexia, and weight loss. Ocular toxocariasis also occurs and usually leads to decreased vision. For symptomatic infections, the treatment of choice is diethylcarbamazine 6 mg/kg/day po tid for 10 days. Asymptomatic infections are not necessary to treat.
Trematodes (flukes): See schistosomiasis above or full discussion and see trematode infection by affected system below. Trematodes, biliary duct-dwelling cause diseases including clonorchiasis and opisthorchiasis. (1) Clonorchiasis (China, Taiwan, Korea, Japan, Vietnam, and other areas of Asia) is a liver fluke (Clonorchis sinensis) infection of the biliary tract following ingestion of raw or pickled fish. Symptoms include upper abdominal pain, irregular high fever, lymphadenopathy, myalgia, and arthralgia. The condition may be chronic and include intermittent fever, vague abdominal symptoms, anorexia, and fatigue. Eosinophilia is pronounced. Treatment is with praziquantel 25 mg/kg po tid for one day. (2) Opisthorchiasis (Eastern Europe and Russia; Thailand) is a liver fluke infection of the biliary tract following ingestion of raw or pickled fish. Most infected persons have no significant symptoms. If the parasite load is high, symptoms may include upper abdominal pain, feeling that something is moving in the liver, hepatomegaly with tenderness, jaundice, intermittent fever, lymphadenopathy, myalgia, and arthralgia. The condition may be chronic and include intermittent fever, vague abdominal symptoms, anorexia, and fatigue. Eosinophilia is pronounced. Treatment is with praziquantel 25 mg/kg po tid for one day.
Trematodes, blood-dwelling (schistosomiasis or Bilharzia): See full discussion (Numerous areas of the world, especially Africa and Asia with variants and locations noted in the full discussion). Schistosomiasis is caused by Schistosoma sp. and encompasses several syndromes, not all of which are evident in all infected persons. Initial symptoms may include a pruritic, papular rash - most commonly in persons who do not live in endemic areas. Acute schistosomiasis (Katayama fever) occurs in primary infection 1-2 months after exposure to heavy parasite loads. Symptoms may include fever of several weeks duration, headache, urticaria, cough, hepatosplenomegaly, lymphadenopathy, diarrhea, and eosinophilia. Hematuria and dysuria occur in some infections. Symptoms tend to gradually diminish over several months, but may intensify as more eggs are deposited. Chronic hepatosplenic schistosomiasis is a consequence of eggs retained in tissue and prolonged infection - usually > 10 years duration. The liver may be large or small and firm with nodularity. Portal hypertension, splenomegaly, or esophageal or gastric varices may occur. Hematemesis and splenomegaly are common presenting symptoms, with normal liver function. Periportal fibrosis and portal hypertension is associated with glomerulonephritis (proteinuria, renal failure) and pulmonary hypertension (cor pulmonale). Granulomatous tissue in the bowel results in bloody diarrhea. The last (chronic) stage varies according to species, with some species primarily affecting the liver and intestines, and one species affecting primarily the urinary tract. In general, patients with chronic schistosomiasis tend to present in developed countries with lethargy, colicky abdominal pain, mucoid/bloody diarrhea, or dysuria and hematuria. Salmonella infection concurrent with schistosomiasis is common and is resistant to treatment unless the schistosomiasis is also treated. Complications include progression of liver, kidney, or other organ dysfunction for many years after transmission has been interrupted - especially with heavy infection and re-exposure. Central nervous system lesions occur, but rarely. Treatment is according to species: For S. haematobium and S. mansoni, praziquantel 20/kg po bid for one day; for S. japonica and S. mekongi, praziquantel 20/kg po tid for one day are the treatments of choice. S. mansoni may also be treated with oxamniquine in a single po dose (with food) of 15 mg/kg. S. haematobium in North and East Africa may be treated with metrifonate 7.5-10 mg/kg every other week for a total of 3 doses.
Trematodes, intestine-dwelling (Asia, Latin America, Africa) include several species ranging in size from 1 mm to 70 mm in length and causing gastrointestinal symptoms such as pain, nausea, vomiting, ascites, and obstruction; and cardiac problems including myocarditis. Treatment in most cases is with praziquantel 25 mg/kg tid for one day.
Trematodes, lung-dwelling cause paragonimiasis (Asia, Latin America, Africa): Paragonimus sp. are lung-dwelling (as well as other sites) trematodes. Infection is most frequently linked with ingestion of incompletely cooked or pickled shellfish. Paragonimiasis may persist for many years and thus present as acute or chronic illness - though chronic is the more common. Acute illness may include fever, cough, pleural effusion, and hepatosplenomegaly. Chronic paragonimiasis is characterized by cough, dyspnea, hemoptysis, brown-flecked sputum, and pleuritic chest pain. X-ray shows (depending on length of illness) diffuse or segmented infiltrates, nodules, cavities, ring cysts, and/or pleural effusions. Extrapulmonary infections may manifest with abdominal pain, diarrhea, and CNS symptoms. Treatment is with praziquantel 25 mg/kg tid for two days.
Trematodes, liver-dwelling cause fascioliasis (Worldwide where sheep and cattle are raised): Infection occurs after ingestion of contaminated water or water-dwelling vegetation, e.g., watercress. Acute fascioliasis is characterized by fever, abdominal pain (especially hepatic), nausea, diarrhea, and hepatomegaly. Cough may also occur. Liver enzymes and erythrocyte sedimentation rates are usually elevated, and anemia is common. Chronic disease results in a variety liver and gallbladder abnormalities. Bithionol 30-50 mg/kg orally qod for 10-15 doses is the treatment of choice as this is written. Bithionol is available in the U.S. from CDC. Triclabendazole in a single dose of 10 mg/kg may become the drug of choice when available in the U.S. (Rosenblatt, 1999).
Trichinosis (trichinella) (Worldwide): Trichinosis is a nematode (roundworm) infection with Trichinella sp. from ingestion of meat that contains cysts, especially undercooked pork or meat from a carnivore. Infection ranges from light and asymptomatic to heavy and life-threatening. Manifestations vary according to the life cycle of the worms: Initially there is malaise, nausea, cramping abdominal pain, and diarrhea. Gastrointestinal symptoms are followed in 1-6 weeks by fever, eosinophilia, periorbital and facial edema, conjunctivitis, dysphagia, dyspnea, cough, myalgia, and muscle spasms. Complications include meningitis and other neurological disorders, myocarditis, pneumonia, and nephritis. The current treatment of choice is mebendazole 300 mg po tid for 10 days (sometimes with prednisone to control symptoms).
Trichostrongyliasis (Africa and Asia): Trichostrongyliasis is a nematode (roundworm) infection with Trichostrongylus sp. (psuedo-hookworm) acquired by eating contaminated vegetables. Heavy infections result in mild anemia and eosinophilia, but infections are usually asymptomatic. Treatment is with pyrantel pamoate 11 mg/kg (maximum 1 gram) in one dose.
Trichuriasis (trichocephaliasis or whipworm) (Worldwide, especially tropical and subtropical areas): Trichuriasis is a nematode (roundworm) infection with Trichuris trichiura. Heavy infections may result in abdominal cramping, nausea, vomiting, flatulence, diarrhea, tenesmus, and weight loss. Mild infections are usually asymptomatic. Treatment is with albendazole single po dose of 400 mg (not FDA approved) or mebendazole 100 mg po bid for 3 days. Ivermectin is sometimes also used in combination with albendazole.