-IBIS-1.5.0-
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digestive system
intestinal worms
diagnoses

definition and etiology

definition:
Intestinal infestation of elongated invertebrates of various species.

etiology:
Many different types of worms can invade the human gut and proliferate. Not all infestations cause disease. Unless otherwise noted, the worms are spread by the fecal-oral route.

roundworms:

• pinworms (Enterobiasis): The infective agent is Enterobius vermicularis. 200 million people worldwide are thought to be infested by the worm, with 30-40 million of those in the U.S. The worm lives by the appendix, cecum, and in the adjacent bowel mucosa.

• whipworm (Trichuriasis): The infective agent is Trichuris trichuria and is uncommon in the U.S. (most patients infested by whipworms are those returning from the tropics). The worms live in the large intestine.

• giant intestinal roundworm (Ascariasis): The infective agent is Ascaris lumbricoides. Perhaps 25% of the world's population is infested by ascaris, including about 4 million Americans. The worm is typically eaten; it then travels from the gut into the lungs, up the respiratory tract until it is swallowed in the pharynx, where it then matures in the jejunum.

• hookworm: The infective agent is Ancylostoma duodenale or Necator americanus. The larvae enter the body through the skin, travel to the lungs, up the respiratory tract until they are swallowed and end up in the small intestines, where they suck blood from the mucosa.

• threadworm: The infective agent is Strongyloides stercoralis. The infection occurs following skin penetration by the larvae, although the fecal-oral route is thought to be another manner of spread. The life cycle then follows that of the hookworm, except larvae, not eggs, are passed in the feces. Severe infestations with threadworm can entail having the biliary and pancreatic tracts, the entire small intestine, and the large bowel colonized.

tapeworms:

• beef tapeworm: The infective agent is Taenia saginata. Humans become infected with the worms upon eating raw or undercooked encysted beef muscle. It takes approximately 2-3 months for the worms to mature in the intestines. The disease is uncommon in the US.

• pork tapeworm: The infective agent is Taenia solium. Humans are infected by eating raw or undercooked pork. The adult worm disease is similar to that of the beef tapeworm. In infections with T. solium, humans may serve as an intermediate host and the larvae may penetrate the intestinal wall and invade any and all tissues of the body. This condition is called cysticercosis.

• fish tapeworm (Diphyllobothriasis): The infective agent is Diphyllobothrium latum. Humans are infected by eating raw or uncooked fish.

• dwarf tapeworm: The infective agent is Hymenolepis nana.

flukes/trematodes:

• intestinal flukes: The infective agents are Fasciolopsis buski (in vegetation) and Heterophyes and Metagonimus (in fresh-water fish). The disease is uncommon in the U.S. and is seen in patients returning from the Orient or tropics.

signs and symptoms

roundworms
:

• pinworms: Almost all patients will complain of pruritus ani, typically at night, as that is the time the female pinworm comes out to lay her eggs. Other symptoms include: vaginal discharge, insomnia and nightmares, and secondary infection of the anal areas from excoriation. Often the condition affects the entire family. Diagnosis is often made by Scotch tape prep and exam.

• whipworms: Complaints will only arise in those with heavy infections. Abdominal pain and diarrhea are common, and in severe disease, anemia, rectal prolapse, and weight loss may occur. Diagnosis is made by finding eggs in the patient's stool.

• giant intestinal roundworms: The manifestations of the condition may be diverse, due to the route the worm takes through the body. Common symptoms include: fever, cough, wheezing, bronchopneumonia (in the lung phase) and abdominal pain, malabsorption, intestinal obstruction (in the abdominal phase). The patient may appear with a full, pale upper lip, and have white lines around his/her mouth. There may be marked nose-picking. Diagnosis includes finding eosinophilic leukocytosis, eggs in the stool or vomitus, or larvae in sputum.

• hookworms: There is often a maculopapular rash, edema and severe pruritus where the larvae have gone through the skin. Pulmonary symptoms do not usually appear, although cough, pneumonia, and fever may occur during large infestations. Intestinal symptoms include epigastric pain. In severe cases with much blood loss, the patient may exhibit anasarca and cardiac insufficiency. Lab findings may include iron-deficiency anemia, hypoalbuminemia, and detecting eggs in the patient's stool. Differential diagnosis includes malaria and beriberi.

• threadworms: Skin eruptions and itchiness may develop when the larvae enter the skin. Lung complaints similar to ascariasis may occur when the worm is in the lungs. Intestinal complaints include epigastric pain and tenderness, nausea, flatulence, vomiting, and alternating constipation and diarrhea. Lab results include eosinophilia and stool analysis for larvae.

tapeworms:

• beef tapeworm: Typically, the infection is asymptomatic. The patient may infrequently experience epigastric pain, diarrhea, and weight loss; sometimes the unhappy patient may feel an active proglottid crawling around the anus. Lab results include recovering eggs in the stool or by Scotch tape prep. Also, segments of the worms are passed with bowel movements and may be clearly noticed.

• pork tapeworm: When humans are infected with the adult worm, the manifestations are identical to that of the beef tapeworm. The clinical presentation of cysticercosis, however, differs dramatically. Cysticerci develop in the subcutaneous tissues, muscles, viscera, eyes, and brain. The patient may exhibit muscular pains, fever, eosinophilia, and weakness: if the brain is infected symptoms resembling meningoencephalitis, epilepsy, or brain tumor may be present. Lab results include finding the adult worm in the stool or by the anus (Scotch tape prep). 50% of patients will have subcutaneous cysts; CT scan can identify brain lesions; CSF is often abnormal; ELISA testing is available for cysticercosis; biopsy of brain, skin or subcutaneous lesion is definitive.

• fish tapeworm: The infection is frequently asymptomatic. Mild gastrointestinal symptoms may be experienced; occasionally a B12-like anemia may develop. Lab results show eggs in the stool.

• dwarf tapeworm: The infection may be asymptomatic, even when the patient has a large infestation. Abdominal cramps and diarrhea may occur in extensive disease. Lab results show eggs in the stool.

flukes/trematodes:

• intestinal flukes: The infestations are typically asymptomatic; occasionally a patient will present with abdominal pain, intestinal obstruction, or diarrhea. Lab results show eggs in the stools.

course and prognosis

roundworms
:

• pinworms: Conventional treatment of pinworms includes improved personal hygiene, washing all clothes and linens, and pyrantel pamoate. Reinfection is common.

• whipworms: Conventional treatment consists of improved hygiene and sanitation and mebendazole (only in heavy infections).

• giant intestinal roundworms: Conventional treatment consists of pyrantel pamoate or mebendazole.

• hookworms: Conventional treatment includes improved nutrition (especially high protein) and specific focus on the anemia. In cases needing anthelmintic drugs, pyrantel pamoate and mebendazole are recommended.

• threadworms: Conventional treatment consists of thiabendazole.

tapeworms:

• beef tapeworm: Conventional treatment consists of the taenicide niclosamide. Obviously, prophylaxis by cooking meat well (or better, by minimizing or avoiding its consumption!) is most recommended.

• pork tapeworm: Conventional treatment consists of niclosamide in the adult worm infestation. Location of the lesions will determine whether drug therapy or surgery is the treatment of conventional choice.

• fish tapeworm: Conventional treatment is niclosamide.

• dwarf tapeworm: Conventional treatment is niclosamide.

flukes/trematodes:

• intestinal flukes: Conventional treatment consists of tetrachloroethylene.

differential diagnosis

• Amebiasis
• Protozoal infections
• IBS
• other causes of gastroenteritis, diarrhea or related symptoms; note the differential of malaria and beriberi for hookworm


footnotes