Ascaris

Background:

Ascaris lumbricoides (see Image 1), a roundworm, causes the most common helminthic infection in the world, ascariasis. Ascariasis is found most commonly in countries with poor sanitary conditions.

Pathophysiology

: Ascaris species is transmitted by fecal-oral spread, primarily from ingestion of agricultural products or food contaminated with parasite eggs. Ascaris larvae, which hatch from swallowed eggs in the intestine, migrate through the blood to the pulmonary circulation. These larvae then penetrate the alveoli 1-2 weeks later as third-stage larvae and migrate up the tracheobronchial tree. At this point, the host swallows the larvae, which then develop into adult worms in the intestine. Worms can reach 10-30 cm in length. Clinical disease results from effects of pulmonary larval migration, intestinal obstruction (IO), or migration through the biliary tree.

Frequency:

· In the US: In the United States, more than 4 million individuals are believed to be infected with Ascaris species. Most infected persons are immigrants from developing countries.

· Internationally: Worldwide, more than 1.4 billion people are infected. Most Ascaris infections are in Latin America and Asia.

Mortality/Morbidity:

Most of the severe complications of Ascaris species infection are the result of complete IO, which may occur following the administration of certain anthelmintic agents to treat partial obstruction, resulting in formation of a worm bolus and leading to complete obstruction.

Race: No racial predilection exists.

Sex: No sex predilection exists.

Age: IO is more common in children because of the smaller diameter of the lumen of the bowel and, often, an increased worm load.
History:

The most common manifestation of ascariasis in children is passing a worm via rectum. Many asymptomatic individuals are diagnosed by the incidental finding of Ascaris species eggs in the stool.

· Pulmonary disease

o Individuals with migration of larvae through the lungs may present with a cough and/or wheezing.

o In persons with more severe pulmonary infection, fever, dyspnea, fleeting patchy pulmonary infiltrates, and, rarely, hemoptysis may be observed.

o The term Loeffler pneumonitis refers to eosinophilic pneumonia, of which Ascaris species is one cause.

· Intestinal disease

o Most intestinal disease in persons with ascariasis produces no symptoms.

o The most common symptom is poorly localized and colicky abdominal pain.

o In younger children and in those with a heavy worm burden, symptoms may be caused by either partial or total IO.

o Localized pain may suggest complete IO or appendicitis, as does the presence of nausea and bilious emesis.

o Ascariasis is often found incidentally after a patient passes an adult worm in the feces or through the nose or mouth.

o Fever, general anesthesia, or subtherapeutic doses of anthelmintics may provoke the worms to migrate.

o Migrating worms have also been reported to cause intestinal perforation.

· Biliary tract disease

o Migration of a single adult worm may obstruct the biliary tree, leading to biliary colic, cholangitis, or gallstone formation.

o Biliary colic is characterized by sharp, intermittent, right upper quadrant pain.

o Toxic appearance and fever suggest the presence of cholangitis.

Physical:

Asymptomatic ascariasis infection may manifest only in growth retardation secondary to malnutrition.

· Pulmonary disease

o Wheezing on auscultation is the most common finding in symptomatic patients.

o The presence of rales or decreased breath sounds suggests bacterial pneumonia, which may occur as a result of bronchial obstruction.

· Intestinal disease

o Most clinical signs of ascariasis result from IO.

o With complete obstruction, decreased or absent bowel sounds, abdominal tenderness, or signs of frank peritonitis may be found.

· Biliary tract disease

o Biliary tract disease may manifest with right upper quadrant pain, fever, and vomiting.

o Obstructive jaundice is relatively uncommon, occurring in fewer than 5% of patients with the disease.

Causes:

Certain conditions may stimulate migration of worms, resulting in clinical disease. These conditions include fever and the use of certain anthelmintic agents that cause a spastic paralysis of the worms.

Lab Studies:

· CBC count may demonstrate peripheral eosinophilia.

· Larvae may be found in gastric or respiratory secretions in pulmonary disease.

· Stool for ova and parasites demonstrates Ascaris species eggs.

Imaging Studies:

· Chest radiography: This study may demonstrate pulmonary opacities in Loeffler syndrome.

· Biliary tract disease

o Endoscopic retrograde cholangiopancreatography (ERCP) is 90% sensitive in assisting the physician in making the diagnosis of biliary ascariasis.

o Ultrasonography has a greater than 50% sensitivity in assisting the physician in making the diagnosis of biliary ascariasis.

o CT scanning is also useful in assisting the physician in making the diagnosis and may demonstrate IO or biliary obstruction.

Medical Care:

· Pulmonary disease

o Most patients with ascariasis respond poorly to anthelmintic agents.

o Treatment of the infection is largely based on symptoms; use appropriate bronchodilators and possibly systemic corticosteroids if marked airway inflammation is present.

o To clear the infection from the GI tract, administer anthelmintics 1-2 weeks after treatment with bronchodilators and possible systemic corticosteroids.

· Intestinal obstruction and hepatobiliary disease

o Treat patients with IO or hepatobiliary disease with appropriate anthelmintics.

o If partial IO is suspected on the basis of symptoms of colicky abdominal pain, anthelmintics that cause a flaccid paralysis are preferred to those that cause spastic paralysis, because anthelmintics that cause spastic paralysis may induce complete obstruction.

o Surgery is often necessary.

Surgical Care

: Surgery is often necessary for IO and hepatobiliary obstruction, especially with high worm loads and particularly in children.

Consultations

: With suspected IO or biliary obstruction, consult with a surgeon.

Diet: Advise individuals with suspected partial IO to avoid peppery or spicy foods, which may induce migration of worms in the intestine.

Anthelmintics rarely affect the course of pulmonary disease. In patients with signs of IO caused by ascariasis, avoid anthelmintics that cause spastic paralysis of the worm (eg, pyrantel pamoate). Mebendazole and pyrantel pamoate are drugs of choice (DOC) for Ascaris species infection that does not produce symptoms.

Drug Category: Anthelmintics - Vermifuges -- DOC for infection that does not produce symptoms. Does not cause paralysis of worms.

Drug Name


Mebendazole (Vermox) -- Causes worm death by selectively and irreversibly blocking uptake of glucose and other nutrients in susceptible adult intestine where helminths dwell. Causes slow immobilization and death of organisms. Administration over 3 d reduces risk of worm bolus formation.

Adult Dose


100 mg PO bid for 3 d

Pediatric Dose


<2 years: Do not administer
>2 years: Administer as in adults

Contraindications


Documented hypersensitivity

Interactions


Carbamazepine and phenytoin may decrease effects of mebendazole; cimetidine may increase mebendazole levels

Pregnancy


C - Safety for use during pregnancy has not been established.

Precautions


Has not been studied extensively in children <2 y (consider risks vs benefits for use in this age group); adjust dose in hepatic impairment

Drug Category: Anthelmintics - Flaccid paralyzing agents -- DOC for treatment of suspected partial IO. Because this agent causes flaccid paralysis, less likelihood exists of worm bolus formation and development of complete obstruction.

Drug Name


Piperazine citrate (Vermizine) -- Recommended for GI or biliary obstruction secondary to Ascariasis. Causes flaccid paralysis of the helminth by blocking response of Ascaris species worm to acetylcholine, thus expels the worm by normal intestinal peristalsis. Readily absorbed from GI tract, partially degraded in vivo, and excreted in urine. Exhibits wide therapeutic index. No longer available in the United States.
The dose of piperazine citrate is expressed in terms of piperazine hexahydrate. For example, piperazine hexahydrate 250 mg = the anhydrous form of piperazine citrate 275.75 mg. The oral solution is equivalent to 500 mg/5 mL of piperazine hexahydrate. The dosage for piperazine (granules) solution, susp, and tabs are not interchangeable.

Adult Dose


3.5 g PO qd for 2 d

Pediatric Dose


Tablets: 75 mg/kg/d PO qd for 2 d; not to exceed 3.5 g/d
Granules (oral solution):
<27 kg: 2 g PO as a single dose
27-41 kg: 2 g PO bid for 1 d
>41 kg: Administer as in adults
Oral suspension:
<2 years: 600 mg PO tid (administer 4 h apart) for 1 d
2-8 years: 1.2 g PO bid (administered 6 h apart) for 1 d
8-14 years: 1.2 g PO tid (administered 4 h apart) for 1 d
>14 years: Administer as in adults

Contraindications


Documented hypersensitivity; impaired renal function; seizure disorders

Interactions


Do not use with pyrantel pamoate because effects of the 2 drugs antagonize each other; coadministration with chlorpromazine may increase toxicity

Pregnancy


C - Safety for use during pregnancy has not been established.

Precautions


Most commonly reported reactions include GI and CNS effects; discontinue therapy if effects become significant; avoid prolonged, repeated, and excessive therapy due to potential neurotoxicity

Drug Category: Anthelmintics - Spastic paralyzing agents -- Main advantage is ability to administer as single dose. Not recommended in persons with suspected IO.

Drug Name


Pyrantel pamoate (Antiminth, Pin-Rid, Pin-X) -- Depolarizing neuromuscular blocking agent. Inhibits cholinesterases, resulting in spastic paralysis of worm. Poorly absorbed from GI tract and partially metabolized in liver.

Adult Dose


11 mg/kg/dose PO as single dose; not to exceed 1 g

Pediatric Dose


<2 years: Not established
>2 years: Administer as in adults

Contraindications


Documented hypersensitivity; hepatic disease

Interactions


Do not administer with piperazine citrate because effects of the 2 drugs antagonize each other; theophylline serum levels may increase in pediatric patients following administration

Pregnancy


C - Safety for use during pregnancy has not been established.

Precautions


Caution in liver impairment, anemia, and malnutrition; may cause nausea, vomiting, dizziness, headaches, abdominal cramps, and elevated transaminases

Drug Category: Systemic anthelmintic agents- -- Alternative therapy for Ascaris species infection.

Drug Name


Albendazole (Albenza) -- Broad-spectrum anthelmintic agent effective against Ascaris species, hookworm, tapeworm, liver fluke, and pinworms. Decreases ATP production in worm, causing energy depletion, immobilization, and finally death.

Adult Dose


400 mg PO as a single dose; may repeat in 3 wk

Pediatric Dose


<2 years: 200 mg PO as a single dose; may repeat in 3 wk
>2 years: Administer as in adults

Contraindications


Documented hypersensitivity

Interactions


Carbamazepine may accelerate albendazole metabolism; dexamethasone increases plasma levels of albendazole metabolites; praziquantel may increase albendazole plasma concentrations; fatty foods may increase bioavailability of albendazole up to 4-5 times

Pregnancy


C - Safety for use during pregnancy has not been established.

Precautions


Discontinue if LFT enzymes rise; may restart when LFTs are at baseline levels; not advised during pregnancy if avoidable


Deterrence/Prevention:

· Prevention consists of improved sanitation and education about the disease. In endemic areas, school screening has demonstrated effectiveness in detection and early treatment of asymptomatic carriers.

Complications:

· Untreated IO may lead to bowel necrosis, peritonitis, sepsis, and death.

Prognosis:

· Treatment with appropriate anthelmintic agents is quite successful in most individuals with ascariasis.

Medical/Legal Pitfalls:

· No large body of medicolegal literature exists with regard to Ascaris species infections. In 1990, Kern described a woman with cerebral Ascaris species infection who subsequently died of cerebral necrosis.

· In a patient with suspected IO due to ascariasis, avoid the use of an anthelmintic that causes spastic paralysis of the Ascaris worm (eg, pyrantel pamoate). Such medications may induce complete IO in these patients. Administer piperazine in persons with IO or biliary obstruction.