para>Children often have a larger parasite load, which can adversely impact physical and cognitive development. é á
EPIDEMIOLOGY
Incidence
- Predominant age
- All ages; children have a heavier worm burden.
- Pinworm infections are more common in children.
- Predominant sex: male = female
Prevalence
- E. vermicularis: most common helminth infection in the United States; no association with socioeconomic status
- T. trichiura: 25% of world population infected; more common in tropics and subtropics; associated with poor sanitation
- A. lumbricoides: most common worldwide human helminth; 1.3 billion infected worldwide; 2% of the U.S. population may be infected.
- N. americanus/A. duodenale: 10% of world 's population infected; requires warm climate with abundant rainfall
- S. stercoralis: up to 25% infected in subtropical or tropical areas
- Mass deworming campaigns are decreasing the prevalence in many parts of the world.
ETIOLOGY AND PATHOPHYSIOLOGY
Life cycles é á
- E. vermicularis: Eggs can survive in a moist environment for several weeks. The entire life cycle takes place in the GI tract. Gravid female worm in the colon migrates to perianal area at night to lay eggs that are autoingested and hatch in duodenum.
- T. trichiura: Larva emerges from ingested egg in small intestine and matures. Adults embed in colonic epithelium. Eggs shed in feces embryonate in soil. Ingestion completes the cycle.
- A. lumbricoides: After ingestion, eggs hatch and the larval form penetrates the intestinal wall, traveling via the bloodstream to the lungs to the trachea where they are swallowed to reach the small intestine and mature to adult worms. Female adults then lay eggs to complete the cycle.
- N. americanus, A. duodenale, and S. stercoralis: Larvae penetrate skin, migrate to lungs via bloodstream, ascend the trachea, are swallowed, and reach the small intestine where they mature to adult worms. Eggs shed in stool hatch in soil if suitable climate. Strongyloides can complete life cycle in human host; autoinfection can occur.
- T. spiralis: Larvae ingested in raw/undercooked meat penetrate the bowel mucosa and release larvae that travel via lymphatics and the bloodstream to encyst in striated muscle.
- Humans can acquire nematodes through ingestion of mature eggs in contaminated food or drink.
- Larval penetration of skin (hookworm, Strongyloides)
- Person-to-person transmission (Strongyloides, pinworm)
Genetics
Genetic predisposition to susceptibility to some nematode infections (i.e., Ascaris and Trichuriasis) (1)[B] é á
RISK FACTORS
- Substandard personal hygiene
- Poor sanitation
- Use of human feces to fertilize crops
- T. spiralis (trichinosis): eating raw or undercooked swine, bear, deer, horse, or cougar meat
COMMONLY ASSOCIATED CONDITIONS
Dientamoeba fragilis might be transmitted through pinworm eggs (controversial). é á
DIAGNOSIS
HISTORY
- E. vermicularis
- Most infections are asymptomatic; nocturnal perianal itching is the most common symptom.
- Abdominal pain possible with high parasite burden
- T. trichiura
- Symptomatic if heavily infected
- Dysentery with tenesmus and bloody stools, rectal prolapse can occur; impaired growth and cognition in children
- A. lumbricoides
- Migratory phase: Transient symptoms occur in newly infected persons:
- Cough, wheezing
- Dyspnea
- Substernal chest pain
- Intestinal phase
- Mostly asymptomatic, obstruction can occur with heavy worm burden.
- Mild abdominal discomfort, nausea, anorexia
- N. americanus/A. duodenale
- Skin lesions at site of larval penetration
- Migratory phase
- Intestinal phase
- Nausea, vomiting
- Epigastric pain; diarrhea
- Symptoms are more common with first infections.
- S. stercoralis
- Migratory phase
- Intestinal phase
- Vomiting, epigastric pain, diarrhea
- Strongyloides hyperinfection/disseminated strongyloidiasis syndrome
- Corticosteroid use is the most common risk factor in developed countries.
- T. spiralis
- Initial infection, enteric phase (1 week)
- Vomiting and diarrhea
- Abdominal pain
- Systemic phase (several weeks)
- Muscle pain, tenderness, and weakness
PHYSICAL EXAM
- E. vermicularis
- Perianal excoriation; may directly visualize pinworms (particularly early in the morning)
- T. trichiura
- If rectal prolapse is present, worms may be visible.
- A. lumbricoides
- Migratory phase
- Rales; if severe eosinophilic pneumonia (Loffler syndrome)
- Urticaria
- Intestinal phase
- Jaundice may be present if migrating worm obstructs bile duct.
- Adult worm in stool or emesis
- N. americanus/A. duodenale
- Pruritic eruption at site of larval penetration
- Intestinal phase
- Acute nausea, vomiting, and diarrhea when larva reach the small bowel
- Iron deficiency anemia from intestinal blood loss; can be severe protein malnutrition in severe cases
- S. stercoralis
- Migratory phase
- Serpiginous skin rash (larva currens; pathognomonic)
- Recurrent urticarial or maculopapular rash on buttocks, thighs
- Intestinal phase
- T. spiralis
- Initial infection (1 week)
- Systemic phase (several weeks)
- Fever
- Facial and periorbital edema
- Conjunctival and subungual hemorrhages
- Eosinophilia
- Cardiac infection " ömyocarditis
- CNS involvement (mental status changes)
DIFFERENTIAL DIAGNOSIS
- Pulmonary ascariasis with eosinophilia: Consider asthma, Loeffler syndrome, eosinophilic pneumonia, systemic lupus erythematosus, Hodgkin disease, tropical pulmonary eosinophilia, toxocariasis, strongyloidiasis, hookworm, or paragonimiasis.
- Worm-induced GI diseases: pancreatitis, appendicitis, diverticulitis, duodenitis, and cholecystitis
DIAGNOSTIC TESTS & INTERPRETATION
- E. vermicularis: pinworm paddle test or adhesive cellophane tape pressed to perianal area in the morning for adherent eggs ( "tape test " Ł)
- T. trichiura
- Stool microscopy for eggs
- Eosinophilia
- A. lumbricoides
- Stool microscopy
- Eosinophilia: especially during larval migration
- Abdominal plain film " ömasses of worms can occasionally be seen within the bowel, particularly children with a heavy worm burden.
- N. americanus/A. duodenale
- Eosinophilia
- Stool microscopy for eggs
- Microcytic anemia: iron deficiency anemia due to blood loss
- S. stercoralis
- Stool microscopy is insensitive; serology is more sensitive and should be considered in persons who reside or travel to endemic areas prior to receiving immunosuppressive therapy. Commercial serologic tests are of variable sensitivity.
- Larvae can be seen in multiple body fluids in disseminated infection (2)[A].
- T. spiralis
- Enzyme immunoassay (EIA): antibodies peak 2 to 3 months postinfection
- Eosinophilia: Highest levels are during 3rd to 4th week of infection.
Test Interpretation
Characteristic species-specific eggs/worms are noted on stool microscopy. é á
TREATMENT
MEDICATION
First Line
- E. vermicularis (pinworm): pyrantel pamoate 11 mg/kg PO once (max 1 g); with a repeat dose 2 weeks later or albendazole 400 mg PO once. Consider treating all household members to avoid reinfection (3,4)[A].
- T. trichiura (whipworm): albendazole 400 mg/day PO for 3 days; heavy infection: albendazole 400 mg/day PO for 5 to 7 days
- A. lumbricoides: albendazole 400 mg PO once; avoid treatment of migratory pulmonary phase because this can lead to increased inflammation or pyrantel pamoate 11 mg/kg PO once (max 1 g all dosages for adults and children),
- N. americanus/A. duodenale (hookworm): albendazole 400 mg once; iron replacement may be needed or pyrantel pamoate 11 mg/kg PO (max 1 g) for 3 days (all dosages for adult and children).
T. spiralis: Alendazole 400 mg PO BID for 10 to 14 days for enteral phase; steroids usually are indicated for severe symptoms in association with antihelminthic therapy. é á
- S. stercoralis: ivermectin (Mectizan) 200 Ä ╝g/kg PO once a day for 2 days or albendazole 400 mg PO BID for 3 to 7 days (has lower efficacy). For severe, complicated infection, ivermectin should be continued for at least 7 days (possibly longer) until larva are no longer detected in stool for at least 2 weeks; an alternative route may be needed if absorption is impaired; broad-spectrum antibiotics should be given as bacterial secondary infection occurs. If possible, immunosuppressive therapy should be reduced. In patients at risk for Loa Loa, screen for microfilaria before administering ivermectin to avoid precipitating encephalopathy that can be life-threatening.
- Note: The FDA considers use of some of these drugs investigational. Mebendazole is no longer available in the United States.
Pregnancy Considerations
Avoid benzimidazoles (mebendazole [no longer available in the United States], albendazole, thiabendazoles), particularly in the 1st trimester. Pyrantel pamoate is an alternative for many helminth infections if treatment during pregnancy is needed. Ivermectin has been used in pregnancy; however, teratogenic effects have been reported in animal studies " öbenefits should clearly outweigh risks.
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ISSUES FOR REFERRAL
Patients with Strongyloides hyperinfection syndrome should be referred to an infectious disease specialist (5)[A]. é á
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Reinfection is possible; immunity does not develop (6)[A]. é á
Patient Monitoring
Follow-up stool studies at 2 weeks; retreat if necessary. Repeat Strongyloides serologies in 3 to 6 months. é á
DIET
May need iron replacement with hookworm infection é á
PATIENT EDUCATION
- Avoid fecally contaminated food, water, and soil.
- Do not use human fecal material as fertilizer.
- Avoid walking barefoot in roundworm-endemic areas.
- T. spiralis (trichinosis): Parasite is killed by cooking meat at 58.5 é ░C for 10 minutes. Freezing at ó ł ĺ20 é ░C for ≥3 weeks will kill T. spiralis in pork but is not effective for horse/game meat.
Pediatric Considerations
A. duodenale may be transmitted through breast milk.
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PROGNOSIS
- Good for light-to-moderate infections
- Ascariasis always should be treated due to the risk of migrating adult worms.
- Strongyloides hyperinfection syndrome carries high mortality.
COMPLICATIONS
- Cholangitis: wormmigration to common bile duct (ascaris)
- Pancreatitis: worm migration to pancreatic duct
- Appendicitis: worm migration to appendix
- Growth retardation
- Liver abscess
- Intestinal obstruction, volvulus, intussusception, bowel penetration
- Anemia (hookworm)
- Hypoproteinemia (hookworm)
- CNS infection (Strongyloides sp.)
- Secondary bacteremia with Strongyloides hyperinfection syndrome
REFERENCES
11 Williams-Blangero é áS, Vandeberg é áJL, Subedi é áJ, et al. Localization of multiple quantitative trait loci influencing susceptibility to infection with Ascaris lumbricoides. J Infect Dis. 2008;197(1):66 " ô71.22 Requena-Mendez é áA, Chiodini é áP, Bisoffi é áZ, et al. The laboratory diagnosis and follow up of strongyloidiasis: a systematic review. PLoS Negl Trop Dis. 2013;7(1):e2002.33 Keiser é áJ, Utzinger é áJ. Efficacy of current drugs against soil-transmitted helminth infections: systematic review and meta-analysis. JAMA. 2008;299(16):1937 " ô1948.44 Swanson é áSJ, Phares é áCR, Mamo é áB, et al. Albendazole therapy and enteric parasites in United States-bound refugees. N Engl J Med. 2012;366(16):1498 " ô1507.55 Greaves é áD, Coggle é áS, Pollard é áC, et al. Strongyloides stercoralis infection. BMJ. 2013;347:f4610.66 Jia é áTW, Melville é áS, Utzinger é áJ, et al. Soil-transmitted helminth reinfection after drug treatment: a systematic review and meta-analysis. PLoS Negl Trop Dis. 2012;6(5):e1621.
ADDITIONAL READING
- Speich é áB, Ame é áSM, Ali é áSM, et al. Oxantel pamoate-albendazole for Trichuris trichiura infection. N Engl J Med. 2014;370(7):610 " ô620.
- Ziegelbauer é áK, Speich é áB, M â Ąusezahl é áD, et al. Effect of sanitation on soil-transmitted helminth infection: systematic review and meta-analysis. PLoS Med. 2012;9(1):e1001162.
SEE ALSO
Intestinal Parasites; Roundworms, Tissue é á
CODES
ICD10
- B77.0 Ascariasis with intestinal complications
- B77.9 Ascariasis, unspecified
ICD9
127.0 Ascariasis é á
SNOMED
- Ascariasis with intestinal complications (disorder)
- Ascariasis (disorder)
CLINICAL PEARLS
- Ascariasis is the most common worldwide nematode infection. E. vermicularis (pinworm) is the most common U.S. nematode infection.
- Eosinophilia is best indicator of infection with N. americanus/A. duodenale. Absence of eosinophilia does not rule out most roundworm infections.
- Serology may be necessary to detect infection with S. stercoralis. Check serology prior to immunosuppressive therapy in persons who may be infected with Strongyloides.