para>Children affected most commonly (1)[A]
Pregnancy Considerations
Many treatments are contraindicated during pregnancy.
EPIDEMIOLOGY
Acquired through lapse in personal, food, and/or water sanitation and/or migration from high-prevalence area
Incidence
- Predominant sex: male = female
- Predominant age: pediatric
Prevalence
- United States: 5-30% of general population has at least one fecal parasite. Random laboratory testing finds at least one GI parasite in 5-10% of all people.
- From daycare surveys: asymptomatic 20-30%; symptomatic 50-80%
- Intestinal protozoa account for most parasitic infections in North America. Helminths account for <10% of GI parasites.
ETIOLOGY AND PATHOPHYSIOLOGY
- Pathophysiology is host-parasite-specific.
- Intestinal parasitic infections are generally self-limiting. Most worms have a defined life expectancy within the host. Autoreinfection occurs in several cases (e.g., strongyloidiasis, pinworm).
- Protozoan pathogens
- Giardia lamblia: common
- Entamoeba histolytica, Cryptosporidium sp., Cystoisospora (Isospora) belli, Balantidium coli, Cyclospora cayetanensis, Microsporida
- Possible protozoan pathogens: Dientamoeba fragilis
- Probable nonpathogenic protozoa
- Amoebas: all other Entamoeba sp., Endolimax nana; all other intestinal flagellates
- Helminthic pathogens
- Nematodes (roundworms): Enterobius vermicularis, Trichuris trichiura, hookworm (Necator americanus, Ancylostoma duodenale), Strongyloides stercoralis, Capillaria philippinensis, Trichostrongylus sp.
- Trematodes (flukes): Fasciolopsis buski, Clonorchis sinensis, Opisthorchis viverrini, Heterophyes heterophyes, Fasciola hepatica, Paragonimus westermani, Schistosoma mansoni, S. japonicum, S. haematobium, S. mekongi
- Cestodes (tapeworms): Taenia saginata, Taenia solium, Diphyllobothrium latum, H. nana, Hymenolepsis diminuta, Dipylidium caninum
RISK FACTORS
- Age (children most commonly infected)
- Low socioeconomic status and poor sanitation-personal, food, water; crowding: daycare centers, institutional care
- International travel or immigration
- Pregnancy; medical comorbidities: gastric hypoacidity, immunosuppression (AIDS, hypogammaglobulinemias)
GENERAL PREVENTION
- Intestinal parasites are usually acquired through the fecal-oral route via ingestion of contaminated food or water. Rarely, infected arthropod vectors are involved in transmission. Person-to-person transmission may occur through fecal-oral means.
- Safe food and water precautions ("Wash it, cook it, boil it, peel it, or forget it"); enteric and hand hygiene is the gold standard for preventing infections. Public health infrastructure systems for safe food and water processing contribute to the low prevalence of intestinal parasites in developed countries.
COMMONLY ASSOCIATED CONDITIONS
- HIV/AIDS, steroid use, immune deficiencies
- Intestinal parasite infection may protect against allergic sensitization (2)[A].
DIAGNOSIS
HISTORY
Historical or physical features alone cannot separate intestinal parasites from other GI infections.
- Acute bacterial or viral GI syndromes tend to be sudden onset and short duration.
- Fever is uncommon with GI parasites unless there is tissue invasion (e.g., amoebiasis, strongyloidiasis).
- Chronic bloating, excessive gas, and intermittent/unpredictable diarrhea without blood is typical of giardiasis.
- Extraintestinal symptoms and signs are uncommon with GI parasites, except invasive strongyloidiasis.
- A water, food, or fecal contamination exposure history (e.g., international travel, migration, high-risk environments [daycare centers, camping]) may suggest a particular parasite.
- Passing a roundworm or tapeworm or a worm segment in the stool
- Excessive gas: bloating, eructation, flatulence
- Nausea or vomiting: intermittent, recurrent
- Diarrhea: persistent and recurrent, chronic but dysentery (i.e., frank GI bleeding) is rare, except with E. histolytica, B. coli
- A family or personal history of inflammatory or irritable bowel syndromes does not exclude GI parasites.
PHYSICAL EXAM
- Patients generally appear well even with GI complaints; usually afebrile
- Diffuse, migratory rash (cutaneous larva currens) with invasive strongyloidiasis (a medical emergency)
- Weight loss and anorexia may be present (e.g., chronic giardiasis, invasive amoebiasis, chronic helminths).
- Borborygmi
- Abdominal pain/tenderness
- May have bowel tenderness. Liver and spleen are usually normal.
- Pruritus ani: E. vermicularis, T. trichiura, S. stercoralis, tapeworms; perirectal or vulvar rash
DIFFERENTIAL DIAGNOSIS
- Other nonparasitic intestinal infections
- Food poisoning
- Malabsorption: commonly lactose, gluten enteropathy; rarely celiac disease, tropical or nontropical sprue
- Inflammatory and irritable bowel diseases
- Hemorrhoid or rectal fissure
DIAGNOSTIC TESTS & INTERPRETATION
- Stool specimens (ova and parasites) that are properly collected, preserved, and transported for examination in a qualified and proficient laboratory by a dedicated parasitology technologist team have the highest diagnostic yield.
- Anemia may be present with heavy hookworm infections.
- Giardia antigen-fluorescent antibody (FA) and ELISA tests: A single FA or ELISA may be at least as sensitive as three stools for ova and parasites.
- Special diagnostics for Cryptosporidium, I. belli, Cyclospora, Microsporidia, and Strongyloides: Give laboratory specific notice.
- Pinworm paddles provide a greater diagnostic yield for E. vermicularis. Multiple tests (2) may be needed.
- Parasite culture for G. lamblia, E. histolytica, and S. stercoralis is rarely indicated; only done in reference laboratories
- Rarely, a biopsy and histology will demonstrate the presence of an invasive helminth on tissue section.
- Tissue biopsies of intestine, liver, or bladder may show granulomatous reactions of schistosome eggs.
- A single stool specimen collected into a preservative (i.e., sodium acetate formalin [SAF]), well mixed to fix and preserve all elements, yields an accurate diagnosis 90% of the time. Additional specimens improve diagnostic accuracy (3,4)[A].
- Serology: useful if parasite is not found in stool samples normally or if low numbers of parasites; available only through reference centers; only indicated for Strongyloides, amebiasis, schistosomiasis
- Drugs that may alter lab results: Use of antibiotics; oil-based laxatives, and barium in the stool interfere with microscopy.
Initial Tests (lab, imaging)
- Screening for eosinophilia is not recommended.
- Diagnostic radiology is rarely needed. Exception: invasive amebiasis-image for colitis, amebomas, and liver abscesses
Follow-Up Tests & Special Considerations
- A single negative stool examination does not rule out intestinal parasitic infection, but when performed under best conditions is highly accurate. Repeat testing increases diagnostic yield if clinical suspicion is high.
- Population-based intestinal parasite screening in North America (e.g., daycare attendees, personal care providers, food handlers, immigrants) has low diagnostic use and is not recommended.
Diagnostic Procedures/Other
- Invasive diagnostic procedures are rarely indicated.
- Egg granulomata of schistosomiasis may be demonstrated in affected tissues.
- With hemorrhagic colitis due to invasive amebiasis, sigmoidoscopy may be diagnostic.
- Upper intestinal endoscopy can yield fluid to be examined for G. lamblia trophozoites and S. stercoralis larvae.
Test Interpretation
- Most intestinal parasites are not invasive and produce few changes in bowel histology.
- Invasive amebiasis produces a classic endoscopic and histologic picture of colonic ulceration and inflammation.
- Protozoa or helminths may be seen on bowel biopsy.
TREATMENT
Select specific antiparasitic treatment based on patient history, parasite biology, and epidemiology.
GENERAL MEASURES
- Not all patients need drug therapy.
- Symptomatic treatment is indicated for patient comfort once specific therapy has been initiated.
- Drugs inhibiting intestinal motility are relatively contraindicated in patients with diarrhea caused by invasive organisms.
MEDICATION
- Protozoa (5)[A]
- E. histolytica: Asymptomatic infection may not require drug therapy.
- Symptomatic intestinal E. histolytica: iodoquinol or diloxanide furoate
- Invasive E. histolytica: iodoquinol or diloxanide furoate plus metronidazole alone or metronidazole alone or emetine + chloroquine phosphate
- G. lamblia: metronidazole or tinidazole or furazolidone or quinacrine. Note: Albendazole, available in the United States only from manufacturer, may have activity against G. lamblia.
- Cryptosporidium: none proven effective
- C. belli protozoa: trimethoprim-sulfamethoxazole
- B. coli: tetracycline or iodoquinol or metronidazole
- Cyclospora: sulfamethoxazole-trimethoprim
- Microsporidia: albendazole (some species)
- Helminths
- Nematodes (except Strongyloides and Trichostrongylus): mebendazole or pyrantel pamoate or piperazine citrate or albendazole (available in the United States only from manufacturer)
- Strongyloides and Trichostrongylus: thiabendazole or albendazole (available in the United States only from manufacturer)
- Cestodes: praziquantel or niclosamide
- Trematodes: niclosamide or praziquantel
Pediatric Considerations
Giardia: Nitazoxanide 7.5 mg/kg PO BID for 3 days or single-dose tinidazole 50 mg/kg (not available in the United States) may be used.
ISSUES FOR REFERRAL
Consultation with specialist in tropical medicine or infectious diseases for treatment failures, complex patients (including drug intolerances or allergies), multiple parasitic infections, and complicated medical (e.g., HIV/AIDS, diabetes, chronic steroid use) patients. Surgical consultation as indicated for obstruction or hepatic abscess
COMPLEMENTARY & ALTERNATIVE MEDICINE
Many complementary and alternative therapies exist, but none are proven effective for primary treatment.
SURGERY/OTHER PROCEDURES
Surgical procedures play little role, except for amebic liver abscesses, which may need to be drained or for bowel obstruction
INPATIENT CONSIDERATIONS
Nosocomial intestinal parasitic infections are rare, as are hospital-based parasitic GI outbreaks.
Admission Criteria/Initial Stabilization
Admission is rarely required except for intestinal obstruction, dysentery, or systemic invasion.
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Patient Monitoring
- For most intestinal parasitic infections, testing for clearance is not indicated. If performed, repeat stool examination for clearance should be timed, taking into account the life cycle of the parasite and the risk of reinfection.
- Consequences of intestinal parasitic infections include lactose intolerance, irritable bowel syndrome, or nutritional calorie-protein deficiencies, dehydration, and vitamin B12 deficiency.
DIET
Many patients experience symptoms of irritable bowel syndrome and/or lactose intolerance during and following bowel infections, especially with G. lamblia.
PATIENT EDUCATION
Personal hygiene and proper food/water sanitation is important to reduce the risk of reinfection or transmission.
COMPLICATIONS
Complications are rare; they include chronic persistent diarrhea, irritable bowel syndrome, and chronic malabsorption (6)[A].
REFERENCES
11 Mahmud MA, Spigt M, Bezabih AM, et al. Efficacy of handwashing with soap and nail clipping on intestinal parasitic infections in school-aged children: a factorial cluster randomized controlled trial. PLoS Med. 2015;12(6):e1001837.22 Feary J, Britton J, Leonardi-Bee J. Atopy and current intestinal parasite infection: a systematic review and meta-analysis. Allergy. 2011;66(4):569-578.33 Strand EA, Robertson LJ, Hanevik K, et al. Sensitivity of a Giardia antigen test in persistent giardiasis following an extensive outbreak. Clin Microbiol Infect. 2008;14(11):1069-1071.44 Senay H, MacPherson D. Parasitology: diagnostic yield of stool examination. CMAJ. 1989;140(11):1329-1331.55 Drugs for parasitic infections. In: The Medical Letter. On Drugs and Therapeutics. 3rd ed. New York, NY: The Medical Letter; 2013. http://secure.medicalletter.org/para.66 Bartelt LA, Sartor RB. Advances in understanding Giardia: determinants and mechanisms of chronic sequelae. F1000Prime Rep. 2015;7:62.
ADDITIONAL READING
- Cama VA, Mathison BA. Infections by intestinal Coccidia and Giardia duodenalis. Clin Lab Med. 2015;35(2):423-444.
- Centers for Disease Control and Prevention. Parasites. http://www.cdc.gov/parasites/az/index.html.
- Escobedo AA, Alvarez G, Gonz Ħlez ME, et al. The treatment of giardiasis in children: single-dose tinidazole compared with 3 days of nitazoxanide. Ann Trop Med Parasitol. 2008;102(3):199-207.
- van Lieshout L, Verweij JJ. Newer diagnostic approaches to intestinal protozoa. Curr Opin Infect Dis. 2010;23(5):488-493.
SEE ALSO
Algorithm: Hematemesis (Bleeding, Upper GI)
CODES
ICD10
- B82.9 Intestinal parasitism, unspecified
- A07.9 Protozoal intestinal disease, unspecified
- B82.0 Intestinal helminthiasis, unspecified
- B80 Enterobiasis
- B71.9 Cestode infection, unspecified
- B66.9 Fluke infection, unspecified
- B76.9 Hookworm disease, unspecified
ICD9
- 129 Intestinal parasitism, unspecified
- 007.9 Unspecified protozoal intestinal disease
- 127.9 Intestinal helminthiasis, unspecified
- 127.4 Enterobiasis
- 126.9 Ancylostomiasis and necatoriasis, unspecified
- 123.9 Cestode infection, unspecified
- 121.9 Trematode infection, unspecified
SNOMED
- Intestinal parasitism (disorder)
- Protozoal intestinal disease (disorder)
- infection due to Class Cestoda and/or Class Trematoda and/or Phylum Nemata (disorder)
- Enterobiasis (disorder)
- Disease due to Nematoda
- Disease due to superfamily Ancylostomatoidea (disorder)
- trematode infection (disorder)
- Cestode infection (disorder)
CLINICAL PEARLS
- GI parasites are relatively common in patients presenting GI symptom and a relevant history of travel, recent immigration, daycare, chronic diarrhea, or visible presence of worms in the stool.
- Properly collected stool specimens detect most intestinal parasites. Exceptions include S. stercoralis, E. vermicularis, Cryptosporidium, Cyclospora, and Microspora sp.
- Eosinophilia is not reliable to screen for intestinal parasites.