Gastrointestinal parasites – an overview
- Gastrointestinal parasitic infections are most common where poor water quality, inadequate sanitation and overcrowding are present.
- Infection rates are highest in children who live in or travel from sub-Saharan Africa, Asia, Latin America and the Caribbean.
- Children with gastrointestinal parasitic infections may have no symptoms or they may experience vomiting and/or diarrhea, failure to thrive and other signs and symptoms, depending on the cause.
- Infection with gastrointestinal parasites can cause malabsorption, malnutrition and resultant stunting, and chronic anemia, conditions which may affect a child’s physical and cognitive development.
- Stool examinations for ova and parasites sometimes yield false-negative results. Rapid diagnostic tests, including polymerase chain reaction (PCR)-based tests on the stool, have been developed for certain parasites.
- Treatment of parasites can improve growth and nutritional status, but licensed treatment options are limited. Some infections require drugs that are only available in Canada through Health Canada’s Special Access Programme.
- Screening with serologic tests for Schistosoma species is recommended for refugees and immigrants newly arrived from endemic areas, such as Africa. If results are positive, treatment is recommended even if a child or youth is asymptomatic.
- Screening with serologic tests for Strongyloides stercoralis, is recommended for refugees and immigrants newly arriving from endemic areas, such as Southeast Asia and Africa. If results are positive, treatment is recommended even if a child or youth is asymptomatic.
- No vaccines are available to prevent gastrointestinal parasitic infections.
Giardia and soil-transmitted parasitic helminth (worm) infections from Strongyloides and Schistosoma species are common infections in refugee populations. Some 2 billion people around the world are infected with worms, such as Ascaris lumbricoides (a roundworm), Trichuris trichiura (whipworm) and Necator americanus and Ancylostoma duodenale (hookworms). An estimated 200 million people are infected with Schistosoma species and 100 million with Strongyloides stercoralis.1 Although often asymptomatic or subclinical, these infections can also cause significant illness and even death. Coinfection with multiple gastrointestinal parasites is common in children from high-risk areas.
Knowing about the intestinal parasites prevalent in different high-risk areas of the world can help the clinician to request appropriate screening tests (Table 1). When the microbiology laboratory reports the results of parasites in the stool, Table 2 can assist with prescribing appropriate antiparasitic therapy for different types of pathogenic parasites. Nonpathogenic parasites do not require antiparasitic therapy. (See Treatment recommendations below.)
|All areas||Africa||Asia||Latin America||Middle East||Eastern Europe|
Most protozoa, especially Giardia intestinalis (lamblia)
Taenia saginata (tapeworm, especially in Ethiopia and Eritrea)
Southeast Asia: Opisthorchis viverrini
South Asia: Taenia solium (pork tapeworm)
Source: CDC, November 2013. Intestinal parasite guidelines for domestic medical examination of newly arrived refugees.
Hookworm (Necator americanus & Ancylostoma)
Trichuris trichiura Strongyloides stercoralis
(S. mansoni, S. haematobium,
Other flukes (Ophisthorchis spp.)
Fasciola, Paragonimus westermani)
|Taenia solium Taenia. saginatum Hymenolepis nana||Entamoeba histolytica*|
Giardia intestinalis (also known as G. lamblia or G. duodenalis)
|Dientamoeba fragilis (diarrhea)|
Entamoeba polecki (diarrhea)
|Blastocystis hominis (diarrhea)||Entamoeba dispar*|
*The cysts of E. histolytica, E. dispar and E. moshkowskii look identical under the microscope. When cysts are detected, stool antigen testing is recommended to distinguish the potentially pathogenic E. histolytica from more common, nonpathogenic species.
|Source: CDC, November 2013. Intestinal parasite guidelines for domestic medical examination of newly arrived refugees.|
More information about common parasitic infections, along with suggested therapies for newcomer children and adolescents, are available in this resource:
Who should be screened?
Although children are at higher risk than adults for intestinal parasites,2 routine screening for these infections in children or in adults has not been part of the required medical examination for new immigrants and refugees to Canada. Also, current recommendations tend to focus on the screening of refugees rather than on immigrants generally.3-5 In 2011, 21% of refugees screened in Minnesota had at least one intestinal parasite, with the highest prevalence in people from Southeast Asia, at 25%. Health authorities there recommended that all refugees should be screened for parasitic infections, even if they were asymptomatic.
Their recommendations included:3
- Blood testing for Schistosoma in refugees and immigrants newly arrived from highly endemic areas, especially in Africa. If results are positive, treatment is recommended even if a child is asymptomatic.
- Blood testing for Strongyloides in refugees and immigrants newly arrived from highly endemic areas, especially in Southeast Asia and Africa. If results are positive, treatment is recommended even if a child is asymptomatic. If a patient has eosinophilia (blood eosinophil count >500/mL), this should be investigated. See Table 3 and the section below.
- Stool examinations for ova and parasites may yield false-negative results. Rapid diagnostic tests, including PCR-based stool tests to detect parasites such as E. histolytica, Cryptosporidium and Giardia are starting to become available in Canada.6
Eosinophilia (blood eosinophil count >500/mL) detected on a complete blood count in asymptomatic or symptomatic newcomers may indicate infection with the soil-transmitted helminthes Strongyloides or Schistosoma. However, Table 3 shows other parasitic and nonparasitic causes that a health care provider should consider.
|Parasites commonly found in stool that cause eosinophilia||Other parasites usually not found in stool that are associated with eosinophilia||Parasites commonly found in stool that are NOT associated with eosinophilia||Nonparasitic causes of eosinophilia|
Entamoeba (e.g., E. histolytica, E. dispar)
|*For these parasites, special testing and/or multiple samples are often needed to establish diagnosis.|
Source: Adapted from CDC, November 2013. Intestinal parasite guidelines for domestic medical examination of newly arrived refugees.
Many protozoan parasites are nonpathogenic and do not require treatment (Table 2). However, their presence indicates that the newcomer patient spent some time in areas where poor sanitation and fecal-oral contamination were common.
Individuals found to have pathogenic parasites when tested (e.g., amebiasis, strongyloidiasis, schistosomiasis), whether they are symptomatic or not, should be treated to minimize long-term complications.5
Consultation with a specialist in paediatric infectious diseases or tropical medicine is recommended for:
- Treating organisms that can persist and cause chronic disease (e.g., strongyloidiasis, schistosomiasis and foodborne trematodes [flukes]).
- Infections requiring medication from Health Canada’s Special Access Programme.
- Patients diagnosed with serious infections such as neurocysticercosis (pork tapeworm, which can involve the brain or spinal cord). These are urgent cases, and specialist consultation is needed to navigate the risks and benefits of medical management.
Health Canada’s Special Access Programme
Practitioners can obtain drugs that are unavailable for sale in Canada through SAP, Health Canada’s Special Access Programme. The program provides access to therapies for patients with serious medical conditions on an emergency basis. More information on the program, along with application forms, are available on Health Canada’s website.
For more information on treatments for children and adolescents with parasitic infections, read:
- Nematodes (roundworms)
- Trematodes (flukes)
- Cestodes or tapeworms
- Pathogenic protozoa and coccidia
No vaccines are available to prevent gastrointestinal parasitic infections.
Since 2001, the World Health Organization has recommended periodic preventive chemotherapy with albendazole or mebendazole to treat soil-transmitted helminths. Subsequent treatments with ivermectin (for Strongyloides) and praziquantal (for schistosomiasis) in school-aged children or for entire communities at risk in endemic areas are also recommended.6
The United States and Australia provide predeparture antiparasitic treatment for refugees from high risk areas. One study of nearly 27,000 African and Southeast Asian refugees clearly showed that treatment with single-dose albendazole significantly reduced the prevalence of any soil-transmitted helminth from 20.8% to 4.7%. This treatment also reduced nematode infections (ascariasis and hookworm) by 77%, though it has little or no effect against protozoal infections (Giardia), S. stercoralis, Schistosoma spp. or tapeworms.1,5,7
The CDC has developed an algorithm to help clinicians manage gastrointestinal parasites in newcomers who have received no treatment before immigrating.1
Gastrointestinal parasitic infections in immigrant and refugee children provides more detailed information related to screening and treatment in Canada.
- Australasian Society for Infectious Diseases. Diagnosis, management and prevention of infections in recently arrived refugees. Sydney, NSW: Dreamweaver, 2009.
- Banerji A, Li P, Navaranjan D. The health and nutritional status of new refugee, immigrant, and uninsured children in Toronto, Canada. CERIS, The Ontario Metropolis Centre, Research Summary October 2012.
- Bradley JS, Nelson JD, Kimberlin DW, et al. 2014 Nelson’s Pediatric Antimicrobial Therapy, 20th edn. Elk Grove Village, IL: American Academy of Pediatrics, 2014.
- Centers for Disease Control and Prevention (U.S.)
- Cherry JD, Demmler-Harrison GJ, Kaplan SL, et al, eds. Feigin and Cherry’s Textbook of Pediatric Infectious Diseases, 7th edn. Philadelphia, PA: Elsevier, 2014.
- Daly R, Chiodini PL. Laboratory investigations and diagnosis of tropical diseases in travelers. Infect Dis Clin North Am 2012;26(3): 803-18.
- Furst T, Keiser J, Utzinger J. Global burden of human foodborne trematodiasis: A systematic review and meta-analysis.Lancet Infect Dis 2012;12(3):210-21.
- Gryseels B. Schistosomiasis. Infect Dis Clin North Am 2012;26 (2):383-97.
- Harhay MO, Horton J, Olliaro PL. Epidemiology and control of human gastrointestinal parasites in children. Expert Rev Anti Infect Ther 2010;8(2):219-34.
- King CH, Dangerfield-Cha M. The unacknowledged impact of chronic schistosomiasis. Chronic Illn 2008;4(1):65-9.
- Manganelli L, Berrilli F, Di Cave D, et al. Intestinal parasite infections in immigrant children in the city of Rome, related risk factors and possible impact on nutritional status. Parasit Vectors 2012,5:265.
- Muennig P, Pallin D, Sell RL, et al. The cost effectiveness of strategies for the treatment of intestinal parasites in immigrants. N Engl J Med 1999;340(10):773-9.
- Pickering LK, Baker CJ, Kimberlin DW, et al, eds. Red Book: 2012 Report of the Committee on Infectious Diseases, 29th edn. Elk Grove Village, IL: American Academy of Pediatrics: 194-5, 239-40, 333-5, 411-3, 453-4, 532-3, 537, 643-5, 689-90, 731-2, 848-68.
- Pottie K, Greenaway C, Feightner J, et al. Evidence-based clinical guidelines for immigrants and refugees. Chapter 10: Intestinal parasites: Strongyloides and Schistosoma. CMAJ 2011;283(12):E865-8: www.cmaj.ca/content/183/12/E824.full.pdf+html.
- Public Health Agency of Canada, CATMAT. Statement on persistent diarrhea in the returned traveller. CCDR, February 15, 2006;32(ACS-1).
- Sripa B. Global burden of foodborne trematodiasis. Lancet Infecti Dis 2012;12(3):171-2.
- Staat MA, Rice M, Donauer S, et al. Intestinal parasite screening in internationally adopted children: Importance of multiple stool specimens. Pediatrics 2011;128(3):e613-22.
- World Health Organization
- Working to overcome the global impact of neglected tropical diseases – First WHO report, 2010
- Working to overcome the global impact of neglected tropical diseases – Update 2011
- Soil-transmitted helminthes. Fact sheet 366.
- Action against worms
- Foodborne trematodiases. Fact sheet 368.
- Preventive chemotherapy in human helminthiasis: Coordinated use of anthelminthic drugs in control interventions; a manual for health professionals and programme managers. 2006
- Schistosomiasis. Fact sheet 115.
- World Health Organization. World Health Day 2014: Preventing vector-borne diseases.
- Wright SG. Protozoan infections of the gastrointestinal tract. Infect Dis Clin North Am 2012;26(2):323-40.
- Zouré HG, Wanji S, Noma M, et al. The geographic distribution of Loa loa in Africa: Results of large-scale implementation of the Rapid Assessment Procedure for Loiasis (RAPLOA). PLoS Negl Trop Dis 2011;5(6):e1210.
- U.S. Department of Health and Human Services, Centers for Disease Control and Prevention (National Center for Emerging and Zoonotic Infectious Diseases), November 6, 2013. Intestinal parasite guidelines for domestic medical examination of newly arrived refugees: Presumptive treatment and screening for Strongyloidiasis, Schistosomiasis and infections caused by soil-transmitted helminths for refugees, Division of Global Migration and Quarantine: www.cdc.gov/immigrantrefugeehealth/pdf/intestinal-parasites-domestic.pdf
- Pottie K, Greenaway C, Feightner J, et al. Evidence-based clinical guidelines for immigrants and refugees. Appendix 8: Khan K, Heidebrecht C, Sears J, et al; Canadian Collaboration for Immigrant and Refugee Health (CCIRH). Intestinal parasites – Strongyloides and Schistosoma: Evidence review for newly arriving immigrants and refugees: www.cmaj.ca/lookup/suppl/doi:10.1503/cmaj.090313/-/DC1.
- Minnesota Department of Health. Minnesota refugee health provider guide 2013: Parasitic infections: www.health.state.mn.us/divs/idepc/refugee/guide/7parasites.html
- Boggild AK, Yohanna S, Keystone JS, Kain KC. Prospective analysis of parasitic infections in Canadian travelers and immigrants. J Travel Med 2006;13(3):138-44.
- Swanson SJ, Phares CR, Mamo B, et al. Albendazole therapy and enteric parasites in United States-bound refugees. N Engl J Med 2012;366(16):1498-507.
- Knopp S, Steinmann, Keiser J, Utzinger J. Nematode infections: Soil-transmitted helminths and trichinella. Inf Dis Clin North Am 2012;26(2):341-58.
- U.S. Department of Health and Human Services, Centers for Disease Control and Prevention (National Center for Emerging and Zoonotic Infectious Diseases, Division of Global Migration and Quarantine), September 17, 2013. Guidelines for overseas presumptive treatment of strongyloidiasis, schistosomiasis, and soil-transmitted helminth infections for refugees resettling to the United States: www.cdc.gov/immigrantrefugeehealth/pdf/intestinal-parasites-overseas.pdf
Heather Onyett, MD
Last updated: April, 2018