Further Outpatient Care

Symptoms usually resolve within 3-4 days after initiation of antiprotozoal therapy in immunocompetent patients with protozoal gastroenteritis. Nevertheless, especially in cases of giardiasis, patients should be monitored with a repeat stool examination if symptoms reappear.

In amebic liver abscess, ultrasonographic abnormalities can persist for months, and another ultrasound is usually not recommended after successful completion of therapy.

Further Inpatient Care

Patients with either necrotizing colitis or liver abscess caused by E histolytica may require further inpatient care only if surgical procedures were performed.

Patients with AIDS or other immunodeficiencies who have spore-forming protozoal infections may require prolonged hospitalization to correct electrolyte imbalance or accompanying conditions.

Inpatient medications

Intravenous medications are indicated only in cases of severe amebic or balantidic colitis or in patients with amebic liver abscess.

Intravenous metronidazole with or without intramuscular dehydroemetine can be used until the patient can start oral therapy.

In some patients with AIDS and in unusual cases in immunocompetent hosts, hospitalization is required, and intravenous solutions are indicated to correct electrolyte imbalance.

Outpatient medications

Oral antiprotozoal therapy is usually administered at home.

Deterrence/Prevention

Standard hospital precautions are used for all hospitalized patients.

Additional control precautions are implemented for children with gastroenteritis, especially for patients using diapers or who have incontinence. This includes use of gowns and gloves for patient care, and hands must be washed after contact. A single room is indicated, if possible.

Prevention of exposure in persons infected with HIV consists in the following:^[26]

Avoid contact with human and animal feces.
Request a veterinarian to examine the stools for Cryptosporidium in puppies or kittens younger than 6 months.
Avoid exposure to calves and lambs.
Avoid drinking water from lakes or rivers.

No chemoprophylactic agents are available for any of these diseases.

Protozoan parasites can survive under ambient and refrigerated storage conditions when associated with a range of substrates. Consequently, various treatments have been used to inactivate protozoan parasites in food, water, and environmental systems. Ozone is a more effective chemical disinfectant than chlorine or chlorine dioxide for inactivation of protozoan parasites in water systems. However, sequential inactivation treatments can optimize existing methods through synergistic effects.

Vaccination

Cryptosporidiosis

Several Cryptosporidium sporozoite antigens have been identified as potential vaccine candidates using traditional methods such as analysis of serum specificities after Cryptosporidium infection.^[27]However, despite the considerable amount of structural and immunological data obtained from characterizations of multiple sporozoite surface antigens, a vaccine is not yet available.

A “reverse vaccinology” strategy using in silico analyses based on the genome sequence information of the organism represents a novel approach to identifying vaccinogens. This approach is particularly useful in organisms like Cryptosporidium, which are difficult to cultivate continuously in the laboratory. The strategy is based on the ability to predict proteins that are associated with the parasite surface and therefore have the potential for interaction with the host immune mechanisms, by in silico screening for signal peptides, glycosylphosphatidylinositol (GPI) signal anchors, and similarities with known pathogenic factors. This strategy has identified 3 promising Cryptosporidium vaccinogens that induce strong humoral and cellular immune responses, although these potential vaccines are still under investigation.

Amebiasis

Vaccinations using native and recombinant forms of the parasite Gal-lectin have been successful in protecting animals against intestinal amebiasis and amebic liver abscess. To date, this immunological approach holds the most promise, but clinical trials are required to validate its efficacy in humans.^[28]

Giardiasis

By the year 2000, a Giardia vaccine was available in the United States for prevention of clinical signs of giardiasis and reduction of cyst shedding in dogs and cats. The vaccine is based on the current state of knowledge of Giardia antigenicity and immunology. However, studies done in humans are still ongoing.^[29]

Matthys B, Bobieva M, Karimova G, Mengliboeva Z, Jean-Richard V, Hoimnazarova M, et al. Prevalence and risk factors of helminths and intestinal protozoa infections among children from primary schools in western Tajikistan. Parasit Vectors. 2011 Oct 7. 4:195. [QxMD MEDLINE Link]. [Full Text].
Alyousefi NA, Mahdy MA, Mahmud R, Lim YA. Factors associated with high prevalence of intestinal protozoan infections among patients in Sana'a City, Yemen. PLoS One. 2011. 6(7):e22044. [QxMD MEDLINE Link]. [Full Text].
Sargeaunt PG, Jackson TFGH, Simjee AE. Biochemical homogeneity of Entamoeba histolytica isolates, especially those from liver abscess. Lancet. 1982. 1:1386-8. [QxMD MEDLINE Link].
Carranza PG, Lujan HD. New insights regarding the biology of Giardia lamblia. Microbes Infect. 2009 Sep 20. [QxMD MEDLINE Link].
Muller N, von Allmen N. Recent insights into the mucosal reactions associated with Giardia lamblia infections. Int J Parasitol. Nov 2005. 35:1339-47. [QxMD MEDLINE Link].
Karanis P, Kourenti C, Smith H. Waterborne transmission of protozoan parasites: a worldwide review of outbreaks and lessons learnt. J Water Health. Mar 2007. 5:1-38. [QxMD MEDLINE Link].
Hunter PR, Thompson RC. The zoonotic transmission of Giardia and Cryptosporidium. Int j Parasitol. Oct 2005. 35:1181-90. [QxMD MEDLINE Link].
Fleming CA, Caron D, Gunn JE, Barry MA. A foodborne outbreak of Cyclospora cayetanensis at a wedding: clinical features and risk factors for illness. Arch Intern Med. 1998 May 25. 158(10):1121-5. [QxMD MEDLINE Link].
Huang P, Weber JT, Sosin DM, et al. The first reported outbreak of diarrheal illness associated with Cyclospora in the United States. Ann Intern Med. 1995 Sep 15. 123(6):409-14. [QxMD MEDLINE Link].
Kashyap B, Sinha S, Das S, Rustagi N, Jhamb R. Efficiency of diagnostic methods for correlation between prevalence of enteric protozoan parasites and HIV/AIDS status--an experience of a tertiary care hospital in East Delhi. J Parasit Dis. 2010 Oct. 34(2):63-7. [QxMD MEDLINE Link]. [Full Text].
Vandenberg O, Peek R, Souayah H, et al. Clinical and microbiological features of dientamoebiasis in patients suspected of suffering from a parasitic gastrointestinal illness: a comparison of Dientamoeba fragilis and Giardia lamblia infections. Int J Infect Dis. 2006 May. 10(3):255-61. [QxMD MEDLINE Link].
Graczyk TK, Shiff CK, Tamang L, et al. The association of Blastocystis hominis and Endolimax nana with diarrheal stools in Zambian school-age children. Parasitol Res. 2005 Dec. 98(1):38-43. [QxMD MEDLINE Link].
Ertug S, Karakas S, Okyay P, Ergin F, Oncu S. The effect of Blastocystis hominis on the growth status of children. Med Sci Monit. Jan 2007. 13:CR40-3. [QxMD MEDLINE Link].
Arellano J, Perez-Rodriguez M, Lopez-Osuna M, et al. Increased frequency of HLA-DR3 and complotype SCO1 in Mexican mestizo children with amoebic abscess of the liver. Parasite Immunol. 1996 Oct. 18(10):491-8. [QxMD MEDLINE Link].
Gupta S, Smith L, Diakiw A. Amebiasis and Amebic Liver Abscess in Children. Pediatr Clin North Am. 2022 Feb. 69 (1):79-97. [QxMD MEDLINE Link].
Tomczak E, McDougal AN, White AC Jr. Resolution of Cryptosporidiosis in Transplant Recipients: Review of the Literature and Presentation of a Renal Transplant Patient Treated With Nitazoxanide, Azithromycin, and Rifaximin. Open Forum Infect Dis. 2022 Jan. 9 (1):ofab610. [QxMD MEDLINE Link]. [Full Text].
Lawrence DN, Neel JV, Abadie SH, et al. Epidemiologic studies among Amerindian populations of Amazonia. III. Intestinal parasitoses in newly contacted and acculturating villages. Am J Trop Med Hyg. 1980 Jul. 29(4):530-7. [QxMD MEDLINE Link].
Sarabia-Arce S, Salazar-Lindo E, Gilman RH, et al. Case-control study of Cryptosporidium parvum infection in Peruvian children hospitalized for diarrhea: possible association with malnutrition and nosocomial infection. Pediatr Infect Dis J. 1990 Sep. 9(9):627-31. [QxMD MEDLINE Link].
Wichro E, Hoelzl D, Krause R, et al. Microsporidiosis in travel-associated chronic diarrhea in immune-competent patients. Am J Trop Med Hyg. 2005 Aug. 73(2):285-7. [QxMD MEDLINE Link].
Osewe P, Addiss DG, Blair KA, et al. Cryptosporidiosis in Wisconsin: a case-control study of post-outbreak transmission. Epidemiol Infect. 1996 Oct. 117(2):297-304. [QxMD MEDLINE Link].
Hunter PR, Hughes S, Woodhouse S, et al. Health sequelae of human cryptosporidiosis in immunocompetent patients. Clin Infect Dis. 2004 Aug 15. 39(4):504-10. [QxMD MEDLINE Link].
Blanshard C, Jackson AM, Shanson DC, Francis N, Gazzard BG. Cryptosporidiosis in HIV-seropositive patients. Q J Med. 1992 Nov-Dec. 85(307-308):813-23. [QxMD MEDLINE Link].
El-Shazly AM, Abdel-Magied AA, El-Beshbishi SN, et al. Blastocystis hominis among symptomatic and asymptomatic individuals in Talkha Center, Dakahlia Governorate, Egypt. J Egypt Soc Parasitol. 2005 Aug. 35(2):653-66. [QxMD MEDLINE Link].
Duggan C, Santosham M, Glass RI. The management of acute diarrhea in children: oral rehydration, maintenance, and nutritional therapy. Centers for Disease Control and Prevention. MMWR Recomm Rep. 1992 Oct 16. 41(RR-16):1-20. [QxMD MEDLINE Link].
Rossignol JF, Kabil SM, Said M, Samir H, Younis AM. Effect of nitazoxanide in persistent diarrhea and enteritis associated with Blastocystis hominis. Clin Gastroenterol Hepatol. Oct 2005. 3:987-91. [QxMD MEDLINE Link].
[Guideline] US Public Health Service and Infectious Diseases Society of America. 1999 USPHS/IDSA guidelines for the prevention of opportunistic infections in persons infected with human immunodeficiency virus. MMWR Recomm Rep. 1999 Aug 20. 48(RR-10):1-59, 61-6. [QxMD MEDLINE Link].
Manque PA, Tenjo F, Woehlbier U, Lara AM, Serrano MG, Xu P, et al. Identification and immunological characterization of three potential vaccinogens against Cryptosporidium species. Clin Vaccine Immunol. 2011 Nov. 18(11):1796-802. [QxMD MEDLINE Link]. [Full Text].
Quach J, St-Pierre J, Chadee K. The future for vaccine development against Entamoeba histolytica.. Hum Vaccin Immunother. 2014 Feb 6. 10(6):[QxMD MEDLINE Link].
Olson ME, Ceri H, Morck DW. Giardia vaccination. Parasitol Today. 2000 May. 16(5):213-7. [QxMD MEDLINE Link].
Abubakar I, Aliyu SH, Arumugam C, Hunter PR, Usman NK. Prevention and treatment of cryptosporidiosis in immunocompromised patients. Cochrane Database Syst Rev. Jan 2007. 24:CD004932. [QxMD MEDLINE Link].
Farthing MJ. Treatment options for the erradication of intestinal protozoa. Nat Clin Pract Gastroenterol Hepatol. Aug 2006. 3:436-45. [QxMD MEDLINE Link].
Hussein EM, El-Moamly AA, Dawoud HA, et al. Real-time PCR and flow cytometry in detection of Cyclospora oocysts in fecal samples of symptomatic and asymptomatic pediatrics patients. J Egypt Soc Parasitol. 2007 Apr. 37(1):151-70. [QxMD MEDLINE Link].
Shlim DR, Hoge CW, Rajah R, et al. Is Blastocystis hominis a cause of diarrhea in travelers? A prospective controlled study in Nepal. Clin Infect Dis. 1995 Jul. 21(1):97-101. [QxMD MEDLINE Link].
Granados CE, Reveiz L, Uribe LG, Criollo CP. Drugs for treating giardiasis. Cochrane Database Syst Rev. 2012 Dec 12. 12:CD007787. [QxMD MEDLINE Link].

Media Gallery

This micrograph stained with chlorazol black, revealed an Entamoeba histolytica cyst.
This is a scanning electron micrograph (SEM) of an in vitro Giardia lamblia culture. This photograph contains both trophozoites and a cluster of maturing cysts (bottom right). At far left, the 2 trophozoite-staged organisms are positionally situated opposite to one another, with the farthest left G lamblia displaying its dorsal, or upper surface, and the protozoan to its immediate right, its ventral, or bottom surface.
This photomicrograph revealed the morphologic details of Cryptosporidium parvum oocysts.
This is an illustration of the life cycle of Isospora belli, the causal agent of isosporiasis.
This photomicrograph of a fresh stool sample, which had been prepared using a 10% formalin solution, and stained with safranin, revealed the presence of 3 uniformly stained Cyclospora cayetanensis oocysts in the field of view.

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Table 1. Protozoa Associated with Intestinal Illness in Humans

Name	Mode of Transmission	Symptoms
Flagellates
G lamblia	Contaminated water, fecal-oral	Nausea, bloating, gas, diarrhea, anorexia
Dientamoeba fragilis	Fecal-oral, associated with Enterobius	Previously thought commensal; may cause diarrhea, abdominal, pain, nausea
Amebas
Entamoeba histolytica	Contaminated water, fecal-oral, contaminated food	Colitis, dysentery, diarrhea, liver abscess, other extraintestinal disease
Spore-forming (Coccidia)
Cryptosporidium parvum	Contaminated water, swimming pools, fecal-oral	Immunocompetent patients: Self-limited diarrhea Immunosuppressed patients: Severe and interminable diarrhea
Isospora belli	Fecal-oral	Same as in Cryptosporidium
Cyclospora cayetanensis	Fecal-oral, contaminated water and food	Same as in Cryptosporidium
Microsporidia (Septata intestinalis, Enterocytozoon bieneusi)	Fecal-oral, contaminated water	Same as in Cryptosporidium
Ciliates
Balantidium coli	Fecal-oral (frequently associated with pigs)	Colitis, diarrhea
Other
Blastocystis hominis	Fecal-oral	May cause mild diarrhea

Table.

Organism	Size (mm)	Stain Used	Other Tests
E histolytica	Trophozoite: 10-60 Cyst: 10-20	Wet mount,* trichrome, periodic Schiff	Enzyme-linked immunosorbent assay (ELISA)
G lamblia	Trophozoite: 9-21 Cyst: 7-12	Wet mount,* trichrome, hematoxylin, Lugol	ELISA*
C parvum	2-5	Modified acid-fast,* auramine-rhodamine, Sheafer method	ELISA*
I belli	30x12	Wet mount,* modified acid-fast*	None
C cayetanensis	8-10	Modified acid-fast,* wet mount	Electron microscopy
Microsporidia	1-2	Modified trichrome*	Electron microscopy, fluorescence methods, small intestine biopsy
D fragilis	7-12	Iron hematoxylin,* trichrome*	None
B. coli	50-200	Wet mount,* concentration techniques	None
B hominis	5-30	Trichrome,* iron hematoxylin*	None
*Preferred screening test in clinical settings.

Table 3. Specific Therapy for Intestinal Protozoal Infections

Organism	Drugs, Pediatric Dose, and Treatment Duration
E histolytica (Luminal disease or colonization)	Iodoquinol: 40 mg/kg/d PO divided tid for 20 d; not to exceed 2 g/d
E histolytica (Luminal disease or colonization)	Paromomycin: 25-30 mg/kg/d PO divided tid for 7 d
E histolytica (Moderate colitis)	Metronidazole: 50 mg/kg/d PO divided tid for 10 d
E histolytica (Moderate colitis)	Tinidazole: 50 mg/kg/d PO for 3 d; not to exceed 2 g/d
E histolytica (Severe colitis or liver abscess)	Metronidazole: 50 mg/kg/d PO divided tid for 10 d
	Dehydroemetine*: 1-1.5 mg/kg/d divided bid PO for 5 d
	Tinidazole†: 50 mg/kg/d PO for 3-5 d; not to exceed 2 g/d
G lamblia	Tinidazole: 50 mg/kg/d PO once; not to exceed 2 g/dose
	Metronidazole: 15-20 mg/kg/d PO divided tid for 5
	Albendazole: 15 mg/k/d (not exceed 400 mg) PO q24 h, for 5-7 days
	Furazolidone: 6 mg/kg/d PO divided qid for 7-10 d
	Paromomycin: 40 mg/kg/d PO divided tid for 7 d
	Nitazoxanide: 200-400 mg/d PO divided bid for 3 d
D fragilis	Iodoquinol: 50 mg/kg/d PO divided tid for 20 d; not to exceed 2 g/d
	Paromomycin: 30 mg/kg/d PO divided tid for 7 d
	Tetracycline: 40 mg/kg/d PO divided qid for 10 d; not to exceed 2 g/d
C parvum§	Paromomycin*: 30 mg/kg/d PO divided tid (duration unknown)
C parvum§	Nitazoxanide: 200-400 mg/d PO divided bid for 3 d
I belli	Trimethoprim/sulfamethoxazole (TMP/SMZ): 20/100 mg/kg/d PO divided bid for 10 d, followed by 10/50 mg/kg/d PO divided bid for 21 d
C cayetanensis	TMP/SMZ: 10/50 mg/kg/d PO divided bid for 3 d
Microsporidia S intestinalis	Albendazole* (adult dose): 800 mg/d PO divided bid
Microsporidia E bieneusi	No treatment recommended; albendazole may decrease the number of organisms
B coli	Tetracycline: 40 mg/kg/d PO divided qid for 10 d; not to exceed 2 g/d
	Metronidazole: 35-50 mg/kg/d PO divided tid for 5 d
	Iodoquinol: 40 mg/kg/d PO divided tid for 20 d
B hominis	Metronidazole: 35-50 mg/kg/d PO divided tid for 10 d
	Iodoquinol: 40 mg/kg/d PO divided tid for 20 d
	Nitazoxanide\|\|: 500 mg/d PO divided bid for 3 d
*Efficacy is unknown. †Drug is available from the CDC Drug Service (phone: 404-639-3670; evenings, weekends, and holidays: 404-639-2888). ‡ Drug is not available in the United States. §Recommended regimens are indicated only in patients who are immunosuppressed. A recent meta-analysis has not shown evidence for a reduction in the duration or frequency of diarrhea by nitazoxanide or paromomycin when compared with placebo in immunosuppressed patients, nevertheless, oocyst clearance was significantly reduced.^[25] \|\|Recent studies have shown effective outcomes when compared to placebo, but no clinical trials have compared with other antiparasitic drugs.

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Author

Enrique Chacon-Cruz, MD, MSc Roster Member, Strategic Advisory Group of Experts in Immunization for the World Health Organization (SAGE-WHO); Member, Scientific Committee for the Ministry of Health, Baja-California, Mexico; Independent Advisor for Clinical Research and Academic Lectures, Houston, Texas (USA)

Enrique Chacon-Cruz, MD, MSc is a member of the following medical societies: Pediatric Infectious Diseases Society, Royal Society of Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Martin Weisse, MD Program Director, Associate Professor, Department of Pediatrics, West Virginia University

Martin Weisse, MD is a member of the following medical societies: Academic Pediatric Association, American Academy of Pediatrics, Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Chief Editor

Russell W Steele, MD Clinical Professor, Tulane University School of Medicine; Staff Physician, Ochsner Clinic Foundation

Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, Southern Medical Association

Disclosure: Nothing to disclose.

Additional Contributors

Ashir Kumar, MD, MBBS FAAP, Professor Emeritus, Department of Pediatrics and Human Development, Michigan State University College of Human Medicine

Ashir Kumar, MD, MBBS is a member of the following medical societies: Infectious Diseases Society of America, American Association of Physicians of Indian Origin

Disclosure: Nothing to disclose.

Acknowledgements

Douglas K Mitchell, MD Associate Professor, Department of Pediatrics, Eastern Virginia Medical School; Chair, Bronchiolitis Clinical Pathway Committee, Children's Hospital of the King's Daughters

Douglas K Mitchell, MD is a member of the following medical societies: American Academy of Pediatrics, American Society for Virology, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, Society for Healthcare Epidemiology of America, Society for Pediatric Research, and Southern Society for Pediatric Research

Disclosure: Nothing to disclose.