Amebiasis - UMass Amherst

1 Mayo Clin Proc. October 2008;83(10):1154-1160 personal use. Mass reproduce only with permission from Mayo Clinic personal use. Mass reproduce only with permission from Mayo Clinic REVIEW FOR CLINICIANSBOBBI S. PRITT, MD, AND C. GRAHAM CLARK, PHDA mebiasis is defined as infection with Entamoeba histolytica,regardless of associated symptomatology. In resource-rich na-tions, this parasitic protozoan is seen primarily in travelers to andemigrants from endemic areas. Infections range from asympto-matic colonization to amebic colitis and life-threatening ab-scesses. Importantly, disease may occur months to years afterexposure. Although E histolytica was previously thought to infect10% of the world s population, 2 morphologically identical butgenetically distinct and apparently nonpathogenic Entamoebaspecies are now recognized as causing most asymptomaticcases.

2 To avoid unnecessary and possibly harmful therapies, clini-cians should follow the diagnostic and treatment guidelines of theWorld Health Clin Proc. 2008;83(10):1154-1160 ALA = amebic liver abscess; PAHO = Pan American Health Organization;WHO = World Health OrganizationFrom the Division of Clinical Microbiology, Mayo Clinic, Rochester, MN( ); and Department of Infectious and Tropical Diseases, London Schoolof Hygiene and Tropical Medicine, London, United Kingdom ( ).Individual reprints of this article are not available. Address correspondence toBobbi S. Pritt, MD, Division of Clinical Microbiology, Mayo Clinic, 200 First StSW, Rochester, MN 55905 2008 Mayo Foundation for Medical Education and ResearchOn completion of this article, you should be able to: (1) request the appropriate tests for differentiating the morphologicallyidentical Entamoeba species E histolytica, E dispar, and E moshkovskii on the basis of initial laboratory reports; (2)recognize symptoms and complications of invasive Amebiasis .

3 And (3) apply the World Health Organization/Pan AmericanHealth Organization guidelines for diagnosis and treatment of is defined by the World Health Organization(WHO) and Pan American Health Organization(PAHO) as infection with Entamoeba histolytica, regard-less of This protozoan parasite has aglobal distribution and an especially high prevalence incountries where poor socioeconomic and sanitary condi-tions In resource-rich nations, infectionsmay be seen in travelers to and emigrants from Most infections are asymptomatic, but tissue inva-sion may result in amebic colitis, life-threatening hepaticabscesses, and even hematogenous spread to distant ,4 Importantly, disease can occur months to yearsafter exposure5 and must remain in the differential diagno-sis in at-risk in molecular technologies have revolution-ized our understanding of this Most notably, 2additional Entamoeba species that are morphologically in-distinguishable from E histolytica have been recognized inhumans.

4 As our knowledge of the global epidemiology andpathogenicity of Entamoeba spp increases, new clinicalalgorithms are The latest nomenclature andrecommendations, although unfamiliar and confusing tomany, are important for appropriate patient care. Our re-view discusses what is known about these 3 Entamoebaspp and clarifies the currently accepted recommendationsfor diagnosis and NEW ENTAMOEBA SPECIES: ENTAMOEBADISPAR AND ENTAMOEBA MOSHKOVSKIIIt is a long-held misconception that 10% of the world spopulation is infected with E histolytica. In fact, most ofthese infections should be attributed to the morphologicallyidentical but nonpathogenic E dispar. Emile Brumpt6 firstproposed the existence of 2 indistinguishable Entamoebaspp, one pathogenic and one nonpathogenic, in 1925. How-ever, not until 1978 was evidence for the existence of 2separate entities provided by new technology (isoenzymeanalysis).

5 7 More recent studies using methodologies ca-pable of distinguishing the 2 species suggest that E disparis up to 10 times more prevalent in asymptomatic patientsthan E histolytica in endemic Little is currentlyknown about their epidemiology in resource-rich nations,where the incidence of both is rare, but previous reports ofinfection with E histolytica based only on morphologylikely represent E discovery of a third morphologically identical Enta-moeba spp further complicated our understanding of theepidemiology of E histolytica. The new species, named Emoshkovskii, was first recognized as a ubiquitous free-living organism in 194112; it has been reported in humansfrom both resource-rich and resource-poor ,14 Al-though largely nonpathogenic, some recent evidence sug-gests that it may have a role in human intestinal remains unknown regarding the pathogenicity andepidemiology of E Clin Proc.

6 October 2008;83(10):1154-1160 personal use. Mass reproduce only with permission from Mayo Clinic personal use. Mass reproduce only with permission from Mayo Clinic DEFINITIVE PATHOGEN: E HISTOLYTICAE histolytica is the pathogenic species responsible foramebic colitis throughout the world. It infects people ofboth sexes and all ages; however, populations at risk mayvary with geographic location, host susceptibility, anddifferences in organism virulence. People in highly en-demic areas probably have recurrent asymptomatic infec-tions, thus accounting for the high reported ,15In developed countries, amebic colitis is most commonlyfound in travelers to or emigrants from endemic coun-tries, institutionalized persons, and patients infected withhuman immunodeficiency Men who have sexwith men were previously thought to have an increasedincidence of infection, but this supposition was based onmorphologic studies.

7 New evidence suggests that thesemen were colonized primarily with E dispar rather than ,20 The simple life cycle of E histolytica begins when infec-tious cysts are ingested in fecally contaminated food This association with poor sanitation explains whyresource-poor nations carry the bulk of the world s ingestion and passage through the stomach, the or-ganism excysts and emerges in the large intestine as anactive trophozoite. Trophozoites multiply by simple divi-sion and encyst as they move further down the large are then expelled with the feces and may remainviable in a moist environment for weeks to ,21 Amebae typically subsist on a diet of intestinal bacteria andpartially digested host food but are capable of tissue inva-sion and dissemination. Most infections ( 90%) remainasymptomatic,5,15 suggesting that tissue invasion is an aber-ration rather than a typical intestinal disease may occur days to years afterinitial infection and is characterized classically by abdomi-nal pain and bloody Watery or mucus-contain-ing diarrhea, constipation, and tenesmus may also clinical picture corresponds histologically with tro-phozoites invading and laterally undermining the intestinalsurface to form the so-called flask-shaped ulcers (Figure1).

8 The right side of the colon is commonly cases of amebic colitis are characterized by copiousbloody diarrhea, diffuse abdominal pain, and (rarely) fulminant necrotizing colitis, the most severeform of intestinal disease, is often Patients at in-creased risk of severe disease include those who are veryyoung, very old, malnourished, or pregnant and those whoare receiving Some evidence suggests thatpatients infected with human immunodeficiency virus areat increased risk of severe disease,22 but this is not univer-sally Complications of intestinal disease in-clude stricture, rectovaginal fistulas, formation of an annu-lar intraluminal mass (ameboma), bowel obstruction, peri-anal skin ulceration, toxic megacolon, perforation, perito-nitis, shock, and ,18 Chronic intestinal Amebiasis isalso well described; patients with this condition can haveyears of intermittent abdominal pain, diarrhea, and rare occasions, E histolytica trophozoites enter thebloodstream and disseminate to other body sites, mostcommonly the liver via spread from the intestine throughthe portal vein.

9 The right lobe is 4 times more likely to beinvolved than the left because it receives the bulk of thevenous drainage from the right Adult men aged 20to 40 years are most frequently affected, although people ofboth sexes and all ages may develop an amebic liver ab-scess (ALA).17,18 Disease can occur years after exposureand may follow the onset of invasion by amebic trophozoites results inmarked tissue destruction with neutrophil recruitment, cel-lular necrosis, and formation of microabscesses that gradu-ally Most patients (65%-75%) present with asingle abscess; however, multiple abscesses may also Abscesses consist of soft, necrotic, acellular yel-low-brown debris, described as anchovy paste. 21 Amebaeare seldom identified in aspirates because they are locatedat the periphery of the White blood cells are alsonot usually seen, presumably because they have been de-stroyed by the amebic presentation of ALA is highly variable andcommonly includes tender hepatomegaly and pain in theFIGURE 1.

10 Flask-shaped ulcer of invasive intestinal Amebiasis (hematoxylin-eosin, original magnification 50). Note that the apexof the ulcer at the bowel lumen is narrower than the base, account-ing for the flask shape. This is formed as trophozoites invadethrough the mucosa and move laterally into the submucosa (direc-tion of ulcer expansion is marked by arrows). Microscopically,trophozoites are localized to the advancing edges of the submu-cosal ulcer. Image courtesy of John Williams, CBiol, MIBiol, LondonSchool of Hygiene and Tropical Clin Proc. October 2008;83(10):1154-1160 personal use. Mass reproduce only with permission from Mayo Clinic personal use. Mass reproduce only with permission from Mayo Clinic upper Unlike amebic colitis, ALA is com-monly accompanied by fever,3 as well as by rigors, chills,and profuse Most patients do not have concur-rent colitis and cysts, and trophozoites are not always seenon fecal smears,3 posing an important diagnostic is not typically present; elevated bilirubin levelsare seen in less than 50% of patients, but elevated alka-line phosphatase levels are Complications in-clude secondary bacterial infection; perforation into peri-toneal, pleural, and pericardial cavities; septic shock; ,18 Perhaps the most serious complication is amebic me-tastasis from the liver.