Prevalence and clinical importance of Entamoeba histolytica in two high-risk groups: travelers returning from the tropics and male homosexuals

This study was undertaken to learn the prevalence of amebiasis and to assess the clinical importance of Entamoeba histolytica in two high-risk groups: 2700 travelers returning from the tropics and 320 male homosexuals. Some 16.3% of the homosexual men and 4.0% of the travelers had E. histolytica infections. Only five travelers showed a pathogenic zymodeme of E. histolytica, which correlated closely with invasive amebiasis with positive amebic serology and clinical symptoms with diarrhea. The homosexual group had neither a pathogenic isoenzyme pattern nor positive amebic serology. Currently, travelers to the tropics have a risk of 0.3% (1:340) of acquiring invasive amebiasis; 92.5% of all E. histolytica infections in travelers remain asymptomatic and are confirmed by serology and zymodeme status. No homosexual presented with invasive amebiasis.     

Gender distribution in asymptomatic and invasive amebiasis

OBJECTIVE: The majority of individuals infected by the protozoan parasite Entamoeba histolytica experience subclinical infections. However, a small proportion of parasitized individuals develop severe invasive disease such as amebic dysentery or amebic liver abscess. Invasive amebiasis affects predominantly men; the usual explanation for this has been that men have a higher rate of asymptomatic infections and therefore experience a higher rate of invasive disease. To date, there is no convincing evidence of an increased rate of asymptomatic infection of men as compared with women. The purpose of this study was to evaluate the evidence supporting the hypothesis that men have higher rates of asymptomatic infection and thus an increased frequency of invasive amebiasis. METHODS: We reviewed published reports of invasive amebiasis and population-based parasitological studies from 1929-1997 to compare the gender ratio of asymptomatic and symptomatic E. histolytica infection. Infections with E. histolytica were differentiated from the nonpathogenic E. dispar whenever possible. RESULTS: The reports of invasive amebiasis (dysentery, liver abscess, colonic perforation, peritonitis, appendicitis, and ameboma) showed a higher proportion of men than women (ratio, male:female = 3.2:1, p < 0.05). This contrasts with the epidemiological surveys, where the rate of asymptomatic infection with E. histolytica was the same (1:1) for both genders (p > 0.05). CONCLUSIONS: Asymptomatic E. histolytica infection is equally distributed between the genders. The high proportion of men with invasive amebiasis may be due to a male-related susceptibility to invasive disease.     

An immunogenic 30-kDa surface antigen of pathogenic clinical isolates of Entamoeba histolytica

A 30-kDa surface antigen was identified by Western blots with human immune sera in all 15 isolates of E. histolytica from patients with invasive amebiasis (pathogenic) but not in 15 strains from asymptomatic patients (nonpathogenic). This antigen is highly immunogenic in naturally infected humans and was recognized by sera from 22 patients with invasive disease but not by sera from 13 patients harboring nonpathogenic strains. Its surface location is supported by its differential extraction in the detergent phase of Triton X-114 and by surface immunofluorescence of live trophozoites. Unlike previously described amebic surface antigens, this 30-kDa antigen is undetectable in axenic strains that were originally isolated from patients with invasive disease but have been adapted to grow without bacteria. Affinity-purified antibody to the 30-kDa antigen did not promote lysis of complement-resistant pathogenic strains. This surface antigen may be diagnostically important in the identification of pathogenic clinical isolates.     

Comparison of antigen-capture ELISA to stool-culture methods for the detection of asymptomatic Entamoeba species infection in Kafer Daoud, Egypt

We performed a prospective field study in the village of Kafer Daoud in Menofia, Egypt to compare the fecal culture method with enzyme linked immuno assay (ELISA) for detection of 170 kDa lectin antigen in feces for diagnosis of asymptomatic Entamoeba histolytica and Entamoeba dispar infection. All subjects with E. histolytica or E. dispar infection detected by culture also had positive ELISA for amebic antigen in their feces and an additional 57 Entameoba infections missed by culture were detected by ELISA (P < 0.001 compared to culture). The presence of fecal anti-lectin IgA antibodies and serum anti-LC3 (recombinant cysteine-rich lectin protein) IgG antibodies were positive predictors for E. histolytica infection (P < 0.03). Of interest, infection with Trichomonas hominis but not Blastocystis hominis was positively associated with E. histolytica infection (P < 0.05). In conclusion, ELISA for detection of fecal lectin antigen is a more sensitive method than fecal culture for detecting asymptomatic E. histolytica infection.     

Hemoptysis in a 49-year-old man. An unusual presentation of a sporadic disease

Although amebiasis is prevalent in tropical and subtropical areas, it occurs sporadically in the United States. Pleuropulmonary involvement is seen in about 20 percent of the patients with amebic liver abscesses. We describe a patient with pleuropulmonary amebiasis who complained of hemoptysis but had no gastrointestinal symptoms. This rather unusual presentation caused a considerable delay in securing the diagnosis.     

The role of hepatitis C in hepatocellular carcinoma: a case control study among Egyptian patients

BACKGROUND: Egypt has one of the highest prevalence rates of hepatitis C virus (HCV) infection in the world; however, the risk and attribution related to HCV in Egyptian patients with hepatocellular carcinoma (HCC) remains unknown. GOALS: The current study was undertaken to estimate the risk of HCC in relation to HCV in Egypt. STUDY: Thirty-three patients with HCC and 35 healthy controls who had a similar socioeconomic status were prospectively enrolled at the University of Cairo National Cancer Institute. RESULTS: Anti-HCV antibodies were present in 75.8% of the patients and in 42.9% of the controls (p = 0.01); hepatitis B surface antigen (HBsAg) was present in 15.2% of the patients and in 2.9% of the controls (p = 0.03). In addition, the sex-and age-adjusted odds ratio (OR) for anti-HCV antibodies was 5.1 (95% CI = 1.5-17.4) and for HBsAg was 13.2 (95% CI = 1.2-148.2). Concurrent Schistosoma mansoni and anti-HCV was associated with an OR of 10.3 (95% CI = 1.3-79.8), which was higher than that for anti-HCV (6.5; 95% CI = 1.6-26.6) and S. mansoni infection (0.2; 95% CI = 0.1-6.2) alone. Finally, we estimated the attributable fraction of HCC to HCV to be 64% in this study population and 48% in the general Egyptian population. CONCLUSIONS: Both HCV and hepatitis B virus infection increase the risk of HCC in Egyptian patients, whereas isolated Schistosoma infection does not. Because of the very high prevalence rate of HCV in the general Egyptian population, it accounts for most HCC cases in Egypt.     

The prevalence of invasive amebiasis is not increased in patients with AIDS.

OBJECTIVE: To determine whether the frequency or severity of invasive amebiasis is increased in patients with AIDS. DESIGN: A case-control sampling approach, based on an autopsy registry. SETTING: General Hospital of Mexico City, Mexico, a large government-supported, tertiary care medical institution. PATIENTS, PARTICIPANTS: Ninety-four patients with AIDS and 335 historical and contemporary, age- and sex-matched controls who were defined as dying, but not because of AIDS. RESULTS: The odds ratio (OR) for mortality from invasive amebiasis was the same for cases and controls (0.7; 95% confidence interval, 0.07-7.2). By contrast, the OR for other diseases, such as miliary tuberculosis, cytomegalovirus infection, Pneumocystis carinii pneumonia and toxoplasmosis was greatly increased. Only one patient with AIDS had amebiasis of the common amebic ulcerative colitis type, without extraintestinal involvement. CONCLUSION: In conclusion, we show that the frequency and severity of invasive amebiasis is not increased in Mexican patients with AIDS.     

Outbreak of amebiasis in Tbilisi,Republic of Georgia, 1998

In 1998, we investigated a suspected outbreak of amebic liver abscesses caused by Entamoeba histolytica in the Republic of Georgia, using a case-control study. A questionnaire was administered and blood samples were obtained from cases and controls for serologic diagnosis. Medical records showed that E. histolytica infections were rarely diagnosed before 1998. However, from July through September 1998, 177 cases of suspected amebiasis were identified. Of 52 persons who had diagnosed liver abscesses, 37 (71%) were confirmed serologically to have antibodies against E. histolytica, compared with 11 of 53 persons (20.8%) diagnosed with intestinal amebiasis. In addition, 9-14% of asymptomatic controls were seropositive. Logistic regression identified the fact that interruptions in the water supply, decreases in water pressure, and increased water consumption were significantly associated with infection. The data support the hypothesis that drinking water was the source of infection, either because of inadequate municipal water treatment or contamination of municipal water in the distribution system.     

Protein A-antibody mediated hemagglutination assay for serodiagnosis of amebic liver abscess

A successful modification of the indirect hemagglutination test to demonstrate antibodies for serodiagnosis of amebic liver abscess has been described in the present study. In the modified test, the protein A-IMA, Staphylococcus aureus (Cowan's strain I) bearing protein A (SAPA) cells were used to enhance hemagglutination of sensitized red cells. Use of SAPA cells markedly enhanced sensitivity of the test and greatly increased the titers obtained with most of the sera. At a diagnostic antibody titer of 1:128 and above, the protein A-IHA could detect 72 (100%) of amebic liver abscess (ALA) cases. Amongst the controls, no false positive reaction was observed in non-amebic liver disease controls. However 1(2%) of sera demonstrated false positive reactions from healthy controls. The protein A-IHA was highly sensitive when compared with that of the indirect hemagglutination (IHA) for serodiagnosis of amebic liver abscess. The novel immunoassay is simple, inexpensive and requires little technical skill. It has the potential for wide application in serodiagnosis of amebic liver abscess.     

Hepato-pulmonary amebiasis: a case report

Infections with Entamoeba histolytica are seen worldwide and are more prevalent in the tropics. About 90% of infections are asymptomatic, and the remaining 10% produce a spectrum of clinical syndromes, ranging from dysentery to abscesses of the liver or other organs. Extra-intestinal infection by E. histolytica most often involves liver. Pleuro-pulmonary involvement, seen as the second most common extra-intestinal pattern of infection, is frequently associated with amebic liver abscess. Pulmonary amebiasis occurs in about 2-3% of patients with invasive amebiasis. We report herein the case of a 45-year-old male presenting with hepato-pulmonary amebiasis. The diagnosis was established from direct examination of sputum, in which trophozoites of E. histolytica were detected, and by serology. Following treatment with metronidazole and chloroquine, the clinical evolution improved significantly. On regular follow-up visits, the patient was asymptomatic. This case report reiterates the need for collaboration between clinicians and microbiologists for timely diagnosis of such infections.     

Correlation of positive syphilis serology with invasive amebiasis in Japan

Approximately 20% of 52 Japanese males with invasive amebiasis confirmed by gel diffusion precipitin test (GDP) were positive by both Treponema pallidum hemagglutination test (TPHA) and nontreponemal antigen tests, and an additional 20% were positive by TPHA alone. However, none of 109 GDP-negative Japanese males without invasive amebiasis were positive on these serologic tests for syphilis. At least 2 bisexuals and 4 homosexuals were among those with invasive amebiasis. All of these biased males were positive on both TPHA and nontreponemal antigen tests. Four of the biased males had liver abscess and 2 had amebic dysentery or colitis. Bisexual or homosexual males were not found in the negative GDP group. These observations suggest that sexually transmitted amebiasis due to Entamoeba histolytica occurs among sexually biased males in Japan.     

Counterelectrophoresis in the Diagnosis of Amebiasis

One hundred eighty-one collected sera were tested for amebic serologic reactivity, using the counterelectrophoresis technic (CEP) and compared to the results of the agar gel diffusion (AGD) and the latex agglutination (LA) methods. Of 23 sera from patients with proven amebic liver abscess, 22 (96%) were positive immediately after CEP for one hour and all were positive within 24 hours. Of eight sera from patients with intestinal amebiasis, five were positive immediately and seven within 24 hours. Of 150 sera from patients with nonamebic illnesses, there were no positives with any method used. The CEP and AGD were in agreement on all sera tested.     

Amebic Liver Abscess

We present a patient with an acute amebic liver abscess with nonreactive serologic tests. Motile hematophagous trophozoites of Entamoeba histolytica were seen microscopically in scrapings from the wall of the abscess. Postoperative serologies revealed rapidly rising then falling titers by SAFA and IHA antibody assays. Serologic tests for amebiasis may be reative in greater than 95% of patients with invasive amebiasis. Nevertheless, a reactive serologic test should not be relied upon exclusively to establish the diagnosis. Sequential serologic testing and surgical intervention to obtain material for microscopic examination, gram stain and bacteriologic culture are warranted in patients with hepatic abscess and nonreactive serologic tests for antibodies to E. histolytica.     

Diagnosis of amoebic colitis by antigen capture ELISA in patients presenting with acute diarrhoea in Cairo, Egypt

We studied 84 consecutive patients presenting with acute diarrhoea (less than 1 week in duration) at an outpatient tropical medicine clinic in Cairo, Egypt. The diagnosis of amoebic colitis was established by the presence of Entamoeba histolytica galactose-inhibitable lectin antigen and the presence of occult blood in stool. Controls were 182 healthy regional people and 64 patients complaining of prolonged diarrhoea lasting more than 1 week. Entamoeba histolytica infection was found more frequently in patients with acute diarrhoea (57.1%) than in healthy controls (21.4%) or patients with prolonged diarrhoea (25%) (P < 0.001). There was a higher prevalence of Entamoeba dispar infection in the two control groups (24.2 and 20.3%, respectively, P=0.004 and 0.061) compared with those with acute diarrhoea (8.3%). Of the 84 patients with acute diarrhoea 32 had amoebic colitis (38%), and of these, 31 (97%) had at least one positive assay for serum amoebic antibodies (P < 0.001 compared with control groups). In summary, as determined by antigen-detection enzyme-linked immunosorbent assay, there is an unexpectedly high prevalence of amoebic colitis among patients presenting with acute diarrhoea to a tropical disease clinic in Cairo, Egypt.     

Review of the human immune mechanisms directed against Entamoeba histolytica

The human immune mechanisms effective against the destructive parasite Entamoeba histolytica have not been established. Humoral responses develop with invasive disease but have not positively correlated with protection against recurrent invasive infection. Though complement is amebicidal, invasive strains of amebas may be resistant. Polymorphonuclear neutrophils have not been active in vitro against virulent amebic strains and could contribute to the pathogenesis of disease. In vitro studies have shown human activated monocyte-derived macrophages and cytotoxic T lymphocytes to be competent cells in killing virulent amebas. Soluble amebic protein preparations have been shown to be mitogenic for normal, uninfected human lymphocytes, apparently because the N-acetyl-D-galactosamine-inhibitable amebic lectin is present. Despite a lower T4:T8 ratio and a heterogeneous lymphocyte proliferation in response to mitogens, patients with amebic hepatic abscess develop sensitization to amebic antigens and specific effector mechanisms. Although antibody, complement, and nonimmune mechanisms, as well as parasite factors, may be important in determining the occurrence of invasive amebiasis, human cell-mediated immune mechanisms may play a major role in combating invasive infection due to E. histolytica.     

Invasive amebiasis as an emerging parasitic disease in patients with human immunodeficiency virus type 1 infection in Taiwan

BACKGROUND: Whether risk of invasive amebiasis due to Entamoeba histolytica is higher among human immunodeficiency virus (HIV)-infected persons than uninfected persons remains unclear, although intestinal colonization by Entamoeba dispar is common among men who have sex with men. Our objective was to determine the prevalence of invasive amebiasis and intestinal colonization by E histolytica and E dispar in HIV-infected persons and uninfected controls. METHODS: We assessed the prevalence of invasive amebiasis by case review of 951 HIV-infected persons and by serologic studies of 634 of the 951 HIV-infected persons, 429 uninfected controls with gastrointestinal symptoms, and 178 uninfected healthy controls using indirect hemagglutination antibody assay. We assessed the rate of intestinal colonization by E histolytica and E dispar by fecal antigen and polymerase chain reaction tests in 332 asymptomatic HIV-infected persons and 144 of the 178 uninfected healthy controls. RESULTS: Forty-nine (5.2%) of 951 HIV-infected persons had 51 episodes of invasive amebiasis. A high indirect hemagglutination antibody titer was detected in 39 (6.2%) of 634 HIV-infected persons compared with 10 (2.3%) of 429 uninfected controls with gastrointestinal symptoms and 0 of 178 uninfected healthy controls (P<.001). Stool specimens from 40 (12.1%) of 332 HIV-infected persons and 2 (1.4%) of 144 uninfected healthy controls were positive for E histolytica or E dispar antigen (P<.001). Ten (25.0%) of the 40 antigen-positive stool specimens from HIV-infected persons contained E histolytica. CONCLUSION: Persons infected with HIV in Taiwan are at increased risk for invasive amebiasis and exhibit a relatively high frequency of elevated antibody titers and intestinal colonization with E histolytica.     

Antibodies to major outer membrane proteins of Escherichia coli in urinary infection in the elderly

The serologic response to infection in elderly bacteriuric subjects and young women with acute pyelonephritis was measured with an enzyme-linked immunosorbent assay (ELISA) using the major outer membrane protein complex (MOMP) of one Escherichia coli strain as antigen. Elderly controls and subjects with asymptomatic bacteriuria had variable titers; control titers were significantly lower than those with asymptomatic bacteriuria. Titers were stable over 2-12 w in asymptomatic subjects. Elderly subjects with invasive infection and women with pyelonephritis demonstrated increases in titer between acute and convalescent serum for E. coli and other Enterobacteriaceae. With a convalescent specimen with an antibody titer greater than or equal to 3 standard deviations (SD) above the acute, the sensitivity of the MOMP ELISA for identifying invasive infection was 74%, the specificity 86%, the positive predictive value 82%, and the negative predictive value 79%. With the criteria of greater than or equal to 3 SD or an initial serum to control ratio of greater than or equal to 15 these parameters were 95%, 82%, 82%, and 95%, respectively. These initial investigations suggest the MOMP of E. coli may be an antigen with wide cross-reactivity, suitable for use as an objective test to identify invasive Enterobacteriaceae urinary infection.     

The presence of liver auto-antibodies induced by Entamoeba histolytica in the sera from both naturally infected humans and immunized rabbits.

Auto-antibodies against normal human liver have been detected in the sera of humans with highly positive indirect hemagglutination (IHA) amebiasis titers and with clinically-proven amebic liver abscess. Sera of amebiasis patients and rabbits immunized with killed Entamoeba histolytica were tested for anti-amebic antibodies by the IHA test and for auto-antibodies by the complement fixation test, using the antigens prepared from extracts of human liver and rabbit liver. A direct correlation was found to exist between high anti-Entamoeba antibody titers and the presence of anti-liver antibody in the serum. It is proposed that, in addition to direct parasite damage to host tissue, immunological damage could result from the attachment of circulating antigen to the cell surfaces of host tissues such as the liver.     

Amebic liver abscess and circulating immune complexes of Entamoeba histolytica proteins

An enzyme-linked immunosorbent assay (ELISA) has been developed to detect amebic antigen in polyethylene-glycol-precipitable circulating immune complexes. Seventy-nine percent of 191 patients with amebic liver abscesses and 46% of 26 Entamoeba histolytica cyst passers had positive tests. None of the samples from 43 apparently healthy controls, 8 patients with past amebic liver abscesses or 31 patients with Giardia lamblia infections were positive. One patient out of 32 with viral hepatitis and 1 patient out of 27 with intestinal tuberculosis had positive tests.     

Negative-ELISA using native and filtrated cystic fluid antigens to rule out cystic echinococcosis

An increasing number of cases of echinococcosis in Thailand have been imported, probably native infections and medical transfers. Serodiagnosis is one diagnostic choice for interpreting infections before a further step is done. Due to limited antigen, indirect ELISA has been used as a negative screening test for IgG-detection to rule out echinococcosis. Native hydatid cystic fluid (HCF) antigen from Belgium was used for such testing, in which the ODs-ELISA of samples were compared with those of two positive controls. Subsequently, hydatid cyst fluid from a Thai patient was obtained and the filtrated cyst fluid antigen [(<30)-(>10) kDa, HCF30.10] was prepared to develop negative screening results for the serum samples. By using HCF, three of twenty-four samples resulted in higher ODs-ELISA than the controls. In an attempt to observe the cross-reactivity of this native antigen, IgG-antibodies from many helminthiases cross-reacted and showed high ODs-ELISA. The HCF30.10 Ag was used to develop the test and analyze IgG-antibodies from 5 positive controls (2 parasite-confirmed and 3 positive-serodiagnosed), 183 heterologous cases of 29 diseases and 50 healthy control sera. At a cut-off value of 0.484, the test had 100% sensitivity and 42% specificity. Only Malayan filariasis, onchocercosis, fascioliasis, amebiasis, giardiasis and blastocystosis gave true negatives. Antibodies from nematodiases strongly cross-reacted with HCF30.10 Ag. Nine of fifty (18%) healthy serum controls produced higher OD-values than the cut-off. The routine ELISA uses the HCF30.10 Ag to produce a negative result to echinococcosis, because limited cystic fluid antigen (Thai patient) for test improvement, a lot of cross-reactions and only two protoscolex-positive controls are available.