Mohamed D. Abd-Alla

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.

Intestinal Antilectin Immunoglobulin A Antibody Response and Immunity to Entamoeba dispar Infection following Cure of Amebic Liver Abscess

ABSTRACT We followed 93 subjects with amebic liver abscess (ALA) and 963 close associate controls at 3-month intervals for 36 months to characterize intestinal and humoral antibody responses to the amebic galactose-inhibitable lectin and to determine whether immunity developed to Entamoeba histolytica or Entamoeba dispar infection following cure of ALA. We found that ALA subjects had a higher prevalence and level of intestinal antilectin immunoglobulin A (IgA) and serum anti-LC3 (cysteine-rich recombinant lectin protein) IgA and IgG antibodies, P < 0.01 and P < 0.05, respectively, compared to controls. The intestinal antilectin IgA antibody response was sustained over a longer time period in ALA subjects (71.8% remained positive at 18 months and 52.6% at 36 months, P < 0.001 compared to 17.6% and 10.3% of controls, respectively). ALA subjects were highly immune to E. dispar infection throughout the study (0% infected at 6 and 36 months, compared to 6.5% and 4.9% of control subjects, respectively, P < 0.05). Upon entry into the study, 6.3% of ALA subjects were infected with E. histolytica; the incidence of new E. histolytica infections in controls (as determined by culture) was too low (1.4%) to determine whether ALA subjects exhibited immunity to new infections. We found that stool cultures every 3 months markedly underestimated the occurrence of new E. histolytica infections, as 15.3% of controls seroconverted after 12 months of follow-up. Unfortunately, under the field conditions present in Durban, South Africa, enzyme-linked immunosorbent assay for detection of lectin antigen in stool yielded unreliable results. In summary, subjects cured of ALA exhibited sustained mucosal IgA antibody responses to the amebic galactose-inhibitable lectin and a high level of immunity to E. dispar infection. Determination of immunity to E. histolytica following cure of ALA will require the use of more sensitive and reliable diagnostic methods.

Mucosal Immunity to Asymptomatic Entamoeba histolytica and Entamoeba dispar Infection Is Associated with a Peak Intestinal Anti-Lectin Immunoglobulin A Antibody Response

ABSTRACT We monitored 93 subjects cured of amebic liver abscess (ALA) and 963 close associate controls in Durban, South Africa, and determined by enzyme-linked immunosorbent assay that the intestinal immunoglobulin A (IgA) antibody response to the Entamoeba histolytica galactose-inhibitable adherence lectin is most accurately represented by a complex pattern of transitory peaks. One or more intestinal anti-lectin IgA antibody peaks occurred in 85.9% of ALA subjects over 36 months compared to 41.6% of controls (P < 0.0001). ALA subjects exhibited a greater number of anti-lectin IgA antibody peaks (P < 0.0001) than controls. In addition, their peak optical density values were higher (peak numbers 1 to 3, P < 0.003), peaks were of longer duration (for peaks 1 and 2, P ≤ 0.0054), and there was a shorter time interval between peaks (between 1 and 2 or 2 and 3, P ≤ 0.0106) than observed for control subjects. A prior E. histolytica infection was associated with the occurrence of an anti-lectin IgA antibody peak (79.1%, P < 0.0001) more so than for Entamoeba dispar infection (57.2%, P < 0.001). The annual number of anti-lectin IgA antibody peaks in ALA subjects was 0.71 per year, compared to just 0.22 in controls (P<0.0001), indicating a higher rate of exposure to the parasite than previously appreciated. Anti-lectin IgA antibody peaks were of higher amplitude following a E. histolytica infection compared to E. dispar (P = 0.01) and, for either, were of greater height in ALA subjects than controls (P < 0.01). ALA subjects demonstrated greater clearance of amebic infection after an anti-lectin IgA antibody peak compared to controls, and only 14.3% remained with a positive culture after the peak, compared to 38.9% in controls (P = 0.035). In summary, this prospective controlled longitudinal study elucidated the dynamic nature of the human intestinal IgA antibody response to E. histolytica and E. dispar infection and revealed that ALA subjects exhibit heightened intestinal anti-lectin IgA antibody peaks that are associated with clearance of E. histolytica and E. dispar infection.

Natural Infection of Baboons by Entamoeba Histolytica Elicits Anti-Gal Lectin Heavy Subunit Iga and Igg Antibodies with Shared Epitope Specificity to That of Humans

Non-human primates, such as baboons (Papio hamadryas anubis), are natural hosts for Entamoeba species; infections can be asymptomatic or result in invasive lethal disease. It was sought to determine whether following natural infection by Entamoeba. histolytica, baboon anti-amebic antibodies recognized native Gallectin, a recombinant portion of the lectin heavy subunit (designated LC3) and specific heavy subunit epitopes; we compared the specificity of anti-amebic antibodies from baboons to that of humans following asymptomatic E. histolytica infection or cure of amebic liver abscess (ALA). Female baboons (n=54), aged one to three years of age and living in captivity were screened for infection by real time PCR. E. histolytica infection was found in 37 baboons and was associated with serum anti-LC3 IgG (73%) and anti-LC3 IgA (46%) or intestinal anti-Gal-Lectin IgA antibody responses (49%), p<0.021 for each compared to that observed with baboons having an E. dispar infection (n=10) or uninfected baboons (n=7). The ELISA OD reading for anti-LC3 or anti-lectin antibodies correlated strongly with the presence of a PCR CT value indicative of E. histolytica infection. In humans with asymptomatic E. histolytica infection or those recently cured of ALA, 63% and 57% had serum anti- LC3 IgA and 65% and 57% had serum anti-LC3 IgG antibodies respectively. Epitope- specific synthetic peptides were used as capture antigens in ELISA; for baboons that possessed anti-LC3 and anti-lectin antibodies, 74% had anti-peptide IgG or IgA antibodies, compared to 86% of asymptomatic humans and 92% of ALA subjects(P>0.05).