Amebiasis in Nicaragua: class specific serum antibody responses.

With the aid of the indirect hemagglutination (IHA) test and IgG ELISA the antibody profile against E. histolytica in León, Nicaragua was investigated in 562 sera from individuals belonging to various age groups. The highest reactivity was invariably recorded in the age group 6-15 years where 48% were seropositive. Several sera reactive by either one of IHA and IgG ELISA were negative by the other test. The main reason for this seems to be reactivity in different Ig classes. Treatment with 2-mercaptoethanol reduced the titre level in 63 of the 66 sera tested. Immunofluorescence using an anti-IgM conjugate showed that 26 of 43 sera contained specific IgM-antibodies, indicating that also unspecific reactions are involved in the IHA test. A comparison was made between class-specific reactivity in three population groups: healthy residents, healthy cyst carriers and patients with recent or acute liver abscess. No significant difference in the prevalence of reactions above the diagnostic significance level was recorded between cyst carriers and healthy residents. However, among the cyst carriers 33% had IgA and/or IgM antibodies but no demonstrable specific IgG. Most patients with recent and all with acute liver abscess reacted significantly above the diagnostic limit in all three tests.