Indirect haemagglutination (IHA) test in the serodiagnosis of amoebiasis

Among 72 patients clinically suspected of Entamoeba histolytica (E. histolytica) infections, 39 positive cases (54%) were detected serologically by the indirect hemagglutination (IHA) test. Parasitologically, microscopic examination of three consecutive stool specimens from all these patients indicated positivity for E. histolytica cysts and or trophozoites in 10 of the patients with IHA antibody titers greater than or equal to 1:128, which is of clinical significance. Another 2 patients were parasitologically positive but showed low IHA antibody titres (1:32-1:64); follow up indicated response to treatment with metronidazole. The highest serological positivity (100%) were detected in patients with liver abscess, all were clinically proven cases of extra-intestinal amoebiasis. IHA antibody levels of clinical significance were seen in all four patients with chronic dysentery with parasitological evidence of E. histolytica in their stools. In a group of patients with abdominal pain nine positives were detected serologically, four of which were positively diagnosed concurrently by parasitology; the remaining five patient's sera showed high IHA antibody titres with absence of cysts or trophozoites in stools, indicative possibly of persistence of antibodies from past infection. The serologic determination of E. histolytica IHA antibodies in a control group consisting of normal healthy school children and adults of both sexes without any clinical evidence of amoebiasis showed the absence of any positive titres of clinical significance; low titres (1:32-1:64) were detected in 5.2% of 232 sera tested. Parasitological examination of three consecutive stool specimens from all individuals in the control group showed the presence of cysts of E. histolytica in just two among 232 tested (0.9%).