Reproducible results were difficult to obtain in early serologic tests for amebiasis, and doubt was cast upon their value because a high percentage of negative tests occurred with serums from persons known to harbor Entamoeba histolytica in their stools. When it became generally recognized that E. histolytica is a facultative parasite and may be either a non-invasive commensal or a pathogen, it seemed plausible to assume that amebic antigens become available for antibody production following tissue invasion by E. histolytica. Varying amounts and strengths of antigen will stimulate production of antibodies with varying reactivity.
The present report summarizes results with the indirect hemagglutination and complement fixation tests as developed by Lewis and Kessel on 455 serums from patients with amebiasis who harbored E. histolytica and from 101 negative controls. The histories and serums were collected and the species of amebae determined either by the authors or the other experts in tropical medicine named under Acknowledgments, from the listed geographic areas. The serums are classified by clinical groups and areas of origin.
In general, it was observed that a close positive correlation occurs between serologic tests and persons with amebiasis. The HA test was positive in 100% of active liver abscess cases, 98% of dysentery cases and 66% of asymptomatic carriers. The test remains positive for many years following the initial infection, although the titer of reactivity may drop gradually. The CF test gave a 100% correlation with active cases of proved liver abscess, but a low correlation with asymptomatic carriers. The CF test titers dropped more rapidly in treated cases than did HA titers, and at times became negative in about one year. Correlation of positive tests and titers with geographic areas is discussed.
Present address: School of Public Health, University of California, Los Angeles, California 90024.
Instituto de Salubridad y Enfermedades Tropicales, Mexico City.