Identification of asymptomatic Entamoeba histolytica infection by a serological screening test: A cross-sectional study of an HIV-negative men who have sex with men cohort in Japan

Author summaryAmebiasis, caused by Entamoeba histolytica, is now spreading not only in developing countries, but also in many of developed countries. Unlike the situation in developing countries, transmission occurs directly from one infected person to another via sexual contact, called sexually transmitted E. histolytica infection. Furthermore, most cases of E. histolytica infection are asymptomatic, who can be a reservoir for sexual transmission in the community. Cost-effective epidemiological strategy is urgently needed. Hereby, we performed a serological test for 312 "asymptomatic" HIV-negative men who have sex with men to assess the effective screening method for E. histolytica infection. We identified 21 seropositive samples (6.7% of seropositivity, 21/312), in which relatively high seropositivity to E. histolytica was seen among the participants with positive serology for Treponema pallidum hemagglutination (TPHA) or hepatitis B core antibody (HBcAb). Finally, we identified current infection (asymptomatic E. histolytica infection) in 8 out of 20 stool sampling cases (40.0%) by polymerase chain reaction. Our serological screening assay provides a potentially practical epidemiological strategy. Active epidemiological survey, in combination with the effective screening strategy for asymptomatically infected individuals are considered for the future control of sexually transmitted E. histolytica infection. BackgroundAmebiasis, caused by Entamoeba histolytica, is spreading in developing countries and in many developed countries as a sexually transmitted infection. Here, we evaluated the efficacy of serological screening to identify asymptomatic E. histolytica infection as a potential epidemiological control measure to limit its spread. Methodology/Principal findingsThis cross-sectional study was carried out between January and March 2021 in an HIV-negative men who have sex with men (MSM) cohort at the National Center for Global Health and Medicine. Serological screening was performed using a commercially available ELISA kit. For seropositive individuals, we performed stool polymerase chain reaction (PCR) to determine current E. histolytica infection. We performed E. histolytica serological screening of 312 participants. None had a history of E. histolytica infection prior to the study. The overall E. histolytica seropositivity was 6.7% (21/312), which was similar to that found by the rapid plasma reagin test (17/312). We identified current infection in 8 of 20 seropositive participants (40.0%) by stool PCR. Conclusions/SignificanceOur serological screening approach constitutes a potentially practical epidemiological strategy. Active epidemiological surveys, in combination with an effective screening strategy for asymptomatically infected individuals, should be applied to help reduce sexually transmitted E. histolytica infections.