Entamoeba histolytica DNA Detection in Serum from Patients with Suspected Amoebic Liver Abscess

Amoebic liver abscess (ALA) is regularly seen in travelers or immigrants from tropical countries. The diagnosis relies on liver imaging that is not specific and on the detection of anti-Entamoeba histolytica antibodies, which cannot distinguish an acute from a former infection. We tested whether E. histolytica DNA detection in serum can improve the diagnosis of ALA. We retrospectively tested available serum samples taken from patients with ALA and non-ALA space-occupying lesions of the liver between 1 January 2010 and 30 November 2019. The quantitative PCR (qPCR) assay tested specifically amplifies a 99-bp fragment of the small-subunit rRNA gene of E. histolytica We analyzed 76 samples (19 ALA and 57 non-ALA samples) collected from 76 patients within 6 days before and after the antiamoebic treatment. Serum qPCR results were positive for 17 of 19 ALA patients and for none of the control patients (sensitivity and specificity were 89.5% and 100%, respectively). In parallel, the sensitivity and specificity of anti-E. histolytica antibody detection were 100% and 89.5%, respectively. The two false-negative qPCR results may be explained by ongoing metronidazole treatment or a possible persistent seropositivity that was not caused by the current liver abscess. Additionally, of 12 abscess pus aspirates (5 from ALA and 7 from non-ALA samples) tested, 5 were qPCR positive and 7 were qPCR negative, with concordant results in serum. This study demonstrates that cell-free circulating E. histolytica DNA can be detected in serum in ALA. This may assist in both positive diagnoses and treatment efficacy follow-up. The origin of this circulating DNA remains to be investigated.