PCR differentiation of Entamoeba histolytica and Entamoeba dispar from patients with amoeba infection initially diagnosed by microscopy

Amoebiasis is a notifiable disease in Sweden and 400-500 cases are reported annually to the Swedish Institute for Infectious Disease Control (SMI). The true number of patients with Entamoeba histolytica infection is unknown as diagnosis mainly relies on cyst detection by microscopy. The main purpose of this study was to estimate the proportions between E. histolytica and E. dispar in patients with amoebic infection, using established PCR technologies. Secondly, we aimed to evaluate the usefulness of ethanol as a transport medium for samples forwarded for Entamoeba-PCR. Faecal samples from 207 patients with initial diagnosis of E. histolytica/E. dispar were referred to SMI for species differentiation. The PCR analysis showed that 165 patients were positive for E. dispar, whereas only 10 patients were positive for E. histolytica. No mixed infections were observed. The remaining 32 patients were negative both by microscopy and by PCR. Ethanol fixation was evaluated on 168 paired samples (transported unfixed or fixed in ethanol). Ethanol was found to be a useful transport medium as in 8 cases only the fixed sample was PCR-positive. This study shows that few patients in Sweden are infected with E. histolytica. The ability to differentiate E. dispar from E. histolytica should reduce the number of unnecessarily treated patients.