Diagnosis of Amebic Liver Abscess and Amebic Colitis by Detection of Entamoeba histolytica DNA in Blood,Urine, and Saliva by a Real-Time PCR Assay

The noninvasive diagnosis of amebic liver abscess is challenging, as most patients at the time of diagnosis do not have a concurrent intestinal infection with Entamoeba histolytica. Fecal testing for E. histolytica parasite antigen or DNA is negative in most patients. A real-time PCR assay was evaluated for detection of E. histolytica DNA in blood, urine, and saliva samples from amebic liver abscess as well as amebic colitis patients in Bangladesh. A total of 98 amebic liver abscess and 28 amebic colitis patients and 43 control subjects were examined. The real-time PCR assay detected E. histolytica DNA in 49%, 77%, and 69% of blood, urine, and saliva specimens from the amebic liver abscess patients. For amebic colitis the sensitivity of the real-time PCR assay for detection of E. histolytica DNA in blood, urine, and saliva was 36%, 61%, and 64%, respectively. All blood, urine, and saliva samples from control subjects were negative by the real-time PCR assay for E. histolytica DNA. When the real-time PCR assay results of the urine and saliva specimens were taken together (positive either in urine or saliva), the real-time PCR assay was 97% and 89% sensitive for detection of E. histolytica DNA in liver abscess and intestinal infection, respectively. We conclude that the detection of E. histolytica DNA in saliva and urine could be used as a diagnostic tool for amebic liver abscess.Entamoeba histolytica is a protozoan parasite that causes amebic diarrhea, colitis, and amebic liver abscess (ALA), mostly in developing countries (5, 7, 22, 25). Eighty percent of infected individuals remain asymptomatic carriers, while the other 20% develop clinically overt disease (7, 9, 22, 25). About 50 million symptomatic cases of amebiasis occur worldwide each year, resulting in 40,000 to 100,000 deaths annually (25). Mortality from amebiasis is mainly due to extra-amebic colitis, of which ALA is the most common.It is difficult to differentiate ALA from pyogenic liver abscess or other space-occupying lesions of the liver. Imaging techniques such as ultrasound, computed tomography, and magnetic resonance have excellent sensitivities for the detection of liver abscess arising from any cause, but there are no findings specific for ALA (13). Further complicating the diagnosis is the fact that most patients with an ALA do not have coexistent intestinal infection with E. histolytica (11). Therefore, detection of E. histolytica antigen or DNA in stool samples is not very helpful for the diagnosis of ALA (1, 6, 8, 12).The current means for diagnosis of ALA is the detection of antiamebic antibody by serological tests combined with aspiration of the abscess. The presence of serum antibodies against E. histolytica and the absence of bacteria in the abscess fluid are consistent with an ALA. A drawback of serologic tests is that the serum antibody levels in people from areas of endemicity remain positive for years after infection with E. histolytica (3, 16, 23). Therefore, antiamebic antibodies in the serum may be due to amebiasis in the past, limiting their specificity for the diagnosis of ALA. A further limitation to the current approach to ALA diagnosis is that collection of liver abscess pus is an invasive procedure that requires technical expertise and can be done only in specialized hospitals.Several groups have reported the detection of E. histolytica DNA in liver abscess pus, stool, and other clinical samples by PCR (14, 15, 18, 19, 21, 24, 26). A real-time PCR assay has also been used for detection of E. histolytica DNA in stool and liver abscess pus specimens (2, 10, 20). Real-time PCR has never been used for detection of E. histolytica DNA in urine, saliva, and blood specimens of ALA patients. In this study, we evaluated a real-time PCR assay to detect E. histolytica DNA in blood, urine, and saliva samples of amebic liver abscess and colitis patients in Bangladesh.