Date Published: April 3, 2019
Publisher: Public Library of Science
Author(s): Aradhana Singh, Tuhina Banerjee, Raju Kumar, Sunit Kumar Shukla, Patricia Talamas-Rohana.
Amebiasis, caused by Entamoeba histolytica (E. histolytica), is a significant cause of morbidity and mortality in developing countries. Mortality due to amebiasis is mostly by extra intestinal infections, amebic liver abscess being the most common one. This study was conducted to determine the current epidemiological status, risk factors, associated microflora and strain variation of E. histolytica causing liver abscesses.
A total of 115 liver abscess cases comprising of 107 (93%) males and 8 (6.9%) females were included in the study. Microscopic examination of pus samples from the abscesses and species discrimination using nested multiplex PCR showed the presence of E. histolytica in 101 (87.5%) cases. Data collected by face to face interviews using a pre tested questionnaire suggested intake of untreated drinking water (ORs: 6.4, p = 0.002), habit of alcohol consumption (ORs: 4.0, p = 0.019) and lack of urban services (ORs: 0.08, p = 0.017) to be major risk factors associated with E. histolytica infections. The study of associated bacterial flora through aerobic culture of liver aspirates and conventional PCR for detection of anaerobes revealed the presence of Fusobacterium (19, 25.5%), Peptococcus (19, 25.5%), Prevotella (18, 24.3%), Bacteroides (8, 10.8%), Staphylococcus aureus (3, 4%), Escherichia coli (2, 2.7%), Peptostreptococcus (2, 2.7%), Clostridium (2, 2.7%) and Klebsiella pneumoniae (1, 1.3%). Further to study the clonality, genotyping of E. histolytica targeting six tRNA-linked polymorphic STR loci (A-L, D-A, N-K, R-R, STGA -D and S-Q) was carried out which showed the presence of 89 different genotypes in the liver aspirate samples.
The findings highlight the high prevalence of genetically diverse E. histolytica from the liver abscess cases in this geographical region. Low socio-economic status and habit of alcohol consumption were important predictors of amebic liver abscess.
Amebiasis is still a major health problem in tropical countries including India. Despite a decrease in mortality due to amebiasis by 14.8% over a decade  the number of affected persons has increased to 500 million people worldwide . Mortality due to amebiasis is mostly by extra intestinal infections, amebic liver abscess being the most common one . In majority of cases, this parasite remains as commensal in the intestine of humans but in some conditions it breaches the epithelial barrier and through blood supply reaches to different organs causing abscesses. Overall 10% of the world’s population is infected with Entamoeba histolytica (E. histolytica) but out of this only 1% becomes symptomatic. Nearly 20% of the Indian population show manifestations of the disease. .
The present study showed a high overall prevalence rate of 87.8% of E. histolytica infections in the cases of liver abscess. This is in concordance with a similar study in our adjoining area which showed the prevalence of amebic DNA in 83.5% of the liver aspirate samples . The sensitivity of PCR was higher as compared with microscopy in agreement with the other studies where PCR was found to be more reliable source of E. histolytica detection [14,15], the reason being that the E. histolytica is morphologically similar to E. dispar and E. moshkovskii and thus cannot be differentiated using microscopy. Additionally, E. histolytica trophozoites remain motile or viable for only a few minutes after coming in contact with air after aspiration, thus making the detection of this parasite by microscopy difficult. However, contrary to our results a study  showed microscopy to be more sensitive mode of detection of amebiasis. The reason behind the less sensitivity of PCR in the study was given to low parasite density and time related degeneration of trophozoites. In our study, high sensitivity of the molecular method can be attributed to use of nested PCR for the detection.