Entamoeba moshkovskii (Tshalaia, 1941): morpho-biological characterization of new strains isolated from the environment, and a review of the literature

Prevalence and molecular characterization of Entamoeba moshkovskii in diarrheal patients from Eastern India

BACKGROUND

Importance of the amphizoic amoeba Entamoeba moshkovskii is increasing in the study of amoebiasis as a common human pathogen in some settings. Limited studies are found on the genetic and phylogenetic characterization of E. moshkovskii from India; hence remain largely unknown. In this study, we determined the prevalence and characterized the E. moshkovskii isolates in eastern India.

METHODS

A three-year systemic surveillance study among a total of 6051 diarrhoeal patients from ID Hospital and BC Roy Hospital, Kolkata was conducted for E. moshkovskii detection via a nested PCR system targeting 18S rRNA locus. The outer primer set detected the genus Entamoeba and the inner primer pair identified the E. moshkovskii species. The 18S rRNA locus of the positive samples was sequenced. Genetic and phylogenetic structures were determined using DnaSP.v5 and MEGA-X. GraphPad Prism (v.8.4.2), CA, USA was used to analyze the statistical data.

RESULT

4.84% (95%CI = 0.0433-0.0541) samples were positive for Entamoeba spp and 3.12% (95%CI = 0.027-0.036) were infected with E. moshkovskii. E. moshkovskii infection was significantly associated with age groups (X2 = 26.01, P<0.0001) but not with gender (Fisher's exact test = 0.2548, P<0.05). A unique seasonal pattern was found for E. moshkovskii infection. Additionally, 46.56% (95%CI = 0.396-0.537) were sole E. moshkovskii infections and significantly associated with diarrheal incidence (X2 = 335.5,df = 9; P<0.0001). Sequencing revealed that the local E. moshkovskii strains were 99.59%-100% identical to the prototype (GenBank: KP722605.1). The study found certain SNPs that showed a correlation with clinical features, but it is not necessarily indicative of direct control over pathogenicity. However, SNPs in the 18S rRNA gene could impact the biology of the amoeba and serve as a useful phylogenetic marker for identifying pathogenic E. moshkovskii isolates. Neutrality tests of different coinfected subgroups indicated deviations from neutrality and implied population expansion after a bottleneck event or a selective sweep and/or purifying selection in co-infected subgroups. The majority of FST values of different coinfected subgroups were <0.25, indicating low to moderate genetic differentiation within the subgroups of this geographical area.

CONCLUSION

The findings reveal the epidemiological significance of E. moshkovskii infection in Eastern India as the first report in this geographical area and expose this species as a possible emerging enteric pathogen in India. Our findings provide useful knowledge for further research and the development of future control strategies against E. moshkovskii.

First molecular identification of Entamoeba moshkovskii in Malaysia

Entamoeba moshkovskii and Entamoeba dispar are microscopically indistinguishable from the pathogenic species Entamoeba histolytica. Although sporadic cases of human infection with E. moshkovskii have been reported, the amoeba is still considered primarily as a free-living amoeba. A cross-sectional study was carried out among Orang Asli communities in 3 different states of Peninsular Malaysia. Fecal samples were examined by formalin-ether sedimentation and trichrome staining techniques and then single-round PCR assay was used to detect E. moshkovskii. Out of 500 fecal samples examined microscopically, 93 (18·6%) samples were positive for E. histolytica/E. dispar/E. moshkovskii complex cysts and/or trophozoites. PCR products were detected in 106 fecal samples. E. moshkovskii isolates were detected in 13 (12·3%) fecal samples. Of the 13 E. moshkovskii-positive samples, 5 were of single isolation of E. moshkovskii, 6 were also positive for E. dispar, and only 2 samples were positive for E. dispar and E. histolytica. Moreover, 3 E. moshkovskii-positive samples were collected from symptomatic individuals while the remaining 10 samples were from asymptomatic subjects. This is the first report on the identification of E. moshkovskii in Malaysia. Further studies are needed to confirm the pathogenicity of E. moshkovskii infection and determine the epidemiology among Orang Asli communities in Malaysia.

Entamoeba moshkovskii perspectives of a new agent to be considered in the diagnosis of amebiasis

During the last decade Entamoeba moshkovskii has become relevant given its capacity to infect humans, especially when considering that it is morphologically indistinguishable from E. histolytica. For a long time, E. moshkovskii was considered as a free living amoeba, but in the last decade it has been demonstrated that E. moshkovskii can infect humans and can be found more frequently in regions where amebiasis shows high prevalence values, becoming a challenge to differentiate it from the E. histolytica/E. dispar complex. Recently there have been studies that raise the possibility that E. moshkovskii could be a pathogenic species, as there are reports in different countries that associated this infection with gastrointestinal symptoms even though others have described it as a non pathogenic species. For this reasons, both clinical and epidemiological studies are required.

Entamoeba moshkovskii is associated with diarrhea in infants and causes diarrhea and colitis in mice

BACKGROUND

Entamoeba moshkovskii is prevalent in developing countries and morphologically indistinguishable from pathogenic Entamoeba histolytica and nonpathogenic Entamoeba dispar. It is not known if E. moshkovskii is pathogenic.

METHODS

Mice were intracecally challenged with the trophozoites of each Entamoeba spp. to test the ability to cause diarrhea, and infants in Bangladesh were prospectively observed to see if newly acquired E. moshkovskii infection was associated with diarrhea.

RESULTS

E. moshkovskii and E. histolytica caused diarrhea and weight loss in susceptible mice. E. dispar infected none of the mouse strains tested. In Mirpur, Dhaka, Bangladesh, E. moshkovskii, E. histolytica, and E. dispar were identified in 42 (2.95%), 66 (4.63%), and 5 (0.35%), respectively, of 1426 diarrheal episodes in 385 children followed prospectively from birth to one year of age. Diarrhea occurred temporally with acquisition of a new E. moshkovskii infection: in the 2 months preceding E. moshkvskii-associated diarrhea, 86% (36 of 42) of monthly surveillance stool samples were negative for E. moshkovskii.

CONCLUSIONS

E. moshkovskii was found to be pathogenic in mice. In children, the acquisition of E. moshkovskii infection was associated with diarrhea. These data are consistent with E. moshkovskii causing disease, indicating that it is important to reexamine its pathogenicity.

Entamoeba moshkovskii infections in Sydney, Australia

Entamoeba moshkovskii is considered to be a free-living ameba, which is morphologically similar, but biochemically and genetically different, to Entamoeba histolytica and Entamoeba dispar. However, recent studies have suggested that E. moshkovskii may be a "potential" pathogen, with infections giving rise to diarrhea and other intestinal disorders. Microscopy and polymerase chain reaction (PCR) targeting the 18S ribosomal (r) DNA was performed on fecal samples collected from patients presenting with diarrhea and other gastrointestinal disorders (test group), as well as fecal samples collected from healthy controls (control group). Of the 110 patients microscopically positive for the Entamoeba species, 55/110 (50%) samples were positive for E. moshkovskii in the test group of patients presenting with diarrhea. E. moshkovskii was the only pathogen detected (including bacteria or viruses) in 3/55 (5.5%) of the test group of patients presenting with diarrhea and abdominal pain. The DNA of E. moshkovskii was not detected in the fecal samples collected from the healthy controls. These results suggest that E. moshkovskii may not simply be a commensal of the human gastrointestinal tract and provides evidence for E. moshkovskii as a "potential" pathogen in the case of diarrhea and other gastrointestinal disorders. Further studies are needed to determine the role of E. moshkovskii in causing diarrheal diseases in our population.

Laboratory diagnostic techniques for Entamoeba species

The genus Entamoeba contains many species, six of which (Entamoeba histolytica, Entamoeba dispar, Entamoeba moshkovskii, Entamoeba polecki, Entamoeba coli, and Entamoeba hartmanni) reside in the human intestinal lumen. Entamoeba histolytica is the causative agent of amebiasis and is considered a leading parasitic cause of death worldwide in humans. Although recent studies highlight the recovery of E. dispar and E. moshkovskii from patients with gastrointestinal symptoms, there is still no convincing evidence of a causal link between the presence of these two species and the symptoms of the host. New approaches to the identification of E. histolytica are based on detection of E. histolytica-specific antigen and DNA in stool and other clinical samples. Several molecular diagnostic tests, including conventional and real-time PCR, have been developed for the detection and differentiation of E. histolytica, E. dispar, and E. moshkovskii in clinical samples. The purpose of this review is to discuss different methods that exist for the identification of E. histolytica, E. dispar, and E. moshkovskii which are available to the clinical diagnostic laboratory. To address the need for a specific diagnostic test for amebiasis, a substantial amount of work has been carried out over the last decade in different parts of the world. The molecular diagnostic tests are increasingly being used for both clinical and research purposes. In order to minimize undue treatment of individuals infected with other species of Entamoeba such as E. dispar and E. moshkovskii, efforts have been made for specific diagnosis of E. histolytica infection and not to treat based simply on the microscopic examination of Entamoeba species in the stool. The incorporation of many new technologies into the diagnostic laboratory will lead to a better understanding of the public health problem and measures to control the disease.

Molecular characterization of peroxiredoxin from Entamoeba moshkovskii and a comparison with Entamoeba histolytica

Peroxiredoxin of the pathogenic parasite, Entamoeba histolytica, is thought to be involved in protection from oxidative attack by host phagocytic cells and endogenously generated hydrogen peroxide. In this study, we cloned peroxiredoxin genes from the nonpathogenic ameba, Entamoeba moshkovskii, and characterized the peroxiredoxin protein. The open reading frame of three cloned cDNAs was demonstrated to encode a polypeptide of 218 or 217 amino acids. Identity of the amino acid sequence of peroxiredoxins between E. moshkovskii and E. histolytica was considerably high (77-81%), but the N-terminus portion of E. moshkovskii peroxiredoxin was shorter than that of E. histolytica. A recombinant peroxiredoxin of E. moshkovskii expressed in Escherichia coli exhibited hydrogen peroxidase activity. Its K(m) and V(max) values of 35 microM and 0.07 micromol/min/mg protein were approximately 1 and 1.5 times greater than E. histolytica peroxiredoxin, respectively. In addition, the protective effect of E. moshkovskii peroxiredoxin against oxidative-nicking of supercoiled plasmid DNA was shown to be greater than that of E. histolytica peroxiredoxin. Confocal laser scanning microscopy, using polyclonal antibody against the recombinant E. moshkovskii peroxiredoxin, demonstrated that this protein was localized in the nucleus and cytoplasm of trophozoites, supporting its function as a protectant against DNA damage. Southern blot and real-time reverse transcription PCR analyses of the E. moshkovskii peroxiredoxin gene demonstrated that it was a multi-copy gene and its expression was comparable to that of E. histolytica. These results suggest that the antioxidant peroxiredoxin is important for protection against endogenously generated hydrogen peroxide in the nonpathogenic ameba.

The Laredo strain and other 'Entamoeba histolytica-like' amoebae are Entamoeba moshkovskii

A small number of Entamoeba isolates from humans, the best known of which is the 'Laredo' strain, have the ability to grow at room temperature. This peculiarity, along with other characteristics, distinguishes the strains from the human pathogen E. histolytica despite their being morphologically inseparable. In contrast, these 'E. histolytica-like' strains share several features with E. moshkovskii, which is most frequently isolated from polluted water. To examine the taxonomic relationships among these morphologically similar organisms, we have used polymerase chain reaction amplification of the small subunit ribosomal RNA gene combined with restriction fragment length polymorphism analysis, 'riboprinting'. The results clearly show that the 'E. histolytica-like' amoebae are indeed strains of E. moshkovskii, and not closely related to E. histolytica.