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Entamoeba histolytica--the virulence of imported strains
M Giboda1, O Ditrich, N Vrchotová
1Institute of Parasitology, Czechoslovak Academy of Sciences, Ceské Budĕjovice.
Abstract:
We tested the virulence of 15 strains of Entamoeba histolytica, imported to Czechoslovakia, by intracaecal inoculation of laboratory rats. According to the scoring system of Neal, none of the 15 strains possessed the virulence index greater than 2. This indicates that all the organisms tested should be classified as avirulent. However, it should be noted that all the strains produced infection of the caecum and thus should be considered infective for rat. For 7 strains, isoenzyme patterns were determined for PGM, HK and ME. One imported strain, obtained from student from Congo, demonstrated isoenzyme pattern for PGM and HK indicated that the strain was virulent. This organisms had the index of virulence 1.8 (avirulent) in animal experiment; it was isolated from cysts of clinically asymptomatic patient. Examination of the rectal mucosa of the donor of the strain indicated typical chronic catarrhal proctitis of mild degree. Examination of the patient's serum demonstrated the presence of anti E. histolytica antibodies by CIEP, while the ELISA test was negative. Twenty-one cyst carriers were examined by rectoscopy. Pathologic changes were observed in 20 of these, as follows: altered vascular structure (13X), roughened mucosa (12X), mucosal reddening (10X), decreased glistening (7X), mucus in mucosa (5X), inflammatory pseudopolypes (2X), ulcers (2X), enanthema (1X). Histological biopsies were obtained in 15 cases. One was considered normal. Remaining 14 biopsies exhibited following morphological changes: increased mucus secretion (8X), edema (7X), lymphocytic and plasmocytic infiltration (6X), lymphocytic and plasmocytic infiltration in addition to the presence of eosinophilic granulocytes (6X), presence of mucophages (5X), haemorrhages (4X), increased vascularity (3X), lymphocytic and plasmocytic infiltration with presence of extremely abundant eosinophilic granulocytes (1X), erosive-ulcerative changes of mucosa (1X). The changes observed indicated chronic catarrhal proctitis with expression to greater or less degree of signs of chronic catarrhal inflammation.
Insights
Most Entamoeba histolytica strains tested were avirulent in rats, though all caused cecal infection. One strain, despite low virulence in animals, showed a virulent isoenzyme pattern and was linked to chronic proctitis in its human host.
Area of Science:
- Medical Parasitology
- Infectious Diseases
- Gastroenterology
Background:
- Entamoeba histolytica is a significant cause of amebiasis worldwide.
- Virulence factors and pathogenic potential of E. histolytica strains vary.
- Understanding strain virulence is crucial for disease management and epidemiology.
Purpose of the Study:
- To assess the virulence of imported Entamoeba histolytica strains in a rat model.
- To correlate isoenzyme patterns with virulence and clinical findings.
- To investigate colonic mucosal changes in asymptomatic E. histolytica cyst carriers.
Main Methods:
- Intracaecal inoculation of laboratory rats with 15 E. histolytica strains.
- Virulence scoring using Neal's system and isoenzyme analysis (PGM, HK, ME) for 7 strains.
- Rectoscopy and histological examination of rectal biopsies from 21 cyst carriers.
Main Results:
- All 15 strains showed low virulence (index ≤ 2) in rats but infected the cecum.
- One imported strain exhibited a virulent isoenzyme pattern (PGM, HK) despite a low virulence index (1.8).
- Rectal pathology, including chronic catarrhal proctitis, was observed in 20 of 21 cyst carriers.
Conclusions:
- Most imported E. histolytica strains appear avirulent in rats, but remain infective.
- Isoenzyme analysis may identify potentially virulent strains missed by animal models.
- Asymptomatic cyst carriers can harbor significant rectal mucosal pathology.