Viability of entamoeba histolytica cysts and morphology of five low-temperature entamoeba histolytica-like amebae
Description
More than a century has elapsed since Losch first described the causal agent of amebiasis in 1875 and much useful information has been obtained. However, much controversy has also arisen, especially as regards the transmission of the infection and the taxonomy and pathogenicity of different 'races' or 'strains' of Entamoeba histolytica. Many questions still remain unanswered and the infection is still a mysterious field in some respects The present study was designed to determine the effect of variations in fecal moisture on the viability of Entamoeba histolytica cysts. The role of the thin fecal film that remains around the anus after defecation, as well as the effect of the perianal layer of wax in the transmission of amebiasis were investigated. The survival of the amebic cysts in soil and in water was also studied To achieve these study objectives, fecal samples positive for Entamoeba histolytica cysts were collected, prepared and exposed to various conditions. The survival of cysts was determined by the ability to grow in modified Boeck and Drbohlav's culture medium Results showed that cysts of Entamoeba histolytica presented a widely variable viability, from as short a period as less than 1 day to as long as 50 days and the survival of cysts varied directly with the degree of fecal moisture It was also noted that the longevity of the amebic cyst depends upon many factors. Among these, the strain of the ameba, the quantity and quality of the cysts, the type of stool and the environmental conditions were the most important. Additionally, the method used to determine cyst viability, and the type of culture medium, influenced the outcome of viability measurements Findings in this study confirmed the beneficial effect of moisture on the viability of Entamoeba histolytica cysts and emphasized the importance of water as a principal means of transmission of amebiasis. The role played by contaminated soil as previously suggested was also reaffirmed. Furthermore, the results, along with some epidemiological observations, suggested a similarity between the transmission pattern of Entamoeba histolytica and that of Enterobius vermicularis and Hymenolepis nana, indicating that under suitable conditions, person to person contact could play an important role in the spread of the infection Using the iron-hematoxylin method, a morphological study was also conducted on some low-temperature strains of Entamoeba histolytica. Five strains were isolated and identified by their ability to grow at 27 as well as at 37(DEGREES)C. It was found that a demarcation between this group of low-temperature amebae and the group of regular or classic Entamoeba histolytica could be established by their ability to grow below 28(DEGREES)C. Some regular strains of the ameba could excyst at this limit while most of them had not problem excysting and growing at 29(DEGREES)C. Below 28(DEGREES)C, however, only low-temperature strains could proliferate Even though the comparison between the morphology of the two groups of Entamoeba did not show any clear-cut differences, three nuclear characteristics deserve attention. They were, in order of importance: (1) the crescent shape of the chromatin layer lining the nuclear membrane, (2) the unusual thickness of this layer, and (3) the apparent absence of the nuclear karyosome. These characteristics, or at least the first two, have been consistently observed in all presently available reports on low-temperature Entamoeba histolytica. A review on the numerous dissimilarities between these amebae and the regular group implied the eventual necessity of establishing a new species