This study was designed to investigate the impact of some environmental factors on the survival and behavior of the larval stages of Heterobilharzia americana, a mammalian schistosome that is restricted in distribution to the Gulf of Mexico states and the Carolinas. The chemostimulation of the miracidia by calcium and magnesium ions in different ratios of the two was also attempted. The effect of light and gravity on the miracidia and cercariae were investigated using tubes in horizontal and vertical positions with different illumination levels. The miracidia were found to be negatively geotropic and positively phototropic. Such behavior facilitates their contact with the snails. The cercariae were also found to behave in the same way, so to bring them to the proximity of the mammalian host. To study the effect of temperature and chemical factors on miracidia, wells of culture plates were used to expose the miracidia to such factors; their survival at different intervals was recorded. The survival of the miracidia increased with a decrease in temperature while snail infection took place at low as well as at high temperatures, with the optimum being at room temperature (24-25(DEGREES)C). The miracidia survived at salinity ranges between 0.02 and 0.1% NaCl with optimum survival occurring between 0.02 and 0.04% NaCl. The optimum pH for survival of the miracidia was found to be between 7 and 8, and they survived better when the pH was alkaline than when it was acidic. The miracidia were found to tolerate calcium better than magnesium, but survival was found to be better when both ions were present. The results indicate that these factors may have a direct impact on larval survival which might affect the distribution of the parasite if extreme ranges of the factors happen to occur in nature. In order to study the effect of calcium and magnesium on miracidial chemostimulation, a modified dialysis membrane chamber (DMC) was used. Chemostimulation of miracidia was demonstrated using well water conditioned by the snail Lymnaea (Pseudosuccinea) columella. Solutions of different Ca('++)/Mg('++) ratios were tested in DMC and their effects were observed. It was found that alteration in the miracidial behavior decreased as the calcium ion concentration increased and the magnesium ion concentration decreases in the solution tested. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI / acase@tulane.edu

acase@tulane.edu

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 / acase@tulane.edu