Effect of some environmental factors on the miracidium and cercaria of Heterobilharzia americana Price, 1929
Description
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