Thesis for: Ph'D, Advisor: Evens Emmanuel et Christian Raccurt


Protozoa of the genus Cryptosporidium are intestinal parasites that infect the intestines of many vertebrates. They often generate an opportunistic parasitosis in immunodeficient individuals. These cosmopolitan protists can be found in different types of water, distribution in particular. The oocyst is the form of resistance and spread of the parasite in the environment. Frequently involved in acute and chronic diarrhea in children and adults, Cryptosporidium is a real public health issue in developing countries. In Haiti, Cryptosporidium oocysts were found in surface water and drinking water, including our study site, the city of Les Cayes.

After having assessed the level of movement of oocysts in the environment of our study site, we tried: i) to identify the sources of this pollution by analyzing feces of animal freely circulating in the city ii) to understand the presence of Cryptosporidium in the aquifer of the city by the study of soil properties (particle size, testing percolation column, static tests) and therefore the mechanisms of transfer of oocysts from the surface to groundwater iii) to assess the health risk of the population.

Of the 129 stool specimens of various species of animals analyzed, the presence of Cryptosporidium coproantigens is noted in 27 by the use of commercial kits from which 17 were confirmed by the detection of oocysts by staining. The soil grain size is ≤ 2 mm. There is an absence of oocysts in the leachate obtained from percolation tests. This result is due to the quality of soil samples and treatments. On the other hand, the tests reveal a static adsorption on the sand of oocysts confirmed by confocal microscopy observation. As for risk estimation, we defined two groups in the exposed population: immunocompetent and immunocompromised. It appears as expected a high risk for the immunocompromised.

The results of our work, after all incomplete to assess the real impact of the movement of oocysts on the health of exposed populations, have nonetheless revealed the extent of the phenomenon and allowed us to consider possible remedial strategies to improve the quality of water available to people. For example, zeolites, which are natural materials, are excellent ion exchangers and their use in the treatment process of water contaminated with oocysts can probably generate a significant level of retention.

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    ABSTRACT: The physico-chemical behavior of Cryptosporidium oocysts was investigated during their transfer through an alluvial formation from Les Cayes (Haiti) via batch tests. Five approximately 3kg soil samples were collected and combined prior to batch tests from the alluvial formations. The experiments were carried out at soil pH by equilibrating different ranges of pure oocysts concentrations and soil samples with 3mM CaCl2 and 1mM NaBr as electrolyte. We used the Debye-Hückel equation describing ion activity in a solution for a given ionic strength. The equilibrium adsorption mechanism is used to enumerate the oocysts in the soil. The results suggest that the oocysts behavior in porous media depends on soil characteristics such as soil pH, the nature of the mineral and organic constituents of the soil and the ionic strength and activities in solution. These results show that a total transfer in batch containing NaBr solutions against a partial one in batch containing CaCl2 solutions depends on the oocysts media concentration. To confirm the oocysts number retained in soil, confocal microscopy was successfully used and the images demonstrate that the majority of oocysts were retained at the range of concentrations tested. The findings from this study demonstrated that the retention of C. Parvum in soils may be influenced by chemical conditions and soils characteristics, which are important for groundwater risk assessment.
    Chemosphere 12/2013; 103. DOI:10.1016/j.chemosphere.2013.11.045 · 3.34 Impact Factor