Bio-écologie des formes de résistance des protozoaires et des helminthes intestinaux dans les milieux aquatiques des zones rurales de la région du Centre (Cameroun) et influence des facteurs environnementaux

Abstract

Protozoa and intestinal helminths are among water contaminants since they are responsible for the most common waterborne diseases in humans. Due to the scarcity of potable water, some of the relatively protected aquatic environments are sometimes the only sources of water supply to populations in rural areas. This study that is aimed at evaluating the dynamics of resistance forms of protozoa and intestinal helminths in the aquatic mediums of Ngoumou, Akono, Obala and Monatélé municipalities (Central Region, Cameroon). More specifically, it involved evaluating the hydrological, morphometric and physicochemical parameters of some water bodies in these different localities; identify and enumerate resistance forms of protozoa and enteric helminths present the water samples; characterize the identified species and determine the abiotic factors influencing their dynamics in this environment. In all the localities 24 sampling stations were selected and 16 of these sampling stations were underground water (wells and sources) and 08 sampling stations for surface water (River Ebongo in Ngoumou, River Akono in Akono, l 'Afamba in Obala and the Sanaga River in Monatélé). Samples for physico-chemical and biological analyzes were carried out from April 2017 to April 2018 following standard methods. Biological analysis of the samples was done under an optical microscope and an electron microscope. Regarding the optical microscopic observations, the Ziehl-Neelsen staining technique was used for the isolation of oocysts, the Ritchie two-phase method for the isolation of cysts, and the formalinether concentration technique for isolation of helminth eggs and larvae. As for the electron microscopy analysis, the technique for isolating the resistance forms of protozoa and enteric helminths was carried out in collaboration with the parasitology laboratory of the University of Mansoura in Egypt. Regarding physicochemical analysis, the water temperature varied from 20 to 30 ° C from one station to another and was lower during the rainy season. These variations do not show a significant difference spatially for both groundwater and surface water (p> 0.05). The values of suspended solids and turbidity for underground water vary between 5 and 23 mg / L and between 6 and 24 FTU respectively. The highest values were recorded in the localities of Akono and Obala. On the other hand, in surface water, they vary between 18 and 24 mg / L for suspended matter and between 21 and 33 FTU for turbidity. The lowest values were observed in Ngoumou. The waters of Ngoumou and Akono are the most acidic with pH values <7. As for conductivity, it was lower in Ngoumou and Akono. For underground water, it varies between 81 and 747 μS / cm and was significant in the Obala and Monatélé wells. On the other hand, in surface water, conductivity remained very low (26 and 70 μS / cm). These waters are generally poorly mineralized and poor in organic matter (1.86 ± 0.8 mg / L), which indicates low organic pollution. The optical microscopic analyzes of the water samples revealed the presence of oocysts of Cryptosporidium spp. (109 cell / L), Entamoeba coli cysts (62 cell / L), Cyclospora cayetanensis oocysts (47 cell / L), Isospora belli (28 cell / L), Entamoeba histolytica cysts (31 cell / L) and Giardia intestinalis (19 cell / L). The genus Cryptosporidium is sporocyst-free and contains 04 sporozoites directly in contact with the cytoplasm. While Cyclospora cayetanensis, Isospora belli, Entamoeba histolytica and Giardia intestinalis are characterized by an intermediate (pre-cystic) form and a mature infesting form. Different eggs and larvae of helminth were observed and represented by Strongyloïdes stercoralis which occurs as a larva (61 cells / L); Ascaris spp. (10 cells / L) and Hymenolepis spp. (3 cells / L) in the form of eggs. This egg is characterized by an ovoid shape. The ellipsoidal shape is a characteristic of Ankylostoma spp. (5 cells / L) and Enterobius spp. (1 cell / L) is distinguished by a flattened side and a domed side. Fasciola spp. (4 cell / L) is very large in size and elliptical in shape; Diphyllobothrium spp. (2 cell / L) is characterized by an ovoid and squat shape. About electron microscopy, images corresponding to oocysts of the genus Cryptosporidium were recorded. The image shows a cluster in the center which corresponds to the 4 sporozoites, there is also a fold in the wall of the oocyst which corresponds to the area of the wall which would give way during the excystation. This observation also allowed us to develop a 4-layer model of the wall structure of the oocyst. The image of Ascaris egg in the electronic microscope shows 3 layers: a nipple outer layer, this nipple could result from erosion by the external environment. The granular surface, under electronic microscope shows a regular organization of protein fibers, the arrangement of which gives the Ascaris egg its rigidity, thin intermediate layer and an inner layer. The results obtained in this work will be useful in the development of policies for the sustainable management of aquatic ecosystems in the towns of Ngoumou, Akono, Obala and Monatélé and to a certain extent in the preventive control of diseases linked to the water.