Étude expérimentale de l'adhésion des oeufs d'helminthes (Ascaris suum): conséquences pour l'environnement

Les oeufs de nématodes sont présents dans les eaux usées et dans les boues résiduaires. Suite à ce constat, l'objectif de ce travail est la mise en évidence d'une éventuelle capacité d'adhésion par contact et fixation des oeufs sur différentes surfaces. L'oeuf d'Ascaris a été utilisé comme modèle et divers paramètres sus- ceptibles d'intervenir ou de modifier les interactions ont été testés. Sur les matériaux de laboratoire, 32,5 % des oeufs se fixent sur les tubes de verre contre respectivement 15,7 % et 9,1 % sur des tubes en polystyrène et en polypropylène. En eau désionisée, les oeufs montrent une forte capacité d'adhésion sur le support hydrophile avec 75 % d'oeufs fixés sur les particules de poudre de verre contre uniquement 1,3 % sur les feuillets hydrophobes de talc. L'adhésion sur la poudre de verre est très rapide avec 55 % des oeufs fixés après 30 secondes. En présence d'une charge en adsorbant de 10 g/l, pour une valeur de pH égale à 9 et pour les concentrations ioniques (CaCl2 et NaCl 0,9M), l'adhésion des oeufs sur la poudre de verre atteint 99 %. Cependant, des températures égales à 2 °C et 3 60 °C ou l'utilisation de solutions éluantes (hypochlorite de sodium, formaldéhyde, détergents an ionique et caffonique) diminuent les phénomènes d'adhésion avec en particulier l'hypochlorite de sodium à 2° chl qui les supprime totalement. Toutes ces informations indiquent que l'adhésion intervient de manière importante. En effet, lors du traitement des effluents, ce phénomène favorise l'épuration par adhésion des oeufs au floc de matière organique avec cependant transfert de contaminants dans les boues.Dans les sols et sur les végétaux, l'adhésion favorise la contamination parasitaire des surfaces. L'utilisation d'effluents ou de boues contaminées devra impérativement respecter les normes ou les recommandations destinées à protéger des risques de transmission à l'homme et aux animaux.Les techniques destinées à évaluer la contamination parasitaire d'échantillons de l'environnement sont dépendantes de ces phénomènes d'adhésion. L'utilisation de solutions éluantes et notamment d'hypochlorite de sodium est indispensable.The intestinal nematodes use the environmental medium to realize their infestation cycle with eggs. In this study, the ability of helminth eggs to create binding in laboratory conditions is evaluated. This information will allow a better knowledge of the characteristics and the behaviour of the eggs in the environment and will give beginning of answer to the main question: are the nematodes eggs bound to sufaces and particulary to suspended matterin the environment or free particles?For this study, the model used is the Ascaris eggs collected in the end of the womb in order to work with fertile coated eggs. They seem to be the most common form found when the eggs are quantified in the water or wastewater medium. However, the aggregate in the suspension create difficulties for the counting and give a protect effect of the outer layer for the eggs into the aggregate. Physically, the aggregate properties are also different from the properties of one isolated egg. To spread out the eggs without bringing modifications of the egg coating, one filtration is performed on l00 µm filter to eliminate the aggregate higher or equal to 4 eggs. Before the study, a possible adhesion on the laboratory materials is performed.On glass materials, a strong adhesion is observed with 32.5% of eggs on the surfaces; on the other hand, on polypropylen and on polystyren, the adhesion is less important, respectively 9.1 and l5.7 % are adsorbed with a significant difference between these two results. Then for this work, polypropylen and polystyren materials are used. In deionised water (pH 6) with one 15 min stirring at 15 rpm, the behavior of the Ascaris eggs is studied on two surf'aces glass powder which is hydrophil particles with electronegative charges and talc which is hydrophob flakes with electronegative charges too. The results show a small adhesion on the hydrophob surfaces (l.3%) for a percentage of 75% on the hydrophil particles with the glass powder. In the same experimental conditions, the adhesion on hydrophil surfaces is confirmed with two other adhesion media: the muscovite and the glass wool which show a significant adsorption (96 and 98.5%). Onglass powder, the adhesion characteristics are developed with the study of 5 parameters: the contact time, the adhesion medium concentration, the pH, the temperature and the ionic concentration. For a low glass powder concentration (1g/l), a good adhesion is obtained with 65% of egg bound. The adsorption is obtained rapidly, 55% are already bound after 30 sec. The pH increase significanty the adhesion at the value 9 and an important decrease is observed atthe low and high temperatures (2 and 60°c). To complete this study, reagents used as desorption solution in the analytical techniques for the research of the helminth eggs in wastewater are tested. The eluting solutions as formalin and detergents increase in a considerable proportion the percentage of eggs non adsorbed, the outer layer properties could be modified by these reagents. For the sodium hypochlorite solution, the activity is stronger.This reagent eliminates the egg adhesion with only 0.1 percent of eggs bound. The action on the outer layer could be a destruction and then the loss of the adhesion properties. The practical implications of these adhesion properties are considerable: the wastewater depuration by physico-chemical treatments with the possibility of adhesion on floc particles for the eggs; the adhesion to the soil particles avoiding percolation and then the eggs accumulation in depth; on vegetables irrigated with wastewater the adsorption can improve the contamination and for the analytical techniques used to quantify parasite eggs in aqueous medium, we have to overcome the problem of the adhesion to the supports, with the use of eluting solution like sodium hypochlorite

Devenir des oeufs d'helminthes et des kystes de protozoaires dans un canal a ciel ouvert alimenté par les eaux usées de Marrakech

Dans la région de Marrakech, les eaux usées sont utilisées pour l'irrigation sans aucun traitement. Par ailleurs ces eaux usées ruissellent dans des canaux à ciel ouvert sur des distances supérieures à 2 km. Nous avons étudié le devenir des kystes de protozoaires et des oeufs d'helminthes sur le parcours d'un canal alimenté par un émissaire d'eau usée (E2). L'analyse parasitologique des eaux usées a montré que ces eaux contiennent plusieurs types de parasites. En effet, nous avons observé la présence des kystes de protozoaires (Entamoeba histolytica, Entamoebacoli, Giardiasp.) et des oeufs d'helminthes pathogènes (Ascaris,Trichuris, Enterobius, Hymenolepis...). L'étude de la charge parasitaire le long du cours d'eau usée montre une diminution du nombre de parasites dans l'eau usée en allant de l'embouchure S0 vers l'aval de l'émissaire E2. Avec des concentrations moyennes de 1,6.105 kystes/L et 145 oeufs/L à S0, alors qu'à 2 km de S0 (SV) il n'est plus retrouvé que 2,7.104 kystes/L et 33,4 oeufs/L. La charge parasitaire dans le sédiment du cours d'eau, contrairement à l'eau, augmente en s'éloignant de l'embouchure S0. Ainsi, les concentrations moyennes de kystes de protozoaires et les oeufs d'helminthes sont respectivement de 1,7.104 kystes/g et de 9,6 oeufs/g à 80 m de S0 et atteignent, 1,4.105 kystes/g et 78,1 oeufs/g à 2 km de S0. Le ruissellement des eaux usées sur un parcours de 2 Km, à ciel ouvert, montre des taux d'abattement importants des parasites. En effet, plus de 83 % des kystes de protozoaires et plus de 77 % des oeufs d'helminthes sont éliminés de l'effluent. Mais ces abattements restent insuffisants pour satisfaire les directives de l'OMS (1989) en matière de réutilisation des eaux usées en agriculture.The use of wastewater in agriculture in what is called "sewage farming" is becoming more widespread, particularly in countries with a severe shortage of water resources. Wastewater from the city of Marrakech is used for irrigation without any treatment. Nevertheless, the wastewater runs into an open channel of 2 km before being used. Thus, the fate of helminth eggs and protozoan cysts in this channel is of great importance for public health. The effluent studied carries wastewater from highly populated residential areas (Sidi Youssef Ben Ali, la Médina...). The primary channel originating from this effluent runs for 2 km with a variable width of 0.7 to 5.5 m in a clay soil. Secondary ramifications on the channel are used for irrigation. Water and sediment samples were collected at different locations on the channel twice monthly for five months (April-August). One litre wastewater samples and 10 g sediment samples were collected, at all stations on the channel. The samples were analysed using the concentration method of Teleman-Rivas as modified by Bailenger (1962) because of its reliability and low cost. Helminth eggs were then counted on MacMaster cells after addition of saturated saccharose solution to the samples. Protozoan cysts were quantified using a Thoma cell after addition of Lugol solution to the samples.Results of water analyses are expressed as the number of cysts or eggs per liter of wastewater and results for sediments are expressed as the number of cysts or eggs per gram of dry matter.- Wastewater samples from the effluent contained helminths as well as protozoa. All wastewater samples contained protozoan cysts. Among three species of protozoa identified, two were pathogenic: Entamoebahistolytica, Giardiasp. and one saprophytic Entamoebacoli. All water samples contained helminth eggs. Analyses for helminth egg revealed the presence of Nematodes (Ascaris, Trichuris, Enterobius) and Cestodes (Hymenolepis, Moniezia). This results mainly from Ascaris eggs that were encountered in all water samples. The concentration of helminth eggs in the sewage was much less than the protozoan cysts. In terms of densities, protozoan cysts were in the range 6.9 x 10[exp]4 to 2.0 x 10[exp]5 cysts /L with an average of 1.6 x 10[exp]5 cysts/L. Pathogenic protozoa represent 49 % of total cysts. The wastewater at the beginning of the channel contained from 102 to 238 helminth eggs/L with an average of 145 helminth eggs/L. Nematode eggs represented 72 % of total helminth eggs. Ascaris eggs dominated in the water samples with 75.6 eggs/L representing 52 % of total helminth eggs. The densities of protozoan cysts as well as helminth eggs in wastewater samples decreased dramatically along the open channel. Protozoan cysts dropped from 1.6 x 10[exp]5 cysts/L at the beginning of the channel to 2.7 x 10[exp]4 cysts/L at a distance 2 km in the open channel. Pathogenic protozoa decreased from 8.1 x 10[exp]4 cysts/L to 1.0 x 10[exp]4 cysts/L for the same distance. The average of helminth eggs also dropped from 145 eggs/L to 33 eggs/L. Ascaris eggs showed the highest decrease from 76 eggs/L to 12 eggs/L. The genus Trichuris showed the lowest decrease from 11 eggs/L to 6.8 eggs/L. - Analyses of sediment samples revealed the presence of all protozoan cysts and helminth eggs. Contrary to water samples, sediments samples showed an increase of all egg and cyst concentrations along the open channel. Protozoan cysts progressively increased from 1.7 x 10[exp]4 cysts/g at 80 m in the open channel to 1.4 x 10[exp]5 cysts/g at 2 km distance in the channel. Helminth parasites also increased from 9.6 eggs/g to 78 eggs/g for the same distance. This increase of helminth eggs and protozoan cysts resulted from the decrease of water flow velocity which caused their sedimentation. Parasites settle out of the water column because of their own weight and because they adsorb to particles accelerating their settling. Among all parasites Ascaris eggs settle out first before all other nematode eggs. Ascaris eggs were detected at 80 m in the open channel while Enterobius eggs were not observed until 560 m in the channel. Trichuris eggs were not observed in any sediment sample. Trichuris eggs are more easily carried by the water flow because of their hydrodynamic fusiform shape which may explain their absence in sediment samples. In conclusion, the parasitic quality of a domestic wastewater in Marrakech showed significant improvement after 2 km in an open channel. Both helminth eggs and protozoan cysts showed significant removal percentage of 77 % and 83 % after 2 km running in the open channel. The best percent removal of protozoan cysts was observed for pathogenic protozoa with 88 % for Entamoeba histolytica and 87 % for Giardia sp. For helminth eggs, Ascaris eggs showed the highest removal percentage with 85 % while Trichuris showed the lowest with 37 %. However, the concentration of helminth eggs and protozoan cysts, after the sewage flows over a distance of 2 km in the open channel, are still higher than the guidelines of the W.H.O. (1989) for the use of wastewater in agriculture (less than one nematode egg per litre). These wastewaters require further treatment before they can be used for irrigation

Wastewater epuration by infiltration-percolation on sand: results in Ben Sergao

International audienc

Stratégie d'échantillonnage et dénombrement d'oeufs d'helminthes dans les boues résiduaires

Récemment, l'attention a été attirée sur l'importance des critères parasitologiques dans l'évaluation de la qualité des eaux usées et des boues. Dans ces conditions, des méthodes de quantification couplées à des stratégies d'échantillonnage bien définies sont nécessaires. Dans cette optique, quatre méthodes de flottation ou de sédimentation ont été évaluées, comportant une étude des différents paramètres susceptibles d'affecter l'échantillonnage : jour et lieu de prélèvement, type de boues. Les effets possibles de ces paramètres ont été analysés à l'aide d'un plan mixte à trois niveaux et répétitions binaires. Enfin, les performances des diverses méthodes ont été testées vis-à-vis de la charge parasitaire, après contamination artificielle, les autres paramètres étant placés sous contraintes. Les résultats de l'étude ont permis de sélectionner la méthode la mieux adaptée en fonction du niveau de contamination et du type de boues

Waste-water treatment by infiltration-percolation on sand: results in Ben Sergao

International audienc

Waste-water treatment by infiltration-percolation on sand: results in Ben Sergao

International audienc