Etude épidémiologique de la schistosomiase urinaire et des helminthiases intestinales chez les écoliers dans deux zones écologiques du Tchad: caractéristation des association parasitaires et impact sur l'état nutritionnel

Abstract

Pathogenic parasites are the cause of countless infections and constitute a major public health problem. Because of their specific diversity and their ubiquity in various environments, most of these organisms infest their hosts simultaneously. Among all pathogens, helminth parasites, which are vermiform metazoans, are ubiquitous and cosmopolitan. In humans, their prevalence reaches 20% for all pathogens, and 51.7% of the taxa listed are parasites of the intestinal tract. They infest approximately 1.5 billion people in the southern hemisphere. Through their spoliating actions, they interfere with feeding, thus aggravating malnutrition in children. In Chad, most of the studies carried out concern the description of helminthiases as well as the factors favoring their propagation, but hardly mention the interactions that may exist between these different helminth species. This was a cross-sectional and descriptive study that took place from September 2021 to February 2022 in the Sudanian and Sahelian zones of Chad. It was undertaken to characterize helminthic associations (intestinal helminths and S. haematobium) and resulting interactions in school-aged children in the Sahelian and Sudanian zones. A total of 1443 pupils were recruited from 19 elementary school (6 in the Sahelian zone and 13 in the Sudanian zone) using three-level cluster sampling. Stool samples collected were examined by the quantitative kato-katz method; while urine samples underwent two (2) analyses namely: dipstick test and centrifugation. The parasitic associations were characterized thanks to the ecological indices of association namely: Dice, Forbes and the tetrachoric coefficient. A total of 10 morpho-species grouped into three classes were identified in this study. These are three (3) Nematodes (Ascaris lumbricoides, Ancylostoma duodenalis and Enterobius vermicularis), three (3) trematodes (Schistosoma haematobium, Schistosoma mansoni and Fasciola hepatica), and four (4) cestodes (Hymenolepis nana, Diphillobotrium latum, Taenia saginata and Taenia solium). Schistosoma haematobium (45.46%), A. lumbricoides (16.41%), S. mansoni (14%), and H. nana (6.53%) were predominantly diagnosed in pupils. Prevalences of 35.87% and 45.46% were obtained for intestinal helminthiasis and urinary schistosomiasis respectively. Except for S. mansoni for which girls were significantly more often infested than boys, no other significant gender differences in infestation were found for the other parasites. Pupils in the 5-9 age group were relatively more often infested with E. vermicularis compared to those aged 10 years and older. Polyparasitism was found in 23.08% of all infested students, with significantly higher frequencies in the Sudanian zone (26.47%) than in the Sahelian zone (16.42%). Pupils harbored 1 to 5 parasite species/infested individual with an average of 1.46 ±0.81 species per carrier individual. Logistic regression analysis revealed that students in the 10-14 age group and those living in the Sudanian zone were xxvi ABSTRACTxxvii significantly more likely to be concomitantly infested with 2 or more parasite species. A total of 29 types of infracommunities were counted in our study population with 14, 9, 5, and 1 of these infracommunities consisting of 2, 3, 4, and 5 parasitic species respectively. Analysis of binary interspecific associations by ecological indices showed that the majority of associations were very weak and weak, appeared more frequently than expected by the laws of chance, with no positive or negative interactions between any two taxa. The mean ovule loads of the different species of intestinal parasites in both ecological zones were moderate, except for A. lumbricoides whose mean EPG ( ̅𝑬𝑷𝑮 ̅̅̅̅̅ )) was light in the Sahelian zone. Geometric Mean Eggs (GME) of S. haematobium were light in both ecological zones. Of the 656 infested pupils, 495 (75.46%) were hematuria positive, while 24.54% microhematuria positive were not infected with S. haematobium. Clear urine was hematuric in 11.55% and red urine in 89.39%. Also, 40.75% of malnourished children were infested by at least one species of helminth, 69.97% by S. haematobium, and 38.49% concomitantly by 2 or more species of parasites. From all of the above, it should be noted that the Sudanian and Sahelian zones of Chad are home to a multitude of parasitic species. This specific richness is at the origin of the high rate of polyparasitism in this part of the country. The State, through the Ministry of Public Health, must assume all its responsibilities in order to promulgate effective control measures against bilharzia and intestinal helminthiasis. It would be important to set up a specialized control program with a well-defined schedule of conditions.