[Historical aspects of the risk factors of Schistosoma intercalatum schistosomiasis].

Bilharziosis is a considerable public health problem. It is caused by many species of schistosoma, four of which have wide geographical distribution: Schistosoma mansoni, S. haematobium, S. japonicum and S. intercalatum. The recently discovered S. intercalatum is limited to central and west Africa. Its spread is progressive and its pathogenicity is not completely known. S. intercalatum bilharziosis is usually manifested in the form of dysentery. The physiopathologic explanation of this clinical manifestation is less clear. Immunopathologically, the formation of an inflammatory granuloma constitutes the origin of its symptoms. This is due to many biological factors including delayed hypersensitivity reactions. All cellular immunity changes will facilitate the appearance of symptoms. Our aim has been to show the importance of malnutrition as a pathogenic factor of S. intercalatum bilharziosis. The initial research hypothesis was as follows: malnutrition plays a role in the evolution of a patient from an asymptomatic state of infection to a symptomatic state of illness. We carried out the study in the suburbs of Bata, in Equatorial Guinea. The inhabitants of Ncolombong, essentially rural immigrants, comprised our study population. Following their consent, we recruited individuals less than 45 years of age who had not taken praziquantel during the last 12 months. We included a total of 297 patients. Our study was a case-control, matching on sex and age. A case was defined as an infected patient with acute or chronic diarrhea occurring within the last month' preceding the stool sample analysis. All cases were retained after exhaustive screening of the study population. Each case (group 1) was matched with one or several asymptomatic infected patients (group 2) and two or several asymptomatic noninfected patients chosen at random (group 3). The definition of malnutrition was as follows: weight/height < or = 90% for children less than 15 years of age or weight/height < or = 90% with a corporal mass index < or = 20 for children more than 15 years of age. Two logistical regression models were performed in order to distinguish pathogenic from infection factors. Among the confusion bias identified, none of the helminthiasis in Bata are risk factors. The risk factors of the infection have been searched with an interrogatory. The bias caused by the interviewer is minimized because all the team staff were trained for a week before the beginning of the study. Apart from malnutrition, the other causes of cellular immunodeficiency do not seem to have any relationship with the development of symptoms. The logistical model of infection identified the classical risk factors of infection: river leisures (OR = 3.97, CI 95%: 1.86-8.47), poor or average quality of walls of the house (OR = 2.53, CI 95%: 1.15-5.58), lack of water well (OR = 2.08, CI 95%: 1.08-4). Our study could not show any relationship between malnutrition and bilharziosis. The nutritional state does not play a significative role in the infection or development of the disease. Nevertheless, the nutritional state of the host probably influences other host or parasite factors. As a result, we still don't know its influence on ADCC (Antibody Dependent Cellular Mediated Cytotoxicity) mechanisms, on adult parasite adaptation and the efficiency of laying of eggs which affects the parasitological charge. We haven't found any relationship between parasitological load and appearance of symptoms. The parasitological load indirectly reflects the efficiency of the laying and nothing proves that it is correlated with the intensity of delayed type hypersensibility reactions. In the logistical model of the disease, a stay of more than 2 months in an endemic area (OR = 0.14, CI 95%: 0.03-0.76) and a poor or average quality of walls of the house decreased the risk (OR = 0.31, CI 95%: 0.11-0.85). This result permits us to suppose that there is a tolerance to schistosomian antigens by cellular immunity