Project Title

Hybridization as a driver for the spread of schistosomiasis: an integrative approach to evaluate the invasive capacity of schistosome hybrids under praziquantel pressure

Project Objectives

Our overall objective is to characterise at the molecular and phenotypic level the hybrid populations between S. haematobium and S. bovis in Senegal to better assess their potential spread and their sensitivity to PZQ. Specific Objectives: To quantify the prevalence and intensities of schistosomiasis in human populations; To study the outcomes of hybridization between S. haematobium and S. bovis on snail infectivity; To evaluate the sensitivity of hybrid schistosome populations to PZQ according to parasite genetic introgression level; To characterize the frequency of hybrids and their level of genomic introgression.

Host Organisation

EDCTP Project Call

Career Development Fellowship (CDF)

Study Design

clinical trial

Project Summary

Schistosomiasis is a parasitic disease that exists in humans and cattle. Human schistosomiasis is one of the most important neglected tropical diseases with an estimated 800 million people at risk in 78 countries. The disease affects 240 million people in low- and middle-income countries in the tropics with more than 200,000 deaths per year. Sub-Saharan Africa countries are the most affected with 90% of the total cases, especially among school-aged children, farmers and fishermen who are the main populations at risk. Animal schistosomiasis is also a very common infection in Africa and Asia, where an estimated 165 million animals are infected. Since in schistosomiasis endemic areas, people and livestock often frequent the same freshwater points, hybridization between human and animal schistosome species can occur with the risk of zoonotic transmission. This is the case in northern Senegal, where hybridization between human-specific schistosome species (Schistosoma haematobium) and a cattle-specific (Schistosoma bovis) is now known to be common in children and adults. The overall objectives of the project are: to quantify the baseline prevalence and intensity of schistosomiasis in human populations; study the results of hybridization between S. haematobium and S. bovis on the infectivity of snails; assess the sensitivity of hybrid schistosome populations to PZQ according to the level of genetic introgression of the parasite using hamsters as an experimental model; characterize the frequency of hybrids and their level of genomic introgression under PZQ pressure. To achieve our objectives, we realized a baseline parasitological survey (S0) in 1,050 children aged 5 to 11 years in 5 villages to quantify the prevalence and baseline intensity of schistosomiasis then a first treatment with praziquantel (T1) was given for all positive children. One month after T1, a second parasitological survey (S1) were cared to control the T1 efficacy in 226 children recruited for follow-up. Six to seven month after treatment, selected participants were surveyed (S2) for the control of the first reinfection (R1) following by a second treatment (T2) and its efficacy control at S3. At each of the next follow survey point (S4, S5 and S6), the second reinfection (R2) at S4 and the third reinfection (R3) at S6 were recorded. This summary for publication reports the global results for the infection dynamic from S0 to S6. A total of 777 children were enrolled in five villages at baseline (S0). Out of them, 464 (59.7%) were infected by S. haematobium. Very high prevalence was found at S0 in the villages of Guia (91.2%) and Khodit (90.6%) frequenting the irrigation canal while moderate prevalence was noted in the village of Ndiawara (45%), and Dioundou (49%) using the river and also in the village of Mbane (43.1%) near the Lac de Guiers. Significant differences in the prevalence intensity of infection were noted between the types of water access. One month after T1 (S1), the heavy infections were drastically reduced from 64.6% to 1.7% in average. The lowest cure rate (88.5%) was obtained in the village using the irrigation canal with high parasite loads before treatment, while high cure rates (96.5% and 98%) and egg reduction rates between 96.7% and 99.7% was observed in all villages. The reinfection rates R1 (46.8 %), R2 (58.8%) and R3 (12.5%) varied from a year to another but were significantly higher in the village near the irrigation canal. Furthermore, at each time point of the survey, from S0 to S6 the schistosome miracidia isolated on FTA cards will be analysis at genomic level. The comparison of the miracidia genomic diversity between the baseline and the following survey points will allow us to see the percentage of pure parasites and hybrids between S. haematobium and S. bovis before and after treatment. Thus, we will verify our hypothesis which was the S. haematobium-S. bovis hybrids are lest sensible to PZQ than the pure parental species and to get an idea on the possible impact of the pressure of the PZQ repeated treatment on the parasites genetic diversity and also possibly detection of PZQ tolerance genes. Therefore, the societal impact of this project is still relevant and will concern not only Senegal but also the others tropical and sub-tropical countries that are endemic for schistosomiasis and even Europe where schistosome hybrids were recently emerged.

Current Organisation

Institut de recherche pour le developpement (IRD)

Current Job Title

Researcher at IRD

Biography

Publications