We consider an heterogeneous model of transmission of bilharzia. We compute the basic reproduction ratio $\mathcal R_0$. We prove that if $\mathcal R_0 <1$, then the disease free equilibrium is globally asymptotically stable. If $\mathcal R_0>1$ then there exists an unique endemic equilibrium, which is globally asymptotically stable. We will then consider possible applications to real data