Two variants of the first Nåsell-Hirsch model

Two models are propounded on the general setting of the first Nåsell-Hirsch model for helminthic infections. They differ from it in the two processes of transmission of the infection, which are treated dissymmetrically. In each model only one of these processes will be deterministic, instead of both as in the Nåsell-Hirsch case, the other process being kept fully stochastic. These new models lead to results that show a general agreement with those of Nåsell and Hirsch but also some interesting differences.