DYNAMICS OF GASTROPOD INFECTION BY 1ST-STAGE LARVAE OF PROTOSTRONGYLID NEMATODES - A MODEL

For the description of the dynamics of snail infection by the 1st-stag e larvae of protostrongylid nematodes, Skorping (1988) used the miraci dia-snail model (Anderson, 1978). Here it is shown that, in contrast t o miracidia, in protostrongylids the instantaneous rate of infection, alpha, is strongly dependent on the experimental design (factors like host size and size of the experimental arena). With respect to this, A nderson's model is modified by incorporation of the experimental desig n. The parameter alpha in its new sense as the rate of penetration (pr obability that the infective larva will penetrate into the host during a time unit) is shown to remain dependent, although much less so, on the experimental design. Only the inclusion of the assumed effect of m ucus, which decreases the rate of penetration, yields a parameter alph a0 (the initial rate of penetration), which is completely independent of the design of the experiment, is species-specific, and also gives t he best fit to the empirical data. As the above-mentioned factors can strongly influence the value of the instantaneous rate of infection in the laboratory experiments, alpha0 is more suitable as a measure of e ither the larval infectivity for the snail or snail susceptibility to infection by the protostrongylid larvae.