Helminth immune modulation

Outcomes of infection are shaped by the host, the parasite, and their environment – but to what extent?

Epidemiological traits in helminth infections of sticklebacks: incorporating evolutionary and ecological perspectives in the study of helminth immune modulation in vertebrate hosts

Research project at the Max Planck Institute (MPI) for Evolutionary Biology, Parasitology Group (Dr. Martin Kalbe)

Epidemiological traits are shaped through effects of the host, the parasite and by their interaction (Figure 1 shows a theoretical illustration of this assumption). The relative contribution of each of the interaction partners may differ along the infection process and depends on the coevolutionary history. Different environments may select for different defence strategies among host populations, which results in immunological heterogeneity (Lazzaro et al., 2009; Graham, 2013). Here, we assessed virulence patterns of a vertebrate host-parasite association on a large geographic scale to test to what extent heterogeneous environments may cause immunological heterogeneity.

Figure 1. Partitioning of host, parasite, and interaction effects on an epidemiological trait. (a, b) Host genotype and parasite genotype main effects. The host effect (vertical spacing between the two lines) indicates the genetic difference between the two host types. Parallel horizontal lines in (a) indicate absence of a plastic response towards infection. Differences among hosts that are infected with the same parasite (vertical spacing between the dots) indicate a phenotypic plastic response of the parasite. The positive slope in (b) indicates different effects of the two parasite types (parasite effect) and thus a phenotypic plastic response of the host and the parasite. (c) and (d) demonstrate host genotype-parasite genotype interaction effects, because the host effect depends on the parasite type. Crossing reaction norms in (d) clearly show the interaction effect; but note in (c) that the main-effect components can cumulate, causing non-crossing reaction norms. (The complete figure can be found here)

We hypothesized that different co-evolutionary trajectories of three-spined sticklebacks (Gasterosteus aculeatus) and their specific cestode parasite Schistocephalus solidus could be seen by specific virulence patterns on a geographic scale. Our data indeed provide evidence that differences in parasite prevalence can cause immunological heterogeneity and that parasite size, a proxy for virulence and resistance, is, on a geographic scale, determined by main effects of the host and the parasite and less by an interaction of both genotypes.

The corresponding publications can be found here and here