Mandy Gibson has published a study in Biology Letters that tests the crucial coevolutionary hypothesis that parasites adapt to specifically target common over rare host genotypes. Working with members of the Morran lab at Emory University, she selected bacterial parasites in genetically heterogeneous populations of the host Caenorhabditis elegans. On average, parasites maintained virulence against common host genotypes but lost virulence against rare host genotypes. The group found, however, that this rare host advantage was slight and varied with the host genotype in question. You may read more about it here.
AK Gibson, PS White, MJ Penley, JC de Roode, and LT Morran. 2020. An experimental test of parasite adaptation to common vs. rare host genotypes. Biology Letters. 16(7)