How much a host moves can affect disease severity
Parasite induced diseases increase morbidity and mortality in human, livestock, and wildlife populations. Understanding factors that influence how much damage a parasite inflicts on its host is important for disease control efforts. The relatedness of parasites within an infection has been shown to alter the amount of damage suffered by a host. Generally, infections with related parasites are less damaging than infections between non-relatives, because relatives can increase host lifespan and prolong their own survival and reproduction while non-relatives must directly compete for limited host resources. So far, research in this area has not looked beyond laboratory studies and we do not have a good understanding of what increases or decreases relatedness of parasites within a host. It is possible that host characteristics, such as their ability to resist infection or even the amount they travel between different areas, could alter the relatedness in parasite infections and ultimately the level of host damage. Many parasites also have multiple host life cycles, in which different hosts not only could impact disease within their own populations but also in the populations of other species. In their Parasitology review Alyssa Gleichsner and Dennis Minchella predict that hosts that move frequently over a large area are more likely to pick up and distribute unrelated parasites and thus increase disease severity in them and in other hosts to which they transmit infection. Likewise, host defenses are likely to resist the most damaging parasites and eliminate them from an infection, increasing relatedness in the infection and decreasing parasite damage. Together, host factors could interact to create cyclical patterns of high and low disease severity in a given host population over time. Future studies will investigate the impact of host characteristics on natural parasite populations to increase our understanding of disease dynamics.
Article: Gleichsner, A.M. and Minchella, D.J. 2014. Can host ecology and kin selection predict parasite virulence? Parasitology 141, 1018-1030