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by Heike LutermannHeike Lutermann

Altered prevalence of raccoon roundworm (Baylisascaris procyonis) owing to manipulated contact rates of hosts
M.E. Gompper & A.N. Wright, 2005, J. Zoology, 266:215-219

Parasites and pathogens are an ubiquitous threat to organisms and can cause substantial reductions in reproductive success and survival of their hosts. Hence, they constitute a powerful selective agent. Transmission of parasites is a key process in host-parasite interaction and is often related to contact rates among hosts. However, such contact rates are difficult to assess and most studies and theoretical models have used population density of the host as a proxy for contact rates. In marked contrast, the study by Gompper and Wright manipulates actual contact rates in racoons (Procyon lotor) by providing food resources in either a clumped or dispersed manner and measures the associated infection with a common nematode parasite before and after manipulation. Clumped resources lead to drastic increases in infected individuals despite population densities being similar in both groups. Remote photography confirmed that this was probably due to higher contact rates among individuals that aggregated at clumped food sources. Their study illustrates that parasite transmission is not a simple density-depend process and hence models based on population density alone are rather over simplistic. Racoons have successfully exploited resources provided by humans such as rubbish dumps and this is associated with even higher parasite prevalence than in the rural population studied. These dramatic effects of human activity have staged a new host-parasite dynamic and it will be exciting to watch this evolution in action.

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