Most efforts to understand the population biology of pathogens have focussed on specialist pathogens, and population biologists have successfully developed a formal understanding of the dynamics and evolution of single-host pathogens. However, most pathogens of humans, animals and plants are multi-host pathogens [1] [2] [3] 20] . As stated by Woolhouse et al. [1] ''understanding the more complex population biology of multi-host pathogens will be one major challenge in the 21st century ''. There is evidence that within an ecosystem the prevalence of multi-host pathogens may differ largely for the different species of their host range [e.g., [21] [22] [23] [24] [25] ]. Similarly, there is evidence of large differences in the prevalence on a host species of the various pathogens that are able to infect it [e.g., [26] [27] [28] [29] ]. However, no attempt has been made, to our knowledge, to analyse if differences in the distribution of multihost pathogens over their hosts are random or if there are associations between hosts and pathogens. The uncovering of associations between hosts and pathogens would be highly relevant to understand and model the population biology of multi-host pathogens, and for understanding the phenomenon of generalism itself.