(This post requires mood music.)
Parasites are typically aggregately distributed among hosts, so that a few hosts have many parasites, while most hosts have few or no parasites. There are some characteristics that make hosts more likely to be in the group that harbors the high parasite burden. Sex is one such characteristic. For instance, male mammals often have higher parasite loads than females.
The distribution of parasites among hosts might also have something to do with how individual animals interact with other animals. Perhaps the hosts that have the most contacts with conspecifics are the most likely to become infected and/or the most likely to transmit pathogens. I just read a 2009 paper by Clay et al. that examined this idea. They found that it wasn’t just the number of contacts or the duration of those contacts, but an interaction between the two that helped to explain variation in Sin Nombre Virus presence/absence in mice.
I’m blogging about this paper because the methods were sweet. To figure out which mice were contacting each other, they covered male mice with fluorescent powder and released them into the wild. Later, they collected a bunch of mice from the area, put them under a blacklight, and looked for powder to see who had contacted who. So all I could think of the entire time I was reading this paper was this:
Clay, C.A., E.M. Lehmer, A. Previtali, S. St. Jeor, and M. D. Dearing. 2009. Contact heterogeneity in deer mice: implications for Sin Nombre virus transmission. Proc R Soc B 276(1660): 1305-1312. (FREE pdf)