Costs and benefits of group living with disease: A case study of pneumonia in bighorn lambs (Ovis canadensis)

Kezia R. Manlove, E. Frances Cassirer, Paul C. Cross, Raina K. Plowright, Peter J. Hudson

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


Group living facilitates pathogen transmission among social hosts, yet temporally stable host social organizations can actually limit transmission of some pathogens. When there are few between-subpopulation contacts for the duration of a disease event, transmission becomes localized to subpopulations. The number of per capita infectious contacts approaches the subpopulation size as pathogen infectiousness increases. Here, we illustrate that this is the case during epidemics of highly infectious pneumonia in bighorn lambs (Ovis canadensis). Weclassified individually marked bighorn ewes into disjoint seasonal subpopulations, and decomposed the variance in lamb survival toweaning into components associated with individual ewes, subpopulations, populations and years. During epidemics, lamb survival varied substantially more between ewe-subpopulations than across populations or years, suggesting localized pathogen transmission. This pattern of lamb survival was not observed during years when disease was absent. Additionally, group sizes in ewe-subpopulations were independent of population size, but the number of ewe-subpopulations increased with population size. Consequently, although one might reasonably assume that force of infection for this highly communicable disease scales with population size, in fact, host social behaviour modulates transmission such that disease is frequency-dependent within populations, and some groups remain protected during epidemic events.

Original languageEnglish (US)
Article number20142331
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1797
StatePublished - Nov 5 2014

All Science Journal Classification (ASJC) codes

  • General Biochemistry, Genetics and Molecular Biology
  • General Immunology and Microbiology
  • General Environmental Science
  • General Agricultural and Biological Sciences


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