Injecting epidemiology into population viability analysis: avian cholera transmission dynamics at an arctic seabird colony

• Published in: Journal of Animal Ecology
• Main Authors: Iverson, Samuel A., Gilchrist, H. Grant, Soos, Catherine, Buttler, Isabel I., Harms, N. Jane, Forbes, Mark R.
• Other Authors: Norman, Rachel, Natural Sciences and Engineering Research Council of Canada, ArcticNet, W. Garfield Weston Foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2016
• Subjects: Arctic; Common Eider; Somateria mollissima
• Online Access: http://dx.doi.org/10.1111/1365-2656.12585; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2F1365-2656.12585; https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2656.12585

Summary Infectious diseases have the potential to spread rapidly and cause high mortality within populations of immunologically naïve hosts. The recent appearance of avian cholera, a highly virulent disease of birds caused by the bacterium Pasteurella multocida , at remote Arctic seabird colonies is an emerging conservation concern. Determining disease risk to population viability requires a quantitative understanding of transmission potential and the factors that regulate epidemic persistence. Estimates of the basic ( R 0 ) and real‐time ( R t ) reproductive number are critical in this regard – enumerating the number of secondary infections caused by each primary infection in a newly invaded host population and the decline in transmission rate as susceptible individuals are removed via mortality or immunized recovery. Here, we use data collected at a closely monitored common eider ( Somateria mollissima ) breeding colony located in the Canadian Arctic to examine transmission and host population dynamics. Specifically, we infer epidemic curves from daily mortality observations and use a likelihood‐based procedure to estimate changes in the reproductive number over a series of annual outbreaks. These data are interpreted in relation to concurrent changes in host numbers to assess local extinction risk. Consistent with expectations for a novel pathogen invasion, case incidence increased exponentially during the initial wave of exposure ( R 0 = 2·5; generation time = 6·5 days ± 1·1 SD). Disease conditions gradually abated, but only after several years of smouldering infection ( R t ≈ 1). In total, 6194 eider deaths were recorded during outbreaks spanning eight consecutive breeding seasons. Breeding pair abundance declined by 56% from the pre‐outbreak peak; however, a robust population of >4000 pairs remained intact upon epidemic fade‐out. Overall, outbreak patterns were consistent with herd immunity acting as a mitigating factor governing in the extent and duration of mortality. Disease mortality is frequently ...