Appendix B. Extended infectiousness.
Although our model captures the majority of latent and infectious periods observed among domestic dogs (Appel 1969, Appel 1970, Greene and Appel 2006), we realize that a small proportion of individuals may be infectious for longer time periods, which could significantly alter our estimates of CCS. We are unaware of any empirical estimates of the proportion of animals to which this extended infectiousness applies, and thus we have no information as to how well our current model approximates reality. To examine the impact of extended infectiousness on our estimates of CCS, we modified our current single-host coyote models to include a second class of infectious individuals that shed virus for an average of 46 days (mode = 40, σ2 = 234; from NegBin(r = 5, p = 0.14) with 10 staging boxes).We ran simulations assuming that this class either made up 5, 10, or 15 percent of all individuals that became infected. Survival while in the extended infectiousness class was adjusted (ds' = 0.9938) such that the same proportion of individuals were expected to survive infection as during the normal infectious period. The remaining model structure and all other parameters were identical to those described in the main text.
As seen in Fig. B1, the CCS for CDV among coyotes is still dependent on host connectivity and survival, but is smaller than in our models that assume a single class of infectious individuals. For the most plausible estimates of connectivity (ε = 4–4.5) and survival (s = 0.45–0.65) CDV requires between 2,500 and >>7,500 packs (25,000 to >>75,000 individuals) to persist for a minimum of 10 years.
Fig. B1. Probability of CDV persistence over 10 years as a function of the proportion of infected individuals characterized by extended infectiousness (A. 5% extended infectiousness; B. 10% extended infectiousness; C. 15% extended infectiousness), the number of coyote packs in the population, inter-pack isolation, ε, and survival. (Simulation run assuming coyote demographics: n = 10, β = 0.16, regular infectious: [ds = 0.9797, LP(μ) = 6 days, IP(μ) = 9 days], extended infectious: [ds’ = 0.9938, LP(μ) = 6 days, IP(μ) = 46 days]).
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Appel, M. J. G. 1970. Distemper pathogenesis in dogs. Journal of the American Veterinary Medical Association 156:1681–1684.
Greene, C. E., and M. J. Appel. 2006. Canine Distemper. Pages 25–41 in C. E. Greene, editor. Infectious diseases of the dog and cat. Saunders/Elsevier, Philadelphia, Pennsylvania, USA.