Rabies cases in foxes have been considered to be rare, dead-end, spillover events from rabid dogs and to have no epidemiologic significance.
Such faster recovery would lead to an even smaller long-term effect of rare pulses of spillover in comparison with low-level leakage.
Therefore, a short-term larger effect of rare pulses of spillover, such as from loss of net pens in storms, might mask a longer-term, greater effect of constant, low-level leakage.
This somewhat surprising result, which suggests a greater impact of constant low-level leakage than rare, large pulses of spillover, arises when strong selection rapidly purges maladapted individuals from highly variable spillover (Box 1; in line with the empirical observations of genetic recovery after an individual escape event in Crozier 2000).
Here, we develop a quantitative framework to evaluate the consequences of (i) the degree of maladaptation in the cultured population, (ii) constant low-level spillover versus rare, large pulses of escapees, (iii) the amount of reduced reproductive success (sterilization efficacy) of cultured escapees in the wild, and (iv) spillover of different life-history stages.
Rare isolation of this virus suggests a limited spillover infection from an otherwise restricted sylvatic cycle.
Across life cycles, how much of spillover occurs in rare, large pulses versus constant, low-level leakage will depend on choices such as net-pen reinforcement to reduce likelihood of loss during a storm, placement of net pens in more sheltered locations, or alterations to net-pen rotation and change practices (Gross 1998; Youngson et al. 2001; Naylor et al. 2005).
Net migration of undocumented immigrants into the U.S. has dropped from 500,000 a year a decade ago to zero today, while crime on the U.S. side of the border has plummeted and incidents of "spillover violence" from Mexico are rare.
