Quantifying the risk of spillover reduction programs for human health
Fig 2
The health burden of zoonotic disease, , as a function of the force of spillover (λ) for disease severity that increases at different rates with advancing age.
As the severity of disease increases more rapidly with advancing age, the scope for spillover reduction to negatively impact human health grows. In this example, the rate at which infected individuals become diseased increases following Eq (8) with the intercept set to μ0 = 1.0 and the slope set such that the rate of transition to disease is independent of age (blue line; α = 0), increases 5-fold (red line; α = 1/15), or increases 10-fold (yellow line; α = 3/20) from the time of birth to age at which an individual reaches their expected natural lifespan (1/δ). The dotted lines are numerical solutions to the exact model that do not assume the rate of transition to clinical disease is rare. The analytical approximations slightly overestimate the clinical burden because individuals leaving the I class as they become diseased are ignored. This gap between approximation and exact solution grows as the rate of progression to clinical disease (μ) increases, although the general shape of the curves remains consistent. The remaining parameters were: b = 100, δ = 1/60, v = 1, γ = 365/14.