Table 1 Details of the transmission model

Susceptible → infected

g _γ (a)λ

with 0 ≤ g _γ (a) ≤ 1.

present → removed (non-infected animals)

$-\frac{1}{S\left(a\right)}\frac{dS}{da}\left(a\right),$

present → removed (infected animals)

$-\frac{1}{{\tilde{S}}_{\gamma }\left(a\right)}\frac{d{\tilde{S}}_{\gamma }}{da}\left(a\right)$