Table 1.

Details of the transmission model

Status change of individuals:	Probability per unit of time:
Susceptible → infected	gγ(a)λ with 0 ≤ gγ(a) ≤ 1.
present → removed (non-infected animals)	$-\frac{1}{S\left(a\right)}\frac{dS}{da}\left(a\right),$
present → removed (infected animals)	$-\frac{1}{{\tilde{S}}_{\gamma }\left(a\right)}\frac{d{\tilde{S}}_{\gamma }}{da}\left(a\right)$

The symbols used are defined in Table 2.