Diagram of the transitions between health states.
S: susceptible; T: transiently-infected; P: persistently infected; M: protected by maternal antibodies; R: immune; R
: immune which have been infected in early, mid and late pregnancy, respectively. Dotted lines concern only calves. The values of the transition rates ϕ
are given in Table 1. The value of the transition rate f is derived from eq. 1 and eq. 2.