Brucellosis Control through Test and Removal

Scenarios combining calfhood vaccination with testing of all animals (cows and buffalo of all age groups using the Rose Bengal test) and immediate removal of test positives were also simulated. Test and removal is assumed to occur at a single point in time, at the inception of the control programme (as proposed in the Brucella free village programme). There is no differentiate infected from vaccinated animals (DIVA) test available for brucellosis, therefore this strategy was not combined with vaccination at the inception of the programme. The number of true test positive animals is sampled from a Bernoulli distribution with the number of trials equal to E_j+ I_j and the probability of testing positive given by the test sensitivity, Se. False positive animals are also sampled from a Bernoulli distribution with number of trials equal to S_j and the probability of giving a false positive result equal to 1 − Sp. Scenario B was not simulated with test and removal as it was not considered an effective use of resources compared with Scenario C (see Results).
Targets for control were set using prevalence (percentage of infected animals in a village), as this is measurable via surveillance. Therefore, we define ‘control’ as animal-level prevalence below 1%, as indicative of a nominally low level of infection whereby Punjab could consider moving towards elimination. The ‘probability of control’ is the percentage of simulations with prevalence less than 1%. Predicted (cumulative) incidence, the percentage of animals infected with B. abortus per year, is also presented.