Assessment of the cost-effectiveness of alternative bovine tuberculosis surveillance protocols in French cattle farms using the mixed interferon gamma test

Abstract

Periodic screening in farms, using intradermal cervical comparative tuberculin test (ICCT), is a component of the French ante mortem surveillance of bovine tuberculosis (bTB). Previous studies have estimated the cost-effectiveness of the French mandatory bTB screening protocols. In these protocols, a second ICCT (ICCT2) is performed 42 days after the first one (ICCT1), either on the entire herd (strict protocol) or in series on animals with non-negative results (reactors) to ICCT1 (compliant protocol). The 42-days interval reduced protocols' cost-effectiveness. To minimize this interval, we suggested two alternative protocols, in which a mixed interferon gamma test (IFNMIX), with better sensitivity than ICCT2 and comparable specificity, replaces the ICCT2, and is carried out directly after the ICCT1. In the strict alternative protocol, reactors to ICCT1 are culled to perform laboratory analyses (PCR, bacteriology). Negative results to these analyses imply the IFNMIX testing of the entire herd. In the compliant alternative protocol, only reactor(s) to ICCT1 are tested with IFNMIX, and animals with positive results to IFNMIX are culled for laboratory analyses. We evaluated these protocols through scenario tree modelling. The estimated cost-effectiveness indexes showed that the compliant alternative protocol was the most efficient. The strict protocols (mandatory and alternative) were never the most efficient, but were the most effective. Therefore, using IFNMIX instead of ICCT2 may be useful in reducing the costs of the compliant protocol used when the probability of infection is considered low. The strict alternative protocol may become more attractive would IFNMIX's price decreased.

Keywords: Bovine tuberculosis; Cost-effectiveness; Interferon; Scenario tree; Sensitivity; Surveillance.