Pooled-sample testing as a herd-screening tool for detection of bovine viral diarrhea virus persistently infected cattle

The study was conducted to develop methodology for least-cost strategies fo r using polymerase chain reaction (PCR)/probe testing of pooled blood sampl es to identify animals in a herd persistently infected with bovine viral di arrhea virus (BVDV). Cost was estimated for 5 protocols using Monte Carlo s imulations for herd prevalences of BVDV persistent infection (BVDV-PI) rang ing from 0.5% to 3%, assuming a cost for a PCR/probe test of $20, The proto col associated with the least cost per cow involved an initial testing of p ools followed by repooling and testing of positive pools. For a herd preval ence of 1%, the least cost per cow was $2.64 (95% prediction interval = $1. 72, $3.68), where pool sizes for the initial and repooled testing were 20 a nd 5 blood samples per pool, respectively. Optimization of the least cost f or pooled-sample testing depended on how well a presumed prevalence of BVDV -PI approximated the true prevalence of BVDV infection in the herd. As prev alence increased beyond 3%, the least cost increased, thereby diminishing t he competitive benefit of pooled testing. The protocols presented for sampl e pooling have general application to screening or surveillance using a sen sitive diagnostic test to detect very low prevalence diseases or pathogens in flocks or herds.