Genetic differentiation of infected from vaccinated animals after implementation of an emergency vaccination strategy against classical swine fever in wild boar

Oral emergency vaccination against classical swine fever is a powerful tool to control disease outbreaks among European wild boar and thus to safeguard domestic pigs in affected regions. In the past, when virus detection was mainly done using virus isolation in cell culture or antigen enzyme-linked immunosorbent assays, modified live vaccine strains like C-strain "Riems", were barely detectable after oral vaccination campaigns. Nowadays, the use of highly sensitive molecular techniques has given rise to an increase in vaccine virus detections. This was also the case during the 2009 outbreak among German wild boar and the subsequent vaccination campaigns. To guarantee a rapid differentiation of truly infected from C-strain vaccinated animals, a combination of differentiating multiplex rRT-PCR assays with partial sequencing was implemented. Here, we report on the rational and use of this approach and the lessons learned during execution. It was shown that positive results in the recently developed vaccine strain (genotype) specific rRT-PCR assay can be taken as almost evidentiary whereas negative results should be confirmed by partial sequencing. Thus, combination of multiplex rRT-PCR assays as a first line differentiation with partial sequencing can be recommended for a genetic DIVA strategy in areas with oral vaccination against classical swine fever in wild boars.