Development of an assay to differentiate between virulent and vaccine strains of lumpy skin disease virus (LSDV).

Lumpy skin disease (LSD) was and still is a constant threat to the State of Israel, since the first outbreaks in 1989 and in 2006-2007. Recently, another massive outbreak occurred, at the beginning of July 2012, in the northern part of Israel. An intensive vaccination campaign with a sheeppox-based vaccine was initiated, in addition to culling symptomatic animals in the dairy herds. In spite of this, there was a need to apply extra efforts to completely contain and control the spread of the disease by introducing for the first time in Israel a vaccine based on the Neethling vaccine virus strain. However, in case of appearance of LSD symptoms it was essential to be able to distinguish between cattle-carried virulent strain and the vaccine strain. This paper describes the development and utilization of a molecular assay that can differentiate between the virulent isolates from the vaccine strain. The system is based on 3 different tests; it was found that the vaccine strain carries 27 bases less than the virulent virus in the extracellular enveloped virions (EEV) gene. A temperature-gradient PCRs were done using primers which are identical to the vaccine strain but differ at the 3' end nucleotides to the virulent virus. PCR-RFLP was carried out on the presence of an MboI site unique to the vaccine strain. Thus, all three tests presented here are able to differentiate specifically between the two viral appearances.