COMPLIMENTARY APPROACHES FOR DISCRIMINATION BETWEEN VIRULENT AND VACCINE LSD VIRUS STRAINS

Lumpy skin disease virus (LSDV), the cause of LSV in cattle, belong to the Capripox genus of the Poxviridae family. The disease was and still is a constant threat to the cattle industry in the State of Israel, since the first outbreaks in 1989 and in 2006-2007. Recently, at the beginning of July 2012 a massive outbreak occurred in the northern part of Israel. It is an infectious, eruptive disease of cattle, which is economically important but rarely fatal. The clinical onset is characterized by fever, loss of appetite, increased nasal secretions and watery eyes; it is especially severe in cows at the peak of lactation, and causes a sharp drop in milk production. To overcome the disease, cattle herds were immunized by a vaccine constituting of attenuated LSDV Neethling isolates. In some cases the Neethling vaccine caused similar symptoms to the field virulent strain. Thus, the need to distinguish between the two types of viruses emerged. Based on divergence in the nucleotide sequences between the two strains a system based on 4 different tests was developed: 1. it was found that the vaccine strain carries 27 bases less than the virulent virus in the LSDV126 gene, belonging to the extracellular enveloped virion (EEV) family of genes. 2. A temperature-gradient PCR using vaccine specific primers. 3. PCR-RFLP based on the presence of an MboI site unique to the vaccine strain. All three of these tests, presented here, are specifically able to differentiate between the two viral appearances. 4. The sequence differences between the virulent and vaccine LSDV strains was the basis for the development of a high resolution melting (HRM) test that enables the distinction between virulent and vaccine LSDV.

The EEV gene has an important role in virus/cell attachment process playing an important role in the efficiency of virus replication. Using the appropriate algorithm it was found that the 9 aa deletion in the vaccine strain changes the EEV antigenic properties thus, probably, modifying or reducing the ability of the vaccine strain to replicate.