Lumpy skin disease outbreaks in Greece during 2015-16, implementation of emergency immunization and genetic differentiation between field isolates and vaccine virus strains

Abstract

The objective of this study is to present epizootiological data from the lumpy skin disease (LSD) outbreaks in Greece during 2015-16, following the implementation of emergency vaccination and total stamping-out, along with laboratory data regarding the genetic differentiation between field isolates and live attenuated vaccine virus strains. Descriptive geographical chronology analysis was conducted to present the progressive shift of the outbreaks westwards, and at the same time, the absence of further outbreaks in previously affected regional units where high vaccination coverage was achieved. Isolation and molecular characterization of LSDV from the first recorded case in Greece (Evros/GR/15 isolate) was performed. The two live attenuated LSD vaccine viruses, currently used for emergency immunization in Greece, were sequenced and compared to the Evros/GR/15 isolate, in 3 genomic regions (GPCR gene, RPO30 gene, and partial LSDV126/LSDV127 genes). Sequence comparisons revealed prominent differences between the Evros/GR/15 isolate and the vaccine strains. Phylogenetic analysis resulted in the classification of the Evros/GR/15 isolate in the same clade with all field LSDV isolates, whereas vaccine strains were grouped in a distinct cluster within the LSDV clade. Additional samples from animals presenting skin nodules (N=13) were characterized by sequencing in the 3 aforementioned genomic regions. Among them, in 5 animals that were vaccinated, the attenuated vaccine virus was identified. A PCR-RFLP method targeting the LSDV127 gene was developed and proved to be able to discriminate between the characterized field and vaccine strains. The findings of the present study substantiate the importance of timely and intensive vaccinations for the control of LSDV epizootic and the genetic differences between the Evros/GR/15 isolate and the vaccine strains. This provides the basis for the development of PCR-based DIVA assays, which would be of major importance for effective disease surveillance and stamping-out during LSD vaccination campaigns.

Keywords: Emergency immunization; Epizootic; Greece; Live attenuated vaccine; Lumpy skin disease virus; Outbreak monitoring; Phylogenetic analysis; Virus isolation.