Capripoxviruses: Exploring the genetic relatedness between field and vaccine strains from Egypt

Abstract

Background and aim: Lumpy skin disease (LSD) and sheep pox are economically important Capripoxvirus-induced diseases of cattle and sheep, respectively. Despite the extensive vaccination program adopted by Egyptian veterinary authorities, LSD and sheep pox are still prevalent and spread throughout the whole country. The current study was designed for molecular characterization and phylogenetic analysis of LSD virus (LSDV) and Sheep pox virus (SPPV) recovered from field cases in Egypt along with vaccinal strains to assess their genetic relatedness.

Materials and methods: Skin biopsies were collected from naturally infected cases of LSD in Ismailia (n=3 farms) and Beni-Suef (n=2 farms) Governorates and sheep pox in Beni-Suef (n=1 flock). Virus isolation was carried out on primary ovine fetal kidney and heart cell cultures. DNA was extracted from infected materials (skin lesions, infected cell cultures) as well as LSDV Neethling vaccine strain and Romanian SPPV vaccine strain. Polymerase chain reaction was performed using oligonucleotide primers targeting the entire open reading frame of G protein-coupled receptors (GPCR) gene and gene sequences were analyzed.

Results: Virus isolation on primary ovine fetal kidney and heart cell culture revealed a cytopathic effect at the third passage characterized by rounding of infected cells and margination of nuclear chromatin. Comparative sequence analysis of GPCR gene revealed that Egyptian LSDV isolated from Ismailia and Beni-Suef shared 99:100% nucleotide and amino acid (AA) identities with each other. In comparison to the vaccinal strains, Egyptian LSDV isolates shared 98:99 nucleotide and AA identities with LSDV Neethling vaccine strain and 93:94% with SPPV Romanian vaccine strain. No differences at the nucleotide or AAs were observed between the SPPV vaccine and virulent strains (100% identity). Phylogenetic analyses revealed that LSDV Neethling vaccine strain is more related to field Egyptian LSDV and clustered within the LSDV group while Romanian SPPV vaccine strain clustered in a separate clade with SPPV field isolates.

Conclusion: Comparative sequencing and phylogenetic analyses of the GPCR gene reveal a minimal genetic variation between LSDV field isolates from different locations and a close relationship between virulent field strains and homologous vaccines.

Keywords: Capripoxvirus; G protein-coupled receptors gene; Romanian; phylogenetic.

Figure-1

Skin lesions in a cow naturally infected with lumpy skin disease virus.

Figure-2

Lumpy skin disease virus and Sheep pox virus cytopathic at the third passage on cell culture.

Figure-3

Gel electrophoresis of G protein-coupled chemokine receptor gene-based polymerase chain reaction. Lane 1: 100 bp DNA ladder, Lane 2: Lumpy skin disease virus (LSDV) (Neethling vaccine strain), Lane 3: Sheep pox virus (SPPV) (Romanian vaccine), Lane 4: LSDV (field strain), Lane 5: SPPV (field strain).

Figure-4

Phylogenetic analysis of the G protein-coupled chemokine receptor gene. The tree was generated using MEGA X program by the neighbor-joining analysis. Bootstrap confidence values were calculated on 1000 replicates according to the maximum likelihood approach. Sequences obtained in this study are labeled ( for lumpy skin disease virus and Sheep pox virus field isolates and for vaccinal strains.