Sporadic cases of lumpy skin disease among cattle in Sharkia province, Egypt: Genetic characterization of lumpy skin disease virus isolates and pathological findings

Abstract

Background and aim: Lumpy skin disease (LSD) is a highly infectious viral disease upsetting cattle, caused by LSD virus (LSDV) within the family Poxviridae. Sporadic cases of LSD have been observed in cattle previously vaccinated with the Romanian sheep poxvirus (SPPV) vaccine during the summer of 2016 in Sharkia province, Egypt. The present study was undertaken to perform molecular characterization of LSDV strains which circulated in this period as well as investigate their phylogenetic relatedness with published reference capripoxvirus genome sequences.

Materials and methods: A total of 82 skin nodules, as well as 5 lymph nodes, were collected from suspect LSD cases, and the virus was isolated in embryonated chicken eggs (ECEs). LSD was confirmed by polymerase chain reactions amplification of the partial and full-length sequences of the attachment and G-protein-coupled chemokine receptor (GPCR) genes, respectively, as well as a histopathological examination of the lesions. Molecular characterization of the LSDV isolates was conducted by sequencing the GPCR gene.

Results: Characteristic skin nodules that covered the whole intact skin, as well as lymphadenopathy, were significant clinical signs in all suspected cases. LSDV isolation in ECEs revealed the characteristic focal white pock lesions dispersed on the chorioallantoic membranes. Histopathologic examination showed characteristic eosinophilic intracytoplasmic inclusion bodies within inflammatory cell infiltration. Phylogenetic analysis revealed that the LSDV isolates were clustered together with other African and European LSDV strains. In addition, the LSDV isolates have a unique signature of LSDVs (A11, T12, T34, S99, and P199).

Conclusion: LSDV infections have been detected in cattle previously vaccinated with Romanian SPPV vaccine during the summer of 2016 and making the evaluation of vaccine efficacy under field conditions necessary.

Keywords: Egypt; Poxviridae; Sharkia province; cattle; lumpy skin disease.

Figure-1

Cattle presenting clinical signs of lumpy skin disease (LSD) in Egypt, 2016. (a and c) Characteristic large firm skin nodules were distributed all over the body, (b) enlarged prefemoral lymph node, (d) small circumscribed dermal nodules (miliary form) on the udder, (e) necrotic skin nodules and ulceration all over the body of a calf, (f) a sitfast lesion developed on the skin of a calf infected with LSD virus after central area of skin nodule was indurated.

Figure-2

Microscopic examination of skin lesions and lymph nodes in lumpy skin disease virus affected cattle. (a) Eosinophilic intracytoplasmic inclusion bodies (arrows). (b) Necrotic vasculitis in dermal arteriole with infiltration of neutrophils (arrow). (c) Zenker’s necrosis in the dermal muscles (arrowheads) and mononuclear cells aggregation (arrow). (d) Severe edema (arrows) and infiltration of neutrophils.

Figure-3

Neighbor-joining (N-J) tree depicting phylogenetic relationships of the lumpy skin disease viruses isolated in this study and other capripoxvirus isolates based on G-protein-coupled chemokine receptor nucleotides sequences. The tree was analyzed by N-J analysis with 1000 bootstrap replicates.

Figure-4

Alignments of the first 140 nucleotides of the G-protein-coupled chemokine receptor gene of lumpy skin disease virus (LSDV) isolates and those of other capripoxvirus recovered from GeneBank. Addition of 21 nucleotides from position 31 to 51 and deletion of 12 nucleotides from position 94 to 105 are evident in the sequences of the newly isolated LSDV when compared with those of goat poxvirus and sheep poxvirus.

Figure-5

Alignment of the first 200 deduced amino acids of the G-protein-coupled chemokine receptor gene of the isolated lumpy skin disease virus (LSDV) isolates with those of capripoxvirus retrieved from GeneBank, showing the unique signature of LSDV (A11, T12, T34, S99, and P199).