Deletion of the Chemokine Binding Protein Gene from the Parapoxvirus Orf Virus Reduces Virulence and Pathogenesis in Sheep.
Orf virus (ORFV) is the type species of theParapoxvirusgenus of the familyPoxviridaeand infects sheep and goats, often around the mouth, resulting in acute pustular skin lesions. ORFV encodes several secreted immunomodulators including a broad-spectrum chemokine binding protein (CBP). Chemokines are a large family of secreted chemotactic proteins that activate and regulate inflammation induced leukocyte recruitment to sites of infection. In this study we investigated the role of CBPin vivoin the context of ORFV infection of sheep. The CBP gene was deleted from ORFV strain NZ7 and infections of sheep used to investigate the effect of CBP on pathogenesis. Animals were either infected with the wild type (wt) virus, CBP-knockout virus or revertant strains. Sheep were infected by scarification on the wool-less area of the hind legs at various doses of virus. The deletion of the CBP gene severely attenuated the virus, as only few papules formed when animals were infected with the CBP-knock-out virus at the highest dose (107p.f.u). In contrast, large pustular lesions formed on almost all animals infected with thewtand revertant strains at 107p.f.u. The lesions for the CBP-knock-out virus resolved approximately 5-6 days p.i, at a dose of 107pfu whereas in animals infected with thewtand revertants at this dose, lesions began to resolve at approximately 10 days p.i. Few pustules developed at the lowest dose of 103p.f.u. for all viruses. Immunohistochemistry of biopsy skin-tissue from pustules showed that the CBP-knockout virus replicated in all animals at the highest dose and was localized to the skin epithelium while haematoxylin and eosin staining showed histological features of the CBP-knockout virus typical of the parent virus with acanthosis, elongated rete ridges and orthokeratotic hyperkeratosis. MHC-II immunohistochemistry analysis for monocytes and dendritic cells showed greater staining within the papillary dermis of the CBP-knock-out virus compared with the revertant viruses, however this was not the case with thewtwhere staining was similar. Our results show that the CBP gene encodes a secreted immunodulator that has a critical role in virulence and pathogenesis.
Department of Microbiology and Immunology, University of Otago Dunedin, New Zealand.
Stephen B
SB
Fleming
Department of Microbiology and Immunology, University of Otago Dunedin, New Zealand.
Catherine
C
McCaughan
Department of Microbiology and Immunology, University of Otago Dunedin, New Zealand.
Zabeen
Z
Lateef
Department of Microbiology and Immunology, University of Otago Dunedin, New Zealand.
Amy
A
Dunn
Department of Microbiology and Immunology, University of Otago Dunedin, New Zealand.
Lyn M
LM
Wise
Department of Microbiology and Immunology, University of Otago Dunedin, New Zealand.
Nicola C
NC
Real
Department of Microbiology and Immunology, University of Otago Dunedin, New Zealand.
Andrew A
AA
Mercer
Orf virus; chemokine binding protein; pathogenesis; poxvirus; virulence; virus immune modulation