Parapoxvirus: basi genomiche della patogenesi
Creators: name: Gallina, Laura <1977>
Publisher: name: Alma Mater Studiorum - Università di Bologna
Year: 2008
Subjects: VET/05 Malattie infettive degli animali domestici

description: Parapoxvirus (PPV) are member of a genus in the family poxviridae which currently
encompasses four species: the prototype orf virus (OV), bovine papular stomatitis
virus (BPSV), pseudocowpox virus (PCPV) and parapoxvirus of New Zealand red
deer (PVNZ). PPVs cause widespread, but localized diseases of small and large
ruminants and they can also be transmitted to man.
Knowledge of the molecular biology of PPV is still limited as compared to
orthopoxviruses, especially vaccinia virus (VACV). The PPV genome displays a high
G+C content and relatively small size for poxvirus. Coventional electron microscopy
displays PPV virions with ovoid shape and slightly smaller in size than the brickshaped
orthopoxviruses. The most striking feature, which readily enables
identification of PPV, is a tubule-like structure that surrounds the particle in a spiral
fashion. PPV genome organization and content is very similar to that of other
poxviruses, the central region contain 88 genes which are present in all poxviruse, in
contrast the terminal regions are variable and contain a set of genes unique to the
genus PPV. Genes in the near-terminal regions of the genome are frequently not
essential for growth in cultured cells encoding factors with important roles in virushost
interactions including modulating host immune responses and determining host
range. Recently it was suggested that the open reading frames (ORFs) 109 and 110 of
the OV genome have a major role in determining species specificity during natural
infection in sheep and goats. This hypothesis is based on the analysis of a few
number of sequences of different sheep and goats viral isolates. PPV replicate into
the cytoplasm of infected cells and produce three structurally different infectious
particles: the intracellular mature virions (IMV), intracellular enveloped virions
(IEV) and the extracellular enveloped virions (EEV). The vaccinia A33R and A34R
hotologue proteins encoded by the ORFS 109 and 110 are expressed in the envelope
of the IEV and EEV.
The F1L immunodominant protein of orf virus is the major component of the surface
tubule structure of the IMV and can post-translationaly insert into membranes via Cterminal,
hydrofobic anchor sequence like its orthologue VACV H3L protein.
Moreover the F1L protein binds to glycosaminoglycans on the cell surface and has an
important role in IMV adsorption to mammalian cells.
In this study we investigated the morphogenesis of the PPV through the construction
of a mutant virus deleted of the F1L protein. A study of the deleted virus life cycle
was conducted in different type of cells and its morphology was observed with
electron microscopy. It was demonstared that F1L protein have important role in
morphogenesis and infectivity. Moreover it is essential to determine the spiral fashion
of the tubule like structure of the virion surface.
Some pathogenetic aspects of the PPV infection were studied, in particular the
protein implicated in the host range were analysed in detail.
An experimental infection with OV and PCPV was conducted in goats and sheep.
After infection, the severity of the lesions were comparable in both the animal
species. The OV did not result in severe disease neither in sheep nor in goats,
suggesting that host factors, rather than virus strain characteristics, may play an
important role in the pathogenesis of the Parapoxvirus infections. The PCPV failed to
produce any lesion in both sheep and goats, ruling out the possibility of any
recombination between PCPV and OV during natural infection in these animal
species. The phylogenetic analysis of the ORFs 109 and 110 from several goats and
sheep viral isolates showed a clustering based on the antigenic content of the protein
that was independent from species and geographic origin.