Morphology large complex virion,ovoid in shape,with rounded ends and characteristic ball of wool appearance.somewhat larger, by electron microscopy than other poxviruses with dimensions of 294x273 nm. The basic infectious form is the mature virion (MV).The extracellular enveloped virion (EV) consists essentially of an MV enclosed by an additional membrane. The thickness(5-6 nm) and density of outer layer is consistent with one lipid membrane bilayer,the outside of which appears corrugated because of irregular protrusions extending 2 to 5nm.The internal structure of the virion is complex, consisting of a dumb bell- shaped core and aggregates of heterogenous material called lateral bodies

Between the concavities and the outer membrane.The core wall seems to be composed of two layers with an allover thichness of 18 to 19 nm.The inner layer appears continous, except for a small number of channels, and has a diameter and density consistent with a lipid membrane.The outer layer has a palisade structure that is possiboly made of T-shaped spikes (8 nm long and 5 nm wide) that are anchored in the putative lower membrane.The ultrastructure of the core is not resolved by cryoelectrontomograghy but appear to consist of two phases: The denser layer just under the core wall has afiberlike morphology, suggesting nucleoprotein. Cylindrical elements that may take an S-shape or more complex flowerlike structures, Presumably representing nucleoprotein, were visualized by other means within poxvirus cores. Fields virology

Genome The genome consists of a single molecule of linear double-stranded DNA (Myrphy). Has linear double -stranded genome(Fields virology). By itself, poxvirus DNA not infectious because the viral RNA polymerase and other enzymes and factors are needed to express the genome in the cytoplasm.(Fields virology) The 151-kbp LSDV genome consist of a central coding region bounded by identical 2.4 kbp-inverted terminal repeats and contains 156 putative genes. Comparsion of LSDV with chordopoxviruses of other genera reveals 146 conserved genes which encode proteins involved in transcription and mRNA biogenesis, nucleotide metabolism, DNA replication, protein processing, virion structure and assembly, and viral virulence and host range. In the central genomic region, LSDV genes share a high degree of colinearity and amino acid identity (average 65%) with genes of other known mammalian poxviruses, particularly suipoxviruses, yatapoxviruses, and leporipoxviruses. In the terminal region, colinearity is disrupted and poxvirus homologues are either absent or share a lower percentage of amino acid identity (average of 43%).

Most of these differences involve genes and gene families with likely functions involving viral virulence and host range. Although LSDV resembles leporipox-viruses in gene content and organization, it also contains homolouges of interleukin-10 (IL-10),IL-1 binding protein, G protein- coupled CC chemokine receptor, and epidermal growth factor -like protein which are found in other poxvirus genera. These data show that although LSDV is closely related to other members of chordopoxvirinae, it contains a unique complement of genes responsible for viral host range and virulence.

Linear map of the LSDV genome. Tulman E R et al. J. Virol. 2001;75:

FIG. 1. Linear map of the LSDV genome. ORFs are numbered from left to right based on the position of the methionine initiation codon. ORFs transcribed to the right are located above the horizontal line; ORFs transcribed to the left are below. Genes with similar functions and members of gene families are colored according to the figure key. ITRs are represented as black bars below the ORF map.

Classification of LSDV according to the International Committee on Taxonomy of Viruses (ICTV) Family:Poxviridae Subfamily:Chordopoxvirinae Genus:Capripoxvirus