Systematic Veterinary Virology

MORPHOLOGY

• The virions are enveloped and slightlyovoid or brick-shaped with 140-260 nm in diameter; 220-450 nm long. The extracellular forms contain 2 membranes (EEV - extracellular enveloped virions), intracellular particles only have an inner membrane (IMV - intracellular mature virions).
• Thin sections in E.M. reveal that the outer surface is composed of lipid and protein, which surrounds the core, which is biconcave (dumbbell-shaped), with two "lateral bodies" (function unknown). The core is composed of a tightly compressed nucleoprotein.
• The virions have 10 enzymes, which are essential for genome replication. The genome is linear, d/s DNA having 130-300kbp. There are approximately 250 genes in the genome of which some are essential for virus and some are not essential. The essential genes are located in the central part of the genome, while non-essential (in tissue culture) genes are located at the ends.