INTRODUCTION
DEBRA BOURNE
Wildlife Information Network, Twycross Zoo — East Midland Zoological Society, Atherstone, UK
Poxviruses are a family of large DNA viruses. Within the poxviruses (family Poxviridae) there are two subfamilies: Chordopoxvirinae, affecting vertebrates, and Entomopox- virinae, affecting insects.
There are nine recognized genera of Chordopoxvirinae : Avipoxvirus, Orthopoxvirus, Parapoxvirus, Capripoxvirus, Cervidpoxvirus, Leporipoxvirus, Sui- poxvirus, Molluscipoxvirus and Ya tapoxvirus; some poxviruses are not yet assigned to any of these genera. The viruses affecting birds are all contained within the avipox- viruses, whereas mammalian poxviruses are assigned to the different genera based on cross-protection in hosts, neutralization assays and genomic DNA hybridization studies. Various poxvirus diseases are important in domestic animals, and some are important zoonoses.Virions contain a dumbbell-shaped core and lateral bodies, enclosed in an outer membrane. Orthopoxviruses and most other poxviruses are 200-400nm long, brickshaped and covered with irregularly arranged tubular elements. The genome is linear double-stranded DNA (both a positive and a negative strand) ranging in length from 134 kb in the parapoxviruses to 330 kb in the avipoxvi- ruses. Virus replication takes place in the cytoplasm of the cell. Transmission of poxviruses usually occurs through contact of infective material with abraded skin or via the upper respiratory tract.
Poxviruses are usually named according to the hosts/ species affected, e.g. Fowlpox virus, Sealpox virus (although it is now accepted that the main hosts of cowpox are rodents). Pox diseases generally involve development of relatively mild lesions of the skin (e.g. a rash) and/or mucous membranes, although systemic, often fatal, disease occurs in some host-virus combinations.
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