Poxviridae

The Poxviridae (pox), also known as poxviruses, are a family of viruses belonging to the group of nucleocytoplasmic large DNA viruses (NCLDV). Poxviridae are the largest viruses known at 400-500nm. The family Poxviridae is divided into the subfamilies Entomopoxvirinae and Chordopoxvirinae. Only in the Chordopoxvirinae subfamily are human pathogenic species found.

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Classification of the human pathogenic Poxviridae:

Orthopoxvirus

• Variolavirus (primary host: human - smallpox disease)
• Vaccinia virus (primary host: human - vaccine diseases e.g. Eccema vaccinatum)
• cowpox virus (primary host: small rodents, possibly cattle)
• Monkeypox virus (primary host: monkeys)

Parapoxvirus

• Milking knot virus (primary host: cattle - milking knots)
• Orf virus (primary host: sheep - Orf)

Yatapoxvirus

• Tanapox virus (primary host: probably monkeys)

Molluscipoxvirus

• Molluscum contagiosum virus (primary host: human - Molluscum contagiosum)

Poxviridae occur in several forms:

• extracellular enveloped viruses (EVs) with 2 lipid envelopes
• intracellular mature viruses (MVs) with a lipid envelope that is also found extracellularly after lysis of the target cell
• intracellular viruses with 3 lipid envelopes (wrapped viruses = WVs).

The structure of the Poxviridae is extremely complex. The extracellular virus particles (EV) have a linear ds (+/-) DNA with a size of 170-330nm which consists of about 130,000 to 375,000 base pairs. The nucleocapsid is enclosed by viral proteins. In the concave indentations of the DNA-containing nucleus are so-called lateral bodies, whose function is still largely unknown (see figure). The lateral body and the core are enclosed by a first shell in which different non-glycosylated proteins are incorporated. The outer boundary of the particle is established by a second envelope. All viruses belonging to the Poxviridae family have a number of virus-specific enzymes and regulatory proteins in the nucleus.