Poxviridae

• These are the largest of the DNA viruses, approaching the size of bacteria. They replicate in the cytoplasm, and thus must carry every protein needed to replicate their DNA. 
• They produce Guarnieri bodies -- big, pink mushy areas in the cytoplasm where the viruses are replicating. 
• A long time ago, an orthopoxvirus caused the disease smallpox. 

•  Smallpox killed around 30% of an infected group. 
•  It is characterized by vesicles that are all in phase (contrast with chickenpox). There are a few other pox diseases that are still around today, but they all have vesicles in phase.
•  The virus is spread by the respiratory route, and quarantine is very effective.
•  Vaccinia was used as the vaccine strain for smallpox, but unfortunately this strain causes problems at a rate of about 1/1000 immunizations, including autovaccinia where someone inoculates their eye from the arm vaccine, disseminated pox, vaccinia gangrenosum, and an atopic form (eczema vaccinatum). We still have the vaccine, but we do not use it since smallpox has been eradicated. Vaccinia is currently being looked at as a vector for other immunizations. 
• The pox disease we are likely to see is molluscum contagiosum. It causes pearly papules to appear all over the body, and they look like warts. You can biopsy them to confirm the diagnosis, and instead of seeing hyperkeratosis characteristic of warts, you will see Guarnieri bodies in the cytoplasm. The disease goes away on its own.
• There are other poxviruses active through the world, including orf, a parapoxvirus that is seen in people who work with sheep and goats. People with this will have one large purple nodule, usually on the hand, which should be biopsied for diagnosis.

Category: Virology