Circoviruses are small viruses with unsegmented genomes that have a single molecule of DNA, which forms a circle, closed by covalent bonds. The genome is 1800-2000 nucleotides long. 

There are two or three genera in the Circovirus family:

  • Circovirus (includes Porcine Circovirus Type 1 and 2, as well as Beak and Feather Disease Virus)
  • Gyrovirus (includes Chicken Anaemia Virus)
  • Anellovirus (includes human virus such as Transfusion Transmitted Virus or Torque teno Virus-TTV)
Anellovirus is technically a "floating genus"; however, it is generally accepted currently as part of the family, circoviridae.  

Circoviruses are relatively poorly-studied.

 (Below: Porcine Circovirus)