Circovirus is a type of virus that primarily affects birds and pigs. It is known for its circular DNA structure, which is unique among viruses. In pigs, the most notable strain is the Porcine Circovirus (PCV), which can lead to various health issues, including respiratory problems and weight loss. In birds, particularly pigeons and parrots, circoviruses can cause feather loss and immune system suppression. These viruses are typically transmitted through direct contact or contaminated environments. While circoviruses can lead to significant health problems in affected animals, they do not pose a risk to humans.