Psittacine beak and feather disease (PBFD) is a viral disease affecting all Old World and New World parrots. The causative virus - Beak and feather disease virus (BFDV) - belongs to the taxonomic genus Circovirus, family Circoviridae. It attacks the feather follicles and the beak and claw matrices of the bird, causing progressive feather, claw and beak malformation and necrosis. In later stages of the disease, feather shaft constriction occurs, hampering development until eventually all feather growth stops. It occurs in an acutely fatal form and a chronic form.