Psittacine beak and feather disease

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. 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. Cracking and peeling of the outer layers of the claws and beak make tissues vulnerable to secondary infection. Because the virus also affects the thymus and Bursa of Fabricius, slowing lymphocyte production, immunosuppression occurs and the bird becomes more vulnerable to secondary infections. Beak fractures and necrosis of the hard palate can prevent the bird from eating. The ornithologist Edwin Ashby observed a flock of completely featherless red-rumped parrots (Psephotus haematonotus) in the Adelaide Hills, South Australia, in 1888. The species then disappeared from the area for several years. The condition is more prevalent in widely occurring Australian species such as the sulphur-crested cockatoo, little corella and galah. The first case of chronic PBFD was reported in a Control and Therapy article in 1972 for the University of Sydney by Ross Perry, in which he described it as 'beak rot in a cockatoo'. Dr. Perry subsequently studied the disease and wrote extensively about its clinical features in a range of psittacine birds in a long article in which he named the disease 'psittacine beak and feather disease syndrome' (PBFDS). This soon became known as psittacine beak and feather disease (PBFD). Beak and feather disease virus (BFDV) is a circular or icosahedral, 14–16 nm diameter, single-stranded circular DNA, non-enveloped virus with a genome size of between 1992 and 2018 nucleotides. It encodes seven open reading frames—three in the virion strand and four in the complementary strand. The open reading frames have some homology to porcine circovirus (family Circoviridae), subterranean clover stunt virus and faba bean necrotic yellows virus (both family Nanoviridae). It was first isolated and characterized by researchers Dr. David Pass of Murdoch University in Perth and Dr. Ross Perry from Sydney, with later work at the University of Georgia in the United States, the University of Sydney and Murdoch University in Australia, and the University of Cape Town, among other centres. The virus was originally designated PCV (psittacine circovirus), but has since been renamed beak and feather disease virus. This is due in part, to the research confirming that this virus is the cause of the disease, and in part to avoid confusion with Porcine circovirus, also called PCV. A variety of tests for the presence of BFDV are available: standard polymerase chain reaction (PCR), quantitative PCR (qPCR) which can detect the virus in extremely small quantities, whole-genome sequencing, histology, immunohistochemical tests, and quantitative haemagglutination assays. PBFD is usually acquired by nestlings from their parents (vertical transmission) or from other members of the flock (horizontal transmission). The immature immune system of young birds makes them susceptible to the PBFDV. The virus may be transferred in crop secretions, in fresh or dried feces, and in feather and skin particles.