Psittacine Beak and Feather Disease is a viral disease affecting all
Old WorldThe Old World consists of those parts of Earth known to Europeans, Asians, and Africans in the 15th century.-Regions:The Old World includes Europe, Asia, and Africa , plus surrounding islands...
and
New WorldThe New World is one of the names used for the non-Afro-Eurasian parts of the Earth, specifically the Americas and possibly Australia. When the term originated in the late 15th century, the Americas were new to the Europeans, who previously thought of the world as consisting only of Europe, Asia,...
Parrots (
PsittaciniTribus Psittacini consists of Afrotropical parrots; there are 10 species in 3 genera. Several of these species have subspecies including the African Grey Parrot which has 2 subspecies...
, Hookbills). The virus attacks the feather follicles and the beak and claws-growing cells of the bird, causing progressive feather malformation and necrosis. In later stages of the disease, the feathers develop constrictions in feather shafts, cease development early until eventually all feather growth stops.
The beak and claws are affected in opposite direction - overgrowth, malformation and necrotic tissue development. Cracking and peeling of outer layers makes it possible for fungi and
yeastYeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with about 1,500 species currently described; they dominate fungal diversity in the oceans. Most reproduce asexually by budding, although a few do so by binary fission...
infections to take place and complicate matters even more. The necrosis of inner layers of the beak may cause it to break, at which point the bird will be unable to feed.
The disease also has a general immunosuppressive effect on the bird, clearing path for secondary systemic viral and bacterial infections which are usually the cause of death, not the PBFD virus itself.
The virus
The first report of featherless, dirty-looking birds in Australian bush was in 1907 by Edwin Ashby. He described the outbreak of PBFD in wild
Red-rumped ParrotThe Red-rumped Parrot , also known as the Red-backed Parrot or Grass Parrot, is a common bird of south-eastern Australia, particularly in the Murray-Darling Basin.-Description:...
in Adelaide hills, South Australia in 1888.
Over the years, Australian people seeing birds like this have thought their condition was caused by exclusive sunflower seed diet, which is often the main source of food for Australian cockatoos in captivity. This is now known to be false.
The virus causing the PBFD was first isolated and characterized by researchers at the University of Sydney, Dr. Pass and Dr. Ross Perry, work later continuing at the University of Georgia, USA, University of Sydney and Murdoch University in Perth, Western Australia. The virus was originally designated PCV - Psittacine Circovirus, but has since been renamed to "Beak and Feather Disease Virus", or BFDV. This is in part due to the research confirming that this virus is indeed the cause of the disease, and in part to avoid confusion with Porcine Circovirus, also shortened to PCV. It is circular in shape, belongs to the family
CircoviridaeThe Circoviridae are a family of viruses, including the following genera:*Genus Anellovirus; type species: Transfusion Transmitted Virus in humans, a.k.a...
, measures 16 nm in diameter and consists of a single strand of DNA, between 1992 and 2018 nucleotides in length.
There are currently two BFDV tests available. A
polymerase chain reactionIn molecular biology, the polymerase chain reaction is a technique to amplify a single or few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence...
(PCR) test is very sensitive, and it can detect the virus in extremely small quantities, as long as the testing samples are reliable. The second test actually gives the viral count and the viral anti-body count (
HemagglutinationHemagglutination, or haemagglutination, is a specific form of agglutination that involves red blood cells . It has two common uses in the laboratory: blood typing and the quantification of virus dilutions.-Blood Typing:...
Assay/Hemagglutination Inhibition), but is not as sensitive as the PCR test.
The virus remains viable in the environment for many years and is resistant to most disinfectants.
Infection paths
The disease is usually acquired by the young nestlings from their parents (
vertical transmissionVertical transmission, also known as Mother-to-child transmission refers to transmission of an infection, such as HIV, hepatitis B, or hepatitis C, from mother to child during the perinatal period, the period immediately before and after birth...
) or other members of the flock (
horizontal transmissionHorizontal transmission is the transmission of a bacterial, fungal, or viral infection between members of the same species that are not in a parent-child relationship....
). The adult birds coming into contact with the virus usually (but not always) develop resistance to it, but the virus is retained in their body and, in most cases, is excreted in feces and feather debris for the rest of their life.
The immature immune system of young birds makes them very susceptible to the PBFD virus in their first few weeks of life. The virus may be transferred in
cropA crop is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion that is found in many animals, including gastropods, earthworms, leeches, insects, and birds.- Bees :...
secretions, fresh or dried
fecesFeces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus during defecation.-Etymology:...
and feather and skin particles.
Disease manifestations
The acute form of the disease is manifested by lethargy, loss of appetite, vomiting and
diarrheaIn medicine, diarrhea , also spelled diarrhoea , is the condition of having frequent loose or liquid bowel movements. Acute diarrhea is a common cause of death in developing countries and the second most common cause of infant deaths worldwide...
. Due to the severe suppression of the immune system, multiple secondary viral and bacterial infections will develop, which will cause the death within two to four weeks.
The simplest way to confirm the diagnosis in the acute form of the disease is autopsy, because it progresses too quickly for the normal signs such as feather loss and beak deformity to appear.
The chronic form of disease takes place if the bird's immune system manages to mount some form of defense against the virus and the secondary infections. The characteristic feather symptoms need time to develop, and they only start appearing after the first
moultIn biology, moulting signifies the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life-cycle.Moulting can involve the epidermis , pelage In biology, moulting (or molting, also known as sloughing, shedding or for...
. In those species that have powder down, it will be affected immediately, as it is continually replenished.
Dr. Ross Perry FACVSc (Avian health) notes that the pattern of disease and the probability of
remissionRemission may refer to:*Remission , the reflection or scattering of light by a material*Remission *Remission *Re-Mission, a video game for young people with cancer...
varies markedly between species; with
BudgerigarThe Budgerigar , is a small parrot and the only species in the Australian genus Melopsittacus...
s,
African LovebirdsA Lovebird is one of nine species of the genus Agapornis . They are a social and affectionate small parrot. Eight species are native to the African continent, while the Grey-headed Lovebird is native to Madagascar...
, lories and lorikeets and
Eclectus ParrotsThe parrot genus Eclectus consists of two species, the extant Eclectus Parrot and the extinct Oceanic Eclectus Parrot ....
presenting with acute to subacute disease being among those more likely to make a clinical recovery just on a "balanced diet", usually based on organic well-formulated pellets or crumbles supplemented with a little of a lot of fresh organic greens, vegetables and fruit, and given extra care for 1-2 moults.
On large Australian and New Guinea cockatoos, the very first sign of the chronic PBFD is the loss of powder down. On smaller, coloured cockatoos, the
EclectusThe parrot genus Eclectus consists of two species, the extant Eclectus Parrot and the extinct Oceanic Eclectus Parrot ....
,
King ParrotThe Australian King Parrot is endemic to eastern Australia. It is found in humid and heavily forested upland regions of the eastern portion of the continent, including eucalyptus wooded areas in and directly adjacent to subtropical and temperate rainforest...
, and many species of lories and lorikeets, first sign is feather discolouration. Coloured parrots seem to be less affected by the disease, often able to spontaneously recover. For the white cockatoo species, the prognosis is much worse.
In Australia, wild cockatoos have adapted very well to the urban environment and are a common sight in the suburbs. It is quite common for the flock to have one or more members visibly affected by the PBFD, without crest feathers, missing some flight and/or tail feathers, etc.
Threat
BFDV has the potential to become a major threat to all species of wild Parrots and to modern
avicultureAviculture is the practice of keeping and breeding birds and the culture that forms around it. Aviculture is generally focused on not only the raising and breeding of birds, but also on preserving avian habitat, and public awareness campaigns....
, due to the increasing international legal and illegal bird trade. Cases of PBFD have now been reported on all continents in at least 42 psittacine species, and this is likely to increase. At least 38 of 50 Australian native species are affected by PBFD, both captive and in the wild. In 2004, PBFD has been listed as a key threatening process by the Australian Commonwealth Government for the survival of five endangered species, including one of the few remaining species of migratory parrots, the
Orange-bellied ParrotThe Orange-bellied Parrot is a small broad-tailed parrot endemic to Australia.The adult male is distinguished by its bright grass-green upperparts, yellow underparts and orange belly patch. The adult female and juvenile are duller green in colour. All birds have a blue frontal band and blue outer...
(
Neophema chrysogaster), of which only an estimated 60 mating pairs remain (as of 2006). An experimental killed virus vaccine has been produced, but the further development to refine it and make it commercially available is progressing slowly due to the lack of funding.
Treatment
There is currently no specific treatment for the virus. The experimental vaccine has been proven to provide protection against the virus, but is likely to accelerate the disease in parrots already infected with the virus.
Supportive care of affected pet birds
Firstly if a bird is infected and is being kept with several other birds, the bird should be quarantined and the pens disinfected. This to prevent spread through the other birds. Therapeutical interventions can only be limited to treating secondary infections (bacterial/fungal). The individual bird can sometimes recover, but it must be noted that this is rare. If only the feathers are affected and the bird suffers not of other signs, an acceptable life can exist. But if the bird's beak or nails get affected, most veterinarians will suggest to euthanise the animal.
Unfortunately no therapies have been found yet. The management of the disease lies thus mostly in prevention. Every new bird that enters a pen with other birds should be quarantined first and be tested for PBFD virus. Birds which are known carriers should not be introduced into new pens, especially not if those contain young birds.
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