Psittacine beak and feather disease

Psittacine Beak and Feather Disease is a viral disease affecting all Old World and New World Parrots (Psittacini, 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 yeast 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 immunosuppresive 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 Parrot 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 the wild. 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 Circoviridae, measures 16nm 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 reaction (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 (Hemagglutination 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 transmission) or other members of the flock (horizontal transmission). 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.

Newly hatched birds do not have their immune system functioning to its' full potential until they are several weeks old, which makes them very susceptible to the PBFD virus. The virus may be transferred in crop secretions, fresh or dried feces and feather and skin particles.

Disease manifestations

Acute form of the disease is manifested by lethargy, loss of appetite, vomiting and diarrhea. 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.

Only way to confirm the virus in the acute forms of the disease seems to be the autopsy. The acute form of disease has no signs of characteristic feather loss and progressess too quickly to allow time for anything else.

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 moult. 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 remission varies markedly between species; with Budgerigars, African Lovebirds, lories and lorikeets and Eclectus Parrots 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 a little tender loving 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 Eclectus, King Parrot, 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 more grim.

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. Unlike the humans, there is no equivalent of Leper colony in the cockatoo world. These birds are not rejected from the rest of the flock, but remain the part of the flock for as long as they survive.

Threat

The BFDV has potential to become a major threat to all species of wild Parrots and to the modern aviculture, due to the increasing international legal and illegal bird trade. The 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 Parrot ("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.

References

*Ashby, E. (1907). The Emu, 6, 183-194.
*Pass, D. A. and Perry, R. A. (1984). The pathology of psittacine beak and feather disease. Aust Vet J, 61, 69-74.
*Pass, D. A. and Perry, R. A. (1985). Psittacine Beak and Feather Disease: An update. Aust Vet Practit, 15, 55-60.
*Raidal, S. R. (1994). Studies on Psittacine Beak and Feather Disease, PhD thesis, University of Sydney, Sydney.
*Raidal, S.R., Johnsen Bonne, N. and Stewart, M. (2005). Development of Recombinant Proteins as a Candidate Vaccine for Psittacine Beak and Feather Disease. Murdoch University, Perth, Western Australia

External links

* [http://numbat.murdoch.edu.au/caf/pbfd.htm PBFD Home page, Murdoch University, Perth, Western Australia]
* [http://www.nationalparks.nsw.gov.au/npws.nsf/Content/Infection+by+Psittacine+Circoviral+beak+and+feather+Disease+affecting+endangered+psittacine+species+and+populations+-+key+threatening+process+declaration Infection by Psittacine circoviral (beak and feather) disease affecting endangered psittacine species and populations - key threatening process declaration]
* [http://www.vet.uga.edu/IVCVM/1998/werther/werther.htm Description of the First Case of Psittacine Beak and Feather Disease in Brazil, 1997]
* [http://www.avianvet.com/medupdates.htm#psittacine Medical update: Important Diseases of Pet Birds]
* [http://www.geocities.com/~calliefeather/hollyspeech.html Circovirus in Lorikeets]
* [http://fedlaw.gov.au/ComLaw/Legislation/LegislativeInstrument1.nsf/previewlodgmentattachments/81FCCCA0AB589760CA25718E00044623/$file/F2005L02255.htm Threat Abatement Plan for Psittacine Beak and Feather Disease Affecting Endangered Psittacine Species] . Australian government. 1999.