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 belongs to the family Circoviridae. 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 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. Previously unpublished data from Dr Ross Perry indicates that aspects of the immune system are working over-time, perhaps similar to an auto-immune disease in chronic PBFD [1]

Contents

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.[2]

The condition is more prevalent in widely occurring Australian species such as the Sulphur-crested Cockatoo, Little Corella and Galah.[3]

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. Dr Ross Perry remembers being taught at Sydney University in 1969 that "a common feather loss disease of cockatoos is caused by too much sunflower seed in the diet"[1]. This is now known to be false.

The first case of chronic PBFD described by a vet was reported in a Control and Therapy article in 1972 for the University of Sydney by Dr Ross Perry, in which he described it as "Beak Rot in a Cockatoo" [1]. Dr. Ross 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) [1]. This soon became known as Psittacine Beak and Feather Disease (PBFD)[1]. The virus causing the PBFD was first isolated and characterized by researchers Dr. David Pass of Murdoch University and Dr. Ross Perry from Sydney, with much 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 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 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.

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 crop secretions, fresh or dried feces and feather and skin particles.

Symptoms and signs

The 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.

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 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 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 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 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 aviculture, 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 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. A new vaccine developed by Dr. Siwo de Kloet protects birds from the virus and does not endanger birds already infected with PBFD.

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 (by definition using pharmaceutical drugs) 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 euthanase the animal. Dr Ross Perry often explores a holistic approach including the use of combinations of nutraceutical supplements to supporting the life and well-being of PBFD-affected pet birds and notes that the need for euthanasia because of suffering can sometimes be postponed for years [1]. 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

  1. ^ a b c d e f Perry, R.A. (2010) pers.com.
  2. ^ Ashby, E. (1907). The Emu, 6, 183–194.
  3. ^ Borthwick, David (May 2005). "Threat Abatement Plan for Psittacine Beak and Feather Disease Affecting Endangered Psittacine Species". Department of the Environment and Heritage website. Department of the Environment and Heritage, Commonwealth of Australia. http://fedlaw.gov.au/ComLaw/Legislation/LegislativeInstrument1.nsf/previewlodgmentattachments/81FCCCA0AB589760CA25718E00044623/$file/F2005L02255.htm. Retrieved 7 December 2009. 

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