When I first started out in practice, I would see the saddest cases of cockatoos with weird feather loss, overgrown beak and claws and a myriad of infectious diseases. We called it Psittacine Beak and Feather Disease, as we knew that it was a syndrome causing many different problems, all related to the bird's defective immune system. Birds usually showed abnormal feathers, lack of powder down, overgrown beaks, often with abnormalities such as beak ulcers, and overgrown toenails. Many theories about the cause had been put forth, with no definitive cause determined. It would seem to pop up in long term captive breeders and pets, with no rhyme or reason. It seemed that no matter what we did, the bird would eventually succumb to a bacterial or fungal infection, often after a protracted illness.
While we classically thought of this as a disease of cockatoos, we would occasionally see the same characteristic lesions and immunodeficiencies in other species of birds, including Amazons, African greys, macaws, lovebirds, pionus and Eclectus as well as other species. While most Old World psittacines that developed PBFD would die, a few New World psittacines with feather lesions have recovered.
A patient of mine back in the 80's, named BJ, was one umbrella cockatoo that I had diagnosed as having PBFD. He was a darling bird, very affectionate, and every time he saw a person, he would shout "Hello, BJ!" To him, everyone was BJ, and everyone was his friend! Due to our close monitoring of his health, BJ lived for almost two years with his disease before finally succumbing to a fungal brain infection.
Once the team at the University of Georgia, headed by Dr. Branson Ritchie, DABVP, discovered that PBFD was caused by a circovirus, in late 1991 and early 1992, and then developed a very sensitive and specific DNA PCR test that would tell if a bird had the virus in the bloodstream, this revolutionized the diagnosis for aviculturists and pet owners. However, feather follicle biopsies are still a valuable diagnostic test for any bird with feather lesions. The original PBFD virus that causes this disease is now called psittacine circovirus 1 (PsCV-1). In recent years, a second variant of the virus was discovered in lories with feather lesions, and this variant is now called PsCV-2. Lories with PsCV-2 and dystrophic feathers may mount an appropriate immune response and eventually recover from the infection.
Even without a diagnostic blood test for PBFD, we were able to diagnose BJ by taking biopsies of feather follicles containing abnormal feathers, which was certainly easy enough to do with BJ. Using an avian pathologist, a patient could be diagnosed by the observation of the characteristic inclusion bodies found in certain parts of infected cells.
Let's start by learning a bit about the history of this viral infection so that we will better understand this devastating disease. It is possible that Australian explorers first identified this disease in 1887, when they described the characteristic feather changes in wild red-rumped parakeets (Psephotus sp.). However, the disease as we have come to know it was first described in several species of Australian cockatoos in the early 1970's. There were many proposed causes of this disease including endocrine abnormalities, polyomavirus, Mycoplasma, Newcastle's disease virus, reo virus, adenovirus, salmonellosis and other infectious agents. To prove that an agent is the cause of a particular disease, one must fulfill Koch's postulate, which means that you must be able to recreate the same disease in another animal by giving it the disease particles. It was possible to give neonatal budgies and rose-breasted cockatoos the disease by using crude feather homogenates. Young sulfur-crested cockatoos and rosies were also given the disease using a partially purified virus preparation produced from feathers from infected birds. Concentrated purified virus particles, called PBFD virions, were able to cause disease in neonatal budgies, African greys, and umbrella cockatoos. Thus, it was proved that the PBFD virus was responsible for causing this terrible disease.
What is a virus? A virus is a microscopic particle that requires a live host in order to reproduce. Viruses are more primitive than bacteria, which are able to reproduce on their own, and the viruses are much smaller. Viruses are not metabolically "alive" until they infect a living cell. Viruses are not affected by antibiotics, which are commonly used to treat bacterial infections. This is why you should not take an antibiotic if you are suffering from a cold or the flu, as those are viral infections. In recent years, scientists and researchers have developed some medications that are active against certain viruses.
In many cases, it is possible to become protected against certain viruses by the use of preventative vaccinations. Prevention is a much better when it comes to viruses, as treatment is not nearly as predictable or effective. When developing a vaccine, often the virus has been killed or made ineffective in causing disease, but the body still produces antibodies against it, which provides immunity. In some cases, a vaccine may provide life-long immunity, and in other cases, vaccines must be boostered periodically to maintain adequate immunity. To produce vaccines in some cases, a closely related virus may be used for a vaccine, but one that is incapable of causing disease in the desired species. Interestingly, many viruses are species specific, or confined to causing disease in closely related species. It is a rare virus like the virus causing rabies, which can infect and cause disease in many different kinds of animal.
So, it is good to know that we humans, who care for our pet birds, are unable to contract the disease caused by the PBFD virus. This is good news for us. But many species of bird in Australia, North America, Europe and Asia are susceptible and over 40 species of psittacine birds have been documented as having developed PBFD from PsCV-1. In addition to the variant PsCV-2, other circoviruses have been discovered. Also, a similar circovirus has been found in doves and pigeons. Other circoviruses have been identified in gulls, geese, canaries, finches and humans. These viruses, however, cannot cause disease in parrots.
Dr. Ritchie and the team at the University of Georgia have been working to develop a vaccine against PBFD, and hopefully, one will be available in the near future. But until such a time that a vaccine is available we must still rely on testing as a way of preventing illness caused by PsCV-1.
It has been reported that up to 20% of some free-ranging cockatoos in Victoria, Australia, may have clinical signs in any one year. Other studies and anecdotal reports indicate that the PBFD virus is causing disease in some other Australian cockatoo flocks, wild crimson rosellas and other wild populations of Moluccan cockatoos, lovebirds and other species of cockatoos.
Generally, PBFD is considered to be a disease of young psittacines, usually up to three years of age. However, older birds, often up to twenty years of age that had been clinically normal throughout most of their lives, can also suddenly break with all the signs of PBFD. It is thought that birds are usually exposed to the PBFD virus at a young age, when their immune systems aren't as strong, and they may appear normal for years before finally developing signs of PBFD. It is suspected that these birds are infected and eventually break down with illness, perhaps years later. If a bird contracts PBFD prior to developing its feathers, as the feathers grow out, they will often show the classic abnormalities. However, if a baby bird contracts PBFD after it has already grown out its feathers, the abnormal feathers may not show up until the bird molts and the normal feathers are replaced with abnormal ones. Occasionally, a young bird that had contracted PBFD would die before developing feather lesions at all. However, in all cases, any bird with feather lesions should undergo feather follicle biopsies to confirm the diagnosis. PBFD may present as a peracute infection, acute infection or a chronic disease.
How is PBFD diagnosed today? Let me give you an example that occurred several years ago in an aviary that I dealt with. A client had an imported timneh grey with poor feathering that was set up as a breeder. Thinking the bird was a feather-picker, he never tested the bird for PBFD. Eventually, this bird bred with a female, and the baby bird was brought into the nursery along with twelve other psittacine chicks, including two pionus, three Jardine's parrot chicks, six African greys and one mini-macaw. When the baby timneh grey began showing abnormal feathers, his vet ran a PBFD blood test (which must be drawn by clean venipuncture stick, and not by clipping a toenail, which may contaminate the sample with viral particles). When the test came back positive, the vet referred the client to me to deal with the problem. The aviary owner was very upset, as you can imagine, as he thought he would probably lose all of his baby birds.
Since the virus is thought to be spread by feather dander, fecal matter and other secretions from infected birds, chances were, the other neonates in the nursery were all exposed. Blood was drawn from all of the baby birds and tested for the presence of the PBFD virus. Out of the twelve babies in the nursery (the timneh was isolated), ten tested positive. But, the good news is that many exposed babies will mount an effective immune response and should not be euthanized based on one positive test. An environmental swab was also taken, of window sills, floorboards and walls to test for the presence of contamination with PBFD virus. The birds with feather lesions underwent diagnostic biopsy of affected feathers and follicles, as well, to confirm the disease.
Any birds that test positive, but have no feather lesions, should be re-tested in 90 days, and that is what we did in this case. A negative test in 90 days indicates that the bird has eliminated the virus from the bloodstream, which is what happened in ten of the babies in this case. The two babies that still tested positive were latently infected and eventually broke with clinical PBFD, but the other eight were basically self-vaccinated and should be considered immune to the virus. The environmental swab tested positive, meaning that the owners needed to perform a thorough cleaning even though many commonly used disinfectants are ineffective in killing this stable virus.
Today, most responsible aviaries have had all susceptible larger breeders tested for the PBFD virus, and have culled positive birds from their breeding programs. Unfortunately, many backyard breeders and many breeders of the smaller birds, such as lovebirds and budgies, have not had their birds tested for PBFD. So, today in the United States, we usually only see PBFD in the smaller birds.
It is thought that, based on the results of antibody titers, that many birds of susceptible species have some detectable anti-PBFD virus antibodies, indicating previous exposure to the virus. Antibody titer surveys in the United States suggest that most birds of susceptible larger species are exposed to the virus at some time in their lives but are able to mount an effective immune response. This is considered natural vaccination, just like the baby birds in the nursery who were all exposed to the virus, tested positive and then later tested negative. Those birds would likely be immune to the PBFD virus for life.
Since there is no preventative vaccine against PBFD at this time, our methods for controlling the disease involve testing susceptible birds and culling any that test positive twice, 90 days apart, if they have no lesions of PBFD. Any birds that test positive that have feather lesions should be considered to be infected. Birds that test positive twice, yet show no signs, should be considered to be infected, and will most likely break with the disease at a later date. This is often what we used to see with pets and breeders. A long time pet or breeder would suddenly develop feather lesions and become ill. A positive test result would result in heartbreaking news for owners, such as the gentleman who cared for BJ. Since a positive diagnosis was a virtual death sentence, as we could not treat the primary viral infection, but only the secondary fungal, bacterial, mycoplasmal, chlamydial or protozoal infections. In spite of our best efforts, birds would eventually develop a debilitating illness from which there was no recovery.
The variant of circovirus, PsCV-2 requires a different DNA PCR test than PsCV-1. There is also a generic circovirus DNA PCR test that can be useful in diagnosing circovirus infections in other species, such as canaries and finches.
Today, in the United States, we are primarily diagnosing active PsCV-1 infections in lovebirds. However, lovebirds that have recovered from polyomavirus infection may show similar feather lesions, so follicle biopsies and DNA PCR tests are valuable in differentiating between the two. It is possible for an infected lovebird to shed the virus and spread PsCV-1 to other susceptible young birds in a pet store nursery, home or aviary. But, I rarely diagnose this disease in psittacines in my practice today, mainly because of the diligent testing performed by my aviary clients years ago. According to Dr. Ritchie, the variant PsCV-2 has not been diagnosed in birds other than lories and that variant differs approximately 10% from PsCV-1.
Once the vaccine becomes commercially available, hopefully, responsible breeders and owners will utilize this resource to eliminate this terrible virus threat from our psittacines. Avian veterinarians will have one more tool in their arsenal to help keep the birds in our country healthy for a very long time.
Copyright © 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
All Rights Reserved
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