Psittacine Circoviral Disease (PCD) or previously, Psittacine Beak and Feather Disease (PBFD), is one of the most insidious infectious conditions of psittacine birds: parrots, cockatoos and lorikeets. It infects all these species (including galahs and corellas), but with varying vulnerability: most Australian, Asiatic and African species are very susceptible to the disease, but some – including cockatiels and South American species such as macaws – are less frequently affected.
PBFD gained prominence in the 1970s when specialist avian veterinarian Dr Ross Perry began ground-breaking studies into the disease, but the condition had been documented in Red Rumped Parrots as early as the late 1880s. Dr Perry and other researchers were able to first demonstrate it was infectious and easily transmissible from bird to bird, then in 1987, the infectious agent – avian circovirus – was isolated.
It is thought PBFD originated in Australia and over the past 200 years spread world-wide through the export (both legal and illegal) of Australian birds.
Disease symptoms vary significantly depending on species, age and the state of moult when the bird first infected.
The acute form of the disease is uncommon and occurs in juvenile birds, usually at fledging. The virus attacks bone marrow, resulting in weak and anaemic chicks that often die within several days.
More commonly, birds develop a chronic form of the disease affecting feathers and, in cockatoos, the beak.
The progression of the disease is usually predictable, with lesions typically starting in the powder down (often noticed over the hips first), then becoming evident in the contour feathers, primary feathers, secondaries, tail and finally, the crest feathers.
As each set of feathers is infected, they retain their sheaths, the shaft fills with blood, the base is often constricted and feathers falls out easily. The overall appearance of the bird becomes disheveled, dirty and messy. Some birds drop their tail feathers, others drop feathers when handled. In budgerigars the condition has been called French Moult and in wild Rainbow Lorikeet populations, affected juveniles have such stunted feathers they are unable to fly and are called ‘runners’.
Only cockatoos appear to develop beak changes but these are severe, with both upper and lower beaks becoming overgrown, blackened and fragile. The diseased beaks break easily and become painful: with the underlying sensitive tissues now exposed the bird becomes reluctant to eat. Cockatoo claws can also be affected.
The impact of the virus on bone marrow also leads to immunosuppression, with birds becoming vulnerable to a range of other infectious diseases. The usual outcome is death within 1 to 2 years.
Caring for affected birds
As yet, there is no treatment or cure for PBFD. Some birds may be supported as the disease progresses with treatment to combat secondary infections.
Affected birds need good nursing, nutrition and husbandry to support them as the disease progresses. The decision to euthanase individual birds should be made when the bird’s quality of life deteriorates – eating will become difficult if the beak is infected, and loss of feathers makes it hard for the bird to stay warm.
Diagnosis and prevention
A vaccine has been developed against PBFD but, like most vaccines, it is not effective if a bird has already been exposed to the virus. The virus is widespread in both wild and pet shop/aviary situations and many of these birds appear normal. Vaccinating these previously exposed birds will not stop the disease developing.
Without a vaccine, prevention through good management is essential. The virus is tough (it is resistant to most disinfectants) and can live for years in the environment, including in nesting boxes – once PBFD gets into an aviary or household it is extremely difficult to eradicate.
A number of tests for PBFD are available – we can test for the disease at Crookwell Veterinary Hospital. Testing is critical to accurately identify infected and/or carrier birds. Quarantining birds is not effective as the incubation period for PBFD can be as short as 3 weeks or as long as several years.
The disease is quite complex. PBFD is spread from bird to bird in feather dust, the droppings and in crop secretions when feeding chicks, but individual birds respond differently to the virus. Birds with a strong immune system can be challenged by the virus, not succumb to the disease, eliminate the virus and remain immune for life. Other, slightly immunosuppressed birds can develop a low-grade form of the disease. These birds may not die, instead becoming carriers and shedders of the virus. These are the birds that transmit the virus to other birds, both in the wild and in aviary situations.
Lorikeets, for example, can become clinically affected, lose their tail and flight feathers but, after a few months, re-grow the lost feathers and appear to recover. Unfortunately, some of these apparently heath birds remain carriers of the virus.
Acknowledgements: Dr Pat Macwhirter, Dr Garry Cross, QLD University Veterinary School.