Avian Polyomavirus (APV) or Budgerigar Fledging Disease

Avian Polyomavirus (APV) infection, otherwise known as Budgerigar Fledging Disease, is the primary cause of this symptom although other factors are often involved.

Budgerigar breeders recognise symptoms of APV in their birds as French Moult.

The term French Moult is a symptomatic description of a disease that may include APV, Psittacine Beak and Feather Disease virus (PBFDS) and other infections.

Preventing APV

Prevention is the only cure as there is no treatment for APV.

An understanding of the disease and other predisposing circumstances will help prevent the disease.

There are three important facets to this disease.

• Polyomavirus (APV) “Carrier” Bird
• Nutritional Stress during the Moult
• Poor Quill Strength

Polyomavirus (APV) “Carrier” Bird

APV is the most common disease of budgerigar studs. In my book “The Budgerigar”, I describe it as the most significant disease of budgerigars, as it often affects immunity thereby having a profound effect on the long-term health and reproductive ability of an infected budgerigar stud.

Infection with APV occurs primarily in young budgerigars between 0-20 days of age. Budgerigars that survive the acute infection will often drop their long feathers in the weaning cage, fail to develop their primary wing and tail feathers, or these may be deformed as the virus damages the feather follicle especially of these long feathers.

APV infection is life long although infection and disease are not synonymous. In fact the vast majority of APV infections are asymptomatic. In most instances the lost flight and tail feathers of weaning budgerigars are regrown soon after recovery from the acute infection. These birds however remain “carriers” of APV and are the most likely birds to lose their tails during the first adult moult.

Small outbreaks in adult birds have been reported but are rare. Psittacine Beak and Feather Disease virus (PBFDS) infection (that often occurs together with APV in budgerigars) is thought to be immuno-suppressive and may predispose adult birds to APV disease.

From my perspective, I consider APV to be a disease confined to young birds but which remains as a life long infection. Most infected birds remain symptomless “carriers” throughout their lives. Some individual “carrier” birds – mostly those possessing exhibition quality feather features – become re-infected with APV following a stressful event.

In my view the loss of tail feathers in adult birds is confined to birds already infected with APV i.e, “carrier” birds. Often these birds have not exhibited any prior symptoms associated with APV. However, in most of these birds there are symptoms of APV prior to the failure of the tail feathers to regrow although they are not obvious to most budgerigar breeders.

A close examination of affected birds often reveals a slow or delayed moult, low vitality, poor feather condition, missing flight feathers, frayed tail feathers, staining of the feathers above the nostrils, preen gland cysts and tumors, feather cysts and other signs of poor general health. Some birds may appear in very good condition but these birds often have lost feathers during the weaning period and regrown them soon after. They are in fact APV “carrier” birds.

Nutritional Stress during the Moult

A failure to regrow tail feathers is most likely to occur in APV “carrier” birds during their first adult moult. These birds are often physically large birds that also possess championship quality feather features.

The regrowth of the paired central tail feathers occurs towards the end of the moult at the same time as the long end flights. Any nutritional deficiency (i.e. stress) is more likely to appear at this time as these feathers are the largest in the body and because their regrowth also occurs towards the end of the moult. Dormant APV infections are likely to be activated in “carrier” birds at this time.

Poor Quill Strength

The quill strength of many championship quality budgerigars is poor. Poor quill strength may be a consequence of APV infection or poor genetic selection. Feather problems (e.g. feather cysts, bacterial follicle infections, feather abnormalities) and a failure to regrow tail feathers are more likely in birds with poor quill strength.

Feather cysts (i.e. retained curled up feathers are trapped beneath the skin) and other feather abnormalities may occur as a result of poor quill strength in the absence of APV infection.

“The Budgerigar” Book

Avian Polyomavirus (APV) infection and methods used to prevent it are covered in even greater detail in my book – “The Budgerigar”.

Note from Gerald S Binks: If you are serious about your hobby, I would urge you to obtain Dr Marshall’s book “The Budgerigar” which took 12 years to compile. Details of how to obtain a copy can be found below.

• Tails You Lose! – Part 1 of 2
• Dr Rob Marshall’s book – “The Budgerigar”

GSB: Apart from an overall treatment in the first instance, if it has never been done before, you should not treat again unnecessarily.

The sensible action is to isolate ALL new arrivals in a separate room and treat them immediately before release into the main stud.

Your outside flight must also be covered on the roof to prevent any indigenous infected birds excreting into it and thus infecting your disease free stud.

There are countless examples of fanciers ignoring these basic rules and budgerigars being lost in good numbers

When buying a bird, what should I check before parting with my hard-earned money?

GSB: Firstly examine the bird closely. Is it tight in feather or loose feathered and huddled? Catch it and check for the following:

1. Is it clean round the vent area and with no stained feathers?
2. Is it full in the hand and has bright eyes?
3. Look for and feel for any cysts around the lower gut area and in particular examine the wing butts where cysts are easy to miss.
4. Feel the crop. Is it normal with some seed inside it or is it bloated – which raises a question about the bird’s digestive tract?

My aviary is completely enclosed. What should I do about the lack of direct sunshine with its vital vitamin D factor?

GSB: Vitamin D that is lost in this way should be replaced artificially via multivitamin solutions and / or cod liver oil bought from your pharmacy.

Should hens be taken to shows?

GSB: Hens are generally more easily stressed during transport and while being moved around inside the exhibition. I suggest that you take them to no more than two to three shows only and certainly not three day shows.

On arrival home from a show, give them every care and attention and allow them access to food and grit before extinguishing the lights should you arrive home late.

Do not overshow them and they will subsequently breed well.