What is Polyomavirus (French Molt)?

Avian polyomavirus is a virus that may cause serious disease or even death in cage birds, particularly in the case of young chicks between one week to two months of age. Avian polyomavirus is a papovavirus, which is a highly contagious DNA virus that sometimes leads to diseases such as French molt or the “feather-losing disease” in birds. French molt affects birds all over the world, primarily budgerigars (commonly called budgies or parakeets) and psittacines (parrots). At the current time, there is no treatment for avian polyomavirus, so a vast number of chicks continue to die each year due to outbreaks.

Because the virus is both deadly and easily spread, bird fanciers and breeders are recommended to have in-depth knowledge of the polyoma virus and French molt, including its signs and symptoms, potential causes, and any steps to minimize the risk of outbreak. Breeding, as well as the showing, buying and selling of birds, can be precarious if the breeder or fancier is not aware of diseases such as French molt. The best way to avoid French molt from infecting your bird or aviary is by taking some preventive measures, including quarantining new birds, maintaining a sanitary environment and providing proper nutrition. A vaccine is also available for adult birds, but, of course, this does not assist birds already diseased. 

Primarily observed in in very young budgerigars (commonly called budgies or parakeets) and parrots, polyomavirus is typically noticed initially due to the condition of the young bird’s feathers. Chicks with the virus are usually born appearing quite normal, but between weeks six to eight, irregularities in the feathers begin to become observable. Soon after weaning, infected chicks will begin to lose plumage, or else fail to develop feathers at all. Fledglings with normally growing plumage may suddenly drop all secondary feathers, as well as tail feathers, which are the longest feathers on the bird. Some birds will drop a few of the larger feathers, but maintain the tail feather.

The smallest feathers, for whatever reason, are usually not impacted by the viral progression. The belly is typically an unaffected area. Unfortunately, most birds infected with avian polyomavirus will never be able to fly due to the loss (or abnormalities) to their wing and tail feathers. Some birds, however, will regrow healthy-appearing feathers, but should still not be selected for breeding. Some owners will choose to cull the bird due to immune system weakness, a condition that may place the entire aviary at risk of infection.

Adult birds are carriers of the virus; they do not typically show signs or symptoms, including the loss or retarded growth of feathers. It’s been documented that adult birds develop antibodies. The reason for this is unknown. What causes French molt, or what brings about the symptoms in one bird as opposed to another, is also debated among aviary specialists.  It is believed that the virus can spread indirectly –from one bird to the next by way of fecal matter, lung secretions and respiratory droplets, dust, feather dust, mites, or dander, among other means. Bird to bird direct contact through egg transmission or parental feeding and care has also been cited as a possible form of contagion. Many young birds will die before showing signs of the disease. In others, there is a quick onset of lethargy, as well as possible bruising and small sores.

Avian polyomavirus is a highly contagious virus that may cause serious disease or even death in infected birds, particularly in budgerigars (commonly called budgies or parakeets) and psittacines (parrots).

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Symptoms of Polyomavirus (French Molt) in Birds

  • Feather loss
  • Lethargy
  • Diarrhea
  • Loss of appetite
  • Tremor
  • Bruising
  • Reddened skin
  • Small sores
  • Swollen belly
  • Sudden death

Causes of Polyomavirus (French Molt) in Birds

Stress, including poor nutrition while breeding, over-breeding, insects, and a mite infestation are factors that could precipitate the condition. Bird to bird transmission (parental feeding or egg transmission) can spread the virus, and it may also be attributable to environmental conditions, including a lack of hygiene in the aviary. Feather dust and bird droppings may be culprits, particularly the ingestion or respiration of contaminated waste in food and water. The introduction of a new bird is always a risk; buying, selling and showing must be taken very seriously due to the highly contagious nature of French molt. The disease is easily spreadable from aviary to aviary.

Diagnosis of Polyomavirus (French Molt) in Birds

The veterinarian will make the diagnosis typically by performing a physical exam, DNA probe and taking a blood sample. The primary characteristic of the disease is the loss of feathers. In absence of other clinical symptoms that suggest a different type of infection, the vet will diagnose the bird with French molt.

If a bird dies, immediately take care to wrap the body and place in a refrigeration unit. Bring the bird to your veterinarian for necropsy so the presence of the virus can be determined. Post-mortem, the virus is diagnosed based, in part, on the appearance of enlarged hearts and livers. The organs (such as the brain) may indicate the presence of spores seen with this virus.

Treatment of Polyomavirus (French Molt) in Birds

There is no treatment for Polyomavirus in Budgies. Some veterinarians believe in treating a clearly infected bird with an antiviral such as acyclovir or AZT. While these are used to treat other viruses, both may be helpful in cases of French molt. Make sure that the ill bird is segregated from other birds.

Recovery of Polyomavirus (French Molt) in Birds

Affected birds can be given special nutritional supplements and silica, per veterinary advice. Prevention is your best course of action. It is imperative for the health of your aviary or bird to keep the living environment disinfected. Your veterinarian can recommend a safe, commercial-grade disinfectant. Thoroughly clean all utensils, wear gloves, and wash your hands between handling your bird; insect control is imperative. 

In the meantime, to prevent the spread of infection within your aviary, it is essential to vaccinate the adults. Please follow up with your veterinarian about this vaccine, as well as a yearly booster.