Chaffinch infected with the Fringilla papillomavirus (FPV).

Warts (viral papillomas)

Agent: The Fringilla papillomavirus (FPV).

Epidemiology: The epidemiology of the disease has not been studied.

Species susceptible: Chaffinches and, to a lesser extent, bramblings. In a large survey of birds captured for ringing in the Netherlands, papillomas were found on 330 (1.3%) of some 25,000 chaffinches examined and both sexes were affected. However, cases usually occur in clusters and quite high proportions of local populations may be affected in outbreaks.

Clinical signs: The disease causes warty outgrowths on the foot or tarsometatarsus (the bare part of the leg). Usually only one limb is affected. The growths vary from small nodules to large irregular shaped and deeply-fissured masses which almost engulf the entire lower leg and foot and which can distort the toes. Affected birds usually seem in otherwise good health but some may show signs of lameness and hop mainly on the unaffected foot and digits may be lost. The warts grow slowly and may progress over many months.

Pathology: The growths have a similar structure to warts in mammals and are due to excessive growth of the keratinised layers of the skin.

Risks to human and domestic species: None known.

Diagnosis: The clinical appearance is strongly suggestive but other diseases can cause swellings on the legs and feet: infestation with Cnemidocoptes mites (there is some evidence for an association between mange due to Cnemidocoptes infestations and the occurrence of papillomas), bacterial infections (bumblefoot), poxvirus infections. Diagnosis can be confirmed by histology or detection of papillomavirus particles.

Impact on populations: It seems unlikely that this disease has an impact on population densities.

Impact on welfare: Even birds with large papillomas often appear to behave normally so, in some cases, the growths may be little more than an inconvenience and relatively minor irritation. However, lameness is sometimes observed and this clearly indicates pain.

Treatment: None. The outcome of the disease is unclear. Birds may die through being incapacitated or through developing secondary infections but it is possible that in some cases the lesions may regress spontaneously.

Control and prevention: The fact that cases occur in clusters suggests that the presence of affected birds presents a risk to others that are susceptible. The mode of transmission is not known but it seems likely that the virus may be spread via surfaces the birds stand or perch upon. If so, hygiene measures and steps to minimise crowding at perching or feeding sites may reduce the risk.