Fowl Pox

Introduction

Fowl pox is a virus of the family poxviridae, which is a double stranded DNA virus causing cell proliferation followed by central necrosis to form the characteristic 'pock' lesion. This is a relatively slow-spreading viral disease characterised by skin lesions and/or plaques in the pharynx. Morbidity is around 10-95% as the disease is moderately contagious and mortality is usually low to moderate at around 0-50%.

Infection occurs through skin abrasions and bites, or by the respiratory route. It is transmitted by birds, fomites, and mosquitoes. The virus persists in the environment for many months.

Signalment

It affects chickens, turkeys, pigeons and canaries worldwide. It affects birds of all ages and is more common in males due to fighting and it is also more common in months when mosquitoes are more prevalent.

Clinical Signs

Pock lesions, which spread and erupt then later form scabs. These are primarily found on the combs and wattles of affected birds. Caseous deposits in mouth, throat and sometimes trachea may also be present. Other clinical signs include depression, inappetance, poor growth and poor egg production.

Diagnosis

History and clinical signs as described above are characteristic for the disease and would lead to a presumptive diagnosis. These signs may be seen in the live bird or at necropsy. On microscopic examination of tissues post mortem, one will see intra-cytoplasmic inclusions (Bollinger bodies) with elementary bodies (Borrel bodies). Presence of intracytoplasmic inclusions is a definative diagnositic indicator.

Treatment and Control 

Control mechanisms include decreasing the risk of transmission by trying to control mosquitoes and fighting of males in bird housing. If there is evidence of secondary bacterial infection broad-spectrum antibiotics may be of some benefit.

Prevention by live pigeon pox vaccination, which is used in all species affected, except the canary. Chickens are vaccinated well before production and turkeys are vaccinated at around 2- 3 months of age. The vaccine is applied by scarification and will provide a partial immunity. There is good cross-immunity among the different viral strains.

References

Bridger, J and Russell, P. (2007) Virology Study Guide, Royal Veterinary College.
Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial.
Jordan, F, Pattison, M, Alexander, D, Faragher, T (1999) Poultry Diseases (Fifth edition), W.B. Saunders.
Saif, Y.M. (2008) Disease of Poultry (Twelfth edition), Blackwell Publishing.