Fowlpox | Vetlexicon (2024)

• Fowlpox primarily refers to infection of chickens by Fowlpox virus. Traditionally, the term Fowlpox included disease in birds caused by pox viruses of the Avipoxvirus genus, these are referred to as Avianpox viruses. Avianpox viruses are host specific, slow spreading viral diseases of commercial chickens and turkeys, pet, and wild birds.
• Cause: Avianpox is caused by numerous species of viruses in the Avipoxvirus genus under the family Poxviridae. Species include fowlpox virus, turkeypox virus, canarypox virus, pigeonpox virus, quailpox virus and sparrowpox virus, which cause disease in chickens, turkeys, canaries, pigeons, quail, and sparrows, respectively.
• Signs: proliferative nodules are present in nonfeathered areas such as the comb, wattle, eyelid, snood, and corners of the beak. Diphtheric lesions may be present in mucosal tissues including the mouth, tongue, esophagus, and trachea.
• Diagnosis: based on the presence of gross lesions and confirmed through histopathology, electron microscopy and molecular detection.
• Treatment: isolation, vaccination, supportive.
• Prognosis: good to poor depending on severity and form.

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• Emaciated birds unable to gain weight.
• Depressed, unthrifty birds.
• Decreased fertility and egg production.
• Blindness in turkeys.
• The disease occurs in two forms the cutaneous form and the diphtheric form.
• The cutaneous form, also known as dry pox, presents with scabs or proliferative nodules are in nonfeathered areas of the body including the comb, wattle, eyelid, snood, and corners of the beak.
• The diphtheric form is also known as wet pox. In wet pox, cutaneous lesions are present as well as diphtheritic mucosal lesions. These canker, or fibrinonecrotic plaques are present in mucosal tissue of the upper respiratory tract. Lesions may be seen in the mouth and on the tongue, esophagus, and upper part of the trachea:
  • Lesions can interfere with eating, drinking, and breathing.
  • Mild or severe respiratory signs similar to those caused by infectious laryngotracheitis virus may be observed.
• A generalized form of the disease that causes great mortality has been observed in canaries.

• Respiratory distress.
• Mortality.

• Pox is a common disease of poultry seen worldwide. Incidence varies based on bird density and vaccine frequency.

• Not of public health significance.
• Avianpox viruses do not cause productive infection in mammalian species. However, a pox virus isolated from a rhinoceros was characterized as fowlpox virus.

• Fowlpox and turkeypox are economically important disease of commercial poultry as they result in a drop in egg production, decreased fertility, slow growth rates, and unexpected mortality.
• Mortality in flocks exhibiting the mild cutaneous form of the disease is usually low. However, diphtheritic forms of the disease and disease complicated by other infections or poor environmental conditions can lead to increased mortality. Under those conditions the economic losses can be significant.

• Avianpox viruses are resistant, enveloped viruses with a linear double stranded DNA genome that replicate in epithelial cells.
• Fowlpox is caused by fowlpox virus, of the family Poxviridae under the genus Avipoxvirus. While initially the term fowlpox included all pox virus infections in birds, it now refers primarily to disease in chickens by the by fowlpox virus species.
• Avianpox viruses are host specific. Other viral species belonging to the Avipoxvirus genus include canarypox virus, pigeonpox virus, quailpox virus, sparrowpox virus and turkeypox virus.
• Avianpox does not cause infection in mammalian species, however, twenty-three of the approximately 9,000 bird species have been reported to have acquired a natural pox virus infection.

Transmission

• Avianpox viruses are transmitted:
  • Directly through contact.
  • Through aerosol.
  • By vectors.
  • Via fomites.
• Fowlpox virus can persist in chicken flocks for extended periods of time, especially in large multiple‐age complexes.
• The aerosol generated by feathers and dried scabs containing fowlpox virus particles can result in both cutaneous and respiratory infection.
• Mechanical transmission from the contaminated poultry house environment and equipment to the injured or lacerated skin is common. For example, mechanical transmission of turkeypox virus from infected toms to turkey hens through artificial insemination has been reported.
• Insects including mosquitoes, species of Diptera and the Dermanyssus gallinae mite can serve as vectors of the virus Dermanyssus gallinae infestation. Mosquitoes can infect a number of different birds after a single feeding on a bird infected with avianpox viral species.

Specific

• Unvaccinated birds are susceptible.
• Birds in high density areas with birds of multiple ages.

• Cells of the mucosa of the upper respiratory tract and mouth are highly susceptible to fowlpox virus in the absence of apparent trauma or injury.
• The virus may reach the laryngeal region via the lacrimal duct and cause infection of the upper respiratory tract.

• Natural infection with fowlpox and turkeypox virus in chickens and turkeys incubates for 4-10 days.
• In chickens, the timecourse of the mild cutaneous form of the disease lasts about 3-4 weeks.
• In turkeys, the timecourse of the mild cutaneous form of the disease lasts about 2-3 weeks, but severe outbreaks can last up to 8 weeks.

• Fowlpox has worldwide in distribution with a variable incidence.
• The incidence of disease is higher in areas with high‐density with multiple‐age birds that are unvaccinated.
• Currently available commercial vaccines provide limited protection.
• Fowlpox virus has been isolated in all regions of the United States from previously vaccinated chicken flocks experiencing high mortality. Strains of fowlpox virus isolated during outbreaks have limited immunologic cross protection with vaccine strains of fowlpox virus:
  • Fowlpox virus has been found to be the culprit of mild cutaneous disease in a small portion of layer and breeder flocks. In these flocks, a small percentage of hens will present with cutaneous lesions around their head, comb, and wattles.
  • Occasionally, more severe diphtheric disease is found.
  • The disease may turn into a flock problem if there is a vaccine or vaccination failure or a preceding immunosuppressive infection with Marek’s disease virus and/or chicken infectious anemia virus.
• In Europe, the disease is reported to be increasing in prevalence although its significance is moderate.
• Fowlpox disease occurs sporadically in chickens and turkeys in countries such as Australia, Zealand, Papua New Guinea, and Fiji and is controlled by vaccination.
• Flocks located in tropical areas are frequently under challenge and even two vaccinations appear to be insufficient to prevent a high incidence of infection.
• Countries such as China, where the flocks are infected with fowlpox virus containing REV provirus appear to have a high prevalence of fowlpox in in long‐lived birds.

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Refereed papers

• Recent references from PubMed and VetMedResource.

Other sources of information

• Lennox A (2021) Dermatological Diseases. In: Backyard Poultry Medicine and Surgery. A Guide for Veterinary Practitioners. 2nd edn. Wiley-Blackwell, USA. pp 259-273.
• Tripathy D N & Reed W M (2020) Pox. In: Diseases of Poultry. 14th edn. Eds: Swayne D E, Boulianne M, Logue C M et al. Wiley-Blackwell USA. pp 364-378.

_{Reproduced with permission from Cheryl B Greenacre & Teresa Y Morish*ta: Backyard Poultry Medicine and Surgery. A Guide for Veterinary Practitioners. © 2021, and David E Swayne: Diseases of Poultry. © 2020, published by John Wiley & Sons.}