Fowl Pox:

• It is slow spreading viral disease characterized by skin lesions.
• It was once widely prevalent worldwide, but with arrival of vaccination, the incidence has been greatly reduced.

Etiology:

• Avipox virus of Poxviridae family
• Enveloped, ds DNA virus
• It is largest virus known.
• It affects birds of both sexes, and all ages and breeds.

Epidemiology:

• Incubation period for fowl pox in chicken and turkey is typically 4-10 days.
• Cutaneous infection has low or moderate mortalities.
• Mortalities rate is higher in diphtheritic form.
• Disease is distributed globally.
• Virus mainly infects chicken and turkeys and has been reported to infect ducks, geese, pheasants, quail.

Transmission:

• Virus is usually transmitted by direct contact through abrasion of skin.
• Skin lesions (scabs) are source of aerosol exposure.
• Mosquitoes and other biting insect may serve as mechanical vectors.
• Virus can survive in dried scabs for months or even years.

Pathogenesis:

• Virus enters skin cell through abrasion/wound
• Virus then spread from cell to cell locally
• Some virus enters blood stream and causes viremia.
• Virus then reaches to internal organs like liver and spleen and secondary viremia occurs.
• Virus again enter into skin cells and a generalized disease can occur, but it is rare.

Clinical Findings:

• Disease appear in 2 forms:
  • Cutaneous or skin form (dry pox)
  • Diptheritic form (wet pox)

1. Dry pox (Cutaneous or skin form):

• Pock lesion are seen on unfeathered skin; head, neck, legs and feet.
• First lesion appears as papule which progresses to vesicle to pustule and finally to crust or scab stage.
• After about 2 weeks, scab falls and healed area is left.

2. Diptheritic form (wet pox):

• Small whitish nodules are observed in upper respiratory tract and digestive tract.
• These nodules merge together to form raised yellow cheesy plaques.
• Most lesion are found in mouth, larynx, trachea and esophagus.
• Difficulty in breathing and/or loss of appetite.
• Lesion in nose leads to nasal discharge and lesion in conjunctiva leads to ocular discharge. In rare cases, blindness occurs.
• Weakness, poor weight gain
• Egg production stops temporarily

Diagnosis:

• Based on history and slow spread of disease.
• Based on clinical findings and lesion.
• Histopathological examination of tissue stained with H&E reveals eosinophilic cytoplasmic inclusion bodies (Bollinger bodies). It is most commonly used method in diagnostic laboratory.
• FAT, Immunohistochemical method
• Elementary bodies (Borrell bodies) in inclusion bodies (Bollinger bodies) can be detected by light microscopy in smear from lesions.
• Isolation of virus in chorioallantoic membrane of developing chicken embryo.
• PCR

Treatment:

• No specific treatment available for disease.
• Symptomatic treatment is done. Wound/lesion are scratched, cleaned with antiseptics.
• Topical ointment for healing skin lesion is applied.

Control Measures:

• Vaccination of poultry flocks with live embryo or cell-culture propagated virus vaccine. It is done at first few weeks after hatching. Booster dose at 12-16 weeks is sufficient.
• Strict biosecurity measures such as sanitation and disinfection should be followed.
• Poultry houses, litter, equipments are sterilized and disinfected.
• Vector such as mosquitoes or biting insects should be controlled.
• Water ditches around poultry houses should be buried to control breeding of mosquitoes.