Fowlpox is the worldwide disease of poultry caused by viruses of the family Poxviridae and the genus Avipoxvirus.

The viruses causing fowlpox are distinct from one another but antigenically similar, possible hosts including chickens, turkeys, quail, canaries, pigeons, and many other species of birds.

The first (dry form) is spread by biting insects (especially mosquitoes) and wound contamination, and causes lesions on the comb, wattles, and beak.

Fowlpox lesions, when in the infected birds mouth and throat can cause difficulty breathing, even death.

[citation needed] Fowlpox has demonstrated the capacity to contain integrated sequence from Reticuloendotheliosis virus (REV).

[10] Wet pox (diphtheritic) forms as ulcerous cheesy masses in the mouth, nose and sometimes throat areas, which can interfere with eating and breathing.

When a bird is given the vaccine they are exposed to a mild version of the active virus, so they should be completely healthy to prevent severe illness.