The fowl pox virus infects birds, including chickens. It spreads through infected birds, contaminated equipment and biting insects, such as mosquitoes. Called fowl pox for good reason, it causes white, then yellow, and then finally brown spots on the bird's comb, wattles, legs, mouth and anywhere there are no feathers. Fowl pox will cause the bird's egg-laying to stop or be severely reduced, and it will hurt growth.
Fowl pox has two types: dry pox and wet pox. The dry pox invades the comb, face and legs; the wet type will attack the mouth, windpipe and throat. Birds die from suffocation if they have the wet type of fowl pox. Dry pox seldom causes death.
Prevalence and Transmission
Fowl pox is found all over the world and has existed in chickens since ancient times. A bird becomes infected through a scratch. Birds that survive fowl pox are carriers and can transmit the disease to new birds through scratches or biting flies, lice, mites and mosquitoes. Birds once infected with fowl pox that recovered can show symptoms when under stress. Wild birds can transmit the disease to chickens through insects.
Although there is no effective treatment for fowl pox, you can vaccinate those birds who do not show symptoms with a fowl pox vaccination for adult birds. This should slow or stop the disease from spreading. To treat and prevent bacterial infections that arise with the virus, for three days you should add 1 tablespoon of powdered Terramycin per gallon to your birds' water. Putting a mix of sulfur power and petroleum jelly (2 teaspoons sulfur per 1 cup petroleum jelly) on the birds' lesions and scabs will soothe the affected areas and keep the parasites away.
Preventing fowl pox is a matter of good poultry management. Vaccinate all your chicks with fowl pox vaccination intended for chicks. Keep all equipment clean. Reducing or eliminating external parasites and putting up mosquito netting will keep mosquitoes out of your coop.
cited from: http://animals.mom.me/chicken-comb-spot-disease-2116.html