Fowl pox is usually spread by mosquitoes, but can be spread from bird to bird by disturbing scabs, or by flies and other insects form bird to bird. A chicken could get pox from a turkey. I'm not an expert, but I think only turkeys get LPD reovirus. Here is an excerpt from Beauty of Birds about fowl pox:
Mosquitoes: Transmission occurs when mosquitos feed on birds that with lesion present. Mosquitoes can harbor and transmit the virus for a month or longer after feeding on infected birds. Other insects, such as stable flies have also shown the capability of transmitting the pox virus.
Infected Birds: The Avian Pox virus can be spread by direct contact with infected birds.
Contaminated surfaces or water / food: One of the primary sources of infections are contaminated bird feeding stations; or contaminated food / water. Bird baths / feeding stations need to be regularly disinfected with a 5% chlorine bleach solution.
Mosquitoes are most likely the cause of transmission within local areas, while wild birds are responsible for outbreaks over greater distances.