Fowl pox is a virus. If bitten by an infected mosquito, they will develop the disease. Once they have had it, they are immune. DE will have no affect unless the mosquitoes decide to take a dust bath in it. Remove standing water or use Mosquito Dunks, which prevent larvae from developing into adults. Thoroughly spray the coops, runs and all areas where mosquitoes like to congregate with malation or a similar product that will kill mosquitos. In addition, every night spray the coops with mosquito repellant.
Treating the lesions will not spread them unless you are careless and scratch or cut a bird than touch that scratch/cut with something containing the germs, such as a swab you used.
People cannot get fowl pox, nor can other mammals. Other birds, however, can. I personally believe that treating the lesions is important--it prevents secondary infection, and may help the bird progress more rapidly through the illness. The scabs remain infective for months, so be sure to thoroughly clean and disinfect the coop after they are well.
