The number of diseases transmitted from chickens to humans is very low; unless you come into very close contact with the chicken's feces, which are densely packed with germs, or with oral/nasal secretions, the likelihood of contracting a disease from a live chicken is negligible. However, it should be noted that animals roaming freely are unprotected against many diseases, especially bird flu, and that products sold unpackaged do not undergo necessary food safety inspections, meaning they could carry these diseases.
For this reason, we suggest that you purchase branded, packaged products with complete label information in order to consume chicken meat with peace of mind.