Answer: Well since food is processed through the digestive system, then that where the infectious disease would be affecting. So, digestive system is your answer.
Explanation: The digestive system in a dog includes all of the organs that are involved in taking in and processing food. It begins with the mouth and includes the esophagus, stomach, liver, pancreas, intestines, rectum, and anus. A dog's digestive system is a long tunnel that runs from their mouth to the anus. Food goes in at the mouth and travels through this tube and at various stages is broken down and either absorbed into the body or excreted as waste at the anus.
Hope this helps ^-^.