Animals have been kept in mixed flocks for centuries. Being aware of inherent risks or problems in mixed-animal operations is the best way to avoid problems before they occur. It is also the best way to fix problems if they happen.
Source: Backyard Poultry, September 16, 2019. Link. Parasites and bacteria are easily transferred between barnyard species. Contaminated drinking water is the most common method of transmission. Poultry feces contain high levels of Salmonella enterica and Campylobacter bacteria.