What diseases can be transmitted while scuba diving?

Any disease that can be transmitted via saliva such as the common cold, the flu, herpes, hepatitis, and HIV/AIDS can technically be transmitted while diving especially if you are using rental equipment that has not been properly cleaned, if you are buddy breathing, or if you are performing CPR.  However, as long as clean equipment and safety precautions are used, the risk of contracting a disease is very low.