Diseases such as HIV infection and hepatitis B, can be spread through body fluids, such as saliva, blood, vomit, and semen.
Protect yourself:

•    Use latex condoms correctly.
•    Do not inject drugs.
•    Limit alcohol consumption. People take more risks when intoxicated.
•    Do not share needles or any devices that can break the skin. That includes needles for tattoos, piercings, and acupuncture.
•    If you receive medical or dental care, make sure the equipment is disinfected or sanitized.

From cdc.gov