my approach on this is a reversible zombification-type virus.

**spreading by bite**

this is fairly easy, the virus is transmitted orally and requires body fluids to exchange, meaning just getting drool on you won't work, the saliva needs to penetrate into the skin and contaminate the bloodstream.

**the transformation**

the transformation is actually much simpler, the muscles swells through inflammation, the skin color transitions into a grayish black, and the infected would suffer from high adrenaline and dopamine secretions, tunnel vision, hallucinations, severe hunger and thirst during this phase.

**triggered by nightfall**

triggering by fullmoon is unlikely, but the virus can instead become dormant during the day, it synchronizes with the body's circadian rhythm, this way the infected would transform during the night.