Currently when a marine is parasited, he is parasited permanently until he gets a medpack from the commander or dies. Structures also are permanently parasited until they're recycled or destroyed. As you can't medpack them.
So the idea is to give parasites a 5-15 second lifespan, on players and structures. Also when a parasite is attached to a player or structure, not only does it show the player, but it shows the line of sight of nearby marines/structures, acting like a mobile mini scan so skulks can potentially spot large groups before they attack. Allowing them to have much greater scouting roles.
Also when a marine has a parasite attached, their vision should be similar to the lerk poison bite effect and they should start to cough periodically until the parasite is gone to give indication to nearby teammates about their parasite. Medpacks can get rid of them immediately as usual.