Infectious disease
In addition to the physical dangers of the world, characters are often accosted by the sniffles and other common ailments. When it comes to sickness and plague, running out of tissues is the least of your worries.
Infectious disease is just one type of illness. Creatures exposed to an invading pathogen must make a Vitality check to avoid infection. The more virulent the pathogen, the higher the DL. Many infectious diseases are contagious. That is, a healthy creature might contract the illness just by hanging around someone infected with it: breathing the same air, eating the same food, or touching the same objects. Some pathogens require more specific transmission methods, like an exchange of blood or saliva.
Creatures who overpower a fightable disease, or outlast a limited disease may gain immunity once the initial infection is eradicated. This immunity could last for months, years, or indefinitely, depending on the disease in question.