This anemia-causing disease comes from the bite of infected leeches.

It is otherwise not contagious. Anybody bitten by an infected leech must make a DC 16 Constitution saving throw or contract the disease. The disease incubates for 1d3 days before causing symptoms. At this point, the anemia causes two levels of exhaustion. The exhaustion cannot be eliminated while the disease is still active. After the symptoms have developed, the victim may attempt a DC 16 Constitution saving throw after every long rest. Two consecutive successful saving throws indicate the victim has thrown off the disease. The exhaustion can then be removed normally. Lesser restoration or similar magical healing eliminates the disease at any point.