Persistent infection keeps immune memory sharp, leading to long-term protection

For many infectious diseases, a single bout of the illness protects a person against contracting it again. Sometimes, the infecting microbe persists in the body long after symptoms resolve. Now, researchers studying the tropical parasite Leishmania have found a clue to explain the link between long-term immunity and long-term infection: The parasite is constantly multiplying and being killed by immune cells, keeping the immune system alert and prepared for any new encounters with the parasite.