By constantly reminding the immune system what the parasite that causes leishmaniasis looks like, a persistent infection keeps the immune system on alert against new encounters, even while it carries the risk of causing disease later in life
Which is better? Long-term immunity with the cost of persistent infection OR complete riddance at the cost of becoming infected again
I think I agree that control persistent infection probably has the most robust evolutionary advantage here as if you are in an area where you are exposed to one of these pathogens it is probably best to harbor long term immunity.
It would be interesting to determine in a follow-up study if location/exposure to conspecific external pathogens increases the duration that the immune system reserves these pathogens.