Modeling the relapse distribution of Plasmodium vivax in different geographies

One of the defining challenges of controlling and eliminating Plasmodium vivax is the tendency to relapse. Months or even years after clearing the initial infection, new blood-stage infections can emerge from hypnozoites in the liver if they are not cleared with radical cure. The relapse phenomenon is further complicated by the fact that P. vivax infections exhibit different patterns of relapse times in different areas. The tropical Chesson variant has a short distribution, with most relapses occurring in the first 3-4 months after initial infection. Other variants have an initial infection, early relapses, and then later relapses, 8-12 months, after the initial infection. Still others have relapses over a year after the initial infection, and some do not exhibit an initial infection at all. We construct a unified mathematical model for the distribution of three important patterns, demonstrate how each distribution is well-suited to the local transmission dynamics in which it is observed, and discuss the implications for control and elimination.