The dynamics of Plasmodium vivax
infection is characterized by reactivation of hypnozoites at varying time intervals. The relative contribution of new P. vivax
infection and reactivation of dormant liver stage hypnozoites to initiation of blood stage
infection is unclear. In this study, we investigate the contribution of new inoculations of P. vivax sporozoites to primary
infection versus reactivation of hypnozoites by modeling the dynamics of P. vivax
infection in Thailand in patients receiving treatment for either blood stage
infection alone (
chloroquine), or the blood and liver stages of
infection (
chloroquine +
primaquine). In addition, we also analysed rates of
infection in a study in Papua New Guinea (PNG) where patients were treated with either
artesunate, or
artesunate +
primaquine. Our results show that up to 96% of the P. vivax
infection is due to hypnozoite reactivation in individuals living in endemic areas in Thailand. Similar analysis revealed the around 70% of
infections in the PNG cohort were due to hypnozoite reactivation. We show how the age of the cohort,
primaquine drug failure, and seasonality may affect estimates of the ratio of primary P. vivax
infection to hypnozoite reactivation. Modeling of P. vivax primary
infection and hypnozoite reactivation provides important insights into
infection dynamics, and suggests that 90-96% of blood stage
infections arise from hypnozoite reactivation. Major differences in
infection kinetics between Thailand and PNG suggest the likelihood of drug failure in PNG.