 The latent or dormant liver form of the parasite (hypnozoite), apparently responsible for the relapses characteristic of P. vivax and P. ovale infections, was first observed in the 1980s. The term hypnozoite was coined by Miles B. Markus while a student. In 1976, he speculated: "If sporozoites of Isospora can behave in this fashion, then those of related Sporozoa, like malaria parasites, may have the ability to survive in the tissues in a similar way." In 1982, Krotoski et al reported identification of P. vivax hypnozoites in liver cells of infected chimpanzees.
