There are situations where some of the sporozoites do not immediately start to grow and divide after entering the hepatocyte, but remain in a dormant, hypnozoite stage for weeks or months. The duration of latency is thought to be variable from one hypnozoite to another and the factors that will eventually trigger growth are not known; this might explain how a single infection can be responsible for a series of waves of parasitaemia or "relapses". It has been assumed that different strains of "P. vivax" have their own characteristic relapse pattern and timing. However, such recurrent parasitaemia is probably being over-attributed to hypnozoite activation. One newly recognized, non-hypnozoite, possible contributing source to recurrent peripheral "P. vivax" parasitaemia is erythrocytic forms in bone marrow.