Out-of-phase circadian biorhythms in gametocytes of Plasmodium falciparum

The individual circadian periodicity in eight hosts of Plasmodium falciparum gametocytes is studied in Senegal. The average time series does not present any periodicity. As for filariasis (Pichon and Treuil, 2004), it could be considered that this lack of global periodicity is in fact due to the coexistence, in each host, of two completely periodic, out of phase rhythms. Here we propose a simple mathematical method to test this assumption, which is confirmed. There is a complete morning rhythm with peak at 10 a.m. and another evening rhythm with peak at 10 p.m., both rhythms being at equal proportions on average. A similar temporal pattern is suggested in Gambia. The same morning rhythm is observed in Tanzania, but the evening rhythm happens two hours earlier, explaining the occurrence of a global subperiodic fluctuation (Magesa et al., 2000). The paradoxical situation of gametocytes following a circadian morning rhythm in spite of the nocturnal activity of vectors is discussed.