The periodicity of the life cycle of malaria parasites during host infection suggests that these organisms are regulated by circadian rhythms. Aidan O'Donnell at the University of Edinburgh, UK, and his team found that parasites whose rhythms were not synchronized with those of their hosts were less able to replicate in, and transmit out of, the hosts.

The researchers 'set' the circadian rhythms of mice and the rodent parasite Plasmodium chabaudi by keeping them in one of two rooms with opposing 12-hour light–dark cycles. They then infected the mice with parasites that were either in or out of sync with the animals' own cycles.

When mouse and malaria rhythms were the same, parasite densities during the replication and transmission stages of infection were double those seen for parasites that were out of sync with the mice.

Proc. R. Soc. B doi:10.1098/rspb.2010.2457 (2011)