Why does someone in malaria endemic area have to report a fever for a year after leaving?

I don't know: Depending on the type of malaria, the disease may present itself months to years after leaving the endemic area.

Might be malaria!: The more severe form of malaria typically causes symptoms within 2 to 4 weeks (longer if you've been taking anti-malaria rx), but there are other species (4 all together) which can lie dormant for months, even a year. Once home, missed diagnosis is a common reason people get delayed treatment, or even die. Doctors forget to ask about travel, so if you have a fever, please remind them!