Although uncommon, it is possible to develop a relapsing type of malaria months to even years after traveling to a malaria infected country, even if you were taking the appropriate malaria medications to prevent the illness. Any returning traveler who develops a fever that lasts more than a few days requires prompt medical attention to screen for a malaria infection.
While malaria medications such as chloroquine, doxycycline, or mefloquine (Lariam) can prevent symptoms of acute malaria from developing by suppressing the infection in the bloodstream, they do not prevent relapses of infection caused by certain strains of the parasite that have a persistent liver phase. Fortunately, the most common type of malaria is the P.falciparum strain that has no relapsing phase, so malaria medications will prevent any symptoms of this infection.
However, it is necessary to continue such medications for four weeks after a possible exposure to ensure that the infection has run its course before the medication can be safely stopped. Other strains of malaria such as P. vivax, ovale, or malariae can infect the liver and persist in a dormant state for months, or even up to several years, after exposure. Because of this risk of relapse, travelers to malarious areas are not allowed to donate blood for up to three years after returning.
In the unfortunate event that you do develop a relapsing case of malaria, it can be easily treated by suppressing the acute symptoms with chloroquine and then erraticating the liver infection with a medication called primaquine. this medication is more toxic and has more adverse effects than chloroquine, especially in individuals with an inherited deficiency in the blood enzyme G6PD that can be easily screened for with a simple blood test prior to treatment.
The best way to prevent relapsing malaria is to prevent getting infected in the first place. this is why it is very important to avoid mosquito bites by using insect repellents and mosquito netting in addition to taking malaria medications. If you do develop a fever and flu-like symptoms after returning from a malarious region, you need to be aware of the possibility of a malaria infection and should see a physician as soon as possible for further evaluation.