Relapsing vivax malaria

TO THE EDITOR: The Australian Defence Force (ADF) has sustained many cases of malaria following service in East Timor. To reliably prevent relapse of malaria caused by the Chesson strain of Plasmodium vivax present in this region, larger doses of primaquine are required2 (up to 6 mg/kg total dose,3 compared with > 3.5 mg/kg to prevent relapse of sub-Saharan vivax malaria4). The ADF uses 1500 mg chloroquine (total base) followed by 315 mg primaquine (total base) for the treatment of vivax malaria, which, in Australia, is commonly treated either without primaquine or with inadequate dosages of either chloroquine or primaquine.5 A fit, 65 kg male soldier who deployed to East Timor from October 1999 to May 2000 experienced one episode of vivax malaria during his deployment and a further four episodes on return to Australia (Box). Having had malaria in East Timor, he complied closely with postexposure prophylaxis with primaquine and tolerated his dose (7.5 mg three times daily with meals) well for the required 14 days (315 mg total). He was seronegative for HIV, hepatitis C, and dengue IgG and IgM, and was not glucose-6-phosphate dehydrogenase deficient. The Table shows that our patient had a parasite that was apparently responsive to chloroquine, although it did not respond as readily in the last episode. In his first episodes of malaria on return from East Timor, he received the recommended dose of primaquine, but developed recurrences in the absence of further exposure to malaria. These relapses presumably indicate an inadequate response to the primaquine. The total dose of primaquine used for postexposure prophylaxis and treatment of the first episodes in Australia was about 4.8 mg/kg. He has subsequently received a treatment of 6 mg/ kg total primaquine (see Table, Episode 5). This follows extended suppression with chloroquine before and doxycycline during a three-month deployment to Malaysia. There has been no further relapse six months after treatment. Chesson-strain vivax malaria is known to be difficult to treat and in which to prevent further relapse. Adequate primaquine to treat vivax malaria from other areas is not adequate for that contracted to the immediate north of Australia. Relapsing vivax malaria from East Timor may require a dose of 6 mg/kg of primaquine to prevent further relapse.