Where is better to go in Vietnam?

have a friend who was in Border Thailand and Cambodia, he stayed for a night there, and he was bitten by mosquito, i think he wasn't bitten just one time maybe more. After that, he was traveling normaly with out symptoms, but nowadays he stars to feel not as well, he feels weak (debil in spanish) with headache, this kind of symptoms is for the last three days, it isn't getting worse. He was bitten 7 days ago. I'm worry if this is a case of malaria, cuz i know is dangerous. Do you think this is a case of malaria?. What should he does?. Actually he is in South of Vietnam, if it is better to go to the hospital, where is better in Vietnam?..... PD: he didn't take pills before go to travel, could he does it now?, this pill will be ok if its malaria? he isn't american.... Thank you a lot for your suggestion, oppinions
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he was in saigon until today, he went to the hospital but on weekend there is high costs... now he is traveling more to the north i don't know the name yet.... but there are good hsopital next city after saigon?