People travelling to Africa from South East Asia and South America should be screened and treated for drug-resistant malaria, experts recommend.
Mosquito bites transmit malaria
Genetic studies show hard-to-treat forms of malaria have spread from these countries to Africa.
The resultant outbreaks are not responding to affordable antimalarials and require more expensive alternatives.
The London School of Hygiene & Tropical Medicine study appears in Science.
Dr Cally Roper and colleagues analysed the genetics of the parasite responsible for Plasmodium falciparum malaria - the most widespread and dangerous form of malaria.
They found mutations that made the parasite resistant to the two affordable antimalaria drugs - chloroquine and sulfadoxine pyrimethamine (SP) - had originated in South East Asia and were then imported and spread across Africa.
Although the exact number of cases imported into Africa is not known, the researchers believe it is likely to be substantial and has spread widely and quickly across the country.
Careful thought should be given to preventing further import of resistant parasites by screening and treating travellers from infected countries like South East Asia, they said.
Dr Roper said it could be made a requirement for travellers to show a valid certificate proving they are not carrying drug-resistant malaria before they enter Africa.
"You could have a malaria-free certificate, very much like you have a yellow fever vaccine certificate."
Checks for travellers
She said high levels of resistance meant more malaria deaths and the need for use of more costly antimalarial drugs that were efficacious.
"There are some very good new drugs but they are much more expensive," she said.
Dr Allan Schapira from Roll Back Malaria said the evidence up until now suggested resistance to SP in Africa was most likely to have developed as a result of the patterns of drugs use.
"SP resistance has been present in Africa since the 1980s at least and the rapid increase has only been seen since SP started to be used on a larger scale.
"Bar far the most important measure to ensure against resistance is rational use of drugs."
He said the World Health Organization was limiting the use of SP to the most vulnerable such as pregnant women and infants.
"But the researchers do have an interesting point. The highest levels of SP resistance which we are seeing now in Africa do have an Asian origin."
But he did not think screening would be any easy way to prevent further resistance.
"It would be an onerous task.
"You would need testing posts in all African airports...and you have to make it voluntary. Then if they were positive you would need treatments available in the airports that would completely cure any infection and they are quite expensive," he said.