Scientists said Sunday they had unraveled the genetic codes of parasites responsible for the bulk of malaria cases outside Africa, and found they were scarily diversified and may be harder to kill.

In a study published in Nature Genetics, researchers said they had sequenced the genomes of four strains of Plasmodium vivax – a parasite that infects about 100 million people every year.

Other research had found that 10 to 20 percent of P. vivax cases occur in Africa south of the Sahara – a region mainly affected by the P. falciparum parasite which causes the most malaria deaths worldwide.

Outside of Africa, P. vivax accounts for half of all malaria cases, mainly in the Middle East, the Western Pacific and Central and South America.

P. vivax is more resilient than its deadlier, tropical cousin, and can stay in remission for longer and tolerate cooler climates.