(Reuters) - Nearly 3 billion people, or two-fifths of the world's population, were at risk of contracting malaria in 2009 and closer study of the mosquito's life cycle is needed to combat the disease, researchers said in two reports.

In the first study, scientists mapped out the geographical spread of the Plasmodium vivax -- the most common parasite that causes malaria -- using reported cases of malaria and details on temperature and aridity.