Global variations in malaria parasites revealed

A team of scientists has found that the malaria parasite Plasmodium vivax is evolving rapidly to adapt to conditions in different geographical locations.

The team determined complete genomes of nearly 200 P. vivax strains that recently infected people in eight countries. Comparative analysis showed the parasites clustered into four genetically distinct populations that provide insights into the movement of P. vivax over time and suggest how it is still adapting to regional variations in both the mosquitoes that transmit it and the humans it infects.

"P. vivax malaria has historically been overshadowed by the more lethal disease caused by P. falciparum parasites," said NIAID Director Anthony S. Fauci, adding "However, there are some 16 million cases of clinical malaria due to P. vivax infection worldwide each year, imposing a large public health burden on many countries. The wealth of genomic information provided by this new research shows the high degree of genetic variability in the P. vivax population and gives us a clearer picture of the challenges we face in developing drugs or vaccines against it."

The study sequenced P. vivax strains from volunteer blood samples taken recently in eight countries, including Papua New Guinea, India, Thailand, Mexico and several in South and Central America. When added to the countries of origin of the monkey-adapted parasite strains, eleven different countries were represented in the new analysis.

Investigators at the Broad Institute developed a technique to increase the amount of parasite DNA in red blood cells and separate it from the much more abundant human DNA also present.

The technique allowed them to sequence parasite DNA and, ultimately, to determine near-complete genetic sequences for 182 parasite isolates, said Dr. Carlton. "We confirmed and expanded our earlier findings regarding the extreme genetic diversity in P. vivax compared with P. falciparum" she said.

The four distinct parasite populations the researchers identified clustered into two groups: parasites from New World countries (Brazil, Peru, Colombia and others) differed greatly from those of the Old World countries (Thailand, Myanmar, India and others).

P. vivax isolated from Papua New Guinea were genetically distinct from elsewhere in Asia, while strains from Mexico formed a fourth genetic grouping. The strains from Mexico were the least genetically diverse, Dr. Carlton said, which may be because P. vivax cases have declined sharply in that country.

The genomes offer clues to the ways P. vivax has traveled the globe and adapted to mosquito species found in the new regions the parasite was carried to by European traders and colonialists.

The study is published in Nature Genetics.