MALARIA: P vivax malaria is greater threat to health than thought

A new study of the prevalence of the malaria parasite Plasmodium vivax shows that it is more widespread and potentially represents a greater burden on human health in some parts of the world than P falciparum, the species usually associated with the greatest mortality and morbidity.
A new evidence based global distribution map of P vivax estimates that 2.85 billion people lived at risk of infection with this parasite in 2009, predominantly in east and central Asia (PLoS Neglected Tropical Diseases, doi:10.1371/journal.pntd.0000774).
The study, conducted as part of the Malaria Atlas Project, a multinational research collaboration funded mainly by the Wellcome Trust, challenges the idea that P vivax transmission doesn’t occur in large swathes of Africa. It used novel methods, including developing new global maps of Duffy negativity, which confers partial protection against P vivax. People who are Duffy negative lack an antigen on the surface of red blood cells that codes for a protein receptor for P vivax.
"This study represents the first step in our efforts to provide the malaria control and research community with an evidence based cartography of P vivax malaria," said one of the coauthors, Simon Hay, reader in infectious disease epidemiology at the University of Oxford. "We can now focus on trying to model the endemicity of the disease to provide more detailed global burden estimates, although this is complicated by the unusual biology of P vivax."
Another coauthor, Carlos Guerra, who is responsible for the design, construction, and maintenance of the Malaria Atlas Project database at Oxford University’s Spatial Ecology and Epidemiology Group, said, "New evidence shows that P vivax malaria is not as benign as was thought and yet, as our study shows, remains the most widespread form of human malaria. Understanding where transmission of this parasite occurs at the global scale is fundamental in planning strategies for the control of this debilitating and sometimes lethal disease."
Dr Guerra explained: "Recent studies from areas where both P vivax and P falciparum are endemic have used advanced diagnostic techniques to confirm that some of the severe complications of malarial infection traditionally attributed to P falciparum are also related to P vivax infection.
"The classical notion that ‘benign malaria’ is a synonym of P vivax infection is being challenged by these new findings."
Globally P falciparum "is undeniably the main killer" of the two, Dr Guerra said. Even though worldwide more people are exposed to risk of P vivax infection than P falciparum, most deaths from malaria are reported in Africa, "where P vivax infection is rather uncommon due to the high prevalence of Duffy negativity in large parts of the continent," he added.
Outside Africa, however, where P vivax transmission is common and causes about half of the reported cases of malaria, observed fatality rates associated with the two species are similar, although more studies are needed to determine which parasite actually causes more morbidity and mortality in these settings, Dr Guerra said.
Although more attention has traditionally been paid to combating P falciparum, the new findings show that P vivax shouldn’t be overlooked in the global campaign against malaria, he concluded.
Further information about the Malaria Atlas Project can be found at www.map.ox.ac.uk.
http://www.bmj.com/cgi/content/full/341/aug03_1/c4188