Mapping ‘the other’ malaria
Four species of the plasmodium parasite are known to commonly cause malaria in humans: P. falciparum, P. malariae, P. ovale, and P. vivax. Of these, P. falciparum is the most deadly and thus most research has focused on this strain. P. vivax is somewhat neglected in research as it has been regarded to be a less serious strain, but is actually the most common strain of human malaria.
The Malaria Atlas Project (MAP) develops global maps of malaria risk to help target health resources to where they are needed most. The team of researchers has already completed maps of P. falciparum disease risk and in 2009 began mapping risk of P. vivax.
The team of researchers constructed the map using reported cases of P. vivax infection, climate data, and population distribution. They also factored in a global map of the prevalence of ‘Duffy negativity’ (the absence of a particular antigen in the blood, which results in partial protection against P. vivax infection).
The first results of that effort are published today in PLoS Neglected Tropical Diseases. They indicate that in 2009 2.85 billion people were exposed to some risk of P. vivax infection – higher than was commonly assumed. Some 91 percent of those at risk live in Central and South East Asia. Africa showed a lower overall risk of P. vivax incidence – although the parasite is common on the continent there is a high prevalence of Duffy negativity throughout Central and West Africa, which significantly reduces the population at risk.
Dr Carlos Guerra, one of the researchers from the University of Oxford said the results provided new evidence that “P. vivax malaria is not as benign as was thought, and yet remains the most widespread form of human malaria.”
The future looks positive, however – more than half of the people at risk of contracting P. vivax malaria live in areas where the transmission of the parasite is low or unstable. This means that control and even eradication of P. vivax in such areas may be possible.
“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 Dr Simon Hay of the University of Oxford, another of the researchers.
“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“.
Ailbhe Goodbody is undertaking a work experience placement at the Wellcome Trust.