Plasmodium falciparum attracts over 95 percent of funding for malaria research and control. Historically, this makes sense; of the four different species of Plasmodium parasites, P. falciparum causes the most severe form of malaria, a disease that is the second leading cause of death from infectious disease on the African continent, and the fifth leading cause of death from infectious disease worldwide.
Plasmodium vivax, another of the four species, also causes malaria, but a less severe strain. Research presented at the American Society of Tropical Medicine and Hygiene’s (ASTMH) annual meeting brings this often forgotten parasite back to the spotlight.
On Monday, Dec. 5, University of Oxford researchers released a map showing the global burden of P. vivax is actually more significant than previously thought, with strong holds in South Asia and parts of Latin America.
The Oxford researchers work on a project called MAP, or the Malaria Atlas Project. They are lead by Peter Gething, PhD. Last year, in an effort to gather information to fight malaria, a map was created to determine where P. vivax is prevalent. The result was alarming.
One of the characteristics of P. vivax parasite that makes it special is that it can remain dormant in the host’s liver for months, without causing a visible infection. Further, there are not simple diagnostic tools to determine the presence of a P. vivax parasite in the liver. Once the parasite is in the bloodstream, it is more easily detected and treatable.
Additionally, P. vivax can only be eliminated from the liver with the drug, primaquine. In what Preeti Singh appropriately calls a “cruel twist of evolution” in her press release for ASTMH, people who live in P. vivax endemic areas may have a genetic condition, G6PD deficiency, which makes primaquine toxic. The artemisinin drug therapies that are used to treat P. falciparum are only effective against acute bloodstream infections (meaning the parasite must have left the liver and entered the bloodstream) of P. vivax.
Another study presented at the ASTMH meeting suggests that P. vivax might actually be killing people at a higher rate than previous believed. However, notes Ric Price, malaria researcher at Australia’s Menzies School of Public Health, it is difficult to determine how many people are dying of P. vivax and with P. vivax, as an indirect cause of death.
Currently, researchers are investigating alternatives to primaquine and vaccines against P. vivax malaria.
For more information on P. vivax and MAP:
http://www.economist.com/node/18741412
http://www.cidrap.umn.edu/cidrap/content/other/news/dec0611malaria.html
http://www.map.ox.ac.uk/
