LONDON (Reuters) - Progress is being made in the fight against the most common form of malaria in Africa, but a long-lasting type of the mosquito-borne parasitic disease has a tight grip on swathes of South Asia and parts of Latin America, scientists said Monday.
In a new global map of the plasmodium vivax malaria parasite, researchers from Britain's Oxford University found the disease -- which is often recurring and can be deadly -- is endemic in substantial parts of the world.
"This map helps us understand just how difficult it is going to be to eradicate malaria," said Peter Gething, who led Oxford's Malaria Atlas Project (MAP) study.
"Unfortunately, the tools for fighting this type of malaria range from ineffective to non-existent."
Vivax is not as deadly as the Plasmodium falciparum malaria parasite that is most common in Africa and causes most of the around 800,000 malaria deaths a year, but it is more common with some 2.85 billion people across the world at risk.
It also has a unique ability to relapse by hiding in the liver for months or years, making it harder to detect and cure.
Among hotspots for vivax malaria highlighted by MAP team are substantial parts of India, including major urban areas like Mumbai, where malaria was previously uncommon.
Papua New Guinea also has a high rate of infections and transmission, as do large parts of Indonesia and Myanmar, said the researchers, who presented the study at an American Society of Tropical Medicine and Hygiene (ASTMH) conference Monday.
In the Americas, the area of greatest concern is a large but sparsely populated part of the Northern Amazon, most of which is in Brazil, but the hotspot also includes parts of Peru, Colombia and Venezuela.
In Central America, almost all of Nicaragua and parts of Honduras and Guatemala are vivax hotspots.
In Africa, Gething said that while vivax does exist, infection rates appear to be "very, very low" in most places, although the study indicated moderate but stable levels of vivax transmission in parts of the Horn of Africa and in Madagascar.
Kevin Baird, who works with the Eijkman-Oxford clinical research unit in Indonesia, said it is becoming increasingly clear that vivax is more of a threat than previously thought.
A few years ago, he said, the consensus view was that vivax gave patients soaring fevers and severe chills, but was rarely fatal. Now that is starting to change.
"We are beginning to suspect...vivax is killing people at far higher rates than anyone...thought even remotely possible," Baird said in a statement.
"We still have very little data on this issue, but what data we do have worries me a great deal."
There are few effective treatments for vivax malaria.
Malaria drugs like artemisinin combination therapies (ACTs) used for falciparum infections can help treat acute bloodstream vivax infections, but only one drug -- primaquine -- can clear vivax parasites from the liver and provide a long-term cure.
The drug needs to be taken for 14 days to work properly -- limiting its success in areas where access to medicines and basic healthcare is poor.
The world's first successful malaria vaccine RTS,S, developed by British drugmaker GlaxoSmithKline, only targets falciparum malaria.
And prevention measures such as nets and indoor sprays, which have helped reduce malaria deaths in Africa, seem to have little impact on vivax, experts say, partly because mosquitoes that transmit vivax typically bite outdoors rather than indoors.
Peter Hotez, president of the ASTMH, said the map showed the importance of stepping up the fight against vivax malaria as well as against falciparum.
"It's time to....stop looking at this form of the disease as relatively mild and tolerable," he said in a comment about the findings.
Editing by Maria Golovnina