Investigators from the University of Oxford’s Malaria Atlas Project (MAP) presented their investigation of disease burden of Plasmodium vivax – a more common and potentially deadly strain of malaria that is harder for the body to get rid of – that is taking hold in parts of Asia and Latin America. The team’s map, which pinpoints where the disease is most prevalent, was presented Monday at the 60th Annual Meeting of the American Society of Tropical Medicine and Hygiene in Philadelphia.
“It shows that in substantial parts of the world, vivax malaria is endemic and transmission is significant. Unfortunately, the tools for fighting this type of malaria range from ineffective to non-existent,” said Peter Gething, PhD, part of the MAP team. They hope the map will be useful in launching effective malaria countermeasures.
Malaria was once thought a disease of largely rural areas, but the map shows that in places like India – one of the map’s “hotspots” defined by the data analysts as infection rates exceeding seven percent – urban areas like Mumbai are covered. Other infection and transmission hotspots include Papau New Guinea, parts of Indonesia and Myanmar, Nicaragua and a large area of the Northern Amazon. Meanwhile, in areas like sub-Saharan Africa, where the Plasmodium Falciparum strain of malaria claims 90 percent of the world’s 1 million deaths per year – infection rates with the vivax strain are very low.
Gething said the body retains a large reservoir of vivax in the liver, even when a person doesn’t exhibit illness. “One person with vivax actually can represent multiple malaria infections over many years in a single community and each time the parasite moves from the liver to the blood, it contributes anew to disease burden and transmission,” he said. A lack of treatment options impedes efforts to control vivax, Gething said. Currently primaquine is the only drug that can provide a long-term cure by clearing vivax parasites from the liver. Many people living in vivax-endemic areas also have G6PD deficiency, a hereditary condition that can render the treatment toxic, making vivax treatment even trickier.
Researchers are troubled by the disease – its persistence has earned it the name “the last parasite standing.” Interventions used to combat malaria found in Africa, such as insecticide-treated bed nets and indoor spraying, have had little impact on vivax. They attribute this to differences among the mosquito-carriers – vivax-carrying mosquitoes typically bite outdoors, whereas the mosquitoes in Africa bite indoors. The malaria vaccine currently in Phase III trials also does not target vivax.