Scientists explain how malaria "goes out of Africa"
August 23, 2018 Source: State Drug Administration
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Malaria caused by Plasmodium vivax has infected Asians and Americans. Image source: Xinhua/eyevine/Redux
Plasmodium vivax is not as well known as its deadly close relative, Plasmodium falciparum, which dominates sub-Saharan Africa. But this "other malaria", which is rare in Africa, causes about 75 million people each year in Asia and the Americas. Nowadays, new genetic evidence reveals how the parasites are on the stage of history, that is, they infect apes and humans in Africa, and then leave the continent to other areas with the early human migration.
Until recently, scientists have also believed that Plasmodium vivax originated from Asian macaques and spread there to humans, and then to Europe and the Americas. But in 2010, scientists began to find evidence of Plasmodium vivax in African chimpanzees, gorillas and bonobos. This indicates the African origin of this parasite.
However, there is little genetic evidence to support this theory; and most of the data from mites are derived from incomplete gene sequences found in feces from non-human primates.
Today, researchers have successfully sequenced the entire genome of parasites infected with six chimpanzees and one gorilla. Blood samples from chimpanzees are collected from protected areas in Cameroon and Gabon, as well as a wild chimpanzee that inhabits the Ivory Coast. The blood sample of the gorilla comes from a piece of "jungle meat" collected in Cameroon.
Scientists published a report in the Proceedings of the National Academy of Sciences this week that the new study of the parasite genome shows that the diversity of mites parasites far exceeds the parasites that infect humans.
David Conway, a malaria specialist at the London School of Hygiene and Tropical Medicine, who was not involved in the study, said the study added a weight to the idea that Plasmodium vivax has infected apes and humans in Africa and followed human migration. To the Eurasian continent and the Americas.
Conway pointed out that the malaria parasite is accompanied by the early spread of modern people in different parts of the world. "There may be only a few original strains that later evolved into Plasmodium vivax in today's human body." Richard Culleton, a malaria specialist at Nagasaki University in Japan, agrees. He said that the new data strongly suggests that soon after the modern human P. vivax escaped from Africa, the human population began to gain immunity. Today, infections caused by Plasmodium vivax are rare in Africa because most people there lack the proteins that parasites use to get into red blood cells.
Paul Sharp, an infectious disease geneticist at the University of Edinburgh in the United Kingdom, and Beatrice Hahn, an infectious disease specialist at the Perelman School of Medicine at the University of Pennsylvania, led the study. Sharp further supports the view that the malaria parasites found in African apes and humans appear to be closely linked to parasites elsewhere.
"We are looking for evidence that the parasitic parasites are somewhat different," Sharp said. "Do they differentiate to the extent that these malaria parasites are independent species? But we haven't found any indication that they are independent."
Sharp pointed out that this and occasional reports said that tourists who traveled in Africa came home and were infected with Plasmodium vivax, which was probably caused by a bite of a mosquito that had been bitten by an infected person. This means that even if the Plasmodium vivax is eradicated in Asia and the Americas, it can hit a free ride from Africa at any time and trigger new outbreaks in other parts of the world.
"This may mean that we can never eradicate Plasmodium vivax unless we try to eliminate them in chimpanzee and gorilla populations," Culleton said.
Malaria is caused by a parasite called Plasmodium, which is transmitted by the bite of infected mosquitoes. According to the World Health Organization, there are about 200 million cases of malaria in the world each year, and about 600,000 patients die, most of which and the deceased appear in Africa. (Zhao Xixi)
Related paper information: https://doi.org/10.1073/pnas.1810053115
Chinese Journal of Science and Technology (2018-08-23 2nd Edition International)
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