Malaria is a blood infection caused by the bite of the Anopheles mosquito. Of the five types of mosquito-borne Plasmodium parasites that cause malarial infection in humans, Plasmodium falciparum is the most dangerous. It is responsible for hundreds of millions of infections and more than one million deaths a year, most of them in Africa.
An international consortium of 22 scientists collaborated on the investigation into the source of Plasmodium falciparum and published their research results in the September 23 edition of the journal "Nature."
Wild western lowland gorilla in the Central African Republic (Photo by Precious Primates)
The research involved conducting DNA sequences of fecal samples collected from wild-living apes. The samples are found in specimen banks collected to investigate the evolution of HIV, including 1,827 from chimpanzees, 803 from gorillas and 107 from bonobos.
Researchers examined nearly 3,000 specimens from numerous field research sites throughout Central Africa.
They found high levels of malarial infection among western gorillas, Gorilla gorilla, and chimpanzees, populations of which act as natural reservoirs for Plasmodium species, but no infections among eastern gorillas, Gorilla beringei, or bonobos.
The data show that western lowland gorillas and chimpanzees represent substantial Plasmodium reservoirs, with P. falciparum being of western gorilla origin.
"An important finding was that gorillas in the Goualougo Triangle in the Republic of Congo, showed high prevalence of Plasmodium infection," said Chicago's Lincoln Park Zoo researcher Dave Morgan, PhD, an author on the study who leads the Goualougo Triangle Ape Project.
"This population of gorillas is very important in terms of understanding the ecology of malaria and its relation with gorillas," Morgan said.
The P. falciparum samples from humans included in the study were most closely related to parasites that infected western gorillas in Cameroon, the Central African Republic and the Republic of the Congo. Researchers believe a single transmission event may be the origin of the gorilla-human malaria link.
"It's a fascinating evolutionary question to ask where these human pathogens came from," evolutionary biologist Paul Sharp of the University of Edinburgh, who worked on the study, told "Nature."
"We're now wondering whether a cross-species jump like this could happen again in the future," he said.
Western lowland gorilla in the Congo Basin (Photo by Martin Harvey / WWF-Canon)
Western lowland gorilla at the San Diego Zoo (Photo by SBGrad)
While much progress has been made in the treatment and prevention of malaria, the origin and reservoirs of P. falciparum remained controversial until now.
"Until recently, the closest known relative of this strain of malaria was a chimpanzee parasite which was assumed to have diverged from its human counterpart at the same time as the ancestors of chimpanzees and humans more than five million years ago," explained Beatrice Hahn, professor of medicine at the University of Alabama at Birmingham and lead author of the study. The new research findings reject that theory.
The authors were surprised to find that no Plasmodium infection was detected in eastern gorillas or bonobos, suggesting that malaria parasites are rare or absent in some wild-living ape communities.
Additional field studies are needed to determine if eastern gorillas and bonobos are infected with Plasmodium at other locations, or if they harbor divergent parasites not detected by current diagnostic assays, the authors said.
"One important question and area of further research is if current gorilla populations represent a source of recurring infection of malaria in humans," Morgan said.
Malaria takes its greatest toll of children. In Africa a child dies every 45 seconds from malaria, according the World Health Organization, and the disease accounts for 20 percent of all childhood deaths worldwide. By far, Africa is most impacted, accounting for more than 85 percent of the world's malaria deaths.
The researchers hope the new information revealed by this study will help in the fight to eradicate malaria.
Morgan said, "Studies like this can assist in developing better malaria eradication strategies as well as provide information on how Plasmodium has evolved and adapted in both apes and humans."
Western lowland gorillas are endangered, but they are more common than their relatives, the mountain gorillas. They survive in the rainforests of Cameroon, Central African Republic, Congo, Equatorial Guinea, Gabon, Angola, and the Democratic Republic of Congo.
The international consortium includes researchers from Centre de Recherche Medicale, Cameroun; Chicago's Lincoln Park Zoo; Harvard Medical School; Harvard University; State University of New York; University of Alabama at Birmingham; University of Edinburgh; University of Kisangani; University of Montpellier; University of New Mexico; VaccinApe; Washington University; Wellcome Trust Sanger Institute and the Wildlife Conservation Society.
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