IT WAS not that the gorillas and the chimpanzees were fighting for a title—but still the chimpanzees lost. Chimpanzees were believed to be the reservoir of Plasmodium falciparum, the drug-resistant parasite responsible for malaria. A research team, now, claims malaria passed on to humans from gorillas.
Microbiologists from University of Alabama at Birmingham in USA examined the genetic diversity of the parasite in the faeces of great apes—chimpanzees, gorillas and bonobos. They collected 3,000 specimens from different parts of Central Africa and studied genes in small organelles of the cells, like mitochondria, to identify and characterize different species of the parasite present. P falciparum infected chimpanzees and western gorillas, but not eastern gorillas or bonobos, the researchers reported in the September 23 issue of Nature. 32-48 per cent of the chimpanzees and western gorillas carried a mix of Plasmodium parasites. P falciparum that infects humans was not very closely related to the Plasmodium species that infect chimpanzees as had been thought; it was close to the species in western gorillas. Now that scientists have mitochondrial genome sequences of Plasmodium from apes, they can look for the sequences in people living near great apes. This can help them pinpoint sources of infection and eradicate malaria.
Edward C Holmes at the Centre for Infectious Disease Dynamics at the Pennsylvania State University said though such studies are conducted to predict the next human pandemic and prevent it, this is difficult considering that successful disease emergence depends on both parasite genetics and epidemiology. Nevertheless, such studies help in understanding the origins of human diseases, he added. “If malaria crossed the species barrier to humans from gorillas, possibly more than once, then even if we eradicate human disease there will remain the potential for the non-human primate malarias to spread the disease again,” Stephen Rogerson, a clinician with the Royal Melbourne Hospital in Australia, pointed out.
The Nature paper is intriguing and underscores the value of continued sampling of non-human hosts as a means to better understand the diversity and evolution of parasites, said Susan Perkins, invertebrate zoologist with the American Museum of Natural History. Perkins had earlier identified malarial parasites in tree-dwelling rats that shared evolutionary relationship with P falciparum and P reichenowi. There are over 200 described species of Plasmodium in hosts such as rodents, bats, birds and lizards, added Perkins.
In January, researchers from the US and France had pinpointed that gorillas carry malignant malarial parasite. They studied the diversity of Plasmodium infecting chimpanzees and gorillas in Cameroon and Gabon, both in wild and in captivity, and found P falciparum among others. The research team concluded that P falciparum originated from a closely related parasite P reichenowi, found in chimpanzees.
The latest study’s conclusion has changed a prevalent theory on the evolution of the malarial parasite and human beings. Earlier, it was believed that chimpanzees carry P reichenowi which is the closest relative of human P falciparum. This relationship suggested that they diverged at the same time as humans and chimpanzees separated thousands of years ago. But recent studies suggested that African primates carried many species of Plasmodium, and P falciparum of humans is simply a strain of P reichenowi that jumped from chimpanzees. But one does not know when.
In 2007, the parasite P falciparum caused around 451 million clinical cases worldwide, according to Oxford University’s Malaria Atlas Project. In India, nearly 88 per cent of the confirmed malaria cases were caused by this parasite in 2009-10.
As for chimpanzees, they are still not off the hook. A PLoS Pathogens study described a malaria agent P gaboni from chimpanzees in Central Africa. This species is a close relative of P falciparum. Chimpanzee is also the reservoir of HIV 1.
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