Did agriculture bring malaria?

If humans had not abandoned their nomadic ways for agriculture, two events would be missing from civilisation: deforestation and domestication of animals. Man would also not have heard of diseases like AIDS and swine flu. The virus is said to have shifted to humans from chimpanzees when forests were cleared. The malaria parasite, plasmodium falciparum, that kills 1.5 to 2.7 million people each year, also came from wild chimpanzees, say scientists. Chimpanzees harbour the parasite plasmodium reichenowi — the closest known relative of p falciparum. So far, studies have attributed the origin of the parasites to the co-speciation theory.

It says they evolved from a common ancestor and diverged with their hosts, ape and man, over the past five to seven million years. But the parasite’s ability to be infectious suggested that it invaded the human body recently. This led a team headed by Stephen M Rich, medical zoologist from the University of Massachusetts, USA, to investigate the parasite’s origin. The team sampled wild and wild-born captive chimpanzees from Côte d‘Ivoire and Cameroon and collected eight isolates of p reichenowi.

When their DNA was examined, the team found a gene (CSP) that encoded similar amino acid sequences for p reichenowi and p falciparum. The team studied DNA segments from three other amino acid coding genes in the eight isolates of p reichenowi and 133 isolated strains of p falciparum. “Two findings came to light. First, the genetic diversity of p reichenowi is much greater than p falciparum, indicating the chimp parasite existed long before the human parasite. Second, the DNA comparisons confirm p falciparum is simply a branch of the genetically diverse tree that is p reichenowi,” said Brian Pike, director of laboratory science of the Global Viral Forecasting Initiative, USA, and author of the study. Published in the Proceedings of the National Academy of Sciences, the study disproves the co-speciation theory. But what made it necessary for p reichenowi to evolve into p falciparum? Research shows all hominids, except humans, can produce a sugar from a glycoprotein found in cell membranes. P reichenowi has a preference for the sugar. In humans, the gene responsible for the conversion is deactivated. Hence P reichenowi mutated into a species that could take up the glycoprotein, to make hosts out of humans. The result was p falciparum. Hunter-gatherers first transitioned to agriculture 10,000 years ago in Africa. Deforestation increased the number of human-wildlife conflicts. Pools of standing water for crops and a gradual warming created conditions favourable for mosquito breeding. Anthropological evidence shows it is around this time that humans developed haemoglobin mutants rendering them resistant to malaria.

Susmita Dey
Down to Earth Features

Squirrel monkeys get gene therapy

Two squirrel monkeys that were colour blind from birth have had their vision restored after receiving gene therapy. The experiment paves the way for the treatment of a range of genetic eye disorders in humans, including some that cause full or partial blindness in millions of people worldwide. Sam and Dalton, two male squirrel monkeys, were able to see the world in colour five months after being treated, doctors said. The animals were born without an ability to see colour red.

The therapy targets specialised ‘cone’ cells in the eye which allow animals, including humans, to see in colour. Genetic damage to cone cells, which causes colour blindness, is the most common type of gene disorder in humans. “Although colour blindness is only moderately life-altering, we’ve shown we can cure a cone disease in a primate, and that it can be done very safely,” said William Hauswirth at the University of Florida. “That’s encouraging for the development of therapies for human cone that are really blinding.” Researchers treated the monkeys by injecting them with a virus that had been modified to carry a corrective gene. When injected behind the retina at the back of the eye, the gene produces a protein that is sensitive to red light.

Ian Sample
The Guardian