Saturday, September 15, 2012

Australia - Malaria Parasite Is Driving Human Evolution In Asia-Pacific

A new study shows that the malaria species widespread in the Asia-Pacific region has been a key driver of human genome evolution.

Malaria is a parasitic disease with devastating effects, causing up to one million deaths annually worldwide. Approximately half the world’s population is at risk of malaria infection. The disease is a major cause of poverty and has been a barrier to economic development.

The most prevalent malaria species in the Asia-Pacific region is Plasmodium vivax, widely considered to be a ‘benign’ form of malaria.

In comparison, Plasmodium falciparum is the species that causes the most severe disease and deaths from malaria. For this reason, P. falciparum has been thought to be the most important driver of human genome evolution.

An international team of researchers now report in PLoS Medicine that the milder P. vivax species is also a significant cause of genetic evolution, which provides protection against malaria.

The team who made this discovery included scientists from the Papua New Guinea Institute of Medical Research and the University of Western Australia, and was led by Professor Ivo Mueller from the Walter and Eliza Hall Institute of Medical Research in Australia.

Early on, the researchers observed that the incidence of a hereditary red blood cell disorder was unusually high in the Asia-Pacific region.

Southeast Asian ovalocytosis (SAO), indigenous to Malaysia and Papua New Guinea, is a condition caused by a genetic defect in a cell membrane protein that results in red blood cells being a different shape from normal.

Up to 35 percent of inhabitants along the coasts of Papua New Guinea carry this genetic defect. Because these are high malaria endemic areas, it is believed that SAO could be associated with improved survival against malaria.

“SAO occurs in approximately 10 to 15 percent of the population in parts of the South West Pacific and is caused by a hereditary mutation in a single copy of a gene that makes a red blood cell membrane protein. This is almost an absurdly high frequency when you consider that inheriting two copies of the mutation is invariably fatal, so we figured it must confer a strong advantage to the carriers,” said Mueller.

The researchers studied 1,975 children, from infants to 14 years of age, in the Madang area of Papua New Guinea. The incidence of infection by the malaria parasites P. vivax and P. falciparum was significantly reduced in SAO-positive children, while the risk of infection was reduced between 46 and 55 percent, depending on the age of the children.

“Humans and malaria parasites have been co-evolving for thousands of years,” Mueller said. “Malaria has been a major force in the evolution of the human genome, with gene mutations that provide humans with some protection against the disease being preserved through natural selection because they aid in survival.”

Controversially, this finding goes against the established theory that P. falciparum, responsible for the most lethal form of malaria, is the only malaria parasite that can drive genome evolution in humans.

“Our results suggest that P. vivax malaria, though until recently widely considered to be a ‘benign’ form of malaria, actually causes severe enough disease to provide evolutionary selection pressures in the Asia-Pacific,” explained Mueller.

Prof. Mueller expects these findings to impact malaria vaccine design and development.

“Studying the mechanisms that cause SAO-positive people to be protected against P. vivax malaria could help us to better understand the mechanics of infection and help us to identify better targets for a malaria vaccine,” he said.

Source: WEHI

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