New research published in the prestigious Science journal has challenged previous notions about how the body fights against malaria infection. Scientists have discovered that platelets, normally known for their role in preventing bleeding, can actually target and kill the parasite that causes malaria as it grows inside red blood cells.
The key to these latest findings is the discovery that a molecule on the red cell – called Duffy – is essential for platelet-mediated killing of the P. falciparum malaria parasite. This research is significant because most people living in Africa lack Duffy, and could provide new explanation for why malaria is more common and more lethal in Africa than elsewhere in the world.
“We know that platelets defend infected people by killing the malaria parasites that infect the blood cells but the weapons used by the platelet were unknown. What we found was that platelets release a molecule called PF4 that kills the parasite, but what was really interesting is that PF4 needs to bind to the red cell Duffy molecule for this to occur,” explains lead author Associate Professor Brendan McMorran, Australian Advance School of Medicine, Macquarie University.
The lack of Duffy on the red cell occurs through a genetic change, known as “Duffy negativity”, and is a separate blood group. Other studies have estimated that 98-100% of individuals living in the equatorial regions of Africa are Duffy-negative.
“We know that Duffy-negativity gives them resilience against another malarial parasite, P. vivax, but as a consequence has produced a chink in the protective armor in these people and suggests another reason why falciparum malaria is major problem in Africa,” says McMorran.
The 2011 World Health Organisation’s (WHO) World Malaria Report estimated 216 million episodes of malaria in 2010 with 81% of these occurring in Africa. Over half a million deaths in 2010 were due to malaria, 91% of these occurred in Africa. The majority of those killed are children aged less than 5 years. This equates to a child dying of malaria every 60 seconds.
The WHO also notes that reducing the burden of malaria remains a greater problem in Africa than the rest of world. Over the past 10 years, incidence and death rates have declined only 1 and 10% respectively in Africa, compared to 17 and 26% in the rest of the world.
“This finding adds to the ongoing challenges to control this disease. Recently reported finding in The New England Journal of Medicine show that our most advanced malaria vaccine candidate is having only marginal success in large-scale trials conducted in Africa,” says Professor Simon Foote, Dean, Australian Advance School of Medicine, Macquarie University.