Parasites hint at antimalarial resistance in Africa

Malarial parasites from Sub-Saharan Africa could be acquiring mutations that make them resistant to artemisinin, the backbone of antimalarial therapy.

A team of researchers from Canada and the United Kingdom studied parasites from travellers who returned to Canada with malaria after trips abroad between April 2008 and January 2011.  

They found that 11 of the 28 parasites grown in the laboratory had a mutation that made them resistant to artemether, one of the artemisinin group of antimalarials.

All 11 came from Africa (from Angola, Cameroon, Congo, Ghana, Kenya, Liberia, Nigeria and Tanzania), the researchers reported last month (27 April) in Malaria Journal.

"We are seeing statistical evidence of resistance in the test tube," author Sanjeev Krishna, a researcher at the University of London, United Kingdom, told SciDev.Net. "If this progresses, and becomes more severe and established, it is likely to cause resistance in terms of treatment failures."

But it is still not clear whether resistance is already affecting treatment in the field.

"At the moment there is not evidence for these types of treatments failing in an important way in African countries, but we need to be alert," said Krishna.

He said it may be easier to detect resistance in travellers to malarial areas than in locals. Resistant parasites are ‘left over’ by drugs and the immune systems of local people are good at mopping them up. But travellers, without experienced immune systems, are less able to mop them up.

Patients with malaria in Africa should continue receiving the standard treatments, he added.

Carol Sibley, scientific director of the Worldwide Anti-malarial Resistance Network, (WWARN), agreed that the results should be treated with caution.  

She said that even though parasites in malaria patients in South-East Asia are showing drug resistance, those same strains do not show up as resistant in laboratory studies, suggesting that the relationship between lab studies and patient treatment is not simple.

The spread of resistance might be exacerbated by the poor quality of antimalarials according to Gaurvika Nayyar, which only kill the weaker parasites and let the fittest survive.

Nayyar co-authored a review study in The Lancet Infectious Diseases published last week (22 May) which found that more than a third of antimalarials in South-East Asia and Sub-Saharan Africa were substandard or fake.

Poor storage and manufacturing, counterfeiting and age all affect the quality of drugs.

"There is no quick solution to this problem," Nayyar said. "But we can’t delay action, because poor-quality drugs are harming people as I speak."

Another study published in The Journal of Infectious Diseases last week (21 May) pinpointed genetic differences as being responsible for reduced sensitivity to artemisinin of malarial parasites in Nigeria.

Link to full article in Malaria Journal [869kB]

Link to full article in The Lancet Infectious Diseases
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Link to abstract in The Journal of Infectious Diseases