ACTS-resistant malaria comes to East Africa

By CHRISTABEL LIGAMI 

Posted  Saturday, May 12  2012 at  12:40

A strain of the deadly malaria parasite Plasmodium falciparum that is resistant to artemisinin, one of the most powerful anti-malarial drugs, has been found in East Africa.

The strain tested positive in blood samples from foreigners who had travelled in Kenya and Tanzania and nine other African countries.

This particular strain had been found at the border of Thailand and Myanmar and had been predicted to be spreading to India and then Africa as resistance to other antimalarial drugs has done before.

(Read: ACTS-resistant malaria on the rise)

The results, according to the researchers from St George’s, University of London, indicate that either the strain has spread to East Africa and the other African countries or the local parasite has developed resistance.

Although malaria control efforts have been scaled up in the region, the researchers say their findings are a further warning that the best weapons against malaria could be rendered obsolete.

Sanjeev Krishna, the study lead researcher and professor at St George’s, University of London, said resistance in parasite samples were taken from 11 of the 28 malaria-infected patients from East Africa and the other African countries.

“On average, artemether’s effectiveness was reduced by half. Each parasite was found to have the same genetic mutations,” said Dr Krishna.

The artemisinin group of drugs is the most effective and widely used treatments for malaria. The drugs in this group are most powerful and less likely to be resisted by the malaria parasite when used with other drugs as artemisinin-based combination therapies (ACTs).

The patients were infected by malaria parasite-carrying mosquitoes while travelling to East Africa and the other nine sub-Saharan African countries, home to 90 per cent of the one million people killed worldwide each year by malaria.

The researchers then later tested samples from patients infected with the Plasmodium falciparum parasite and the parasites were assessed for their sensitivity to four artemisinins — artemisinin itself, artemether, dihydroartemisinin and artesunate.

The results showed that 11 parasites showing artemether resistance had the same genetic mutations in an internal system called the calcium pump (this is used to transport calcium, crucial for the parasite to function).

“We already suspected that the calcium pump which we first showed was a target for artemisinins to work on in 2003 had the potential to develop artemisinin resistance. But this had been difficult to confirm until now,” said Dr Krishna.

“Artemether and ACTs are still very effective, but this study confirms our fears of how the parasite is mutating to develop resistance. Drug resistance could eventually become a devastating problem in Africa and not just in south east Asia where most of the world is watching for resistance.”

Dr Krishna noted that the effectiveness of the other artemisinins was not significantly affected by the mutations. This may be because they were able to work on other transport systems in the parasite, compensating for the effects of resistance mutations in the calcium pump.
“At the moment, we do not know if the other artemisinins will follow suit, but given the shared chemistry they have with artemether it is tempting to think that they would,” he added.

The scientists argued that the resistance could be a result of the increasing use of ACTs, 300 million doses of which were dispensed worldwide in 2011.

Greater use could offer the parasites more opportunities to develop genetic mutations that provide resistance. They say this could lead to a repeat of how the parasite developed resistance to pre-artemisinin drugs such as chloroquine. Incorrect use of anti-malarials, such as not completing the treatment course or taking substandard drugs, could aid this process.