Over the past decade, there has been a major expansion of rapid diagnostic testing around the world. Manufacturers surveyed by WHO for the World Malaria Report 2015 reported a total of 314 million RDT sales in 2014 compared to 50 million RDT sales in 2008. Approximately 80% of these RDT sales are in the WHO African Region, where the disease burden is highest.
Malaria RDTs enable timely and appropriate treatment, especially in remote areas with limited access to quality microscopy services. Together with insecticide-treated mosquito nets and artemisinin-based combination therapies, the wide use of RDTs has contributed significantly to recent successes in global malaria control. According to WHO estimates, there was a 37% decline in malaria incidence and a 60% decline in malaria mortality globally between 2000 and 2015.
How malaria RDTs work
Currently available RDTs work by detecting a specific protein in the blood of a person infected by malaria. In the case of P. falciparum – the most deadly malaria parasite globally, and the most prevalent in Africa – RDTs are designed to target a protein called Histidine Rich Protein 2 (HRP2). The blood test is typically administered at the point of care through a finger-prick and results are available within 15-30 minutes.
Rapid diagnostics tests are not fail proof: false negative results can occur due to poor RDT product design or quality and/or poor transport and storage conditions. WHO is currently investigating reports of genetic mutations that cause the malaria parasite to stop producing the protein targeted by the test.
A missing gene: pfhrp2
In 2010, a study sponsored by WHO and FIND found that some P. falciparum parasites in Peru lacked the pfhrp2 gene; without this gene, the parasite cannot produce HRP2 and cannot be detected by HRP2-based RDTs. This was the first report to confirm the absence of the pfhrp2 gene among P. falciparum parasites in a clinical setting.
More recently, surveys in several African settings have also found a varying proportion of P. falciparum parasites lacking the pfhrp2 gene. The prevalence of this genetic mutation reportedly varies between and within countries; if confirmed, RDT procurement and case management practices will need to be tailored accordingly.
HRP2-based RDTs may need to be replaced by other RDTs that detect alternative proteins. WHO has evaluated several commercially available RDTs that are not based on HRP2 detection and some perform well.
Malaria Threats Map
This interactive map presents data on the status of P. falciparum gene deletions.
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WHO response
WHO is rigorously reviewing these recent surveys of P. falciparum genetic mutations to determine their accuracy. The Organization is directly supporting Member States to investigate suspected false negative test results consistent with pfhrp2 gene mutations and helping them address the implications for case management.
“WHO is monitoring the situation closely and supporting countries as they respond to this emerging issue of potential public health concern,” said Dr Pedro Alonso, Director of the WHO Global Malaria Programme. “At this point in time, there is no reason to question the critical role that RDTs play in diagnosing malaria and in ensuring timely and appropriate treatment. RDTs continue to be one of our core malaria control tools.”
For more information, please contact:
Dr Jane Cunningham
Prevention Diagnostics and Treatment Unit
email: cunninghamj@who.int