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Malaria bug that can dodge rapid tests

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New Delhi: Government scientists have urged intensified vigilance for a genetic mutation in a deadly malaria parasite that renders the bug invisible to rapid diagnostic tests and could lead to infected patients being misleadingly labelled as uninfected.

The mutation in the parasite that causes cerebral malaria, first detected in Peru eight years ago, has since then surfaced in Gujarat, Madhya Pradesh, Maharashtra, Jharkhand and Odisha and could threaten malaria elimination efforts, the scientists have said.

The diagnosis of Plasmodium falciparum infection now relies on rapid diagnostic tests that look for a surface protein on the parasite called histidine-rich protein (HRP) 2, which serves as its molecular signature. But a genetic mutation that has deleted the HRP2 protein allows the parasite to evade detection through the standard rapid diagnostic tests.

"The HRP2 protein is not essential to the parasite's survival - so the mutated parasites continue to infect and cause disease in humans," said Praveen Kumar Bharti, a scientist at the National Institute of Research in Tribal Health (Nirth), Jabalpur.

An infection caused by such a mutated parasite is not picked up by the standard rapid diagnostic tests. So patients with high fever and other malaria symptoms may be misleadingly labelled as uninfected by malaria, leading to likely delays in treatment.

In a report published this week in the journal Lancet Infectious Diseases, the Nirth scientists have called for "timely mapping and monitoring" of parasites without HRP2, saying this will be a crucial step towards malaria elimination.

India's malaria control efforts have helped reduce the number of cases from about 1.9 million in 2004 to 1.1 million in 2014. The Union health ministry's malaria elimination milestones seek to achieve zero local cases and deaths by 2024, interrupt all local transmission of malaria by 2027, and maintain a malaria-free status across India by 2030.

But Nirth director Aparup Das and his colleagues have now cautioned that the deletion of HRP2 in the malaria parasite may make the elimination challenge even more difficult. They have highlighted that India's public health sector alone had during 2016 relied on over 19 million rapid diagnostic tests to look for malaria in patients with suspected symptoms.

The HRP2-deleted parasite appears to have emerged in the Peruvian Amazon in 2010. Within three years, scientists at the National Institute of Malaria Research, New Delhi, reported finding similar mutated parasites in India.

Surveys have since then indicated that up to 8 per cent of parasites picked up from sites in Gujarat, Jharkhand, Madhya Pradesh, Maharashtra and Odisha lack the HRP2 protein.

The scientists have also called for research to design alternative molecular diagnostic tests that could help overcome the deletion of the HRP2 protein.

"Otherwise this hole of Plasmodium falciparum HRP2... deletion might sink the ship of malaria management and elimination in India," they wrote in their report.

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