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Trouble in Parasite

The malaria parasite’s formidable adaptability has helped it evade new drugs and experimental vaccines and continue to cause disease and death in 97 nations.

columns Updated: Apr 26, 2014 23:06 IST
Sanchita Sharma

Malaria cases in India fell to 1.06 million in 2012 from 2.03 million in 2000, but the parasite’s rising resistance to drugs and the Anopheles mosquito’s to insecticides threatens to make the countdown to elimination far from easy.

For decades now, the malaria parasite has displayed a formidable ability to evade all attempts to destroy it. Armed with the safe, inexpensive drug chloroquine and the powerful insecticide DDT, the World Health Organisation (WHO) launched the Global Malaria Eradication Programme way back in 1955. The goal was to eliminate the disease within 10 years. More than a billion dollars was spent on distributing chloroquine; fogging with DDT became a part of public health programmes across the mosquito-infected world, including in India.

The parasite not only lived, but thrived. So did the mosquito.

And so malaria survived new drugs, insecticides and habitat changes to continue to infect and kill people in 97 nations. Each year, around 207 million people get infected worldwide and 627,000 die, mostly children under-5 in Africa, estimates the WHO.

Malaria is caused by single-celled Plasmodium parasites, with P. falciparum and P. vivax between tehm causing most of the infections in India. The parasite spreads between people through the bites of mosquitoes, invading the liver first, then the red blood cells. At first, the symptoms are generic -- fever, headache, sweats and chills, vomiting – and at this stage, the immune system usually manages to control the infection. If untreated, malaria kills by disrupting blood supply to the vital organs, including the brain, causing seizures and death.

Half the world’s population is at risk. In India, 85% of the population lives in areas where infection persists.

“In India, Anopheles culicifacies is the principal vector of rural malaria and accounts for 60-70% of annual cases, while An. stephensi is dominant in urban areas,” says Dr K Raghavendra, scientist, National Institute of Malaria Research (NIMR). “Irrespective of the type of mosquito spreading infection, the disease remains the same.”

Over the past few years, the parasite is steadily developing resistance to every frontline antimalarial drug. The first chloroquine-resistant P. falciparum was first reported near the India-Myanmar border in 1973. Chloroquine-resistant P. vivax was unknown in India until 1995, when two cases were detected in Mumbai. Since then, several cases have been reported across the country.

The parasite is now so entrenched that some strains can be controlled only using a combination of drugs. With artemisinin-resistance being reported in East Asia, public health experts in India are not taking any chances.

India has rolled out the WHO-approved fast-acting combination of drugs classified as artemisinin combination therapy (ACT) across the nation in 2010. ACTs are made using artemisinin-based compounds in combination with other classes of anti-malarials. Of the five combinations approved by the WHO, four are approved for use in India.

“The ACT combination of artesunate + sulphadoxine-pyrimethamine (AS + SP) is the first-line treatment for uncomplicated falciparum malaria, which accounts for over 90% deaths. Under the national programme, ACTs are provided free for all, as are long-lasting insecticidal nets, which stay effective for three years and help in lowering transmission,” says Dr Neena Valecha, director, NIMR.

With cases of resistance to AS+SP reported in the Northeast, the Centre gave its nod to the AS + AL combination for use in the region in April 2013.

Work is on potential vaccines, with GSK targeting 2015 for the launch of the world’s first vaccine against malaria. The vaccine, however, is only partially effective and at cannot eliminate, malaria.

Adding to the problem is the mosquitoes growing resistance to insecticides, “The vector (mosquito) has grown resistant to DDT and malathion,but is still mostly sensitive to pyrethroid,” says Dr Raghavendra.

To be declared malaria-free, India has to go through four distinct phases: control, pre-elimination, elimination and prevention of reintroduction. “Stepping up surveillance for early detection and treatment detect and tracking ‘migration malaria’, where an infected person travels to other areas and causes outbreaks will help eliminate malaria. Now that we’re on track, we can’t afford to slow down,” says Dr Valecha.