New Delhi: The most common strain of malarial parasite found in India and responsible for around a million cases of malaria every year, may be beginning to turn lethal in a transformation that could have significant impact on the country’s response to the disease and its health budget.

A team of experts from the Union health ministry investigating two recent cases of suspected malarial deaths in Goa confirmed on Tuesday that the cause of malarial infection was plasmodium vivax, or p. vivax, a strain of malarial parasite transmitted to humans by the anopheles mosquito. Although there are around a million cases of malaria caused by p. vivax every year in India, none of these results in death.

Nine out of every 10 deaths from malaria here are caused by plasmodium falciparum, or p. falciparum, the most virulent of the four malarial parasites found in India. In the other instances, the deaths are caused by co-infection or infection by more than one malarial parasite, but even in these instances the falciparum parasite is the dominant one, causing cerebral malaria, kidney failure and, eventually, death. The falciparum parasite is the cause of malaria in around 800,000 people in the country every year.

Advances in medicine have kept fatalities low — between 800 and 1,000 every year — but scientists are worried that instances such as the two deaths in Goa indicate a looming problem from an unexpected quarter. Malaria is the most common parasite-induced ailment here and, according to the Malaria Vaccine Initiative, an international non-profit organization, India spends nearly half its health budget on malaria control programmes.

In the case of the Goa deaths, experts had always suspected p. vivax but it was only on Tuesday that they ruled out a co-infection where p. falciparum was also involved.

“The purpose of our investigation was to rule out co-infection and we can confirm that only p. vivax was involved,” said G.P.S. Dhillon, director of the National Vector Borne Disease Control Programme, an official body that investigates vector-borne diseases (those transmitted to humans or other animals by insects) in the country.

There are no official records of death due to infection by p. vivax in India. “There have been reports of vivax malaria causing severe complications such as cerebral malaria in India, but they are extremely rare,” added Dhillon.

In 2005, Dhanpat Kochar, a neurologist at the Sardar Patel Medical College in Bikaner, Rajasthan, reported that 11 malarial patients, with p. vivax infections were exhibiting a host of complications ranging from jaundice to cerebral fever. And, there have also been reports of malaria caused by p. vivax not responding to the usual medication.

“Cases of chloroquine resistance as well as severe complications in p. vivax malaria have been reported since 1995,” said A.P. Dash, director of the government-run National Institute of Malaria Research. “But these are sporadic. There is cause for concern, but not worry yet,” he added.

Some scientists believe the virulent expressions of p. vivax may have more to do with the people afflicted than the parasite itself. “It could happen that the organ failure and cerebral malaria may have been caused by different undetected reasons, probably a weak immune system, and that may sometimes cause the vivax to behave more virulently,” said C.R. Pillai, emeritus scientist, Indian Council for Medical Research, the apex body governing medical research in the country.

In the Goa case, clinical studies are on to rule out just such a possibility, said Neena Valecha, senior scientist at the National Institute of Malaria Research, and part of the investigating team.