Malaria has made a comeback.

After heading for eradication in the 1950s and 1960s, malaria has had a resurgence in India. Now a study that has just been published suggests that the most dangerous form of the disease could be at levels much higher than previously estimated.

In 1953 when a national eradication programme was launched, some 75 million malaria cases and eight lakh deaths were estimated to be occurring in India which then had a population then of about 360 million. With the eradication programme in full swing, incidence of the disease dropped rapidly. By 1965-66, there were just one lakh cases and deaths were completely eliminated.

But malaria, instead of being wiped out from the country, made a comeback. Obstacles such as insecticide resistance, changes in mosquito behaviour, drug resistance in the malarial parasites and lack of adequate resources to fight the disease characterised the return of malaria in India, observed V.P. Sharma in a journal paper. Dr. Sharma was the founder-director of the Malaria Research Centre, now the National Institute of Malaria Research, in New Delhi.

Infection by Plasmodium falciparum has also risen. This single-celled organism is responsible for much of the severe cases of malaria and deaths from the disease. Worldwide, it is among the leading causes of death from a single infectious agent, according to the World Health Organisation (WHO).

According to figures published by the Union Government's National Vector Borne Disease Control Programme, there were over 1.5 million cases of malaria, more than half of them caused by P. falciparum, and 1,068 deaths in 2009.

“It is now well accepted that the reported incidence of malaria at the national level on the basis of surveillance carried out in the primary health care system at best reflects a trend and not the true burden of malaria,” observed scientists at the National Institute of Malaria Research in a journal paper published in 2007.

Studies had pointed to deficiencies in coverage, collection and examination of blood smears for signs of infection and in reporting systems. Consequently, the actual incidence of malaria in the country was “definitely far more than presently known,” they remarked.

Deaths due to malaria too were likely to be higher than reported.

Estimating the true disease burden of malaria in the country is a challenge, considering its varied epidemiology and dynamics of transmission, said one Indian scientist working on malaria.

In its World Malaria Report 2008, the WHO estimated that there had been 10.6 million cases of malaria and 15,000 deaths from the disease in India during 2006. (The Government figures put the number of malaria cases at nearly than 1.8 million and deaths at about 1,700 for that year.)

Now scientists from the 'Malaria Atlas Project' have used a map-based approach to estimate the global burden of P. falciparum malaria.

Their paper, which has just been published in the open-access journal PLoS Medicine, puts the extent of disease caused by P. falciparum in India at about 102 million cases in 2007. But with the uncertainty associated with the estimate, the figure could range from 31 million cases up to 187 million cases.

“India remains a massive source of uncertainty in our cartography-based estimates, contributing over three-quarters … of the uncertainty range in the global incidence estimates,” said the scientists in their paper.

“Clearly we need to collect more information to 'tame' the uncertainty in these predictions and understand the true extent of the malaria burden in India,” remarked Simon I. Hay of the University of Oxford, the first author of the paper, in an email to this correspondent.

After India, Nigeria, the Democratic Republic of Congo and Myanmar were estimated to have next largest clinical burden of P. falciparum malaria. But there were large uncertainties in the estimates for these countries too.

A national survey of prevalence in these four countries would “transform the information we have available in each and by extension improve dramatically our ability to estimate clinical burden at the global scale,” observed Dr. Hay.

In India, P. falciparum infections are particularly high in forested areas inhabited by ethnic tribes in the states of Orissa, Jharkhand, Madhya Pradesh and Chhattisgarh. There is also malaria caused by Plasmodium vivax, which is usually less deadly than P. falciparum. P. vivax is said to account for almost half the reported cases of malaria in the country.

Getting a true picture of the burden of malaria in India would enable priorities to be set in the planning and resource allocation for its control, observed scientists at the National Institute of Malaria Research in a paper published in the Journal of Biosciences in 2008.

(The web site of the Malaria Atlas Project can be found at http://www.map.ox.ac.uk/ and of PLoS Medicine at http://www.plosmedicine.org/ )

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