An unusually warm phase in early-November and unseasonal rain have prompted the civic authorities to continue its malaria surveillance till the first week of December.

The drive begins in the last week of May and usually continues till October-end.

According to health officials, over 74,000 people are suffering from malaria, of whom nearly 11,000 have malignant malaria. The total number was less than 60,000 last year.

Chief municipal health officer DebDwaipayan Chattopadhyay said there appeared to be a rise in malaria cases as more patients were being brought under the scanner.

Another reason for extending the malaria drive is an “alarming” rise in drug-resistant cases.

While drug-resistant cases formed only 7 per cent of all patients suffering from malignant malaria caused by the Plasmodium falciparum virus a decade ago, the number has shot up to nearly 60 per cent. This means the conventional malarial drug, Chloroquine, does not work on these patients.

A sample survey conducted by the central government’s Regional Office for Health and Family Welfare in Bowbazar and Mirzapur revealed that about 60 per cent of those infected with Plasmodium falciparum are drug-resistant in the two areas.

In actual numbers, among 10,700 malignant malaria patients, 6,000 were found to be infected with the drug-resistant strain.

But death due to malaria has been lesser this year — four in 2008 and one till November 22, 2009. Another vector-borne disease, dengue, has been less virulent this year.

There were no dengue deaths in 2009. Four people died of the disease last year.