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The MCD as well the civic agencies of some other states appear to be blissfully unaware about the idiom ‘ forewarned is forearmed’. Else they would not have ignored an alert issued in February on the possibility of dengue erupting in a big way this year.

Around 6000 cases have been reported from all over the country so far. Delhi has officially recorded 322 cases and one death. However, doctors say the number of cases being reported in this part of the year is unusually high.

“We knew that there will be more cases in 2010 because of the hectic construction activity taking place for the Commonwealth Games. In addition, the cyclical nature of the disease indicated that there would be a spurt this year. All the risk factors for the spread of the disease have been there,” Dr A. C. Dhariwal, the director of the National Vector Borne Disease Control Programme, said.

“After an analysis of the situation, a letter was written in February to officials in states — including Delhi, Kerala and Karnataka — alerting them about the possibility of a dengue outbreak and the need to be prepared,” he said.

The trend this year is that though the number of cases is high, the mortality is less, Dhariwal said. Investigations have revealed that this year the predominant dengue virus is type 1 or DEN- 1. The dengue virus, Flavivirus, is of four types — from DEN- 1 to DEN- 4. Each of these may have several subtypes.

Infection caused by any one of them confers lifelong immunity to that particular virus subtype.

To make matters worse there have been good rains this monsoon, making conditions at construction sites even more conducive for mosquito breeding, experts said. “ The whole environment has favoured the resurgence of dengue,” Dr Randeep Guleria from the department of medicine at AIIMS said.

Guleria said the cases had increased drastically over the past few weeks. “ The cases are more than normal for this part of the year. Generally, we see a peak during September- October, but this time we are getting many cases in August. The authorities should have taken preemptive action to prevent the outbreak,” Guleria added.

Scientists say the disease is endemic to Delhi and some other parts. “ Unless you clear the mosquito- breeding sites, the disease will keep striking,” Dr Pradeep Seth, a virologist who had investigated the 1996 outbreak, said.

Though dengue is seen as a cyclical disease which peaks every three to four years, data indicates that its incidence is being reported annually.

There was a major outbreak in 1996 when the country reported over 16,000 cases and over 500 deaths. The cases fell during 1997- 2001, but the number has increased since then. Last year, there were over 14,000 cases and the figure was around 12,000 in 2008. However, the number of deaths in these years was low at approximately 100.

Dengue is caused by a virus and transmitted to humans by the Aedes aegypti mosquito. Generally, the disease develops five to six days after the mosquito bite.