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Milder strain and higher immunity behind sharp drop in dengue cases in Delhi

The capital has reported 1,020 cases of dengue so far this year — less than half the number (2,884) it reported during the same time last year. Authorities have so far confirmed the death of only a 12-year-old girl in the capital so far.

Written by Astha Saxena | New Delhi | Updated: October 29, 2018 10:04:32 am
dengue, spread of dengue, dengue cases, dengue deaths, dengue cases dropped, dengue cases in delhi, dengue cases in capital city, indian express A mosquito breeding site behind Nizamuddin Basti. (Express photo by Abhinav Saha)

The capital has reported 1,020 cases of dengue so far this year — less than half the number (2,884) it reported during the same time last year, data compiled by South Delhi Municipal Corporation shows. The reason: Dengue virus type III being the predominant strain.

Dengue is transmitted by several species of mosquito within the genus Aedes. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash similar to measles. There are four types of dengue strain, with type II and IV considered more severe and normally requiring hospitalisation. Authorities have so far confirmed the death of a 12-year-old girl, apart from five other suspected dengue deaths, in the capital so far.

Experts said the strain has been there for the last three years, which has made much of the local population immune to this particular type of the disease. “The type III strain has been there in the capital for three years, which is one of the reasons for fewer cases this time. If a same type remains in circulation for over a period of time, a large proportion of the population develops immunity to it. We had expected that type III will continue this year. The reappearance of one of the serotypes that has not been around for a while can lead to a spurt in cases. We’ll keep monitoring the strains throughout the season to identify the serotype in the coming days,” said Dr Lalit Dar, professor of microbiology, AIIMS.

Dengue cases reported in the capital so far are the lowest in the last four years. The number of people affected by the disease during the same period in 2017, 2016 and 2015 stood at 2,884, 3,009 and 12,531 respectively.

“If there is any migration from a state having a different type of strain, it can spread among the public and can lead to a complex situation. Aedes mosquito in northern India is highly domesticated; it means you can find it inside the house or a garden. One must stay covered during the day,” said Himmat Singh, scientist at the National Institute of Malaria Research (NIMR).

Delhi witnessed its worst outbreak in 2015, with over 15,000 cases and 60 deaths. According to experts, awareness among the people is extremely important to control the disease. Cases peak mostly in the months of October and November. “We are expecting that the cases that will come next month are going to stay a little longer, as the tail of any disease is always long. It is important for the public to stay aware and the authorities to be more vigilant,” said Dr Atul Kakkar, senior consultant, department of medicine, Sir Ganga Ram hospital.

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