City anchor: Mutation of virus gives dengue strains deadlier sting

The mosquito-borne dengue virus has mutated several times over the years, leading to five outbreaks of the disease in the Capital since 1996, doctors said.

This comes at a time when scientists from All India Institute of Medical Sciences (AIIMS) and National Centre for Disease Control (NCDC) were preparing tests to identify this year's dengue strain.

"There are four strains of the virus, commonly categorised as dengue-I,II, III and IV. It is a myth that the virulence of the disease is determined by the strain. Any strain can lead to aggressive forms of the disease. Since most people don't have immunity against new strains, a greater number are affected," Dr Shobha Broor, the head of microbiology in AIIMS, said.

She said type-II has been responsible for most cases of dengue haemorrhagic fever (DHF) the world over. This is the most aggressive form of the virus and usually causes dengue shock syndrome.

The four strains can show a wide range of symptoms — from simple fever to haemorrhages and shock syndrome, which can prove fatal if not treated properly.

Dengue-I, which is most common, is termed as the "classic", while type-II is known for haemorrhagic fever and shock syndrome.

A patient having type-III or IV dengue shows severe symptoms, but generally don't suffer from shock or haemorrhagic situations.

"Analysis of dengue cases from 1960 in the country, including sporadic incidents in the 1970s and 1980s, reveal that type-I and III have been the most common strains, particularly in Delhi. It is important to understand that the severity of symptoms can be caused by any strain, if ignored," a senior virologist in NCDC said.

Delhi health officials said two of the three deaths recorded in the city this year were from the shock syndrome. They said haemorrhagic fever was also seen in the three cases.

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