Microbiologists at AIIMS have identified a strain of dengue, known to cause the most severe symptoms of the viral disease, in serological test of samples this year. The dengue-II strain, which is identified world over as the most deadly strain of the virus, leads to a significant drop in platelets and haemorrhagic fever.
This strain, in high number, was last reported in the Capital in 1996.
Dr Shobha Broor, head of microbiology at AIIMS, said: “Till 2010 — when we saw a lot of dengue cases — and 2011, dengue -I was the prevalent strain. Before that till 2007, we saw maximum cases of dengue-III. This is the first time since 1996, that we have identified so many cases of dengue -II, which is known to cause severe symptoms of the viral disease.”
According to doctors, change in the prevalent strain could be a reason for the high virulence of dengue this year. “If there is a new strain, more people are affected, since they may not be immune to it,” Dr Broor said.
The team at AIIMS virology laboratory tested seven culture samples over the past month — three were identified as dengue-II. “For culture sampling, where the samples are grown on ice, three out of seven is a substantial number,” a microbiologist from AIIMS said.
Doctors said sporadic cases of the type-II strain might have been reported during the past decade. “Three of seven samples from a single institution makes the data indicate that a substantial proportion of the strain is prevalent this year,” the scientist said.
The dengue virus has four known strains. Of these the relatively milder strains include type-I, which is known as the classic dengue fever, and type-III that causes high-grade fever without shock.
The severe strains are: type-IV that leads to fever with shock and type-II, which causes thrombocytopenia or a drop in platelets, hemorrhagic fever, organ failure and Dengue Shock Syndrome. Globally, dengue-II has been identified to be the most common cause of Dengue Haemorrhagic Fever. Types I and III have been the most common strains in the Capital since 1960, as per analysis by scientists from the National Centre for Disease Control and AIIMS.
The first dengue outbreak, when virological analysis was performed, was in 1996. At the time, type-II was found to be the most prevalent strain, among the samples screened at AIIMS.
The next outbreak of dengue was in 2003, when all four strains of the virus were found. In 2005, isolates of types I and III were seen, and combined infections were also seen. In 2006, when the next epidemic like situation of dengue was seen, type III was the most common strain. In 2010, when large number of cases of dengue were reported again, type-I was found to be the most common strain.