The All India Institute of Medical Sciences (AIIMS) has told the Centre that the chikungunya virus strain this year is “similar” to the 2006 virus, when the disease had emerged in outbreak form in the country after a gap of 32 years.
Sources said AIIMS informed the National Vector Borne Disease Control Programme that no new strain was found, setting aside speculation about the possibility of mutation of the virus causing the outbreak of the mosquito-borne infection in Delhi.
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The 2006 chikungunya outbreak was caused by central/East African genotype of CHIKV, and at least 14 lakh cases were reported across the country.
Sources at AIIMS told The Indian Express that the increase in population density in the last seven years and migration were among the likely reasons for the chikungunya outbreak this year. “There was very less circulation of the virus in the past years in Delhi. However, with increase in population and migration, the circulation has increased,” said a source.
Meanwhile, Dr Lalit Dar, Professor, Department of Microbiology, AIIMS said since chikungunya has a single serotype, a likely change in the genotype would not explain the reason for the outbreak. Serotype is associated with viruses and refers to the variation within the subspecies. And in case of chikungunya, there are three genotypes which determine the genetic constitution of the virus.
He had earlier said, “In 2006-07, when chikungunya cases were reported in Delhi, 14 lakh cases were reported in the country. Those 14 lakh people have been protected this time around as chikungunya immunity is usually a life-long immunity. What is more important to understand is that in the last seven years, there have been very few cases of chikungunya. During the same period, there has been an increase in the population density and migration in Delhi. This also would include the newborns. Hence, persons who have not developed immunity in this period, have become susceptible to chikungunya this time, which has resulted in a surge in cases.”