Delhi is witnessing a definite surge in dengue this year. With cases touching 3,800 till September 19, there is every indication that this year’s case could outnumber 2010’s outbreak of 6,000 cases. Seventeen deaths have been confirmed already by the municipal corporations as against only 8 cases in 2010. Experts say this is the highest confirmed death toll from dengue in recent times.
But does that mean H1N1 commonly known as swine flu will hit Delhi just as bad? Speculation is rife but as experts point out the two viruses have little in common. They circulate independently of each other, in different weather patterns and with different modes of circulation.
The H1N1 virus, similar to a virus circulating in the respiratory tracts of pigs, was first isolated in pigs the USA, 1930. Since the 2009 outbreak, it now circulates like other influenza viruses in humans and spreads through droplet infections.
Every year when temperatures dip usually after Diwali, cases see a spike, and continue till March- April. The dengue virus is observed in the post monsoon months and is transmitted by a vector – the Aedes Aegypti mosquito.
With current trends of the H1N1 virus, it is unlikely that cases will see a spike this year according to microbiologists. Last year, Delhi reported the sharpest rise in H1N1 cases since 2009 when the virus surfaced. This spike came after a significant slump in the intervening years.
Last year’s “outbreak” stretched well into this year with cases surfacing till May 2015. This was attributed to the general cycle of the virus. Like dengue, the H1N1 virus (and all other viruses) have a cycle. A cycle is the period after which every virus rises in numbers due to several factors — depleting immunity or a change of strains by way of mutation of the virus, environmental factors — or a combination of all of these. After every spike in the cycle, a population always develops immunity for the next few years. As time passes, this immunity slumps. When the general population is immune, fewer people get affected by the virus.
Last year’s jump in cases prompted the National Centre for Disease Control (NCDC) and AIIMS to conduct serological tests to see if the H1N1 strain had mutated given the sudden rise in cases. The same H1N1 strain from 2009 was found in all samples with the Indian Council of Medical Research (ICMR) also confirming it, this year.
So unless the H1N1 virus mutates this year or there are severe environmental triggers, given the general cycle of the virus, we should actually see a dip in its numbers.
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