Updated: October 7, 2016 5:04:53 pm
Dengue is now ‘endemic’ in India. This term is used when a virus, disease circulates throughout the year as is the case with dengue in northern, central and eastern India.
Since 1996 when the first outbreak occurred to recent times a change in the pattern of its occurrence in the capital has been noted by a number of microbiologists who have published papers reiterating that the virus no longer has a “season” in India.
That being said, conditions like stagnant water and damp weather, seen during and after the monsoon are ideal for the virus to grow and proliferate. The vector mosquitoes grow in numbers in these conditions. So dengue cases see a sharp spike in the months immediately after the monsoons, in this instance, late August and September.
Stagnant water includes sources like open drains and any water stored in the household — bathrooms, kitchens and coolers. Household potted plants like money plants which absorb water slowly can be sources of mosquito breeding. Whenever there is a growth in construction work as in 2010 during the Commonwealth Games in the capital, cases of dengue rise. Experts say construction waste is a major source of stagnant water which is often ignored in anti-mosquito activities. Potholes in roads where water collects is also an often ignored source.
In Delhi, the municipal corporations have collected data of cases throughout the year, but from August to about November when cases are at their peak, daily reports are put together and advisories issued to hospitals to ensure cases are reported. In these months, not just dengue but other viruses including influenza and other fevers also witness a sharp rise.
After November, when temperatures dip, the virus cannot survive beyond a point and cases slide. This year, according to experts, Delhi has seen intermittent rains from early in the year so cases of dengue began to surface as early as from March but still saw a peak in August. It should be noted, the peaks usually occur after the rains and not during the rainy season because the virus needs time to grow and complete its life cycle. The Aedes aegypti vector mosquito which breeds during the rains continues to reproduce and add to its numbers usually till the winter months.
Taken together, these factors indicate that dengue cases surface well after the rains may have subsided until temperatures fall.
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