Incidence of dengue higher due to erratic rainfall this year
The high number of dengue cases in many states around the country has grabbed headlines as the national tally of cases this year is nearly twice the number recorded during the same period last year.
While the burden of this disease is higher in southern states, the outbreak in Delhi is being seen as the result of poor preparedness on part of the administration. The rapid progression of the disease has taken many by surprise as the high incidence is unseasonal compared to earlier trends. The dengue virus usually strikes the city only after the end of the monsoons in October.
The reason for the temporal shift, say experts, is the erratic weather and rainfall that the country has witnessed this year. Many scientific studies in the recent past have drawn connections between weather variables and the incidence of dengue. Many scientists are in agreement that a combination of higher mean temperature in a region and high humidity fosters higher rates of dengue transmission and incidence.
A C Dhariwal, director of National Vector Borne Disease Control Programme (NVBDCP), agrees with the correlation cited in the studies but adds that the prime reason for the unseasonal susceptibility of the country to multiple dengue outbreaks this year has been the unusual monsoon. The monsoon season was characterised by intense wet spells followed by long dry spells.
"Usually when it rains, the rainwater flushes away stagnant pools that act as sites for mosquito breeding. This year, we saw rainfall early in the season which was followed by long dry spells during which there has been high humidity, especially in Delhi. This has enabled a shift from the usual trend of dengue transmission that we have observed and the virus has struck parts of the country earlier than usual," he says.