Rising dengue cases in Delhi, despite the heat, cause for concern: Experts

MCD data shows that between January 1 and June 25 this year, Delhi reported 134 dengue cases. Curiously, the monthly dengue cases, since January, has been the highest ever recorded since 2017, when the civic agency started proper bookkeeping.

Even as Delhi awaits the onset of monsoon, the city has already recorded 134 cases of dengue this year—the highest for the period since the Municipal Corporation of Delhi (MCD) started keeping records of vector borne diseases in 2017. Public health experts said the rising dengue numbers this year is worrying as well as baffling as since March this year, the city has been experiencing hot and dry weather conditions, which is understood to be not conducive for mosquito breeding.

A municipal worker fumigates amid Dengue scare at Pandav Nagar Market area in New Delhi, India. (Photo by Raj K Raj/Hindustan Times)

Senior officials from the civic agency said mosquito breeding surveillance has been impacted this year -- first, by the impending municipal elections in February and the lack of funds to pay salaries of domestic breeding checkers (DBCs) and, then, by the unification of the civic body -- with the result that dengue cases have been high.

However, officials said surveillance has been stepped up and a close watch is being kept on mosquito breeding.

“We have seen that vector borne diseases, especially dengue, have become continuous instead of seasonal. This could be because aedes aegypti mosquito (which spreads dengue) is evolving and its breeding pattern is changing, not to mention the changing rainfall patterns of the city. We have ramped up surveillance and we are also imposing heavy fines,” said an official from the health department of the municipality, asking not to be named.

MCD data shows that between January 1 and June 25 this year, Delhi reported 134 dengue cases. Curiously, the monthly dengue cases, since January, has been the highest ever recorded since 2017, when the civic agency started proper bookkeeping. The figures for the corresponding period in 2021 was 34, 20 in 2020, 22 in 2019, 30 in 2018, and 55 in 2017.

In June (till June 25), the city has already recorded 23 dengue cases, as opposed to seven during the same month in 2021, one in 2020, 11 in 2019, eight in 2018 and 17 in 2017.

Delhi recorded 23 dengue cases this January, 16 in February, 22 in March, 20 in April and 30 cases in May, as per the MCD books.

Weather forecasters said \Delhi this year has largely seen dry heat, characterised by higher than normal temperatures and low humidity. Such conditions are usually not conducive for the breeding of mosquitoes.

Mahesh Palawat, vice-president (meteorology and climate change) at Skymet Weather Services, said short and intense rain spells, which the city has been experiencing, could be the reason for dengue infections remaining consistent.

“With short, intense rain spells, the chances of water-logging increases. Stagnant water is the perfect breeding ground for mosquitoes. Rapid urbanisation has ensured that there is no clear soil for the water to seep in and as such, leads to an increase in vector breeding points,” said Palawat.

Raghu Murtugudde, professor of atmospheric and oceanic science and earth system science, University of Maryland, and visiting professor at IIT-Bombay, explained that while health outcomes of dengue can be complicated, its basic ingredients are mosquito population and human population that carry the virus.

“Heat means that people are less covered by clothing and a certain share of population also sleeps outside during summer months. There is also a sizeable population of workers that has to spend a considerable time outdoors,” said Murtugudde.

He said, “The arrival of the monsoon and the continued irrigation around Delhi would have provided enough water and humidity for mosquitoes to breed. Warm temperatures favour pathogen growth and the monsoon spreads it via the travelling population. We need to consider environmental connectors as well as human connectors. Even within Delhi, poor people and outdoor workers probably get infected more.”