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Friday, June 25, 2021

Rainfall, humidity and minimum temperatures over Pune linked to dengue and malaria cases: Study

Pune receives its maximum rainfall quota during July and August. From about 180 cases reported in 2010, Pune's dengue cases in October reached close to 600 in 2017.

Written by Anjali Marar | Pune |
Updated: June 8, 2021 7:36:27 am
Rainfall, humidity and minimum temperatures over Pune linked to dengue and malaria cases: StudyAn increase in rainfall results in the creation of more breeding sites for mosquitoes; thus, there are greater chances of the adult female mosquito to obtain the pathogen. (Express Photo by Ashish Kale)

CASES OF dengue have been steadily rising in Pune since 2010 and are closely linked to Pune’s rainfall and relative humidity patterns. This was found in a pilot study conducted to assess the effect of climate change on the incidences of vector-borne diseases in Pune and Pimpri-Chinchwad municipal corporations.

The joint study, conducted by experts from India Meteorological Department (IMD), Indian Institute of Tropical Meteorology (IITM) and state health department, used cases of vector-borne diseases reported between 2010 and 2018 to conclude that dengue spiked during September to November, followed by August and December.

Transmission of dengue viruses is climate-sensitive for several seasons. Earlier studies have established that temperature changes affect vector-borne disease transmission and the epidemic potential by altering the vector’s reproductive rate, biting rate and extrinsic incubation period of the pathogen.

Alongside, rainfall affects the adult female mosquito’s density. An increase in rainfall results in the creation of more breeding sites for mosquitoes; thus, there are greater chances of the adult female mosquito to obtain the pathogen.

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But non-climatic factors like large presence of breeding sites, timely vector control and surveillance in Pune needed to be plugged, researchers said.

Pune receives its maximum rainfall quota during July and August. From about 180 cases reported in 2010, Pune’s dengue cases in October reached close to 600 in 2017.

“It is seen that after the monthly rainfall attains peak, the monthly dengue occurrences also peak, which takes place approximately in one to three months later. Similar positive correlation in dengue cases was noted with respect to monthly average humidity over Pune,” the study found.

This is the reason why maximum cases are observed during the September to November period, stated the study, which was published in the IMD’s quarterly journal Mausam.

Dengue hotspots were found in Pune when monthly average temperature ranged between 20 and 25 degrees Celsius for a corresponding average relative humidity between 55 per cent and 60 per cent.

Hotspots also emerged in the city when average monthly temperature as well as relative humidity spiked. That is, monthly average temperature remained between 25 and 30 degrees Celsius with a corresponding average relative humidity of 65 per cent to 70 per cent, which also favoured Pune turning into a dengue hotspot.

Positively, cases of malaria in both civic jurisdictions have been on a decline since 2010, the study highlighted. Between 2010 and 2018, cases during the peak have dropped from an estimated 87 to nine, respectively, in Pune and Pimpri-Chinchwad.

Malaria cases mostly emerge during June to September, which is the monsoon period. Malaria cases in Pune were found to reach their peak in July.

Experts have traced close association of malaria incidences with average monthly minimum temperatures over Pune.

Higher relative humidity, ranging between 70 to 80 per cent and average temperatures between 25 and 30 degrees Celsius, was linked with the creation of malaria hotspots in Pune. The case load was positively affected when the city’s monthly total rainfall was 50 mm to 180 mm, the study noted.

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