PUNE: Abundant rainfall years don’t always bring good tidings. A study between Pune-based
National Institute of Virology (NIV) and the Indian Institute of Tropical Meteorology (IITM) has linked more cases of chikungunya in India, and in Maharashtra and
Karnataka in particular, to high rainfall years and fewer cases in the less rainfall years.
Infected mosquitoes transmit chikungunya to humans who suffer from high fever and severe joint pain.
Researchers found that between 2010 and 2014, chikungunya, affecting over 1.19 lakh people, was reported from all over the country except Jammu & Kashmir, Himachal Pradesh and Arunachal Pradesh.
West Bengal with 28,044 cases, Karnataka with 25,320 cases and Maharashtra with 17,238 cases had the largest share. The researchers investigated the effects of climatic factors such as temperature and monsoon rainfall with confirmed cases of chikungunya in India.
Pratip Shil, a scientist at NIV who worked on the project, told TOI that the research found that the number of confirmed chikungunya cases in the country was modulated by rainfall from 2010 and 2014. “In Maharashtra and Karnataka, positive association of rainfall was observed with the number of chikungunya cases higher in high rainfall years and lower in less rainfall years,” Shil said.
Both states are in the Deccan plateau of peninsular India and share a similar topography of mountainous terrain (Western Ghats), grasslands and some basins of rain-fed rivers having a semi-arid grassland type of climate. Abundant rainfall boosts mosquitoes and hence there is more disease transmission, Shil added.
In the case of West Bengal, a highly populated state with plenty of water bodies, dense vegetation and mostly hot and humid climate which is ideal for mosquitoes, there were 20,503 confirmed cases in 2010 alone, the study said.
“Our analyses also revealed that from 2010 to 2014, the largest number of rural outbreaks of chikungunya occurred in peninsular India whereas only a few occurred in the northern parts of the country,” the researcher added.
The team compared the number of cases with the annual average maximum temperature and annual average minimum temperature to investigate the impact of surface air temperature. It was observed that the number of cases increased with the rise in both the maximum and minimum temperatures.
Dilip Kothawale, a retired IITM scientist who worked on the project, said, “We observed that prevailing temperature range during the outbreaks was favourable for chikungunya propagation and the occurrences were determined by average rainfall. Overall, for India, favourable climatic conditions have contributed to incidences of chikungunya during the study period.”
