New Delhi: Climate change is rapidly having an impact on the spread of vector-borne diseases. While dengue, Japanese encephalitis and chikungunya, virtually unknown in the Odisha until the past decade, are rapidly increasing and the season conducive for the spread of such diseases has been extending to virtually half the year, found a study.

The study, titled, ‘Climate change and public health: a study of vector‐borne diseases in Odisha, India’ was published in the Natural Hazards Journal. The study has been authored by Mithun Karmakar of the National Health Mission-Odisha and MM Pradhan, National Vector Borne Disease Control Program of Department of Health & Family Welfare, Odisha government.

The study analysed the number of heat wave days and said, “The analysis indicates an increase in number of heat wave days in the month of June in recent years, which may be an indicator of gradual shift of monsoon season in Odisha. The results also indicate that vector-borne disease conducive season extends from July till November, nearly half of the year.”

While malaria, a disease that had once been synonymous with Odisha, has long been the government’s focus in terms of vector-borne diseases and its control in the state, the study flagged a warning. It said, “The other vector-borne diseases observed in Odisha since last decade include dengue, Japanese encephalitis and chikungunya. The mid-June period is usually characterized by onset of South West monsoon in Odisha in past.”

It added, “Further, the dengue and chikungunya are more prevalent in coastal districts, whereas malaria and JE have been experienced in interior districts.

For instance, the National Vector Borne Disease Control Program (NVBDCP) reported an increase of dengue cases by 46% (from 99,913 in 2015 to 188,401 in 2017). This has a distinct parallel in Odisha, where these VBDs hadn’t been reported until the past decade.

Cases of JE in India has almost doubled in the past five years (from 7,825 to 13,672 during 2013-18). Dengue has seen a similar increase. It was in 2010 that Odisha first reported 29 cases of dengue. By 2018, this number had jumped to 5,198. Until 2013, Odisha was among the eight states in India that had not reported even a single case of JE. This is no longer the case.

“The epidemiological analysis reveals that dengue, JE and chikungunya have also emerged as VBD threats in Odisha since the year 2010, added with malaria. The occurrence of these VBDs has increased in recent years. Further, dengue is more prevalent in nine coastal districts, whereas malaria and JE are more prevalent in mountainous, highland and upland regions,” the study said.

There is a growing body of scientific research that has studied the ways in which increasing temperatures can acutely impact transmission of vector-borne diseases - ranging from increased transmission of dengue with mosquitoes reproducing faster and biting more frequently to higher temperatures reducing the time between a vector feeding on an infected host and being able to transmit the pathogen.

“Scientific evidence establish the fact that the impacts of climate change are having wide immediate, as well as, long-term indirect effects on public health. Especially the focus is on climate change impacts in terms of increased severity, frequency and spread of vector-borne diseases. Climate changes in terms of increased average temperatures, more intense rainfall, extended summer season and less intense winters can impact the range and incidence of infectious and vector-borne diseases,” the study notes.

Of the 11 nations that account for 70 percent of the global malaria burden, only India was able to reduce its disease burden (a drop of 26 percent from 2016 to 2017) and this was largely due to work done by authorities in Odisha, found the World Malaria Report 2018. This period saw an 80 percent drop in cases, from 347,860 in 2017 to 66,301 in 2018.