Dengue outbreak in Himachal points to climate change?

The news escaped notice for the most part. This year, Himachal Pradesh was hit by a dengue outbreak affecting more than 2,800 people till the third week of September, and killing three. The invasion of the hill state by a disease traditionally known to occur in the plains has stirred scientists who study climate change and its impacts. They say it’s a clear sign of how climate change silently alters the disease profile of a state and throws up new public health challenges.

The signs had been there for some time. Himachal Pradesh experienced 322 dengue cases in 2016 and 453 cases last year. But a seven-fold increase severely impacting the lower hill districts has taken the health administration by surprise with the Indian Council of Medical Research and National Centre for Disease Control rushing teams to the hill state to understand the disease dynamics. The worst affected districts are Bilaspur, Solan, Mandi, Kangra and Una.

For researchers who study climate change and its impacts, the outbreak was not a surprise. They predicted such a trend long ago. Using modelling studies, they warned about the spread of vector-borne diseases like dengue and malaria to new locations like the Western Himalayan hills and North East states. With an increase in temperature and change in rainfall pattern, they said, the transmission window would expand too.

Prolonged monsoon

“In Himachal, there has been a change in monsoon pattern. The monsoon sets in early and withdraws late, prolonging the season. In June and September, we get 10-15% more rainfall whereas 60-70% rainfall happens in July and August. Overall there is a decline in rainfall, but unusual heavy rains are now more common even in those areas that traditionally received barely any rainfall,” says Manmohan Singh, director of India Meteorological Department’s Shimla unit.

In 2017, dengue cases were reported in September-October, but this year the first case happened in May even before the rainy season, says a state health department official, who doesn’t wish to be identified. What compounded the problem was a steady decline in natural water sources because of the changing climate. With natural sources drying up, people tend to store water. Most times, the containers don’t have a lid, thereby turning into a breeding ground for Aedes aegypti mosquito.

“Climate change triggers water scarcity. People tend to store water in the absence of piped supply, giving the insects more breeding space. Increased temperature helps, too, because 28 degrees Celsius is considered ideal for a mosquito to grow and survive. The outcome is there in Himachal Pradesh for everyone to see.”

-- R C Dhiman
Head of the Department of Science, and Technology-ICMR Centre of Excellence on Climate Change and Vector Borne Diseases in Delhi.

To contain the outbreak, the state health department undertook a unique “dry day” intervention. On every Thursday, water supply is stopped in the morning and a team of officials visits every home asking the people to spend the stored water. The water supply is restored in the evening. While the intervention works to some extent, officials admit that habits die hard.

Road construction, too, has its share of blame. “In a cluster of 56 families in Mandi, it was found that mosquitoes bred in pools of water created inside the girders left by highway construction authorities. An early spell of rain turned them into breeding sites,” says Suresh C Attri, Principal Scientific Officer (Environment) in the Himachal government.

Scrub typhus

Dengue is not the only disease with a climate change connection. Health officials said such a link was seen in Scrub typhus cases too, as the numbers went up with increasing temperature. In 2016, there were 1,175 cases with 37 deaths. The numbers rose to 1,484 in 2017 with 32 deaths and this year there are 885 cases (till September 19) with 11 deaths. Cases of cutaneous leishmaniasis too are increasing in the state.

More than a decade ago, a link between typhus outbreak and enhanced rainfall was noticed by epidemiologist Omesh Kumar Bharti when he, along with colleagues from Himachal health department and National Institute of Epidemiology, Chennai, probed a tick typhus outbreak in Kangra in 2007. Even though the disease was a little different from Scrub typhus, Bharti’s study gave a clear indication of how such typhus cases proliferate in moist environments.

Around the same time, two researchers from Pune University and a third one from Defence Research & Development Organisation collaborated to demonstrate how the North Western Himalayas (NWH) had warmed up in the last hundred years. “Unlike other high mountainous regions such as the Alps and Rockies, where the minimum temperatures have increased at an elevated pace, the rise in air temperature in the NWH has been primarily due to rapid increases in both the maximum as well as minimum temperatures, with the maximum temperature increasing more rapidly,” they reported in 2007.

The trio showed an increase in air temperature in the this region by 1.6 degrees Celsius with winter warming at a faster pace. The warming trend was seen in Met stations at Shimla, Bahang, Solang, Dhundi and Patseo.

Such favourable weather conditions and population pressure have led to a rise in dengue cases in urban areas across the country and hills are no exception.

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“New studies suggest an increased transmission of dengue by 2030. Currently, we are working with the latest climate models on vector-borne diseases in view of projected scenario of climatic parameters. The findings suggest the opening of a few new foci in the Himalayan region. The threshold for dengue transmission is lower than what it used to be,” says Dhiman.

Dhiman first noticed those trends in the last decade while working on India’s first National Communication (NATCOM) to the United Nations Framework Convention on Climate Change. Models had shown that hilly areas like the states of Himachal Pradesh and Arunachal Pradesh would emerge as regions where transmission windows for malaria would open up.

Initial results showed that Himachal Pradesh, where the average altitude is above 1,800 metres, might become malaria-prone under the changed climate conditions by 2050s. Subsequent research showed that invasion by the mosquito would happen faster as transmission windows would increase in Hamirpur, Kangra, Sirmaur and Una by 2030.

“But when it comes to climate change, health is a low priority area. Our focus is on agriculture and water management,” points out a Himachal government official.

(The story is being published as part of GIZ-CMS Media Fellowship)

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