In temperate Nepal, climate change paves way for tropical dengue fever - Mongabay.com
- Nepal is experiencing its worst outbreak of dengue fever in recorded history, which health experts attribute in part to a changing climate.
- Wetter monsoons and warmer temperatures have made for ideal breeding conditions for the mosquitoes that carry the virus.
- Poor water and waste management are also factors, allowing for water to stagnate for long periods and giving the mosquitoes a place to lay their larvae.
- Experts say it will take a combination of personal responsibility — to eradicate mosquito-breeding grounds — and government leadership — to coordinate the public health response — if dengue is to be eradicated in Nepal.
KATHMANDU — Hindus in Nepal marked Tihar this past week, the festival of lights that takes place at the same time as the better-known holy day of Deepavali. But for Richa Sharma, a 38-year-old resident of Kathmandu, there was no celebrating; she was bedridden for the past week.
The combination of high fever, body aches and burning eyes left her hardly able to speak, she told Mongabay, "let alone sleep."
As of Oct. 21, Sharma was one of the 43,685 people (and counting) in Nepal who have been diagnosed with dengue fever, transmitted by mosquitoes and also known as breakbone disease, because of the muscle spasms and joint pains that it induces. Nearly three-fifths, or 25,182, of the cases have been reported in the Kathmandu Valley; 52 people have already died due to the disease.
"Dengue is everywhere in Kathmandu," said Rajendra Pokhrel, another city resident. "It's like COVID-19. Everyone knows at least two, three friends or family members who have been infected by the disease."
Nepal is experiencing its worst dengue outbreak in history, according to the World Health Organization. The last large-scale outbreak of the disease was reported in 2019, when 17,992 cases were recorded nationwide, according to figures from the government's Epidemiology and Disease Control Division. In 2021, there were just 540 cases.
For epidemiologists, policymakers, and affected residents, the outbreak has raised a key question: Why is Nepal, a country at the foot of the Himalayas, currently in the grip of what's long been considered a tropical disease?
Various studies, some of them commissioned by the government, show that environmental mismanagement, aggravated by climate change, is to blame for the outbreak of the disease, first reported in a traveler returning from India in 2004.
The WHO says dengue cases, first reported in the southern plains, where the conditions for dengue-bearing Aedes mosquitoes to breed are ideal, are increasingly being reported at higher elevations. It attributes this to factors that may include climate change.
"The dengue vector [mosquito] requires at least 10-12° Celsius [50-53.6° Fahrenheit] to survive," said Meghnath Dhimal, chief environmental health researcher at the Nepal Health Research Council (NHRC). "Due to climate change, the number of cold nights in winter is declining and the temperature doesn't fall much below the 10-12°C mark.
"We have also seen that in the past, when mosquitoes reached higher altitudes, they would die," he added. "But now they are surviving and breeding even at altitudes of 2,100 meters [6,900 feet]."
A 2009 report coordinated by Dhimal and prepared by the NHRC and the WHO noted that as population pressure increases in the country's urban areas, unplanned settlements expand without adequate infrastructure related to the management of water and solid waste. This, it warned, could trigger the spread of waterborne and vector diseases such as dengue.
"The environmental factors triggering the spread of vector-borne diseases such as dengue are mainly related to water and waste management, and have long been overlooked in Nepal's urban areas," Dhimal said. "Things haven't improved a lot since the publication of the report 12 years ago when we didn't have a large outbreak of the disease."
As pointed out by the report, the urban poor still live in areas with dark and damp rooms in buildings with leaking pipelines. Many residents are still forced to store drinking water in plastic and tin buckets, which are usually uncovered, as piped water supplies are erratic. These vessels make ideal breeding grounds for mosquitoes that carry the dengue virus.
Similarly, cities across Nepal face routine disruptions in solid waste management, leaving piles of solid waste unattended for long near human settlements, which then become breeding grounds for mosquitoes.
In addition to this, many roads in cities such as Kathmandu feature inadequate drainage and are infamous for their potholes, where water remains stagnant for a long time, again providing refuge for mosquitoes. Broken-down cars parked haphazardly are another repository of stagnant water.
"To add to that, this year's pre-monsoon and monsoon seasons were wetter than normal," Dhimal said. "Wet weather has been associated with an increment in dengue vector transmission."
Reshma Tuladhar, associate professor of microbiology at Tribhuvan University in Kathmandu, said that what makes dengue particularly dangerous is a phenomenon called antibody-dependent enhancement.
"When a person is infected with dengue, he or she develops antibodies against the virus," she said. "The antibodies help fight the infection next time, but only if the virus is of the same serotype."
In Nepal, however, there are currently four different dengue serotypes known to be circulating. If a person with antibodies for one of them is infected again with a virus of a different serotype, the antibodies will facilitate the entry of the virus into the cells, rather than fight them, she said.
Tuladhar said officials tend to focus on mosquito control only when dengue cases spike. But action needs to be taken well in advance, especially as the temperatures peak in the summer and the monsoon rains start, she said.
Dhimal said every citizen must take responsibility for searching for and destroying mosquito larvae, if dengue is to be eradicated. "We should not count on the government to come to our houses and look for mosquito larvae," he said. "Each of us should do that on our own."
But he added the government, too, has a key role to play. "It seems that the government hasn't learned from the COVID-19 pandemic," he said. "It showed that the municipal, provincial and central governments need to coordinate efforts to deal with public health issues, especially related to sanitation and use of water."
At her home in Kathmandu, Sharma said she hopes to recover soon and get back to work. "I hope Kathmandu has learned its lesson this year, and we don't take the disease lightly," she said, "especially during the next monsoon."
Banner image: People queue up for water in Kathmandu, where a water crisis forces people to store water in containers that provide refuge to dengue-transmitting mosquitoes. Image by Wayan Vota via Flickr (CC BY 2.0)
Citation:
Dhimal, M., Thakur, A. K., Shrestha, S. M., Banerjee, M. K., & Bhattarai, L. (2009). Environmental conditions associated with vector of dengue and corrective actions for its prevention in Nepal. Nepal Health Research Council. Retrieved from: https://nhrc.gov.np/wp-content/uploads/2017/02/Dengue-Report.pdf
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