‘Warmer Kathmandu’ largely behind unprecedented dengue outbreak

Signs of increasing incidence of vector-borne disease underway, according to the experts

A dengue patient receiving treatment at Teku Hospital. Photo: Swasthyakhabar Files

Kamala Gurung

  • Read Time 4 min.

Kathmandu: In October, after suffering from a high fever along with fatigue, muscle pain, and a loss of appetite, a 40-year-old male resident of Kadaghari was diagnosed with dengue and was rushed to the hospital.

Similar is the experience of a 23-year-old youth residing in Kathmandu. He also reported symptoms such as a high fever accompanied by severe muscle pain, fatigue and loss of appetite. It took him almost a week to recover from dengue.

As of November 20, a total of 13,933 cases of the infection have been reported. With the number of cases escalating, dengue has now been considered as an endemic disease in Nepal, according to the World Health Organization. And, according to the experts, ‘warmer Kathmandu’ is to be blamed.

According to Dr Meghnath Dhimal, department chief at Nepal Health Research Council, with the growing population and unmanaged urbanization, the temperature has been rising, creating a fertile ground for mosquitoes to thrive. The increasing temperature of Kathmandu has led to a conducive atmosphere for the mosquitos to spread the tentacles much more comfortably than before.  

“We can feel that Kathmandu is getting warmer, temperatures are different these days. And there are other mismanagements leading to the dengue outbreak,” he noted. 

The prevalent practice of storing water for future use amid acute water shortage in the period of monsoon and early pre-monsoon, water seepage in potholes, tyres and balconies contribute to dengue endemic in Kathmandu, Dr Dhimal pointed out.

“When the temperature is suitable, they need other bases to survive and thrive. The mosquitoes that carry dengue love scattered tyres. With more vehicular movement in Kathmandu and increasing number of workshops for fixing automobiles parts including replacement of tyres, Kathmandu has become highly prone to dengue infection”, he elaborated.

Meanwhile, he also mentioned a research that showed a positive correlation between the incidence of dengue and certain meteorological factors like temperature, humidity, wind speed, air pressure and vegetation index. Rising temperatures, changing precipitation patterns and seasonal changes have exacerbated the threat of dengue as a vector-borne disease in cities like Kathmandu. “Increasing temperature facilitates the completion of the life cycle of this mosquito and the rate of infection also becomes high as temperature continues to be hot”, Dr Dhimal reiterated.

Sporadic dengue cases from 2004-2022

A closer analysis of the number of dengue cases each year during this period indicates the irregular pattern of change in the number of infections. While the number of cases was 3 in 2006, it rose to 4 in 2007, declined to 1 in 2011, increased to 7 in 2014 and declined again to 1 in 2015. Though cases continue to emerge and often exhibit a pattern of increment, this disease didn’t take the form of an epidemic until 2022. As a matter of fact, dengue spread in all seven provinces and 77 districts of Nepal this year. Among the most affected districts was Kathmandu. According to the statistics of the Ministry of Health and Population (MoHP), a total of 52,557 people have been affected by dengue since July this year, out of which 60 people have died.

The spread of dengue is attributed to infected female mosquitoes of species named Aedes aegypti which are available in urban and suburban settings with growing population density.  This viral infection that has spread to the hilly and mountainous region of Nepal was primarily only prevalent in the Terai region.

Dengue was detected for the first time in Nepal in 2004, some 18 years ago. Only one infection was reported that time. In the aftermath of this detection, dengue continues to aggravate its impact in the nation according to the statistics of the Epidemiology and Disease Control Division of the Ministry of Health and Population. While the total number of cases was less than 1000 until 2018, the number rose significantly later on.

According to the statistics of  MoHP, a total of 13,933 infected patients were from Kathmandu this year. This was followed by 9,555 in Lalitpur and 5,662 in Makwanpur. The onset of dengue infection detected from early January reached its tipping point in September.

“Kathmandu is an epidemic zone. Storage of water for a long time in balconies and nurseries, unmanaged sewage and storage of water on tyres are the main reasons for increasing dengue cases in the valley. All these factors contributed to a favorable environment for mosquito breeding”, says  Dr Chumanlal Das, Director at Epidemiology and Disease Control Division of MoHP

Growing urbanization, poor sanitation and hygiene, potholes around the residential area are also contributing factors for the rapid increment in dengue cases, he added.

Doctors on the frontline worried  

Dr Sher Bahadur Pun, a specialist doctor at Sukraraj Tropical and Infectious Disease Hospital, treats more than 150 patients everyday. Due to massive flow of patients and absence of adequate beds, his hospital has been treating patients in open space with a separate dengue clinic. According to Dr Pun, out of the patients, a maximum number of them are from Kathmandu. 

“Dengue outbreaks in one or two pocket areas in every Sep-Oct is not a new phenomenon in Nepal. But the outbreak started from the middle of the monsoon period this time”, added Dr Pun.

Mutation of the Aedes aegypti has added to the problem. According to Dr Pun, the mosquitoes that used to be active only during the day are now also seen during the night. 

Although an adult mosquito can only survive a temperature between 10 to 35 degree Celsius, the larvae of the mosquito can survive even in minus degrees.

With suitable temperatures and favorable environments, based on the recent trends, it is likely that the dengue outbreak will occur every two years.

However, with the temperatures of the valley dropping, the problem of dengue will gradually decrease. Due to extreme hot temperatures in Tarai, this time, dengue didn’t spread rapidly, according to Dr Dhimal. He also considers the problem of solid waste management an important factor for increasing dengue infection in the capital city.

The problem of vector-borne disease like dengue is not only observed in Nepal but also other Himalayan countries. Factors like altitude, temperature, rainfall and relative humidity have a greater role in spreading such diseases including Chikungunya.

There is a definite possibility of vector borne disease like dengue spreading in coming years, say virologists and public health experts. While the problem of climate change is growing, the government hasn’t taken any concrete measures for mitigating the spread of dengue.

An estimate of the World Health Organization shows that 70 percent of the total population living in Asia are at the risk of catching vector-borne disease like dengue. Globally, 100-400 million people are suffering from dengue infection annually, according to the WHO.