Nepal’s worst dengue outbreak was in 2022, when at least 88 were killed nationwide and 54,000 were diagnosed. In 2024, there were 10,000 cases in Kathmandu Valley alone, although the real figure was many times higher.

With heavier than usual pre-monsoon showers in April, public health experts warn that there could be another upsurge of the deadly mosquito-borne infection this year.

The first ever case of dengue in Nepal was reported in a traveler returning from India in 2004. But since then, dengue is locally transmitted and as the atmosphere warms the vector is moving up the mountains.

Dengue is spread by the daytime bite of the female of two species of mosquitos, the Aedes aegypti, and the Aedes albopictus. Researchers have found that A. albopictus in particular has adapted to colder conditions and is moving to higher elevations.

Warns virologist Sher Bahadur Pun at Sukraraj Tropical and Infectious Disease Hospital in Kathmandu: “If we go by past cycles, we are due for a major outbreak because it takes place every 2-3 years, and it could be the worst yet.”

There are four serotypes of dengue, and each consecutive infection by a different strain can be increasingly more severe. The same goes for outbreaks, Pun adds, and Kathmandu could face two more major outbreaks, possibly by 2030.

Infected Aedes mosquitos breed in stagnant water and hatch infected offspring. August-September during the monsoon is usually when dengue cases peak, and rain followed by sunshine is the ideal condition for the larvae to metamorphose into pupae and hatch.

“The longer the gap between dengue occurrences, the bigger the outbreak,” explains Sudeep Adhikari at the Oxford University Clinical Research Unit (OUCRU) Nepal office. “There are three scenarios: a new serotype that the population isn’t immune to yet, the same serotype for which the population has lost its immunity, and a mix of more than one serotype.”

Vaccines are now available and the WHO recommends them for children in high dengue burden areas, but they are not as effective as they do not equally prevent infections from all serotypes. In Nepal it is not yet available and the newer vaccines haven’t existed long enough to analyse their long-term effectiveness.

Prevention, therefore, is the best form of cure. Draining clear stagnant water in the city and in the home from drains, used tyres, flower pots, even bottle caps, will prevent mosquitos from breeding. People are advised to wear full-sleeve shirts, rub insect repellent on exposed skin, and use treated mosquito nets.

“If we don’t control mosquitos at the larvae stage and wait for the outbreak to deploy search and destroy mode, that is too late,” says Pun. “At most, we will manage to contain the spread in that specific area. But this is a daytime biter, and people going to school or work could be infected at any point.”

Despite rising temperatures and early rains, there is no sense of urgency at the public and government level. He laments: “We are all too busy with hardcore politics to care about public health. Local governments, especially, must immediately mobilise volunteers to clear stagnant pools of water before the outbreak hits.”

Many who are infected are asymptomatic, but can spread the virus through mosquito bites. The mortality rate among patients is low, but dengue is called break-bone fever because patients suffer unbearable pain in the joints and eyes, severe headache, and vomiting, which can only be managed but not treated.

“Because there is no treatment, people just go about their daily lives despite the infection, treating it like a common cold, further spreading the disease as well as aggravating their condition,” says Pun, who now calls the fever “walking dengue”.

Because regular dengue fever is extremely painful, it is often not easy to identify when an individual has progressed to severe haemorrhagic dengue. That is when dengue patients tend to crowd hospitals because of persistent and extreme symptoms, occupying beds for weeks at a time when there are other infections.

“There must be a public understanding of what constitutes a normal dengue case versus a severe case, and we have to upgrade hospital services to prepare for the dengue season,” says Adhikari.

He adds: “Ultimately, Nepalis are reactive and therein lies the problem. Preparedness is an on-going process, and public awareness is of paramount importance to actively identify stagnant bodies of water before an outbreak, not after.”

HOW TO PREVENT DENGUE:

Drain clear stagnant water in neighbourhood, wear full-sleeve shirts (especially mornings and evenings), rub insect repellent on exposed skin, use treated mosquito nets.