Over the past few weeks, thousands of Nepalis have been infected with the dengue virus. Dharan Sub-Metropolitan City has been identified as the epicentre of the current 2023 dengue outbreak. The virus is spreading at an explosive rate to other parts of the country. Observers are curious to see whether this outbreak will hit the capital Kathmandu too, as it did in 2019. Nepal witnessed a series of big dengue outbreaks in 2019 and again in 2022. Deaths attributed to dengue complications have been increasing with every successive outbreak (0.03 percent in 2019 and 0.16 percent in 2022), which means the dengue virus is becoming deadlier.

Dengue is a viral infection transmitted by the bite of infected mosquitoes, known as the Aedes mosquito. Aegypti and Albopictus are well established Aedes mosquitoes in Nepal and are mainly active during the monsoon and the post-monsoon season. Aedes mosquitoes are active even in the pre-monsoon season if there is a favourable environment. In 2019, a dengue outbreak started in Dharan before the monsoon season had entered Nepal.

Number of deaths

Symptoms of the dengue virus develop four to 10 days after being bitten by an infected mosquito. Febrile, critical and recovery phases are the natural course of the dengue illness. The febrile phase includes sudden high-grade fever, pain behind the eyes, feeling like the eyeballs are dropping, severe joint and lower back pain, calf muscle pain, trouble falling asleep, loose motion, rashes, nausea or vomiting. Symptoms of this phase were exclusively seen during the 2019 outbreak in Kathmandu.

The 2022 dengue outbreak was found to be severe and more fatal. Dozens of patients lost consciousness during their hospital visits, and several others had a history of becoming unconscious or collapsing at their own homes. This indicates that many patients were in the critical phase during the 2022 dengue outbreak. As a result, the number of deaths was nearly 15 times higher in 2022 (88 deaths) than in 2019 (six deaths). According to the Epidemiology and Disease Control Division, a total of 7,253 dengue cases had been detected in various parts of the country and 13 deaths had been reported (six of the dead had underlying health conditions) as of August 3. This translates into a dengue death rate of 0.17 percent, which is similar to last year.

It should be noted that the current outbreak is just the beginning and is expected to continue for several weeks and or even months. It is worth mentioning that the 2019 dengue outbreak was observed for at least more than six months. Thus, it can be assumed that more severe and fatal cases are expected in the coming days.

It is reasonable to think if dengue is becoming a more fatal virus in Nepal. Last year, Kathmandu witnessed one of the worst dengue outbreaks of all time in Nepal, and it is believed that it happened due to a change in the serotype of the dengue virus. A study conducted in Kathmandu and published in the journal Transactions of the Royal Society of Tropical Medicine and Hygiene in 2021 showed that DEN-2 was the major serotype behind the 2019 dengue outbreak in Dharan and Kathmandu.

Dengue has four distinct serotypes known as DEN-1, DEN-2, DEN-3 and DEN-4, and all serotypes have been reported in Nepal previously. As per some media reports, DEN-2 is mainly responsible for the current dengue outbreak in Dharan while other media reports pointed to DEN-3. It seems that multi-serotypes are circulating and are responsible for the ongoing outbreak in Dharan, and it could even be spreading to other parts of the country. We must bear in mind that those who are re-infected with a different serotype during this outbreak will possibly become very sick or face the risk of developing complications. Several studies have pointed out that the DEN-2 serotype is associated with severe disease or complications compared to other serotypes. However, we did not observe more severe dengue cases during the 2019 outbreak (when the major causative agent was DEN-2) compared to the 2022 outbreak. In fact, DEN-1 was found to be the main causative serotype of the 2022 outbreak which emerged as a fatal serotype in Kathmandu. Severe dengue complications associated with specific genetic variants in certain populations can be another possible explanation, as shown by several studies.

Self-medication habit

One of the reasons behind developing severe dengue is the behaviour of self-medication. During the 2022 dengue outbreak in Kathmandu, I saw several patients who had developed sub-conjunctival haemorrhage (bleeding in the eyes) after taking non-steroidal anti-inflammatory drugs (like Flexon, Brucet or aspirin). Paracetamol is a recommended drug to use to suppress pain after contracting the dengue virus. Since the pain is extremely severe, paracetamol may not be sufficient, so people usually take medicines such as Flexon, Brucet or aspirin, which leads to severe complications. In some cases, patients are compelled to take such medicines due to a shortage of paracetamol in the market.

The series of outbreaks shows that the dengue virus is becoming more severe and even fatal in Nepal. However, solid scientific evidence for this is yet to be known. At present, a safe and effective vaccine against the dengue virus is not widely available, and more fatal dengue outbreaks are inevitable in the coming years. Thus, larvae destruction campaigns and awareness programmes remain the best way to prevent future outbreaks.