Prof. Dr. Shyam P Lohani

Dengue is one of the neglected tropical diseases that largely affects low-income communities on all the continents. This disease is expected to put a tremendous burden on the already overstretched healthcare systems in developing countries like Nepal. Dengue fever is a mosquito-borne tropical disease inflicted by Dengue virus. It is a single positive-stranded RNA virus of the family Flaviviridae and genus Flavivirus. Four serotypes (DENV 1, DENV 2, DENV 3, DENV 4) of the virus have been found, all of which can cause the full spectrum of disease. The earliest outbreaks have been recorded in 1779 and its viral cause and spread were understood only at the beginning of the 20th century (Wikipedia, 2019).

Outbreak
The total of around 40 per cent of the world’s population (about 3 billion people) is living in the areas with a risk of Dengue (CDC, 2019). In 1970, dengue was epidemic to only nine countries but now, it is endemic to more than 125 tropical countries in the world. Every year up to 400 million people are infected with dengue, out of which, around 100 million develop dengue fever and about 22,000 die of dengue (CDC, 2019).
The first case of dengue was detected in Nepal in 1999 and since then sporadic cases and outbreaks have occurred. Initially, those cases had travel history of a neighbouring country, however, in recent times, they are of indigenous origin. Several studies have confirmed all serotypes of dengue in Nepal. Female mosquitos mainly, Aedes aegypti and, to a lesser extent, Aedes albopictus transmit dengue virus. However, it cannot be transmitted from one person to another person. The same mosquitos are responsible for chikungunya, yellow fever, and Zika infection. This year, about 5,000 cases with six deaths have been confirmed since the outbreaks of dengue in Nepal.
The symptoms usually start in four to six days and may last for 10 days. People infected with dengue virus may have symptoms such as high fever, severe headache, pain behind the eyes, severe muscle and joint pain, fatigue, nausea, vomiting, skin rash developing two to five days following fever, and mild bleeding such as nose bleeding, bleeding gums and easy bruise. The symptoms of dengue fever are often mistaken with that of flu or other viral infections.
The people who never had dengue in the past and younger children are likely to have milder cases than older children and adults. The people with weakened immune symptoms are more likely to develop Dengue Hemorrhagic Fever (DHF). The Dengue Hemorrhagic Fever is characterised by high fever, damage to lymph and blood vessels, bleeding from nose and gums, enlargement of liver and failure of the circulatory system. These symptoms further develop into massive bleeding, shock, and death called Dengue Shock Syndromes (DSS).
It is important to keep in mind that only about 25 per cent of people infected with dengue virus develop dengue fever and among them only about 10 per cent develop severe symptoms. Since the large majority of people infected with dengue virus do not develop dengue fever, therefore, cases are often underreported and/or misclassified to other viral infections. The incidence of dengue cases has increased considerably in recent times and corresponding numbers of dengue fever and DSS among those infected. The epidemiological patterns show hyper endemicity of different serotypes of dengue virus in many countries with enormous consequences to public health and the country’s economy (WHO, 2019).
The diagnosis of dengue fever can usually be made with clinical symptoms by the healthcare professionals and can be confirmed in the laboratory with Rapid Diagnostic Test Kits (RDT), however enzyme-linked immunosorbent assays (ELISAs) have greater sensitivity. Once diagnosed, the infected person should not take antipyretics (fever medications) that are potential to complicate bleeding such as aspirin, and ibuprofen. For fever, however, paracetamol is found to be safe. In mild dengue cases, symptoms are self-limiting and do not need hospitalisation but they should be under close monitoring of healthcare providers, take plenty of fluids and have complete rest. There is no cure for dengue, its treatment is often symptomatic and supportive. The use of antibiotics in dengue is not useful thus irrational.
The growing effect of climate change, less knowledge on prevention among general population mingled with unplanned urbanisation, people’s movement with easy transportation, lack of sanitation, irregular garbage collection, insufficient surveillance system, and ineffective vector control may result in more extensive outbreaks throughout the world, including in Nepal in the coming days. Having said many factors responsible for the spread of dengue, the most important is to control vector or prevent bites from mosquitos in tropical areas. The dengue virus, Aedes aegypti bites from early in the morning to the evening before dusk. Therefore, sleeping under the mosquito nets in the night time will have little prevention from dengue. Fogging in public places with the use of pesticide is not effective for controlling dengue vectors rather it causes immediate health effects to the public. Unfortunately, there is no vaccine against dengue virus.

Preventive measures
The preventive measures such as wearing a long-sleeved shirt, long pair of pants and socks when outdoors, use of mosquito repellent creams containing 20-30 per cent DEET or 20 per cent picaridin, securing doors and windows with nets, staying away from standing water and use of mosquito nets should be practiced. For the control of vectors, we should get rid of places where mosquitos can breed including old tires, cans or flower pots that retain water. The government should involve local communities for sustained vector control endeavours in Nepal. It is equally important to carry out nationwide extensive awareness campaign to make general people aware of dengue and vector control measures inside their home and surroundings.

(Prof. Lohani is the Clinical Director of the Nepal Drug and Poison Information Centre and can be reached at lohanis@gmail.com)