Dengue fever is a disease of the tropics and subtropics with approximately 400 million people affected each year. It is caused by any one of the four related viruses transmitted by day- biting aedes mosquitoes. It is a common illness in many Asian countries and came to Nepal in a big way in 2010 with subsequent smaller outbreaks, with the 2016 outbreak confined mainly to Chitwan and Jhapa. The aedes mosquitoes carrying dengue are mostly confined to urban areas where they breed in the relatively clean water found in storage jars, discarded tyres and tin cans. Because the mosquitoes bite during the day (especially late afternoon) as well as the night it makes it hard to avoid exposure. Once bitten by an infective mosquito a person will become sick within two to eight days.
The disease is characterized by sudden onset of high fever, pain behind the eyes, headache, backache, joint and muscle pains. It is often accompanied by a rash that looks like a red flush on the back, chest and abdomen. Fever returns to normal within a week. In a traveler arriving from an area where dengue is a problem who develops fever and headache within a few days of arrival, dengue fever should be suspected. However, because dengue often exists in countries where other fever causing illnesses are present (malaria, typhoid), it is important to rule out other illnesses as well. No specific treatment is available and spontaneous recovery is the rule.
The most important aspect of prevention is to avoid being bitten by mosquitoes, by covering up where practical, and by the use of insect repellent DEET in 30% strength. Staying inside screened/air conditioned accommodation is an effective way to avoid being bitten by mosquitoes. The first Dengue fever vaccine (Dengvaxia) that has been in licensed for use in 19 countries around the world from 2015, has been found to cause severe disease in persons who have no prior immunity to dengue. WHO has recommended that it only be used after confirming prior dengue infection in individuals.
There are regular dengue epidemics in India, Sri Lanka, Thailand, Malaysia, Singapore, and Indonesia that are popular travel destinations. Nepal is no longer an exception but risk appears to be lower in Nepal. In SE Asia, dengue is transmitted all year round, but occurs mainly during the summer wet months and post- monsoon. In India, dengue fever shows a marked seasonal pattern, with most travelers becoming exposed during late September and October after the seasonal rains have stopped.
Dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS).
These are complications of dengue fever that are mostly confined to the people that live in an area where dengue fever is a problem, causing death mainly to indigenous population. With the increasing incidence of dengue worldwide due to urbanization and failure of mosquito eradication campaigns, it is likely that these complications may become more common in the increasing number of travelers to dengue endemic countries. DHF is characterized by persistent vomiting, severe abdominal pain, leaky blood vessels causing fluid leakage inside the abdomen and pleural space as well as bleeding complications and low platelets. These patients require immediate hospitalization and supportive treatment.