Now that summer is here, it may be useful to look at what our unfriendly mosquitoes are up to, especially in spreading dengue fever. Dengue emerged from Africa during the slave trade from the 15th through 19th century and spread into Asia through commercial exchanges in the 18th and 19th centuries. With the advent of increased travel and trade in the past 50 years, the global presence of dengue is now clear.
In recent years, dengue has been widespread in the Tarai regions especially during summers. Even in Kathmandu dengue has been seen in the occasional patient.
This spread is not surprising because of two reasons: a migrant population with the disease and an abundant supply of the particular vector (carrier) mosquitoes. Due to our porous border with India, many migrant labourers (both Nepalis and Indians) with the disease enter Nepal. The vector mosquito enjoys a blood meal from these infected patients and transmits the disease to a healthy person after a bite.
Importantly, different species of mosquitoes transmit different diseases. So the mosquito that transmits malaria will not transmit dengue. Mosquitoes that transmit dengue are called aedes, whereas it is the female anopheles which transmits malaria. The other important vector (culex mosquito) transmits Japanese encephalitis.
The diagnosis of dengue should be strongly considered in any patient presenting fever that has developed within 14 days of even a brief trip to dengue-endemic places like Bangkok and Delhi. The dengue mosquito is generally a city dweller, unlike the malaria mosquito which prefers a rural environment.
In most patients, dengue illness, which comprises of fever, headache, eye pain and joint aches, subsides in about a week's time. Doctors will treat only the symptoms in dengue as there is no specific antidote.
There is, however, good news. It was believed that a second dengue infection predisposes patients to dengue haemorrhagic fever, the dreaded form of dengue; but this does not seem to be true.
For prevention, use mosquito repellents like (odomas or DEET) and wear full length clothing even during the day as dengue mosquito is a day time insect unlike the malaria mosquito which is active at night. In addition, turn over watering cans and pails after use so that the dengue mosquito does not breed in them.
As with many viral illnesses, it is hard to predict how severely the population will be affected this summer. However, it is clearly a good idea to take precautions and avoid mosquito bites.