Dengue fever (pronounced deng-gay) is caused by an insect borne virus. Dengue virus is flavivirus, which are members of the Flaviviridae. The flaviviruses are all carried by biting insects such mosquitoes or ticks. The type virus of the flaviviruses is the yellow fever virus and the name flavivirus comes from the Latin “flavus” which means yellow. Flaviviruses are spherical RNA viruses between 40 nm and 60 nm in diameter.
There are four serologically different types of dengue virus Den 1, Den 2, Den 3 and Den 4. Infection with one of these will confer lifelong immunity to that virus but not to the others. For this reason, it is possible to catch dengue up to four times in a lifetime. Dengue fever is endemic in tropical and subtropical areas around the world
The insect vectors for dengue fever are the Aedes species mosquitoes most frequently A. aegypti although A. albopictus is also implicated as a vector. A person can only catch dengue when a mosquito, which has already bitten an infected person, bites them. Direct person-to-person infection does not occur with this virus.
Following a bite by a mosquito carrying the virus there is an incubation period of usually five to eight days. The incubation period has been known to be as short as three days or as long as fifteen days. The classic symptoms of dengue make up the dengue triad these are high fever (104°F, 44°C), rash and severe headache. The rash is a red petechial rash normally starting on the lower limbs before appearing over most of the body. The palms of the hands and the soles of the feet can appear very red and swollen. These symptoms are accompanied by arthralgia and myalgia (bone and muscle pains) of the lower back and limbs. These muscle pains can be very severe and have given dengue fever the name of “break-bone fever” as sufferers have likened the pain to that of breaking a bone. Other symptoms seen in dengue are lymphadenopathy, slow heartbeat (bradycardia) and low blood pressure (hypotension).
The symptoms normally last for between 1-2 weeks. After the first few days, a dengue patient will experience a drop on temperature and will feel as though they have recovered for a day before the symptoms return. This is known as a biphasic illness.
Treatment of dengue requires pain relief medication. The recommended drugs are codeine or acetaminophen (Tylenol™). Aspirin or non-steroidal anti-inflammatory drugs should not be used as they have an adverse effect on blood clotting, which can exacerbate dengue’s hemorrhagic tendencies. Rest and plenty of fluids to keep the patient hydrated will aid recovery. At present, there are no recommended antiviral drugs for the treatment of dengue. There is laboratory evidence that the anti-viral drugs mycophenolic acid and ribavirin may be useful in treating the disease. as yet, no controlled in-vivo study has been carried out to confirm this in human infections.
Normally dengue has a death rate of less than 1%. There is a more severe presentation of the disease known as dengue hemorrhagic fever (DHF) or dengue shock syndrome. This combines the symptoms of normal dengue fever with hemorrhagic symptoms such as gastrointestinal bleeding with blood in stools and the vomiting of blood. Patients may experience nosebleeds and bleeding from the gums. Respiratory symptoms such as sore throat or pneumonia are also seen in DHF. Patients frequently experience shock, which is shown as a weak but rapid pulse and cold clammy skin. DHF is more common in children and death rate of between 5-30 percent have been reported for the condition. DHF requires hospital treatment with intravenous fluid treatment for shock and sometimes blood transfusions to replace blood volume lost by hemorrhage.
At present, there is no vaccine available for dengue fever. A number of possible vaccines are undergoing clinical trials.
Control of dengue in endemic areas currently concentrates on the control of the vectors. Aedes species are daylight-biting mosquitoes with a peak of activity at dawn and dusk. Wearing long sleeved shirts and full-length pants rather than shorts will protect much of the skin from mosquito bites. The use of an insect repellant contain DEET will also protect an individual from bites. The mosquitoes are attracted to standing water so the elimination of possible sources of water by emptying water filled flowerpots or old tires is recommended. If rainwater is being stored, a covered water butt should be use to prevent the mosquitoes gaining access. Avoiding water sources such as rivers and ponds during the early morning or late evening can also protect persons from being bitten.
Inhibition of dengue virus replication by mycophenolic acid and ribavirin Ratree Takhampunya, Sukathida Ubol, Huo-Shu Houng, Craig E. Cameron and Radhakrishnan Padmanabhan Journal of General Virology (2006), 87, 1947–1952
Dengue Vaccine: The Current Status Maj MS Mustafa, Lt Col VK Agrawal