What Is Dengue Fever?
Dengue fever is a mosquito-borne tropical disease caused by the dengue virus.
The dengue virus is spread mainly by the female Aedes aegypti mosquito. The virus has five serotypes and infection with one type gives lifelong immunity to that type, but only short-term immunity to the other types.
Dengue fever virus (DENV) is an RNA virus of the family Flaviviridae; genus Flavivirus which also includes viruses such as:
- yellow fever virus
- West Nile virus
- Zika virus
- St. Louis encephalitis virus
- Japanese encephalitis virus
- tick-borne encephalitis virus
- Kyasanur forest disease virus
- Omsk hemorrhagic fever virus.
Though likely discovered as far back as the 16th century, its viral cause and spread were understood at the beginning of the 20th century, and it has since been declared a global problem since the Second World War. Dengue is common in more than 120 countries, mainly in Southeast Asia, South Asia and South America. The annual global tally of people infected by dengue stands at roughly 400 million, with half a million requiring hospitalisation, and approximately 40,000 dying.
Symptoms of dengue fever
Symptoms of dengue fever typically begin three to fourteen days after infection and these include:
- high fever
- muscle and joint pain
- a characteristic skin rash
Complications due to dengue include:
- low levels of blood platelets
- dangerously low blood pressure
In a small number of cases, dengue fever develops into a more severe dengue hemorrhagic fever which results in bleeding, low levels of blood platelets and blood plasma leakage. In some cases it develops into dengue shock syndrome, which is caused by dangerously low blood pressure.
Prevention and control of dengue
An approved vaccine for dengue fever is commercially available in many countries, though it is generally recommended in individuals who have been previously infected. Other preventive methods include:
- Preventing breeding of mosquitoes by:
- identifying mosquito breeding grounds and spraying them with insecticide.
- burying empty containers and draining pools of stagnant water where mosquitoes might breed.
- Killing adult mosquitoes by spraying with insecticide.
- Preventing mosquito bites by:
- using mosquito nets.
- using insect repellents.
- wearing long sleeved shirts and long trousers especially in the evenings.
Treatment of dengue fever
- For mild to moderate cases treatment of dengue includes giving fluid to the patient either by mouth or intravenously.
- For more severe cases, blood transfusion is usually required.
- Paracetamol is recommended instead of nonsteroidal anti-inflammatory drugs (NSAIDs) for fever reduction and pain relief in dengue due to an increased risk of bleeding from NSAID use.
Life cycle of the dengue virus
Humans and other nonhuman primates are hosts of the virus, can be infected via a single bite from a female infected mosquito. If the bitten person is infected with dengue fever, the mosquito takes a blood meal containing the virus and during the initial 2- to 10-day febrile period, the mosquito itself becomes infected with the virus. Approximately 8–10 days later, the virus spreads to the mosquito’s salivary glands and is subsequently released into its saliva. The virus seems to have no effect on the mosquito and the mosquito remains infected for life.
- The mosquito bite then introduces the dengue virus from the mosquito’s saliva into a person’s blood.
- The virus enters the white blood cells, and reproduces inside the cells as the cells move throughout the body.
- As a result of the virus entering them, the white blood cells respond by producing several signaling proteins, such as cytokines and interferons, which are responsible for many of the symptoms, such as the fever, the flu-like symptoms, and the severe pains.
- In severe cases, many more organs such as the liver and the bone marrow can be affected and fluid from the bloodstream leaks through the wall of small blood vessels into body cavities due to capillary permeability. This results in less blood circulating in the blood vessels, and the blood pressure becomes too low to supply sufficient blood to vital organs.
- dysfunction of the bone marrow due to infection of the stromal cells leads to reduced numbers of platelets, which are necessary for effective blood clotting; this increases the risk of bleeding, the other major complication of dengue fever.