Dengue (pronounced as “dengi”) fever is caused by flavivirus (there are four types of dengue virus, dengue 1-4 and all of these 4 types cause similar clinical symptoms). There may be sporadic cases of dengue fever even in endemic areas and during epidemics. In endemic areas the dengue fever occurs throughout the year.

How dengue fever is transmitted?

The incubation period of dengue fever is 2-7 days. Dengue fever virus (flavivirus) is transmitted by mosquito bite, mainly Aedes aegypti mosquito (all 4 types of dengue virus). During summer the number of vector mosquito (Aedes aegypti) are most numerous and the spread is maximum. Large epidemics can occur during hot summer months. Aedes aegypti typically breeds near human habitation, using relatively fresh water which is accumulated in the water jars, vases, discarded containers, coconut husks, and old tires. Aedes aegypti generally dwells and bites during the day time. Favorable conditions to dengue transmission exist in the southern United States also, and bursts of dengue fever activity can occur in the United States also, particularly along the Mexican border.

What is the epidemiology of dengue fever?

Dengue fever is prevalent in many tropics and subtropics, generally between latitudes 25°N and 25°S, but can occurs to as far north as Philadelphia in the United States. Dengue fever is prevalent in the Caribbean region (including Puerto Rico), Mexico and its neighboring countries, Indian subcontinent, South East Asia (Indonesia, Malaysia, Myanmar, Thailand, Vietnam, Philippines, Cambodia etc.) and south western Pacific. Large areas of the world (especially tropics and subtropical areas which do not have dengue fever prevelence) have become vulnerable to the introduction of dengue viruses (by air travel of infected humans) and both dengue fever and the dengue hemorrhagic fever are becoming increasingly common due to increasing spread of the vector mosquito throughout the tropics and subtropics.

Can immunity develop against dengue fever?

A single attack of dengue fever can give protection for about 9 months. After several attacks a degree of immunity is attained, which can be termed as “permanent” immunity against dengue fever virus. Some cross immunity also exists between dengue and other similar arboviruses (flavivirus) like yellow fever virus.

What are the clinical features of dengue?

The severity of disease varies in different individuals and can range from subclinical infection to severe form of disease leading to death. Clinical features of dengue generally start as headache and malaise (vague feeling of discomfort). Fever is a prominent symptom of dengue fever, which can be continuous or ‘saddle back’ with a break in fever on 4^th or 5^th day. Dengue fever can occur as acute illness with anorexia, nausea, vomiting, fever, generalized body pain, backache, painful red eyes, tearing in the eyes, depression, lymphadinopathy, low heart rate despite fever (generally there is increase in pulse rate in fever). There may be skin rash which are present on the dorsal aspect (back of hand and upper surface of feet) of hands and/or feet and spread centripetally (moves towards a center).

What is dengue hemorrhagic fever?

Dengue hemorrhagic fever (also known as dengue shock syndrome) is very severe form of dengue fever with bleeding which starts after 3 -4 days of fever. Bleeding generally is accompanied by petechiae (minute red spot due to presence of blood which has escaped), ecchymosis (a hemorrhagic spot smaller than petechiae), melena (dark color stool due to presence of blood), epistaxix (nosebleed) etc. and can lead to circulatory failure and death. Dengue hemorrhagic fever is seen only in South East Asia and very rarely in other areas. Bleeding and other complication are thought to be due to hypersensitivity to the dengue virus. Hypersensitivity to the dengue virus causes compliment activation and disseminated intravascular coagulation and bleeding. Even with proper treatment the case fatality is approximately 10%.

How to diagnose dengue fever?

Diagnosis of dengue fever is generally easy in endemic areas and during epidemics due to the typical symptoms and characteristic signs of dengue fever. But if the cases are mild, they may look like other viral disease.

Laboratory diagnosis of dengue fever is done by IgM ELISA (enzyme linked immunosorbant assay), paired serology during recovery or by antigen-detection ELISA during the acute phase. There is also leucopenia (lees number of leukocytes or white blood cells, generally less than 5,000) and thrombocytopenia (reduced number of platelets in circulating blood). Dengue virus also can be easily isolated from blood in the acute phase by using mosquito inoculation or mosquito cell culture.

How dengue fever is treated?

There is no specific treatment for dengue fever and treatment of dengue fever is essentially symptomatic. The pain (even severe pain) and fever can be reduced by paracetamol and only rarely opiates are required to relieve severe pain. In case of dengue hemorrhagic fever maintenance of electrolyte balance by fluid replacement, blood transfusion if necessary and corticosteroids are generally required for treatment.

How to prevent dengue fever?

Dengue fever is spread by mosquitoes (Aedes aegypti mosquito), and controlling this mosquito is very important in preventing dengue fever. Breeding places of Aedes aegypti mosquito should be abolished and the adult mosquitoes destroyed by use of insecticide. To prevent spread of dengue fever through mosquito bite, the patients should be nursed under a mosquito net.