Dengue is a viral disease, transmitted by the infective bite of a particular mosquito known as Aedes Aegypti. Human being develops disease after 5 – 6 days of being bitten by an infective mosquito. It occurs in two forms: Classical Dengue fever also known as “break bone” fever and Dengue Haemorrhagic Fever (DHF) which is life threatening. It is very common after rainy season. It is highly contagious and spreads from one person to another through mosquito bites. It is widespread in tropical and sub-tropical regions.
It is a very common disease in India since last two decades. Dengue can affect everybody, irrespective of their age and gender. However, deaths are common amongst children during DHF outbreak.
The disease is endemic in more than 100 countries in the WHO regions of Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific. The America, South-East Asia and Western Pacific regions are the most seriously affected.
In the year 2015, According to National Vector Borne Disease Control Programme (NVBDCP) maximum numbers of cases were reported from Delhi followed by Punjab, Haryana, West Bengal, Gujarat , Karnataka, Maharashtra, Kerala, Tamil Nadu, Rajasthan, Andhra Pradesh, Uttar Pradesh, Orissa, Madhya Pradesh, Arunachal Pradesh, Bihar, Uttarakhand, Telangana and other states.
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The content of this module has been validated by Prof. U. Datta, National Institute of Health & Family Welfare (NIHFW), on 28th November 2014.
Symptoms usually develop within 3-14 days after being exposed to the dengue virus (also known as incubation period). The average incubation period is around 4-7 days.
Symptoms of dengue are:
Dengue virus is an RNA virus. Transmission of this virus occurs in a cycle. An infected human is bitten by a female mosquito. The infected mosquito then bites another human, and the cycle continues.
Aedes aegypti mosquitoes most commonly bite at dusk and dawn, indoors, in shady areas, or when the weather is cloudy. They can bite and spread infection at any time of day and all year long.
The mosquitoes prefer to breed in areas of stagnant water, such as flower vases, uncovered barrels, buckets, water coolers and discarded tires. Some of the dangerous areas are wet floors and toilet tanks, as they allow the mosquitoes to breed in the residence.
Although the lifespan of an adult A. aegypti is two to four weeks depending on conditions, the eggs can be viable for over a year in dry state. This allows the mosquito to reappear after a cold winter or dry spell.
There are four serotypes of the virus that cause dengue (DEN-1, DEN-2, DEN-3 and DEN-4)
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A probable diagnosis is based on occurrence of fever along with some of the following symptoms.
The diagnosis also takes into account whether the suspected person lives in endemic (high prevalence) area.
Virus isolation - Cell culture is the most widely used method for dengue virus isolation
Nucleic acid detection- Reverse transcriptase-polymerase chain reaction (RT-PCR) assays offer better sensitivity compared to virus isolation. Dengue virus (Nucleic acid) can be detected in the blood about first 5 days after onset of symptoms.
Detection of antigen-NS1 antigen test (non-structural protein 1) -Dengue NS1 antigen test is useful in the diagnosis of dengue fever in the first week of the illness.
PRNT- Plaque Reduction and Neutralization Test (PRNT) and the microneutralization PRNT can be used to detect specific serotype of dengue virus.
Rapid diagnostic test: It is a method for specifically detecting anti-dengue IgG and IgM antibodies. The test can detect all four serotypes of dengue.
There is no specific medication for treatment of a dengue infection. Persons suspected of dengue can use analgesics (pain relievers) and avoid those containing aspirin. They should take plenty of fluids, rest and consult a physician at the earliest possible. If condition does not improve after 3-5 days, then one should seek further medical advice.
A person with dengue may develop a severe and life threatening form of dengue known as dengue shock syndrome. This may be accompanied by a sudden and severe drop in blood pressure. Other symptoms of dengue shock syndrome are as follows:
The patients may seek medical advice immediately.
There is no vaccine to prevent dengue yet. The best way to prevent getting the disease is to avoid being bitten by mosquito. Some of the preventive measures are as follows: