What is dengue fever?
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.
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:
- Sudden-onset fever
- Headache (typically located behind the eyes)
- Muscle and joint pain
- Chills (shivering)
- Facial flushing
- Loss of appetite
- Sore throat
- Abnormal bleeding such as nosebleeds, bleeding gums and/or blood in your urine.
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)
Some facts about Ades mosquito-
- Ae. aegypti is closely associated with human environments and can breed in indoor (flower vases, concrete water tanks in bathrooms), and artificial outdoor (vehicle tyres, water storage vessels, discarded containers) environments.
- The eggs can survive up to 1 year without water. Once water is available (even small quantities of standing water), the eggs develop into larvae and then adult mosquitoes.
- Aedes mosquitoes are active during daylight hours, and usually bite during the morning and late afternoon/evening hours.
- Female Aedes mosquito acquires the virus while feeding on the blood of an infected person.
- Female Aedes mosquito usually flies an average of 400 metres. But it may be transported accidently by humans from one place to another (e.g. in the back of the car, plants).
A probable diagnosis is based on occurrence of fever along with some of the following symptoms.
- Nausea and vomiting
- Generalized pain
The diagnosis also takes into account whether the suspected person lives in endemic (high prevalence) area.
- Microscopic examination: This is done in order to detect dengue. The earliest change detectable is a low white blood cell count which may then be followed by low platelets and metabolic acidosis.
- Haematocrit -Haemoconcentration, as estimated by an increase in haematocrit of 20% or more compared with convalescent values, is suggestive of hypovolaemia due to vascular permeability and plasma leakage.
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.
- MAC-ELISA –IgM antibody capture enzyme-linked immunosorbent assay (MAC- ELISA) can be used for detection of IgM antibody five days or more after the onset of fever. According to WHO ELISAs performed better than rapid tests.
- IgG ELISA– the IgG ELISA is used for the detection of recent (if paired sera are collected within the correct time interval) or past dengue infections. A fourfold or greater increase in IgG antibodies in acute and convalescent paired sera can be used to detect recent infections. These tests are not in wide use.
PRNT- Plaque Reduction and Neutralization Test (PRNT) and the microneutralization PRNT can be used to detect specific serotype of dengue virus.
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:
- Cold, clammy skin
- A weak rapid pulse
- Dry mouth
- Reduced flow of urine
- Fast breathing
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:
- Use insect repellents and mosquito nets to avoid being bitten. Bodies could be protected from mosquito bite by applying insect repellent (containing DEET) on the clothes and exposed part of the body especially when you travel to Dengue Fever endemic areas.
- Wear long-sleeved clothes and long trousers while going outdoors.
- The best preventive measure for residents living in areas infested with Aedes aegypti is to clean the places where the mosquito lays their eggs, primarily artificial containers that store water. Items that collect rainwater or are used to store water (for example, plastic containers, drums, buckets, or used automobile tires) should be cleaned or discarded. Pet watering containers and flower vases should be emptied and scrub dried at least once a week. This will eliminate the mosquito eggs, larvae and reduce the number of mosquitoes present in these areas.
- The risk of being bitten by mosquitoes can also be reduced by screening the windows and doors.
- Patient should stay under bed net or in a place with intact window/door screens to prevent Aedes mosquito bites during first week of illness. This will prevent further spread of dengue to other persons.
- Cover water containers tightly so that mosquitoes can’t get in to lay eggs.
- In cultivation ponds, water tanks or large containers, biological controls such larvivorous fishes (gambusia/guppy) and biological larvicides (Bacillus thuringiensis) would be a good option.
- Chemical larvicide such as Temephos can be safely used in potable water.
- Pesticide spraying or “fogging” can also be effective.