What is dengue?
- Dengue is a viral infection transmitted by the bite of a mosquito, which acts as a vector for this fever
- Several species of mosquitoes from the Aedes type, mainly Aedes aegypti, is the cause of infection
- The virus causing dengue belong to the Flaviviridae family and have an RNA strand as their genetic makeup
- Four distinct serotypes of the virus, are present:
- Dengue is often called as breakbone fever
- Severe forms of this disease can cause dengue shock syndromes and dengue hemorrhagic fever (DHF)
- The fever has flu-like symptoms that affect infants, young children and adults
- No specific treatment has been found for dengue fever
- Fever can be potentially lethal, but early diagnosis and careful management by experienced health care professionals can help to save lives
- 2.5 billion people or 40% of the worldwide population live in risk of dengue transmission
- 70% of the occurrence of this disease, is concentrated in South-East Asia and Western Pacific
- There has been a recent increase in dengue cases globally. This has been mainly due to factors like:
- Movement of people and goods
- Favorable climatic conditions
- Lack of trained staff
- Prevention of this disease is the most important step and mainly includes avoiding mosquito bites
How is the dengue virus transmitted?
- Primarily Aedes mosquitoes or A. aegypti is the cause of dengue transmission
- Other species of mosquitoes that help in transmitting this disease, are:
- A. albopictus
- A. polynesiensis
- A. scutellaris
- The mosquitoes usually live in between the latitudes of 35° North and 35° South, below an elevation of 1000 meters
- Usually, they bite during early morning and in the evening. But they may spread infection, throughout the day
- Humans are the main hosts of the virus, but it can circulate in primates (like apes and monkeys) too
- Infection can be caused by a single bite
- Cycle of Transmission:
- A female mosquito takes in the blood of a dengue-infected person and becomes a dengue vector (a carrier of disease)
- In the initial 2 to 10 days, the mosquito itself gets infected with the virus in its gut
- The virus spreads to all other tissues including the salivary glands, after a period of 8 to 10 days. Ultimately, the saliva is also infected.
- The mosquito itself, is not adversely affected due to the virus. It continues to be infected for life, which can span from three to four weeks.
- Aedes aegypti is especially known to spread fever, as it prefers to live in close proximity to human beings. It lays eggs in stored water containers and feed on humans rather than other vertebrates.
- The infected mosquito then transmits the virus to a person while feeding
- The saliva of the Aedes aeypti prevents the host's blood from clotting. So the infection transfers from the vector to the host.
- Four days after being bit by the mosquito, a person develops viremia (a condition where there is a large amount of dengue virus in the blood), which can last for five to twelve days.
- For the first four days of viremia, no symptoms can be seen. On the fifth day, the person develops signs of dengue fever.
- If an Aedes aegypti mosquito bites a person during the viremia stage of infection, that mosquito again becomes the carrier of the dengue virus
- In some rare cases, dengue might be transmitted in ways other than through mosquito bites. They are:
- During blood transfusions from infected donors
- Infected mothers might transmit it to their fetus
What is dengue shock syndrome?
- Dengue shock syndrome is a condition affecting children below the age of 10
It can cause:
- Abdominal pain
- Circulatory collapse (Shock)
- This syndrome is also referred to as dengue hemorrhagic fever (DHF)
- Fever starts with:
- High continuous fever
- Sore throat
- Abdominal pain
- After 2 to 6 days, there may be onset of shock:
- Sudden collapse
- Clammy hands and feet
- Weak pulse
- Circumoral cyanosis (blueness around the mouth)
- Bleeding and easy bruising
- Petechiae (blood spots in the skin)
- Hematemesis (spitting up blood)
- Melena (blood in the stool)
- Bleeding Gums
- Epistaxis (Nose bleeds)
- Heart muscle inflammation (Myocarditis)
- Mortality rate is 6 to 30%, most of them being children
- Dengue can be fatal for infants under the age of one
What are the causes of dengue?
- Dengue or breakbone fever, is spread by infected mosquitoes, primarily the Aedes aegypti and albopictus varieties
- Transmission occurs in a cycle: An infected human is bitten by a mosquito which then further bites some other human, and the cycle continues.
- The mosquitoes normally bite during the day, especially early morning or in the evening before dusk
- Pools of stagnant water often serve as breeding grounds for mosquitoes. Other places where mosquitoes multiply,
- Containers near buildings under construction
- Discarded human waste
- Old car tyres where water accumulates
- Major cities in developing countries have higher rates of dengue as they have poor sanitation
Who are the people at risk of contracting this disease?
People living in larger cities and towns in the developing world, have a higher probability of catching dengue.
Parts of the world where the virus is common are:
- South East Asia
- The Indian subcontinent
- South and Central America
- The Caribbean Islands
- The Pacific Islands
Is dengue fever contagious?
Dengue fever is not contagious, as it cannot spread directly from person to person contact. It can only be transmitted by a bite from an infected mosquito. As the fever is caused by a virus, antibiotics cannot help in its treatment.
What are the symptoms of dengue fever?
The symptoms of this disease can vary according to its severities:
How long does it take to display symptoms of dengue?
After being bitten by an infected mosquito, symptoms might take around two weeks to develop. Then it takes about a week to subside (refer question 7).
Can a person die of dengue fever?
Most people contracting this fever have no possibility of it turning fatal. But sometimes, complications might develop, like dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). In such cases, there is a probability of death. But, under experienced medical supervision, patients suffering from DHF and DSS can recover fully.
What are the tests recommended by a doctor to diagnose dengue?
Dengue fever testing determines whether a person displaying symptoms and recent exposure to dengue, has been infected. It is difficult to diagnose, as some symptoms resemble that of malaria.
Two types of tests available are:
What is the cost of dengue tests in India?
The rates for performing dengue tests can vary according to several factors. They are, the type of test, the city where the diagnosis is being performed and also, the type of hospital or test centre. To view a comprehensive list of the rates for dengue fever testing, from all over India, click here.
What does dengue IgG positive mean?
IgM and IgG tests are used to detect dengue antibodies. Positive IgM means that the person undergoing the test has suffered an infection recently. If IgG is positive, and IgM is negligible, then it signifies that the person had been infected by a mosquito in the past.(refer question 10)
What is ns1?
The NS1 antigen test, where NS1 stands for nonstructural protein 1, is the latest test for dengue which was introduced in 2001. Rapid diagnosis of the fever can be performed on the first day itself, even without the appearance of the antibodies in response to the infection. It was first introduced in India in 2010.
How long does it take to recover from dengue?
Most individuals infected with the disease, have a period of incubation from 10 to 14 days. After that, a week of severe symptoms follow along with a few days of recovery. In total, the fever does not last for more than two weeks.
What are the treatment methods for dengue fever?
Currently no medication has been found that can cure dengue. Treatment involves, only relieving the symptoms, as well as letting the infection run its course.
- Paracetamol can be used to relieve pain and fever. Aspirin, ibuprofen or nonsteroidal anti-inflammatory drugs (NSAIDs) are not recommended as internal bleeding can be triggered for people with dengue.
- Hydration is of prime importance and plenty of fluids should be taken at all times to maintain body fluid volume
- Plenty of bed rest is required
For severe forms of the fever
- Intravenous fluid supplementation (IV drip): Patients unable to take in fluids orally are required to take IV drips.
- Blood transfusion: Severe dehydration can be treated with this process.
- Hospitalization: It is important for medical professionals to monitor vital signs of a patient in case situations take a turn for the worse. Experienced heath care-providers can save lives, if complications arise due to the fever.
Is there a cure for dengue fever?
As dengue is caused by a virus, no specific medication or antibiotics can be used treat it. The only treatment is to treat the symptoms. Relieving the symptoms include taking plenty of rest and adequate hydration.
How can dengue fever be prevented?
The primary method to prevent transmission of dengue virus is to combat mosquitoes. This can be done by:
- Preventing mosquitoes to access environments conducive to breeding
- Proper solid waste disposal and removing man-made habitats
- Covering, changing and cleaning domestic water containers, weekly
- Using insecticides in outdoor water storage vessels
- Ensuring that households have:
- Coils and vapourizers
- Involving communities to participate in pest control (especially vectors)
- Spraying insecticides during outbreaks, for emergency control
- Wearing loose, full sleeved clothing to avoid skin exposure. Mosquitoes are able to bite through tight fitting clothes, so they should be avoided.
- Applying insect repellents (N-diethyl-meta-toluamide or DEET); especially around dawn or dusk
- DEET should not be applied on babies younger than two months
- Younger children should only apply low concentrations of the repellents (20 to 30% DEET)
What are the complications of dengue fever?
A small percentage of people who have dengue might develop a serious form of disease known as dengue hemorrhagic fever.
The risk factors for developing this fever are:
- Having antibodies left over from previous infections
- Being a child under the age of twelve
- Being female
- Having a weakened immune system
This rare disease is characterized by :
- High fever
- Damage to the blood vessels
- Damage to the lymphatic system
- Nose bleeds
- Gum bleeding
- Circulatory System failure
- Liver enlargement
Symptoms of the fever can trigger dengue shock syndrome. This form is very severe and can lead to excessive bleeding and even death.