Dengue fever is a mosquito-borne viral infection that causes flu-like symptoms including high fever, headache, and joint pains. It is transmitted to humans through the bites of infected Aedes aegypti mosquitoes. While most cases are mild, severe dengue can cause bleeding, organ impairment, and death if not treated properly. There is currently no vaccine, so prevention focuses on eliminating mosquito breeding sites and using insect repellent and protective clothing.

1. DENGUE FEVER
Introduction
Dengue fever, also known as break-bone fever, is a mosquito-borne infection that can lead to a
severe flu-like illness. It is caused by dengue viruses and spread by Aedes aegypti mosquito. It
occurs in tropical and subtropical areas of the world. Symptoms typically begin three to fourteen
days after infection. This may include a high fever, headache, vomiting, muscle and joint pains,
and a characteristic skin rash. Recovery generally takes two to seven days. The dengue virus
belongs to the Flaviviridae family of viruses that cause diseases in humans. Dengue is the most
common infection caused by viruses transmitted by mosquitoes. The dengue virus (DEN)
comprises four distinct serotypes (DEN-1, DEN-2, DEN-3 and DEN-4).
Virus classification
Group: Group IV (+) ssRNA
Order: Unassigned
Family: Flaviviridae
Genus: Flavivirus
Species: Dengue virus
Morphological character
 Virus structure
 Roughly spherical shape.
 40-60 nm in diameter
 (+ve) sense ssRNA virus.
 Icosahedral symmetry
 The nucleocapsid is surrounded by an envelope
 4 serotypes
Figure: Structure of dengue virus

2. Genome structure
The dengue virus genome is a single strand of RNA. It is referred to as positive-sense RNA
because it can be directly translated into proteins. The viral genome encodes ten genes. The
genome is translated as a single, long polypeptide and then cut into ten proteins.
Three are structural proteins: the capsid (C), envelope (E), and membrane (M) proteins. Seven
are nonstructural proteins: NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5. These
nonstructural proteins play roles in viral replication and assembly.
The functions for all the individual NS-proteins are not well characterized. NS1 protein has been
shown to interact with the host immune system, and known to evoke T cell responses.
In dengue virus infection, patients have measurable levels of NS1 protein in the blood, which are
utilized as a diagnostic marker of the infection.
Figure: Dengue virus genome
Host specificity
 Human
 Monkey &
 Aedes aegypti mosquito

3. Symptoms
Symptoms vary depending on the severity of the disease.
 Mild dengue fever
Symptoms can appear up to 7 days after being bitten by the mosquito that carries the virus. They
include:
 aching muscles and joints
 body rash that can disappear and then reappear
 high fever
 intense headache
 pain behind the eyes
 vomiting and feeling nauseous
 Dengue hemorrhagic fever
At first, symptoms of DHF may be mild, but they gradually worsen within a few days. As well as
mild dengue symptoms, there may be signs of internal bleeding. A person with Dengue
hemorrhagic fever may experience:
 bleeding from the mouth, gums, or nose
 clammy skin
 damage to lymph and blood vessels
 internal bleeding, which can lead to black vomit and feces, or stools
 a lower number of platelets in the blood
 sensitive stomach
 small blood spots under the skin
 weak pulse
 Dengue shock syndrome
DSS is a severe form of dengue. It can be fatal. Apart from symptoms of mild dengue fever, the
person may experience:
 intense stomach pain
 disorientation
 sudden hypotension, or a fast drop in blood pressure
 heavy bleeding
 regular vomiting
 blood vessels leaking fluid

4. Transmission
The dengue virus is transmitted to humans via the bite of an infected mosquito. Only a few
mosquito species are vectors for the dengue virus. When a mosquito bites a person who has
dengue virus in his or her blood, the mosquito becomes infected with the dengue virus. An
infected mosquito can later transmit that virus to healthy people by biting them. Dengue cannot
be spread directly from one person to another, and mosquitoes are necessary for transmission of
the dengue virus.
Figure: Transmission of dengue fever
Treatment
Dengue is a virus, so there is no specific treatment or cure. However, intervention can help,
depending on how severe the disease is. For milder forms, treatment includes:
 Preventing dehydration: A high fever and vomiting can dehydrate the body. The person
should drink clean water, ideally bottled rather than tap water. Rehydration salts can also
help replace fluids and minerals.
 Painkillers, such as Tylenol or paracetamol: These can help lower fever and ease pain.
 Non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin or ibuprofen, are not
advised, as they can increase the risk of internal bleeding.

5. More severe forms of dengue fever may need:
 Intravenous (IV) fluid supplementation, or drip, if the person cannot take fluids by mouth
 Blood transfusion, for patients with severe dehydration
 Hospitalization will allow the individual to be properly monitored, in case symptoms get
worse.
Diagnosis
Diagnosing dengue fever can be difficult, because its signs and symptoms can be easily confused
with those of other diseases - such as malaria, leptospirosis and typhoid fever. It is usually
diagnosed by blood tests for antibodies to the virus. Laboratory tests can detect evidence of the
dengue viruses; however the results often come back too late to assist in directing treatment.
Isolation of the dengue virus by tissue culture in sera obtained during the first few days of illness
is diagnostic. Demonstration of rising antibody titres by neutralization (most specific),
haemaglutination inhibition or complement- fixing antibodies in sequential serum samples is
evidence of dengue virus infection.
Prevention
Till date, there is no vaccine which can prevent dengue. The first precautionary step to prevent
dengue is to avoid mosquito bite and to reduce the population of mosquitoes. Anyone who lives
in or travels to an at-risk area can use a number of ways to avoid being bitten.
 Clothing: Reduce the amount of skin exposed by wearing long pants, long-sleeved shirts,
and socks, tucking pant legs into shoes or socks, and wearing a hat.
 Mosquito repellents: Use a repellent with at least 10 percent concentration of
diethyltoluamide (DEET), or a higher concentration for longer lengths of exposure. Avoid
using DEET on young children.
 Mosquito traps and nets: Nets treated with insecticide are more effective, otherwise the
mosquito can bite through the net if the person is standing next to it. The insecticide will kill
mosquitoes and other insects, and it will repel insects from entering the room.
 Door and window screens: Structural barriers, such as screens or netting, can keep
mosquitos out.
 Avoid scents: Heavily scented soaps and perfumes may attract mosquitos.
 Camping gear: Treat clothes, shoes, and camping gear with permethrin, or purchase clothes
that have been pretreated.
 Timing: Try to avoid being outside at dawn, dusk, and early evening.
 Stagnant water: The Aedes mosquito breeds in clean, stagnant water. Checking for and
removing stagnant water can help reduce the risk.

6. Reference
Gubler DJ. (2006). “Dengue haemorrhagic fever: history and current status’’. Novartis Found
Symp 277:3–16
Guzman M. G. et al. (2010). “Dengue: A continuing global threat”. Nature Reviews
Microbiology 8, S7–S16 (2010).
Kularatne SA. (September 2015). "Dengue fever". BMJ. 351: h4661. doi:10.1136/bmj.h4661.
PMID 26374064.
Rodenhuis-Zybert. Izabela A. Wilschut Jan. Smit Jolanda M. (August 2010). “Dengue virus life
cycle, viral and host factors modulating infectivity”. Cellular and Molecular Life Sciences. 67
(16): 2773–2786.
WHO (2009). “Dengue Guidelines for Diagnosis, Treatment, Prevention and Control (PDF)”.
World Health Organization. ISBN 92-4-154787-1.