The incidence of Dengue in huimans has increased  three fold in the world population in the past decade.

The Dengue virus threatens both underdeveloped as well as developed nations alike. In India alone  there have been major outbreaks in dengue from time to time suggesting the importance of thourough knowledge of the epidemiology, pathogenesis and prompt treatment of the disease.

The three entities of Dengue, i.e, Dengue Fever, Dengue Hoemorrhagic fever and Dengue Shock Syndrome heve been documented in the infection with Dengue virus.

 There has been epidemiological evidence to suggest that the more serious manifestations of the Dengue infection namely Dengue Hoemorrhagic Fever (DHF) , Dengue Shock Syndrome (DSS) occur in people who are infected with two serotypes.There have been three outbreaks in northIndia in the past decade alone showing the importance of current knowledge on the disease and treatment.



Acute fever (39 to 40 C) manifesting with myalgias, headache, retro orbital pain, maculopapular rash, with or without leucopenia, thrombocytgpenia


High fever ,hemorrhagic phenomena ,hepatomegaly, signs of impending circulatory failure (poostural hypotension,resting tachycardia,diaphoresis.

Significant thrombocytopenia and hemoconcentration


The above syndrome with features of extensive plasma leakage leading to third compartment collection of fluids (pleural effusions,etc.) extreme dehydration, coagulopathy, shock represents DSS.



DEN1 , DEN 2, DEN 3 and DEN 4, serotypes  have been identified





                                         Aedes aegypti






Fact Sheet: Dengue and Dengue Hemorrhagic Fever


















                                                                Table 1

                     Algorithm for the virological diagnosis of Dengue




Outbreak mode







Time of collection






Test of



Delay for report



Investigative and

Evaluation modes






Less than 4 days after onset


Let blood clot at room temperature then store at 4°C.


Ship on ice (at 4°C)


Virus isolation


2-4 weeks




2-7 days




After 1 week after onset




1-7 days


Monitoring mode




Call the laboratory before taking and submitting the sample as laboratory resources may be overwhelmed


Always, regardless of the mode/phase  of the outbreak






Less than 4 days after onset


Let blood clot at room temperature then store at 4°C.


Ship on ice (at 4°C)


Virus isolation


2-4 weeks




2-7 days



1st serum


Result will be reported in 1-7 days only if titer is high. Otherwise the laboratory will wait for

2nd serum




After 1 week after onset


IgM Elisa


1-7 days




2-3 weeks after onset



2nd serum


1-7 days




Heart blood, liver, kidney or spleen


As soon as possible after death


In sterile container with saline or PBS.


Virus isolation


2-4 weeks




2-7 days

                                                                      Table 2

                                       Interpretation of test results




Type of test




Positive result


Negative result


Virus isolation and typing


Serum taken less than 4 days after onset


Confirms etiology and identifies the Dengue virus type


Does not rule out Dengue infection. The rate of false negatives depends mainly on the conditions of shipment


RT-PCR (reverse transcriptase-polymerase chain reaction)


Under investigation. The general impression is that under routine conditions it will yield less false negatives than virus isolation




Serum taken after the first week of onset


Confirms that the etiology is a Flavivirus (*)


False negatives are common in sera taken very close to the onset of the disease (**)



Inhibition Assay  (HAI)


Single serum taken within the first week after onset


Single serum: Titer >/= 1280

Suggestive of secondary infection


Single serum: tited < 1280

Not informative


Paired sera: 1st serum taken during the first week after onset and  the 2nd one taken 10 to 15 days after the 1st.


Paired sera: 4-fold increase in titer

Confirms that the etiology is a Flavivirus (*)


Paired sera: less than 4-fold increase in titer

Rules out that the etiology is a Flavivirus

(*) Together with Clinical presentation and epidemiological knowledge it confirms a recent exposure to a Dengue virus.

(**)  This is the reason to prefer sera taken after the first week.




Clinical and Laboratory Guidelines for Dengue Fever and Dengue Haemorrhagic

 Fever/Dengue Shock Syndrome for Health Care Providers


General aspects


Dengue is an endemic tropical viral disease in many areas in the World. Although cases may be detected all year-round, the number of cases is clearly related to cyclic changes in weather: an increase in the number of cases usually follows the onset of the rainy season.


The agent of Dengue is the Dengue virus, a member of the Flavivirus group. There are four acknowledged types of Dengue Viruses designated as types 1, 2, 3 and 4. Although these four types share common antigens, antibodies against each of these types are only able to neutralize the same type that elicited the response. Periodic epidemics are associated with the emergence or re-emergence of different serotypes.


The reinfection of an individual by a different type (heterotypic reinfection) may trigger complex immunopathologic mechanisms leading to the two most severe manifestations of the disease: Dengue Haemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS).


Dengue Viruses are transmitted by mosquitoes of the Aedes group. These are relatively small mosquitoes that feed exclusively in humans.  Predominantly on humans and less so on other animals. They tend to bite during the day and are usually found resting in dark places inside human housing. They breed in small deposits of relatively clean water in or around human housing (flower pots, saucers under plant pots, old tires, etc.)




Dengue Fever

Clinical Description

Sudden onset

High fever (> 100° F)

Headache / myalgias

Retro-orbital pain

Lymphadenopathies (cervical/occipital)

Maculo-papular rash

Other associated elements may include upper/lower respiratory involvement, pharyngitis, vomiting and diarrhea

Haematology laboratory results


Differential diagnosis


Acute viral exanthems (Measles, Rubella)



Dengue Haemorrhagic Fever (DHF)

Clinical description

Possibly more frequent in children and young adults

Similar onset as Dengue Fever

Complications usually start when fever subsides

Facial flush

Epigastric and abdominal pain


Haemorrhagic tendencies

Petechiae, Bruises, Hematuria, Hematemesis, Epistaxis, Melena/Blood in stools, Gingival bleeding

Positive tourniquet test

Haematology laboratory tests

Platelet count < 100,000/mm3

Elevated haematocrit (hemoconcentration) > 20% the average value for the age

Differential diagnosis


Acute abdomen

Other forms of purpura or viral hemorrhagic diseases


Dengue Shock Syndrome (DSS)

Clinical description

Similar onset as Dengue Fever

Patient deteriorates after a few days of fever

Cold, clammy skin, cyanosis

Tachycardia, low pulse pressure or hypotension

Abdominal tenderness

Recurrent lipothymias (repeated fainting)

Altered mental status (restlessness)





Laboratory results

Increased hematocrit (hemoconcentration)

Metabolic acidosis       

Differential diagnosis

Acute abdomen


Acute Meningoccemia


Case definitions

(When met, the cases are reportable to Public Health authorities)

Dengue Fever (DF)


An acute febrile illness with two or more of the following manifestations:


Retro-orbital pain




Haemorrhagic manifestations

Occurring at the same location and time as other confirmed cases of dengue.


A case with at least one of the following:

- An Haemagglutination In hibition titer equal or higher than 1280

- Sero-conversion (four-fold change in titer) by haemagglutination inhibition

- Positive for IgM anti-Flavivirus antibodies during a time consistent with the occurrence of the disease

- Isolation and typing of a dengue virus from an early blood specimen.


Dengue Hemorrhagic Fever (DHF)


Recent history of fever

Haemorrhagic tendencies (see above)

Thrombocytopenia at or below 100.000/ mm3

Haematocrit 20% above average for that age, sex and population


Add the same criteria as for confirmed cases of DF.                 


Dengue Shock Syndrome (DSS)


All four criteria for DHF plus elements of shock:

Cold, clammy skin

Rapid weak pulse

Narrow pulse pressure or hypotension


Add the same criteria as for confirmed cases of  DF                             



 Probable diagnosis of Dengue Fever


Home or ambulatory treatment

Analgesics and antipyretics (no aspirin! Due to risk of bleeding)


1 yr      - 60 mg/dose

1-3 yr   - 20-120 mg/dose

3-6 yr   - 120 mg/dose

6-12 yr - 240 mg/dose

Watch for signs of DHF/DSS (see below)


 Probable diagnosis of Dengue Hemorrhagic Fever


Hospitalized (outpatient observation room or rehydration ward)


Analgesics and antipyretics as for the preceeding group


Serial hematocrit and platelet counts (daily)


Fluids ingested by mouth

WHO Oral rehydration solution

Fruit juices


Monitor for signs of shock (shock usually occurs after the third day during transition from febrile to afebrile phases)           


I/V rehydration therapy

the fluid and its volume should be determined according to the degree of dehydration and electrolyte loss.


Probable diagnosis of Dengue Shock Syndrome


Hospitalized (Intermediate treatment room)


Analgesics and antipyretics as for the preceeding group


Serial hematocrit and platelet counts (daily) to monitor treatment and recovery I/V resuscitation therapy

Ringer=s acetate or 5% glucose I PSS at a rate of 10-20 ml/kg of body weight per hour (or as fast as possible).

If shock persists after 20-30 ml/kg of body weight add a plasma expander at the rate of 10-20 ml/kg per hour.

If shock persist significant internal bleeding should be suspected

Continuation of intravenous therapy should be adjusted according to hematocrit and the rate should be reduced to 10 ml/kg per hour. In general there is no need to continue the therapy beyond 48 hours






 The physical examination for suspected dengue should include an assessment of:









This is an example of a patient with visible petechiae, a common hemorrhagic manifestation.

Tourniquet Test

The tourniquet test assesses capillary fragility. You inflate the blood pressure cuff to a point midway between the systolic and diastolic blood pressures for five minutes. After deflating the cuff, wait for the skin to return to its normal color, and then count the number of petechiae visible in a one-inch-square area on the ventral surface of the forearm. Twenty or more petechiae in the one-inch square patch constitutes a positive test.






Imaging Studies:




        Virus isolation (serum taken within 3 days after onset)

This study requires serum taken from the patient within three days of onset (hence the importance of indicating the date of onset and the date of collection in the submitting form). The serum should be separated from the clot and should never be frozen but should be kept refrigerated (4° C) or on ice until its reception in CAREC. This test may take several weeks as it requires serial passages in tissue cultures (in mosquito cell lines).


IgM ELISA (serum taken after 1 week of onset)

IgM antibodies rise quickly and fade down several weeks after the infection. Although IgM antibodies can appear very fast after infection,  they can be consistently detected in most patients only after the first week. CAREC recommends the use of sera taken at least five days after onset. In earlier sera the result is diagnostic only if positive. A  positive results indicates that the patient has been exposed to the virus in the recent past. The test is unable to identify the viral type. Strictly speaking, the test is not specific to Dengue as there can be cross-reaction with other Flavivirus as (Yellow Fever, Yellow Fever Vaccination and other Flavivirus or more rare occurrence in the Caribbean). However, in conjunction with the clinical presentation and the epidemiological knowledge it can strongly support the diagnosis of Dengue virus infection.

           Hemagglutination Inhibition Assay (HAI) (acute serum if DHF/DSS is suspected)This test detects IgG antibodies. If paired sera are provided it can be used to determine HAI titers in both the acute and convalescent sera and a four-fold increase in titer is diagnostic of primary dengue infection.  Often individuals that were previously infected by a different Dengue virus type will have very high titers in their acute serum (equal or higher than 1280). This test is provided for cases suspected of DHF/DSS, but results are delayed in comparison with Dengue IgM.



This slide demonstrates the use of mosquito cell cultures to detect dengue virus. The results for this patient's blood sample are positive: the fluorescing cells seen here are infected with dengue virus.




Virus Isolation: Mosquito Inoculation


Virus Isolation: Fluorescent Antibody Test



The ELISA detects the presence of anti-dengue IgM in a patient's blood sample, indicating a recent dengue infection. An ELISA plate is shown here. The more intense the color reaction, the greater the level of anti-dengue IgM antibody in the samples.


The tests for diagnosis of dengue infection are time dependent.






Acute acalculous cholecystitis


Fulminant hepatitis

Edematous gall bladder wall on ultrasound


Aute renal failure

 The hemorrhagic manifestations may mimic intracranial bleeding,seizures and myelitis.




Ramu  is a 12 yr old boy living in a densely crowded city in India. He develops fever (39.5 C) at the time of consultation with the doctor. There were no other complaints except mayalgia and heaviness around the eyes. He was prescribed antipyretics for the fever and an oral antibiotic. The fever showed signs of improvement in the following days but the body pain continued. The fever subsided on day 5. On Day 6 , Ramu developed petechiae around the medial aspects of the ankles.

On lab evaluations the following picture emerged

Platelet count   80,000 cells per

Hematocrit       40 %

What is the possible diagnosis?


The above case is a classical presentation of a case of Dengue Hemorrhagic Fever. The points to be noted here are that children below the age of 15 yrs are  more prone for the complications of Dengue Infection.

The rising hematocrit and the falling platelet count contribute to the diagnosis. The heaviness around the eye is a common feature (retroorbital pain) that accompanies the disease.

The hemorrhagic complications mostly arise after the fever subsides.


Micheal Jones is a Journalist who is based in the UK, has come to India to shoot a documentary in New Delhi, India. He has been vaccinated for typhoid , cholera. Ten days after his arrival he develops high fever of 40 C. He then visits a doctor. Past history suggests  that he had been diagnosed as having dengue fever for a similar episode while on a previous assignment to Puerto Rico in South America. That episode subsided with no sequale. On clinical examination his heart rate was 120/min. His pulse was normal.

On measuring BP, several petechiae developed distal to the cuff. Further examination showed that he had an enlarged liver about 2 cm below the mid clavicular line. Hematology revealed thrombocytopenia and hemoconcentration.

Lab investigations showed the presence of IgM antibodies for both DEN 1 and DEN 3 serotypes of the dengue flavivrus. the patient was then managed with antipyretics, namely Paracetamol, tepid sponging was given, and patient was hydrated with IV fluids.


Protection against one serotype of the Dengue Flavivirus does not confer protection against another. In fact there has been epidemiological evidence to show that presence of antibodies against one serotype actually increases the susceptibilty to acquire infection from another serotype.





 What is Dengue fever (DF)?

Dengue infection is caused by a virus. It occurs commonly as dengue fever. Occasionally the patient suffering from dengue may develop bleeding. Common sites for bleeding are nose, gums or skin. Sometimes, the patient may have  coffee ground vomiting or black stools. This indicates bleeding in gastro intestinal tracts and it is serious. The patient with dengue who has bleeding has dengue haemorrhagic fever (DHF ). Rarely the patient suffering from dengue may develop shock, then it is called dengue shock syndrome ( DSS).

 When should I suspect Dengue?

Dengue should be suspected when you have sudden onset of fever. The fever is high 103-105 degrees F or 39-40 degrees C. It is accompanied with severe headache (mostly in the forehead), pain behind the eyes, body aches and pains, rash on the skin and nausea or vomiting. The fever lasts for 5-7 days. In some patients, fever comes down on 3rd or 4th day but comes back. All the above symptoms and signs may not be present in the patient. The patient feels much discomfort after the illness.

 There are several types of fever, when should dengue be suspected?

The characteristics of dengue that make it different from other causes of fever are the pain behind the eyes, severe pains in the muscles, severe joint pains, and skin rashes. These features make the diagnosis of suspected Dengue likely. The severe joint pains caused by DF is the reason why DF is also called break-bone fever.

How can someone get dengue fever?

Dengue fever occurs following the bite of an infected mosquito Aedes aegypti.This type of mosquito has a peculiar white spotted body and legs and is easy to recognize even by laymen. It breeds in clean water (see Question 20) and has a flight range of only 100 – 200 metres.The mosquito gets the Dengue virus after biting a human being infected with dengue virus.


Can I get dengue fever from another person?


Dengue does not spread directly from person to person. It is only spread through the bite of an infected mosquito.

When does dengue develop after getting the infection?

After the entry of the virus in the person, it multiplies in the lymph glands in the body. The symptoms develop when the virus has multiplied in sufficient numbers to cause the symptoms. This happens generally about 4-6 days ( average) after getting infected with the virus.

Can people suffer from dengue and not appear ill?

Yes. There are many people who are infected with the virus and do not suffer from any signs or symptoms of the disease. For every patient with symptoms and signs there may be 4-5 persons with no symptoms or with very mild symptoms.

Can dengue fever be treated at home?

Most patients with dengue fever can be treated at home. They should take rest, drink plenty of fluids that are available at home and eat nutritious diet. Whenever available, Oral Rehydration Salt/ORS (commonly used in treating diarrhoea) is preferable. Sufficient fluid intake is very important and becomes more important in case DF progresses into DHF or DSS where loss of body fluid / blood is the most salient feature.It is important to look  for danger signs and contact the doctor as soon as any one or more of these are found.

What is the treatment? Is it curable?

Like most viral diseases there is no specific cure for dengue fever. Antibiotics do not help. Paracetamol (can be purchased without prescription) is the drug of choice to bring down fever and joint pain. Other medicines such as Aspirin and Brufenshould be avoided since they can increase the risk of bleeding. Doctors should be very careful when prescribing medicines. Any medicines that decrease platelets should be avoided.

Can dengue fever become dangerous?

The infection can become dangerous since it may cause damage to the blood vessels. The damage may range from increased permeability of the blood vessels, causing leakage of blood fluid/plasma into various organs to completely broken blood vessels that causes bleeding.The symptoms and signs of dengue haemorrhagic fever and dengue shock syndrome are related to damage to the blood vessels and derangement in functioning in components of blood that help it to clot.


Where does the mosquito that spreads dengue live?


The highly domestic mosquito Aedes aegypti rests indoors, in closets and other dark places. Outside it rests where it is cool and shaded. The female mosquito lays her eggs in water containers in and around the homes, and other dwellings. These eggs will develop, become larvae, and further develop into adults in about 10 days.

Can people die from dengue fever?

People who suffer from dengue fever have no risk of death but some of them develop Dengue Haemorrhagic Fever or Dengue Shock Syndrome. In some of these cases death can occur. With proper treatment, the patients with Dengue haemorrhagic fever and dengue shock syndrome can recover fully. Good treatment provided in time can save most lives.

How can I prevent mosquito bites to prevent dengue?

There is no way to tell if a mosquito is carrying the dengue virus. Therefore, people must protect themselves from all mosquito bites.

Dengue mosquitoes bite during the day time throughout the day. Highest biting intensity is about 2 hours after sunrise and before sunset.

Wear full sleeves clothes and long dresses to cover as much of your body as possible.

Use repellents- be careful in using them in young children and old people.

Use mosquito coils and electric vapour mats during the daytime also to prevent dengue.

Use mosquito nets to protect children, old people and others who may rest during the day. The effectiveness of these nets can be improved by treating them with permethrin (pyrethroid insecticide). This bed-net is called Insecticide Treated Nets and are widely used in the prevention of malaria.

Is there any advice for the patient with dengue fever to prevent the spread of the disease to others.

The spread of dengue from a patient to others is possible. The patient should be protected from contact with the mosquito. This can be achieved by ensuring that the patient sleeps under a bed-net. Effective mosquito repellents are used where the patient is being provided care. This will prevent the mosquito from biting the patient and from getting infected and spreading it to others.

What should the doctors treating dengue do ?

Patients suspected to be suffering from dengue haemorrhagic fever or dengue shock syndrome should be admitted to a hospital without delay.

The progress of these patients should be monitored regularly at 1-2 hours interval.

Platelet counts and haematocrits should be monitored repeatedly to review the progress of patients.

If the haematocrit levels fall  dangerously then a blood transfusion should be considered. A fall of more than 20 % as compared to previous levels may be an indication for transfusion.

If the haematocrit values rise the patient should be given fluids intravenously and the fluids carefully monitored to ensure that the patient does not get excess fluids. A rise of more than 20 % as compared to previous levels may be an indication for IV fluids. The doctor should decide based on best judgement of patient's condition.

 What should the doctors treating dengue avoid?

Do not prescribe aspirin and brufen or any other medicine that reduces the platelets or increases the  tendency to bleed.

Avoid giving IV fluids unless the patient is bleeding or the haematocrit level is rising progressively.

Avoid rushing into giving blood transfusion unless the haematocrit is falling dangerously.

Do not give platelet transfusion unless the platelet count is very low or unless there is bleeding.

What can the community do to prevent dengue?


In fact, the community is the key to dengue prevention. As elaborated above, prevention of dengue relies heavily on preventing the mosquito (Aedes aegypti) that transmits dengue from breeding inside and in the vicinity of homes. Every household can undertake the very simple measures to prevent existing water collections from becoming places for breeding of A.aegypti by draining out water from various containers, by regular changing of water plus cleaning flower vases and other items or, in the case of unused items, by discarding/destroying them.

Since the mosquito does not travel far, "house cleaning" by all members of a community will ensure that no breeding places exist, preventing dengue from occurring.

The main strategy in the prevention and control of dengue is "source reduction", or prevention of breeding places, mentioned above.




There are some common misconceptions about DHF that should be mentioned.

One commonly believed but false idea is that dengue plus bleeding equals dengue hemorrhagic fever. The truth is that there are four established criteria for defining DHF, and the critical difference between dengue fever and DHF is not bleeding, but the increased vascular permeability that occurs in DHF—this is what causes shock and death.

Another misconception is that DHF kills only by hemorrhage. Though these patients may have severe hemorrhage, the more common scenario is that the patient goes into irreversible shock because of excessive vascular permeability, and this shock is what causes fatalities.

A third misconception is that dengue patients who are not given adequate treatment will develop DHF. It is true that if dengue is mismanaged, the patient is more likely to develop a more severe illness. However, dengue and DHF are distinct conditions: although they are caused by the same virus, and present with the same symptoms in the first days of the illness, DHF is not just a worsening of dengue fever. Even a patient who receives the best possible care may develop DHF.


Positive tourniquet test = DHF

Another misconception is that a positive tourniquet test result equals a diagnosis of DHF. Again, the four criteria must be present for a diagnosis of DHF; the tourniquet test is a nonspecific indicator of capillary fragility.



Another common misconception is that dengue hemorrhagic fever is a pediatric disease. Many textbooks on dengue are based largely on the experience in Southeast Asia, where this is true, but all age-groups are involved in the Americas. Likewise, in travelers it can occur in all age-groups





The viruses that cause dengue fever and dengue haemorrhagic fever are transmitted by the mosquito Aedes aegypti, and in Asia to a lesser extent by Ae. albopictus. Aedes aegypti breeds mainly in water collections in artificial containers in the environment of human settlements, but not in groundwater pools and puddles, nor in swamps or other large natural bodies of water. Effective prevention and control of epidemic dengue requires control of Ae. aegypti.

There is no vaccine to prevent dengue infection, nor are there drugs to combat the disease in infected persons.

Aedes aegypti in the tsunami stricken areas

All countries affected by the Tsunami are endemic to dengue.

In temporary shelters where drinking water comes from outside sources or from rainwater harvesting, there will be a tendency to store drinking water in containers that may become breeding places of Ae. aegypti (and to a lesser extent of Ae. albopictus). The accumulation of rainwater in other containers and items of debris in the affected areas may also become Aedes breeding sites.

As these mosquitoes bite during daytime, insecticide-treated nets to sleep under will offer little or no personal protection.


Prevention of mosquito breeding in drinking water containers, by covering them to exclude mosquitoes, frequently emptying them (at least once per week), or treating them with insecticide, e.g., temephos 1% sand granules, will contribute to the prevention of dengue outbreaks. However, this may not be sufficient in settlement areas where there are small, freshwater collections in other artificial containers and miscellaneous debris. Depending on feasibility, chemical larvicides may also be applied to these containers. Application of insecticidal space sprays against the adult Ae. aegypti mosquitoes may also be warranted in settlement areas where there are larval habitats or where dengue transmission is occurring. Portable equipment will be needed in areas with difficult road access. To the extent possible, affected populations may be provided with mosquito repellents. The use of space sprays and of repellents will also contribute to temporary relief from the discomfort caused by nuisance mosquitoes.

Surveillance for dengue fever and dengue haemorrhagic fever should be included in the post-disaster surveillance system. Hospital facilities should be prepared to respond in the event of outbreaks.