To diagnose dengue fever, particularly if you are experiencing fever after travel to a tropical or subtropical destination
Dengue Fever Testing
When you develop a high fever within 2 weeks of travel to an area where dengue fever is endemic or an outbreak is occurring
A blood sample drawn from a vein in your arm
Dengue fever is a viral infection transmitted to humans by mosquitoes that live in tropical and subtropical climates and carry the virus. Blood testing detects the dengue virus or antibodies produced in response to dengue infection.
According to the Centers for Disease Control and Prevention (CDC), dengue infections have been reported in more than 100 countries from parts of Africa, the Americas, the Caribbean, the Eastern Mediterranean, Southeast Asia, and the Western Pacific. It is a fast emerging infectious disease, according to the World Health Organization (WHO), with an increasing number of cases and countries affected throughout the world. The actual number is not known because about 75% of cases are asymptomatic, but a recent estimate put the number of annual dengue infections as high as 390 million. Approximately 50 to 100 million symptomatic cases occur annually worldwide.
In the U.S., the majority of dengue cases occur in travelers returning from areas where dengue is endemic. Most dengue cases in U.S. citizens occur in people who live in Puerto Rico, the U.S. Virgin Islands, Samoa and Guam. Outbreaks where a large number of cases occur in a defined area are rare in the U.S. In recent years, there have been small outbreaks in Texas and Hawaii and a few cases diagnosed in southern Florida.
Many individuals will develop no symptoms at all, or have only a mild illness when exposed to one of the four serotypes (1-4) of the dengue virus. For those who do develop symptoms, prognosis is still very good for full recovery within a few weeks. The most common initial symptoms are a sudden high fever (104°F or 40°C) and flu-like symptoms that appear roughly 4 to 7 days after being bitten by an infected mosquito (this is called the incubation period and can range from 3 to 14 days). Additional signs and symptoms may include severe headache, especially behind the eyes, muscle and joint pain, skin rash, nausea, vomiting, and swollen glands.
Some people who develop a fever will recover on their own with no lasting ill effects while others may progress to severe dengue fever (sometimes called Dengue Hemorrhagic Fever). If the disease progresses to this form, a new wave of symptoms will appear 3 to 7 days after initial symptoms and as the fever recedes. These may include nose bleeds, vomiting blood, passing blood in the stool, difficulty breathing and cold clammy skin, especially in the extremities. During the second phase, the virus may attack blood vessels (the vascular system), causing capillaries to leak fluid into the space around the lungs (pleural effusion) or into the abdominal cavity (ascites).
The loss of blood and fluid during the second phase, if untreated, can worsen and can be fatal. In order to avoid that complication (sometimes called Dengue Shock Syndrome), a healthcare practitioner may hospitalize a patient with severe dengue fever so that falling blood pressure and dehydration caused by the loss of blood and fluids can be managed while the disease runs its course generally a period of one to two weeks. During the following week of recovery, a person may develop a second rash that lasts a week or more.
Dengue fever is usually diagnosed via some combination of blood tests because the body's immune response to the virus is dynamic and complex. Laboratory tests may include:
- Molecular tests for dengue virus (PCR)detect the presence of the virus itself; these tests can diagnose dengue fever up to 7 days after the onset of symptoms and can be used to determine which of the 4 different serotypes of dengue virus is causing the infection.
- Antibody tests, IgM and IgGdetect antibodies produced by the immune system when a person has been exposed to the virus; these tests are most effective when performed at least 4 days after exposure.
- Complete blood count (CBC)to look for low platelet count typical of the later stages of the illness and to detect the decrease in hemoglobin, hematocrit, and red blood cell (RBC) count (evidence of anemia) that would occur with blood loss associated with severe dengue fever
- Basic metabolic panel (BMP) to monitor kidney function and look for evidence of dehydration that can occur with severe illness
A blood sample is collected by inserting a needle into a vein in the arm.
No test preparation is needed.
- How is it used?
Dengue fever testing is used to determine whether a person with signs and symptoms and recent potential exposure has been infected with the dengue virus. The infection is difficult to diagnose without laboratory tests because symptoms may initially resemble those of other diseases, such as chikungunya infection. Two primary types of testing are available:
Molecular testing (polymerase chain reaction, PCR)—this type of test detects the genetic material of the dengue virus in blood within the first week after symptoms appear (fever) and can be used to determine which of the 4 serotypes is causing the infection. One type of Real Time RT-PCR test can detect dengue and the two other mosquito-borne viruses, Zika and chikungunya, and distinguish between the three. Only certain public health laboratories are able to provide the test after verifying that they can successfully perform the assay. Though the test is not available in hospitals or clinics, healthcare practitioners are able to order it through their state and local public health departments. Results can take from four days to two weeks, according to the Centers for Disease Control and Prevention (CDC).
Molecular tests of blood are not likely to detect the virus after 7 days of illness. If the result of a PCR test is negative, an antibody test can be used to help establish a diagnosis, according to the CDC (see below).
Antibody tests—these tests are primarily used to help diagnose a current or recent infection. They detect two different classes of antibodies produced by the body in response to a dengue fever infection, IgG and IgM. Diagnosis may require a combination of these tests because the body's immune system produces varying levels of antibodies over the course of the illness.
IgM antibodies are produced first and tests for these are most effective when performed at least 7-10 days after exposure. Levels in the blood rise for a few weeks, then gradually decrease. After a few months, IgM antibodies fall below detectable levels.
IgG antibodies are produced more slowly in response to an infection. Typically, the level rises with an acute infection, stabilizes, and then persists long-term. Individuals who have been exposed to the virus prior to the current infection maintain a level of IgG antibodies in the blood that can affect the interpretation of diagnostic results.
- Molecular testing (polymerase chain reaction, PCR)—this type of test detects the genetic material of the dengue virus in blood within the first week after symptoms appear (fever) and can be used to determine which of the 4 serotypes is causing the infection. One type of Real Time RT-PCR test can detect dengue and the two other mosquito-borne viruses, Zika and chikungunya, and distinguish between the three. Only certain public health laboratories are able to provide the test after verifying that they can successfully perform the assay. Though the test is not available in hospitals or clinics, healthcare practitioners are able to order it through their state and local public health departments. Results can take from four days to two weeks, according to the Centers for Disease Control and Prevention (CDC).
- When is it ordered?
Testing may be ordered when individuals have signs and symptoms associated with dengue following travel to tropical locations where the dengue virus is present. Some of the main signs and symptoms include:
- Sudden high fever (104°F or 40°C)
- Severe headache or pain behind the eyes
- Joint, muscle and/or bone pain
- Gum and nose bleeds
- Easy bruising
Low white blood cell count
Molecular testing is ordered within one week of the onset of symptoms to detect an acute infection, while antibody testing may be ordered more than 4 days after symptoms appear. If antibody testing is performed, an additional blood sample may be collected after two weeks of symptoms to determine if the antibody level is rising.
- What does the test result mean?
Molecular testing—a PCR test that detects the presence of the virus itself is generally considered the most reliable means of diagnosis. A positive result from a PCR is considered conclusive. A negative result on a PCR test may indicate that no infection is present or that the level of virus is too low to detect, as may happen if the test was performed after the 7-day window during which the virus is present in the sample collected for this test. A negative PCR result is followed by antibody testing (below).
Antibody testing—antibody tests may be reported as positive or negative, or may be reported as an antibody titer with an interpretation of which type(s) of antibody (IgG or IgM) is present.
Positive IgM and IgG tests for dengue antibodies detected in an initial blood sample mean that it is likely that the person became infected with dengue virus within recent weeks. IgM antibody tests can be positive if a person has been infected with a similar virus, such as chikungunya (called cross-reaction). If an initial IgM antibody test is positive, a second test called the Plaque Reduction Neutralization Test (PRNT) is used to confirm the presence of antibodies to dengue virus and to help rule out other viral infections.
If the IgG is positive but the IgM is low or negative, then it is likely that the person had an infection sometime in the past. If the dengue IgG antibody titer increases four-fold or greater (e.g., titer of 1:4 to a titer of 1:64) between an initial sample and one taken 2 to 4 weeks later, then it is likely that a person has had a recent infection.
Negative tests for IgM and/or IgG antibodies may mean that the individual tested does not have a dengue infection and symptoms are due to another cause, or that the level of antibody may be too low to measure. The person may still have a dengue infection – it may just be that it is too soon after initial exposure to the virus to produce a detectable level of antibody.
The following table summarizes results that may be seen with antibody testing:
IgM Result IgG Result Possible Interpretation Positive Negative Current infection Positive Positive Current infection Low or negative or not tested Four-fold increase in samples taken 2-4 weeks apart Recent infection Low or negative Positive Past infection Negative Negative Too soon after initial exposure for antibodies to develop or symptoms due to another cause
- Is there anything else I should know?
Physical symptoms like rash or aching joints are not a reliable means for diagnosing dengue fever because the symptoms are not likely to appear until after the initial fever has passed.
Antibody tests for dengue fever can be positive if a person is infected with another arbovirus such as West Nile virus. A healthcare practitioner will consider a person's test results, medical history, and recent travel history in making a diagnosis.
No laboratory test can predict whether or not the infection will progress to the more severe form, but those who have been previously infected with dengue are at an increased risk for developing severe dengue during the second infection.
- Can dengue fever be prevented?
Currently, there is no immunization that will prevent a person from contracting dengue fever if exposed to the virus. Limiting exposure to the virus depends upon protecting against mosquito bites. When traveling in tropical climates, wear insect repellent that contains DEET and long sleeved-shirts and long pants. Stay indoors during dawn and dusk when mosquitoes are most active.
- Can dengue fever be passed from person to person?
No, the virus is not spread by person-to-person contact or by exposure to respiratory secretions. The virus is spread when a mosquito bites an infected person, then bites a healthy person. It may be transmitted in rare cases through a blood transfusion, organ donation, or mother to fetus.
- If I have had dengue fever, can I get it again?
Yes. There are four types (serotypes) of the dengue virus. You may be infected with one serotype and then infected later with a different serotype. There is no cross-protective immunity to all dengue viruses when you are exposed to one serotype. In addition, a subsequent infection with a dengue fever virus is usually associated with more severe disease.