DENGUE AND DIAGNOSTIC TESTING
What is dengue?
Dengue is a mosquito-borne viral disease caused by the dengue virus. Dengue viruses are spread to people through the bite of an infected Aedes species (mainly of Ae. aegypti, and to lesser extent Ae. albopictus) mosquito. These mosquitoes are also vectors of chikungunya, yellow fever and Zika viruses.
Each year, up to 400 million people get infected with dengue. Approximately 100 million people get sick from infection, and 40,000 die from severe dengue. There are four distinct, but closely related, serotypes of the virus that cause dengue (DENV-1, DENV-2, DENV-3 and DENV-4). Therefore, a person can be infected with a dengue virus as many as four times with different dengue serotype in his or her lifetime.
Dengue symptoms can range from none to severe flu-like symptoms after infection. Although severe dengue is less common, the complications associated with the disease, such as bleeding, organ impairment, and plasma leakage, can raise the risk of death when not managed or treated properly. Secondary infections by other serotypes increase the risk of developing severe dengue.
In 2020, dengue was reported in several countries, with increased numbers in Bangladesh, Brazil, Cook Islands, Ecuador, India, Indonesia, Maldives, Mauritania, Mayotte (Fr), Nepal, Singapore, Sri Lanka, Sudan, Thailand, Timor-Leste, and Yemen. In 2021, dengue continues to affect Brazil, India, Vietnam, the Philippines, Cook Islands, Colombia, Fiji, Kenya, Paraguay, Peru, and Reunion Island.
DENGUE AND DIAGNOSTIC TESTING
Sign and Symptoms
Dengue symptoms can range from asymptomatic or mild symptoms to severe flu-like illness that affects infants, young children and adults, but rarely causes death. Symptoms usually last for 2-7 days, following an incubation period of 4-10 days after the bite from an infected mosquito.
Dengue
Dengue should be suspected when a high fever (40°C/104°F) exists together with two of the following symptoms for 2-7 days:
- Severe headache
- Pain behind the eyes
- Muscle and joint pains
- Nausea
- Vomiting
- Swollen glands
- Rash
Severe Dengue
A patient enters the critical phase normally about 3-7 days after illness onset.
During the 24-48 hours of critical phase, a minority of patients may show a sudden worsening of symptoms. It is at this time, when the fever is dropping (below 38°C/100°F) in the patient, that warning signs associated with severe dengue can manifest.
Severe dengue is a potentially fatal complication, due to plasma leaking, fluid accumulation, respiratory distress, severe bleeding, or organ impairment.
Warning signs that doctors should look for include:
- Severe abdominal pain
- Persistent vomiting
- Rapid breathing
- Bleeding gums or nose
- Fatigue
- Restlessness
- Liver enlargement
- Blood in vomit or stool.
If patients show these symptoms during the critical phase, close observation for the next 24-48 hours is essential so that proper medical care can be provided, to avoid complications and risk of death. Close monitoring should also continue during the convalescent phase.
DENGUE AND DIAGNOSTIC TESTING
Diagnostics
Several methods can be used for diagnosing a dengue infection. Different diagnostic methods need to be selected and applied appropriately, depending on the time of patient presentation. During the first week of illness, patient samples collected should be tested by both methods mentioned below.
Viral detection methods
The virus may be isolated from the blood during the first few days of infection. Various reverse transcriptase–polymerase chain reaction (RT–PCR) methods are available and are considered the gold standard. However, they require specialized equipment and training for staff to perform these tests.
The virus may also be detected by testing for a virus-produced protein, called NS1. There are commercially-produced rapid diagnostic tests available for this, and it takes only ~20 mins to determine the result, and the test does not require specialized laboratory techniques or equipment.
Serological methods
Serological methods, such as enzyme-linked immunosorbent assays (ELISA), may confirm the presence of a recent or past infection, with the detection of anti-dengue antibodies. IgM antibodies are detectable ~1 week after infection and remain detectable for about 3 months. The presence of IgM is indicative of a recent DENV infection. IgG antibody levels take longer to develop and remains in the body for years. The presence of IgG is indicative of a past infection.
Dengue Virus Antigen Detection (NS1 Detection)
What is the test?
NS1 tests detect the non-structural protein NS1 of dengue virus. This protein is secreted into the blood during dengue infection. The test use synthetically labeled antibodies to detect dengue NS1 protein.
What specimen types should be used?
Whole blood collected by fingerstick, plasma or serum.
How should it be used and at what time during infection?
NS1 is detectable during the acute phase of dengue virus infections. NS1 tests can be as sensitive as molecular tests during the first 0-7 days of symptoms. After day 7, NS1 tests are not recommended.
While combined testing with a NS1 and IgM antibody test can usually provide a diagnostic result during the first 1-7 days of illness, a second, convalescent phase specimen should be obtained and tested for IgM when both antigen and antibody tests are negative.
How to interpret the results?
A positive NS1 test result confirms dengue virus infection without providing serotype information.
In general, knowing the serotype of the infecting virus is not necessary for patient care. However, serotype information is useful when a person gets secondary infections by other serotypes because of the increasing risk of developing severe dengue. For surveillance purposes, the sample should be tested by NAT.
A negative NS1 test result does not rule out infection. People with negative NS1 results should be tested for the presence of dengue IgM antibodies to determine possible recent dengue exposure.
