Dengue Fever Screen

DENGUE FEVER TESTING

Question 1. What is Dengue Fever?

Dengue fever is a viral infection caused by dengue virus. It has 4 serotypes; dengue 1, 2, 3 and 4.

Question 2. How is Dengue Fever Transmitted?

It is transmitted through bite of a mosquito species called Aedes aegypti. This species of mosquito also transmits zika and chikungunya viral infection also seen in PNG and pacific. When a mosquito bites an infected person, it can acquire the virus and transmit that to another person during feed which occurs both at night and day time.

Question 3. What are the signs that I have dengue fever?

The following are features of dengue infection

Fever

Headache

Eye pain

Skin rash

Muscle, Joint & Bone pain or aches

Nausea with or without vomiting

Dengue infection is more serious in pregnancy, in children and in persons with multiple medical problems. Dengue complaints commonly last only less than 2 weeks and it’s rare for dengue patient to be ill for over 2 weeks.

Question 4. Is Dengue Fever infectious?

No. Dengue fever virus is transmitted through bite of a mosquito and cannot be transmitted to another person simply by sneezing and shaking hands as is like for the ‘common flu viruses’.

Question 5. Is there any complication?

Yes. Fortunately, majority of dengue infections are only mild and recovery is complete within 1-2 weeks of infection. 5% of patients will develop serious complication such as bleeding (mucosa, gum, skin) and collapse with severe vomiting and can die if untreated. About 80-90% of dengue fever patients have low platelet count.

Onset of severe dengue fever can occur within 2-3 days of fever.  You should visit your doctor or emergency without delay if you have any signs of severe infection as bleeding or vomit repeatedly or severe abdominal pain or feel very weak.

Question 6. How is it diagnosed?

Simple blood test looking viral antigen, antibodies or genetic material is used to diagnose dengue virus infection. If antibody test is negative and you have been sick for less than 5-7 days, another sample must be taken and tested after 7 days to confirm or exclude disease.

Antigen test (NS1). 

Dengue NS1 (non-structural protein1) is a glycoprotein that is common to all dengue serotypes and once detected confirms dengue fever infection. NS1 is useful in either primary or secondary infections (repeat) in the earliest stages (1-5 days). The onset of dengue symptoms is marked by the presence of dengue NS1 antigen in the patient’s serum. Blood NS1 may be undetectable after 9 days of infection as immune system kicks in to clear the dengue virus.

Although NS1 test is 97-100% specific test, it lack sensitivity in that NS1 test may still show negative in 20-45% of patients even in the presence of dengue infection. In this case, a repeat testing or IgM antibody test is required since NS1 may disappear after 9days of infection.

Antibody tests—these tests are primarily used to help diagnose a current or recent infection. They detect two different classes of antibodies (protein produced to fight infection) i.e., IgG and IgM produced by the body in response to a dengue fever infection. Diagnosis may require a combination of these antibody tests because the body's immune system produces varying levels of antibodies over the course of the illness.

IgM antibodies are produced first and therefore indicated more recent infection. IgM levels can be detected following at least 7-10 days of mosquito bite or infection. 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. These tests are not available in all laboratories in PNG.

 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.

 Question 7. How is Dengue Antibody test Interpreted?

Question 8. Is there any false positive result?

While many companies try their best to minimize false positive IgM or IgG antibody test results, there are known interferences with antibody tests. Dengue antibody tests can cause false positive reaction in the presence of Arbovirus or chikungunya infections (called cross-reaction) which are also seen in PNG. In such cases, confirmatory tests such as Plaque Reduction Neutralization Test (PRNT) can be done to help rule out other viral infections. Discuss with your lab the type of test kit available locally.

Question 9. How is Dengue treated?

No specific treatment is available for dengue. Treatments are directed towards controlling your complaints like fever, pain, headache, dehydration and rarely bleeding. You should get plenty of fluids to keep yourself well hydrated. Take simple paracetamol for fever, pain and headache but avoid aspirin, ibuprofen, indomethacin, or diclofenac. Beware of over-the-counter purchasable combination medicines that may contain these drugs such as stoppain, neurofen plus, and aspalgin. These drugs collectively known as Non-steroidal Anti-inflammatory Drugs or NSAID should not be taken until you see your doctor or a health care provider as the drugs will increase your change of bleeding in dengue infection.

Question 10. Can I get another attack of Dengue?

Yes. Dengue has 4 serotypes; 1, 2, 3 and 4. Infection with one serotype does not protect another; hence you can get repeated infection from dengue virus.

Question 11. How can I prevent Dengue?

Avoid mosquito bite by taking all necessary steps similar to what you would normally do to prevent malaria infection.

Question 12. What about Dengue Vaccine?

 A vaccine to prevent dengue (Dengvaxia®) is licensed and available in some countries for people ages 9-45 years old. The World Health Organization recommends that the vaccine only be given to persons with confirmed prior dengue virus infection.

 The vaccine manufacturer, Sanofi Pasteur, announced in 2017 that people who receive the vaccine and have not been previously infected with a dengue virus may be at risk of developing severe dengue if they get dengue after being vaccinated.

In May 2019, Dengvaxia® was approved by the U.S. Food and Drug Administration (FDA) in the United States for use in children 9-16 years old living in an area where dengue is common (the US territories of American Samoa, Guam, Puerto Rico and the US Virgin Islands), with laboratory confirmed prior dengue virus infection.

Further Information:

https://www.cdc.gov/dengue/healthcare-providers/testing/serologic-tests.html

https://www.who.int/csr/resources/publications/dengue/034-47.pdf?ua=1