Dengue Fever – Symptoms and causes

Microorganisms, including bacteria, viruses, fungi, and other unicellular organisms, cannot be seen by the naked eye and are thus invisible creatures. Among microorganisms, viruses like dengue virus are intracellular organisms that always require a host for their replication and development. Dengue viruses have a simple yet complex structure, providing specific characteristics and differentiating them from other microscopic organisms.

The basic structure of dengue viruses consists of genetic material like RNA, a capsid or a protein coat that protects genetic material and gives shape to the virus. These viruses look like simple creatures but are culprits behind several deadly diseases that wiped out numerous other living organisms in the past. Let’s look at a disease caused by a hemorrhagic fever virus like Ebola, which becomes lethal if not treated promptly and carefully.

What is Dengue Fever?

It is a hemorrhagic fever caused by the dengue fever virus (DENV). Dengue fever virus belongs to the family flavivirus. It is an arbovirus because it mainly spreads through arthropods such as mosquitos and ticks.

Arthropods:

 Arthropods are the invertebrate animals that have a rigid external skeleton. Examples of arthropods are mosquitoes, ticks, lice, flies, and fleas. Other arthropod-borne viruses are yellow fever virus, West Nile virus, Zika virus, Omsk hemorrhagic fever virus, chikungunya virus, and Kyasanur forest disease virus.

Dengue fever virus contains RNA as its genome and various structural and non-structural proteins. There are four serotypes of the dengue fever virus, including DENV-1, DENV-2, DENV-3, and DENV-4, which belong to the genus flavivirus.

Transmission of Dengue Virus Disease

A female mosquito, Aedes aegypti, is an essential vector in the transmission of the dengue fever virus from person to person. Some species, including Aedes albopictus, Aedes polynesiensis, and Aedes scutellaris, are also known to spread this viral disease at a limited rate.

Humans and other mammals serve as primary hosts for this virus. Aedes aegypti can be differentiated from other mosquitoes by having a small, dark body and white dots all over the body. These mosquitoes prefer to live in areas with warm climates and dwell near humans.

Transmission cycle from human to human

Playing a single batch of eggs by female Aedes aegypti always requires multiple blood meals.

• If a person is already infected with the dengue virus, then during a specific period, his blood contains many viruses; this stage is called viremia.
• When a female mosquito, Aedes aegypti, feasts on that person’s blood during the viremia stage, the mosquito itself gets infected and serves as a vector for transmitting the disease to other persons.
• The virus then enters the mosquito, spreads inside its body, and eventually reaches its salivary glands within 8 to 12 days after the bite.
• The mosquito then becomes a source of transmission of the virus.
• It can infect other healthy individuals by injecting the dengue virus’s saliva. Dengue virus has no killing effects on mosquitos.

Mother-to-fetus transmission

It is also known as maternal transmission. When a pregnant woman is infected with the dengue virus, it can also cause infection in the fetus, leading to low transport of oxygen from mother to fetus, premature birth, and low birth weight.

Other modes of transmission

Organ transmission and blood transfusion are ways to transmit the dengue virus among persons.

Signs and Symptoms of Dengue Virus Disease

The incubation period ranges from 4 to 10 days. In most cases, patients show mild symptoms or no symptoms. Few people tend to have severe viral hemorrhagic fever.

The Dengue infection has three stages: febrile, critical, and recovery. So, a patient exhibits different symptoms with respect to these stages:

Febrile Phase Symptoms

The febrile phase consists of the following signs:

• A high-grade fever of 40 degrees Celsius
• Pain behind the eyes
• Rash
• Nausea
• Vomiting
• Muscle and joint pain.

Therefore, dengue is also referred to as breakbone fever. Rashes occur 2 to 3 days after the first symptom in almost 50-80% of the cases. This phase takes 2 to 7 days to resolve.

Critical Stage

 Most people start to recover after the febrile phase. But in some people, it proceeds to the critical stage where a patient experiences the following symptoms:

• Excessive fluids accumulate in the patient’s chest and abdominal cavity due to the discharge of plasma from blood vessels
• Blood volume starts to decrease
• Bleeding occurs from the nose, gums, and digestive tract due to a decreasing count of platelets.

This critical phase often results in dengue shock syndrome in 5% of the cases. This is called dengue hemorrhagic fever or severe dengue.

Recovery Phase

The next phase is the recovery phase, lasting from 2 to 3 days, in which the leaked-out fluids are re-absorbed by blood vessels. Dengue patients feel lethargic for some weeks.

Some other conditions are associated with dengue fever, which affects other body organs and their function. Heart and liver infections are also rare complications of dengue fever.

Diagnosis of Dengue Virus Disease

It is difficult to diagnose this disease as its symptoms relate to malaria, typhoid fever, and the zika virus. By taking tests, a doctor or physician can get to know about this disease’s presence.

Several other diagnostic methods are used to diagnose dengue fever virus in a patient’s blood sample. These tests may be serological, molecular, and antigen detection tests.

Serologic detection of dengue virus

Different types of antibodies are produced during infection and start their action to neutralize the pathogen that has invaded the human body. Among those antibodies, IgM antibody is produced in considerable amounts after 4 to 5 days from the appearance of the first symptom and remains in the stream for about 12 weeks.

MAC-ELISA test process:

• Detecting the virus through the MAC-ELISA test, which stands for IgM Antibody Capture Enzyme-Linked Immunosorbent Assay, is relatively more straightforward.
• This method uses serum or cerebrospinal fluid samples. The test is run in a microtiter plate already coated with anti-human-IgM antibodies.
• Suppose a serum sample containing IgM antibodies against dengue virus is poured into the container. In that case, the antibodies will bind to the already coated anti-human-IgM antibodies. Thus, no agglutination occurs, confirming a positive result for the presence of dengue virus in the blood.

Dengue virus antigen detection (NS1)

NS1 protein refers to non-structural protein 1 of the dengue virus, and it is present in the patient’s blood. NS1 tests are sensitive and are suggested within seven days of the infection onset.

NS1 test process:

• Serum, plasma, or blood can also be used in this test.
• This test employs rapid test kits or cassettes for NS1 detection.
• Specimen containing NS1 antigen binds to the gold antibody; as the reaction proceeds, this antigen-antibody complex will bind with Dengue NS1 antibody already coated on the membrane. This will give a dark pink to purple color, which indicates a positive test.

Besides serologic and antigen detection tests, real-time PCR is also a practical approach to detecting RNA of the dengue virus in patient samples. PCR and dengue NS1 detection tests give high-precision results during the first seven days of the infection onset.

Treatment of Dengue Virus Disease

There are no specific antiviral drugs designed to treat dengue infection, but various pain relievers and antipyretics are suggested to alleviate the severe pain in joints and headaches. Besides this, supportive care is also recommended to keep patients calm and less perplexed. Supportive care includes:

• Staying hydrated and maintaining sustainable body fluid volume
• Taking acetaminophen to reduce pain and body temperature
• Take a bath with lukewarm water
• Do not take anticoagulant drugs like aspirin and ibuprofen because they dilute the blood and increase the risk of blood leakage.
• Patients having infection under the febrile phase should avoid mosquito bites to avoid the further spread of dengue.

Supportive care, transfer of blood to level the loss of blood, and intravenous fluid are recommended to patients experiencing severe cases of dengue.

Vaccine Against Dengue Fever Virus

 Dengvaxia, a vaccine product by Sanofi, was introduced for people aged 9 to 45. This vaccine is delivered to patients in 3 doses for a duration of 12 months.

This vaccine is suggested to people who have already gone through dengue infection once, which means it is seropositive. It’s not recommended to a seronegative person because catching dengue infection from another serotype can initiate severe dengue and cause dengue hemorrhagic fever. Therefore, administering the vaccine to people who never had a dengue infection can cause severe dengue upon catching the dengue virus for the first time.

Prevention of Dengue Virus Disease

• Use insect repellants that contain DEET (N, N-diethyl-meta-toluamide) in an effective concentration against repelling mosquitoes and ticks.
• Fully cover your body, especially when going out in the evening.
• Discard contained water sources such as buckets and tubs, as Aedes prefer these places to lay eggs.
• Keep doors and windows closed in the morning and evening or night.
• If you are sleeping outdoors, using a mosquito net is an effective way to prevent mosquito bites.
• Stay in an air-conditioning house with screened doors or windows
• Check water-containing containers indoors and outdoors
• Avoid traveling to areas where dengue is common, especially when you are pregnant.
• While using sunscreen, apply sunscreen first, then use mosquito repellant

Preventive measures for children

• Dressup them with a whole arm and neck cover
• Cover the baby carries with the mosquito knitting
• Do not apply insect or mosquito repellant to the child’s hands, mouth, eyes and any infected area.

Final Thoughts

Dengue is a mosquito-borne disease, which means it’s a viral infection. It was first discovered in the 1950s in the region of South Asia. Central America, South America, Africa, the Caribbean, a few parts of Asia, and the Pacific islands are the regions where the dengue fever virus is commonly found. European countries such as Italy, France, Spain, and Croatia have also reported several dengue cases. Approximately 400 million people catch the virus each year.

The unique aspect of it is its severe symptoms, which include hemorrhagic fever, which leads to bleeding and organ damage; in some potential cases, these severe symptoms ultimately cause death. The mortality rate of dengue globally is estimated at 10,000 deaths, which makes this infection a public concern.

Frequently Asked Questions – FAQs

About the author

Dr Madilyn Adams is a PhD in molecular medicine from Harvard University and has been working as a medical blogger for seven years.

References

1. https://www.webmd.com/a-to-z-guides/dengue-fever-reference
2. https://www.who.int/news-room/fact-sheets/detail/dengue-and-severe-dengue
3. https://www.cdc.gov/dengue/about/index.html
4. https://www.mayoclinic.org/diseases-conditions/dengue-fever/symptoms-causes/syc-20353078
5. https://www.cdc.gov/dengue/index.html