Dengue Fever

Dengue is a viral disease caused by a virus spread by the Aedes mosquito. An infected female Aedes aegypti mosquito is the “vector” of this disease, which means that it carries and spreads the dengue virus from one person to the other. The mosquito itself acquires the virus while feeding on the blood of an infected person. It is also known as ‘break-bone’ fever as it is typically associated with severe muscle and joint pain.

Over the last several years, there have been numerous outbreaks of dengue. Older data suggest an average of 5 to 10 crore cases of dengue fever and 5 lakh cases of dengue hemorrhagic fever occurrences worldwide, with 22,000 deaths, mostly in children. Approximately 40%-50% of the world’s population in around 112 tropical and subtropical countries are considered at high risk of contracting dengue. Antarctica is the only continent yet to experience the spread of dengue. In 2015, Delhi alone recorded 15,000 cases of dengue, the highest since 2006.

Once an infected Aedes aegypti mosquito bites a person, that person also gets infected. After this, that person acts as a source of the virus to uninfected mosquitoes. These mosquitoes then become the main carriers where the dengue virus can multiply and increase in number. The virus keeps multiplying and circulating in the blood of the infected person for two to seven days (incubation period) after which the person starts developing symptoms. After the incubation period, the dengue virus usually follows a life cycle that can be divided into the following three stages:

• Febrile stage
  This stage begins with the onset of symptoms and lasts for approximately a week. Proper monitoring is essential at this phase to prevent complications.
• Critical stage 
  It begins around the time when the temperature of the body drops to less than 38°C and remains as such. This stage is critical for monitoring the blood counts (blood platelets) as they can fall considerably, causing complications.
• Recovery or Convalescent stage 
  This is the stage when the person shows a sudden improvement in health.

A person suffering from dengue fever usually has a history of recent visit to a region where the disease is endemic or a visit from an individual living there. Dengue is associated with the following signs and symptoms:

• A sudden onset of high fever (40°C/ 104°F), and the temperature has a continuous or ‘saddle-back' pattern, with a break on the fourth or fifth day and then again followed by an upsurge. The fever usually lasts for seven to eight days.
• An intense headache.
• Nausea and vomiting.
• Pain in the joints, muscles and behind the eyes.
• Weakness.
• An altered taste sensation, and reduced appetite (anorexia).
• A sore throat.
• Swelling of the glands and lymph nodes.
• Rashes, comprised of an initial flushing of the skin along with the appearance of a faint macular rash within the first couple of days. Flat red rashes that are covered with small confluent bumps that blanch on pressure start appearing from the third to fifth day. They generally develop on the trunk from where they spread to other areas. Only the palms and soles are spared. The onset of a rash is usually associated with a reduction in body temperature. The rash may come off in flakes or give rise to small red spots (due to bleeding) that are called as petechiae.
• Mild bleeding symptoms that include bleeding gums, nosebleed, abnormally heavy bleeding during menstruation and the presence of blood in urine.

After an infected mosquito transmits the virus to a person, the symptoms prevail for two to seven days, after an incubation period of approximately four to ten days.

Severe dengue is a very serious complication that can be fatal. It occurs three to seven days after the first symptoms occur. Along with a reduction in body temperature (less than 38 °C), the warning signs to look out for include:

• Persistent vomiting.
• Blood stained vomit.
• Rapid or difficulty in breathing (respiratory distress).
• Bleeding gums.
• Severe stomach pain.
• Fatigue.
• Restlessness.
• Dengue shock syndrome
  This is a serious complication of dengue fever. It results when a person who is already infected with the dengue virus gets another infection from a different dengue virus. The development of dengue shock syndrome with consequent multi-organ failure proves fatal.

The recovery period lasts for a long time and may require up to two weeks. The person may feel fatigue and exhaustion for a long duration even after the symptoms have subsided. 

Causes

Dengue may be caused by any one of the four types (DENV-1, DENV-2, DENV-3, and DENV-4) of dengue virus, which are spread by the female Aedes aegypti mosquito commonly found in and near human settlements. The infected Aedes aegypti mosquito bites a person, in turn, infecting them. Once infected, that person becomes the source of virus for other uninfected mosquitoes. Thus, the person not only carries the virus but the body also becomes a host for the multiplication of the dengue virus. The virus then circulates in the blood of the infected person for two to seven days (incubation period). Shortly after the incubation period, the infected person starts developing initial symptoms of dengue. After recovery from dengue fever, the person develops immunity to the type of virus that caused the infection, but not to the other three types of the virus.

The Aedes aegypti mosquito mostly breeds in the water that gets collected in the man-made containers. It feeds during the day, especially in early morning and right before dusk. During each feeding period, the female Aedes aegypti mosquito can bite and infect several people.

The Aedes albopictus mosquito, yet another type of dengue transmitter in Asia. According to the WHO reports, this mosquito has spread to other countries as well. It has been found to inhabit and breed in the used tyres that are exported to the European countries. Because of its adaptive nature, even harsh and cold temperate regions do not threaten its survival.

Risk Factors

The risk factors of acquiring dengue fever are:

• Visiting or living in a dengue endemic area.
• Ignoring preventive measures that provide protection from mosquito bites.
• Weak immunity.
• Unhygienic surroundings and living or working in crowded places.
• Unhealthy lifestyle.

The most optimum way to prevent getting dengue is to avoid being bitten by an infected mosquito. Preventive measures to achieve this include:

• Wearing long-sleeved clothes that minimise skin exposure.
• Applying mosquito repellents generously on exposed areas of the skin before stepping out.
• Staying in well-ventilated and well-screened places.
• Using indoor sprays to get rid of mosquitoes. Use of mosquito nets treated with a mosquito repellent or insecticide provides sufficient protection, especially to the sick, elderly, infants, and late night workers.
• Avoiding water stagnation. Dengue larvae breed in stagnant water. So, in order to manage their breeding, water storage vessels should be properly, covered and frequently cleaned.
• Recycling or properly disposing off the old tires and containers, as they may be a potential breeding ground for dengue larvae (if rainwater accumulates in them).
• Using insecticides, vaporisers, aerosol products, and mosquito coils to manage indoor mosquitoes.
• Getting timely immunization.

In 2015, the first dengue vaccine, Dengvaxia (CYD-TDV) was registered for use in individuals between 9 to 45 years of age who live in endemic areas that have a higher prevalence of dengue. 

Since dengue fever has symptoms that could be easily confused with other viral infections, your doctor will recommend specific blood tests to confirm the diagnosis. These include:

• Dengue NS1 antigen test 
  In this test, the blood serum level of NS1 antigen, a protein produced by the dengue virus, is checked. This test is performed within the first week of the appearance of symptoms. High levels of NS1 antigen suggests the presence of high levels of dengue virus in the blood.
• Dengue IgM/IgG serological test 
  This test is usually carried out on the fifth day of the onset of illness. NS1 antigen remains detectable only up to the ninth day of illness. Thus, the infected person may test negative for dengue later, if tested just for the NS1 antigen.

Besides the tests mentioned above, the following tests may also be advised:

• Complete blood cell (CBC) count
  A complete blood count involves estimating the levels of haemoglobin, platelets and white blood cells. A fall in platelet count is typical of advanced stages of dengue. 
• Liver function tests 
  These include testing for liver enzymes like liver proteins, alkaline phosphatase, ALT, AST, bilirubin, chlorides, GGT, and urobilinogen in urine.
• Metabolic panel test 
  It is of two types:
  • Basic metabolic panel (BMP) 
    These tests check for calcium, blood sugar, electrolytes, and creatinine levels.
  • Comprehensive metabolic panel (CMP) 
    This test includes all the tests of the basic metabolic panel in addition to tests that check for levels of cholesterol, protein and assessment of liver function and its enzymes.

Certain other illnesses have symptoms similar to those of dengue, and therefore dengue can sometimes be misdiagnosed. Hence, the following conditions should be considered in the differential diagnosis of dengue:

• Influenza or flu.
• Viral Hepatitis, i.e., an inflammation or swelling of the liver due to the hepatitis virus.
• Typhus, which is a bacterial infection spread by parasites and insects.
• Malaria that is a mosquito-borne disease caused by the parasite Plasmodium.
• Chikungunya, a viral disease caused by the Chikungunya virus and spread by Aedes aegypti.
• Rickettsial Infection, a type of bacterial infection.
• Leptospirosis, a bacterial infection.
• Idiopathic Thrombocytopenic Purpura (ITP), a disorder that leads to excessive bleeding or bruising.
• Yellow Fever, a viral disease caused by the yellow fever virus and spread by mosquitoes.
• Meningitis, an inflammation of the coverings of the brain and the spinal cord.
• Ebola fever, a viral haemorrhagic (causing haemorrhage) fever caused by the Ebola virus.
• Zika virus infection, a mosquito-borne infection.
• Roseola infantum, a common childhood infection caused by the herpes virus.
• Scarlet fever, a type of bacterial infection.
• Haemorrhagic fever.
• Rocky Mountain Spotted Fever (RMSF), a bacterial illness spread through the bite of an infected tick.
• Sindbis virus infection transmitted by Culex mosquito.

No specific antiviral treatment has been employed for dengue fever till date. The disease is usually self-limiting, i.e., it resolves by itself over a period of time. However, self-care and lifestyle modification are required to control and reduce the intensity of symptoms.

You should contact your doctor if you develop a fever or flu-like symptoms within two weeks of returning from an area where the dengue virus is endemic. Also, if you live in an area where dengue is common, go to the doctor if you develop any such symptoms.

Supportive care with medicines to bring down the fever along with adequate hydration and bed rest are recommended. Acetaminophen may be used to resolve fever. Painkillers (such as aspirin) and corticosteroids should not be taken in dengue without a doctor’s consultation. For the relief of skin rashes, you may apply calamine lotion. Those who improve are monitored in an outpatient setting.

Hospitalisation is recommended if there is:

• Persistent vomiting.
• Blood in the vomit.
• Signs of dehydration.
• Rapid breathing (respiratory distress).
• Bleeding from the gums.
• Severe pain in the abdomen.
• Severe fatigue and restlessness.

Lifestyle management

people with dengue fever may have to make certain changes in their lifestyle to recover faster. These are:

• Drinking ORS (Oral Rehydration Solution) if the person is able to take fluids orally.
• Drinking fruit juices.
• Taking adequate rest.
• Avoiding physical activities that worsen fatigue and weakness. 
• Using insecticide-treated mosquito nets to prevent secondary infection by the other types of dengue viruses.
• Using mosquito repellents and insecticides indoors as well as outdoors.

Prognosis

Dengue fever is mostly self-limiting if proper medical and supportive care is provided. Even after treatment, the death rate associated with severe dengue is 2%-5%. However, if left untreated, the death rate may shoot up to 20%. A person who recovers from dengue develops a lifelong immunity to the type of virus that had caused the infection.

Factors that affect disease severity include:

• Nutritional status of the affected person.
• Age.
• Ethnicity.
• The type of dengue virus infection.
• Pregnancy.
• The sequence of infection with different types of dengue viruses.
• Quality and extent of medical care available. If appropriate medical care is available at the onset, then the progression of the disease can be halted.

Complications

Some people may develop serious complications. These include:

• Dengue hemorrhagic fever 
  It is a condition in which there is a high fever, bleeding from the gums and nose, swelling of the liver and failure of the circulatory system.
• Disseminated intravascular coagulation (DIC) 
  This is a condition in which small blood clots develop throughout the bloodstream, blocking small blood vessels.
• Dengue shock syndrome 
  It is caused when the dengue fever is left untreated and it results in stomach pain, bleeding and circulatory collapse (shock).
• Hepatitis 
  Inflammation or swelling of the liver.
• Encephalitis 
  Inflammation of the brain tissues. It may also be associated with bleeding or haemorrhage in the brain.
• Cranial nerve palsies 
  It is the dysfunction of the cranial nerves.
• Rhabdomyolysis 
  Rhabdomyolysis is characterised by destruction of the skeletal muscle resulting in leakage of the muscle protein into the urine.
• Myocarditis 
  Myocarditis is an inflammation of the heart muscle.
• Mother-fetal transmission 
  Transmission of the virus from the mother to the baby if infection occurs within five weeks of delivery.