In several Asian countries, severe dengue fever is the main cause of serious illness and death. The transmission, clinical manifestation, diagnosis and prevention of dengue fever along with the vaccination updates by WHO are elucidated in this article.

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Dengue fever

Due to dengue fever's acute viral nature, it has the potential to cause large-scale outbreaks. Dengue risk has increased in recent years as a result of rapid urbanisation, lifestyle changes, and inadequate water management, including inappropriate water storage techniques in urban, peri-urban, and rural regions.

An arthropod-borne viral illness known as dengue fever is spread by mosquitoes. There are many other names for it, including "breakbone fever," "dandy fever," and "seven-day fever," all of which refer to how long symptoms last. Even though the vast majority of instances go unnoticed, serious disease and death may occur.

Clinical and laboratory data are combined as part of a broad-based examination to provide a comprehensive picture of a patient's overall health and current therapy. Fluid infusion parameters such as volume, rate, and type are all based on this knowledge. Dengue-related fatalities may be prevented in the vast majority of cases.

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Transmission

Spread using the mosquito bite

1. Four separate serotypes of dengue viruses (DENV 1-4) of single-stranded RNA viruses of the genus Flavivirus cause dengue illness. The virus is spread to humans largely via the bites of infected female Aedes albopictus mosquitoes.
2. After feeding on a person infected with DENV, the virus replicates in the midgut of the mosquito before spreading to secondary tissues, such as the salivary glands. The duration between viral ingestion and transmission to a new host is known as the extrinsic incubation period (EIP). The EIP takes between 8 and 12 days when the ambient temperature is between 25 and 28 degrees Celsius.
3. Variations in the extrinsic incubation period are not only affected by ambient temperature, but also by a variety of other variables, including the amplitude of daily temperature oscillations, the virus genotype, and the initial viral concentration. Once infected, the mosquito may spread the virus for the remainder of its life.

Human-to-mosquito spread

1. DENV-infected individuals may transmit the virus to mosquitoes. This may be a person with asymptomatic dengue infection, a person who has not yet developed symptoms (they are pre-symptomatic), as well as asymptomatic individuals (they are asymptomatic).
2. Human-to-mosquito transmission may occur up to two days before the onset of symptoms and up to two days after the fever subsides.
3. The risk of mosquito infection is positively correlated with a patient's high viremia and fever. The average duration of viremia is 4-5 days, although it may extend as long as 12 days.

Various other methods of transmission

There have been rare instances of transfer by:

• Blood products
• Organ donation
• Transfusions

Although low there is evidence however of vertical transmission from a pregnant mother to her baby and it is related to the timing of the dengue infection during the pregnancy.

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Clinical manifestations

While the majority of dengue infections are asymptomatic or have moderate symptoms, it may produce severe flu-like disease in babies, young children, and adults, but rarely results in death. Symptoms typically persist 2–7 days after an incubation period of 4–10 days after a mosquito bite.

Dengue

During the febrile phase (2-7 days), Dengue should be considered when a high fever (40°C/104°F) is accompanied by two of the following symptoms:

• Muscular and joint discomfort.
• Severe headache.
• Retro-orbital pain.
• Rash( the rash is a maculopapular or macular confluent rash over the face, thorax, and flexor surfaces beginning on day 3 and persisting for 2-3 days) 
• Nausea, vomiting.
• Enlarged lymph nodes.

Severe dengue

About 3-7 days following the commencement of the disease, a patient reaches the crucial period. A small percentage of patients may have a dramatic worsening of symptoms during the critical period, which lasts 24-48 hours. When the patient's fever drops below 38 degrees Celsius (100 degrees Fahrenheit), warning indications of severe dengue might appear.

Due to plasma leaking, fluid buildup, respiratory difficulty, severe bleeding, or organ dysfunction, severe dengue is a potentially lethal consequence. The following are red flags that medical professionals should be on the lookout for :

• Severe abdominal pain.
• Recurring vomiting.
• Tachypnea
• Gum or nose bleeding.
• Exhaustion and restlessness.
• Enlargement of the liver.
• Blood in the stool or vomit.

If these symptoms appear during the critical period, patients must be closely monitored for the following 24–48 hours in order to get effective medical treatment and prevent complications and death. During the convalescent period, close surveillance should be maintained.

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Diagnosis

DENV infection may be diagnosed using a variety of ways. Different diagnostic procedures may be more or less suitable depending on the time of the patient's presentation. Both procedures listed below should be used to analyse patient samples taken during the first week of sickness.

1. Virus isolation methods

1. Reverse-transcriptase polymerase chain reaction (RT-PCR) for detection of viral genomic sequences in serum, or cerebral spinal fluid (CSF) samples
2. Serum dengue virus antigen (NS1) detection using commercially-produced rapid diagnostic tests takes only ~20 mins to determine the result.

2. Serological methods

Anti-dengue antibodies may be detected using serological techniques such as enzyme-linked immunosorbent assays (ELISA), which can establish the existence of a recent or prior infection. IgM antibodies may be detected one week after infection and last for roughly three months. The presence of IgM indicates that you have recently been infected with DENV. IgG antibody levels take longer to develop and might last for years in the body. The presence of IgG indicates a previous infection.

Consider the diagnosis of Dengue Haemorrhagic Fever if the patient has a confirmed diagnosis of dengue fever with the following symptoms:

• Petechiae, ecchymoses or purpura.
• Haematemesis or malena.
• GI or injection site bleeding.
• Thrombocytopenia

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Management

Dengue fever does not have a particular therapy. Patients should get plenty of rest, drink plenty of water, and seek medical guidance. Patients may be sent home, sent for in-hospital care, or need emergency treatment and urgent referral, depending on the clinical symptoms and other conditions.

To treat the symptoms of muscular aches and pains, as well as fever, supportive care such as fever reducers and pain relievers may be used.

1. Acetaminophen or paracetamol are the best treatments for these symptoms.
2. NSAIDs, such as ibuprofen and aspirin, should be avoided. These anti-inflammatory medications thin the blood, and blood thinners may worsen the prognosis of an illness with a risk of bleeding.

In the case of severe dengue, the medical treatment provided by doctors and nurses who are familiar with the disease's symptoms and course may save lives, lowering fatality rates to less than 1% in the majority of nations.

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Dengue vaccine

Sanofi Pasteur produced the first dengue vaccine, Dengvaxia (CYD-TDV), which was authorised by regulatory bodies in 20 countries in December 2015. The findings of an additional investigation to establish serostatus at the time of immunisation were released in November 2017. When compared to unvaccinated individuals, the subgroup of trial participants who were inferred to be seronegative at the time of first immunisation had a greater risk of severe dengue and dengue hospitalisations. As a result, the CYD-TDV vaccination is intended for those aged 9 to 45 who live in endemic regions and have had at least one episode of dengue virus illness. Several more dengue vaccine candidates are being tested.

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WHO views on vaccine CYD-TDV

The live attenuated dengue vaccine CYD-TDV has been demonstrated in clinical studies to be effective and safe in people who have had a past dengue virus infection, according to the WHO position paper on the Dengvaxia vaccine (September 2018). (seropositive individuals). Pre-vaccination screening is the recommended technique for nations contemplating vaccination as part of their dengue control programme.

Vaccination should be explored as part of a comprehensive approach to preventing and controlling dengue fever. Other disease prevention strategies, such as well-executed and prolonged vector control, must continue to be followed. If somebody develops dengue-like symptoms, whether or not they have been vaccinated, they should seek medical attention very once.

Prevention and control

1. If you have dengue, avoid being bitten by mosquitoes during the first week of your sickness. Viruses may be circulating in your blood during this period, and you might spread them to fresh uninfected mosquitoes, who could then infect other individuals.
2. At the moment, the primary technique for controlling or preventing dengue virus transmission is to attack mosquito vectors. This is accomplished by:

• Mosquito breeding prevention.
• Personal mosquito bite protection.
• Active mosquito and virus surveillance.

As a result of the COVID-19 pandemic, global health care and management systems are being put under tremendous strain. During this pandemic, WHO has stressed the necessity of continuing efforts to prevent, diagnose, and treat vector-borne illnesses such as dengue and other arboviral infections, as case numbers rise in various countries, putting urban people at risk for both diseases. The combined effects of the COVID-19 and dengue fever outbreaks might be disastrous for the communities at risk.

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This is the next article of our monsoon series. To read the earlier articles of the series, click here: Malaria in monsoon: Recent updates

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Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.

The author is a practising super specialist from New Delhi.