Dengue fever

Severe dengue fever affects most countries in Asia and Latin America. Globally there are approximately 390 million dengue fever infections per year, of which 96 million have a clinical manifestation. An estimated 500,000 people with severe dengue fever require hospitalization each year, and about 2.5 per cent of those affected die. The risk of epidemics is present in areas where the vector (Aedes mosquito) exists. 

The following are standard case definitions to allow national health authorities to interpret data in an international context. However, during an outbreak case definitions may be adapted to the local context and the Red Cross Red Crescent should use those agreed/established by national health authorities. NB: Consider that during community-based surveillance, volunteers should use broad (simplified) case definitions (referred to as community case definitions) to recognize most or all possible cases, provide relevant risk communication and appropriate actions and encourage them to seek care. Other actors such as healthcare workers or investigators studying the cause of a disease, on the other hand, can use more specific case definitions that may require laboratory confirmation.

Probable dengue fever:

• Fever AND two or more of the following criteria: nausea/vomiting, rash, aches and pains, clinical test for capillary fragility positive (tourniquet test), low white blood cells or warning signs.
• Warning signs can be: abdominal pain or tenderness, persistent vomiting, clinical fluid accumulation, mucosal bleed, lethargy, restlessness, liver enlargement greater than 2cm; laboratory: increase in haematocrit concurrent with rapid decrease in platelet count.

Confirmed case: A probable case with laboratory confirmation.

WHO case definition source of information: https://www.who.int/docs/default-source/outbreak-toolkit/updates-documents_july-5/dengue-outbreak-data-collection-toolbox---inis-3-july-1.pdf?sfvrsn=ec3ffcf3_2#:~:text=WHO%20surveillance%20case%20definition,leukopenia%2C%20or%20any%20warning%20sign.

At the local level a single dengue case may trigger action. At state or provincial level, the increase in reported cases above an established baseline for the same week or month in preceding years or increasing vector density may indicate impending epidemic activity. At national level, the detection of changes in virus serotype, subtype or genotype distribution, clinical severity or seropositivity rate, or the introduction of a dengue vector into a new ecological niche, are signals that should be investigated without delay.

• Dengue is widespread throughout the tropics with local variations in risk influenced by rainfall, temperature, relative humidity and unplanned rapid urbanization.
• Mosquitoes carrying the dengue virus often live in urban habitats and breed mostly in man-made containers that hold water, like buckets, bowls or flowerpots.
• Outbreaks of the disease are of particular concern when they occur in overcrowded settings with inadequate water supply and waste management services that allow the mosquitoes to breed easily.
• Aedes aegypti is a daytime feeder; its peak biting periods are early in the morning and in the evening before sunset. People being outside at this time are at higher risk of being bitten. Children and elderly who sleep outdoors during daytime in endemic areas are at greater risk.
• When infected during pregnancy, women can transmit a dengue infection to their foetus.
• People needing blood transfusion or organ transplantation in endemic areas.

Attack rates will vary from one outbreak to another. In case of an outbreak, consult the latest information provided by health authorities.

During epidemics of dengue fever, attack rates among susceptible populations are often 40–50 per cent, but may reach 80–90 per cent.

• People with weakened immune systems such as people with HIV infection, those receiving chemotherapy or transplant recipients.
• People with chronic diseases.

Dengue virus: four serotypes of dengue viruses exist.

Vector: Mosquitoes (Aedes aegypti and Aedes albopictus) that carry the dengue virus.

Humans.

Vector-borne:

• Mosquito bite (mainly of the species Aedes aegypti and, to a lesser extent, Ae. albopictus).
• The mosquitoes usually bite during the daytime (peak biting periods are early in the morning and in the evening at dusk).

Congenital transmission: From mother to child during pregnancy.

Vehicle-borne transmission: Through organ transplants or blood transfusions from infected donors.

Four to seven days (range three to ten days).

Patients who are already infected with the dengue virus can transmit the infection (four to five days; maximum 12) via Aedes mosquitoes after their first symptoms appear.

• Up to 75 per cent of people infected with dengue have no symptoms.
• 25 per cent of people have symptoms: biphasic disease which starts with sudden fever, muscle and joint pain and possible additional symptoms (stadium 1).
• Additional symptoms can be severe headache, pain behind the eyes, nausea, vomiting, swollen glands and a rash.
• After 3—5 days of transient fever, a new fever increase marks the begin of stadium 2 with possible rash.
• In some very severe cases (1—2 per cent), dengue fever can cause severe abdominal pain, difficulty breathing and life-threatening bleeding (known as “dengue haemorrhagic fever”). This is particularly the case in consecutive infections of a person with different serotypes. The second infection by a different serotype to the first is thought to be associated with the highest risk of severe dengue, while the third and fourth infections are usually associated with a milder clinical course.

Zika virus disease, chikungunya, Lassa fever, Crimean-Congo fever, Ebola virus disease, yellow fever, Marburg virus disease, hantavirus pulmonary syndrome, malaria, typhoid fever and other haemorrhagic infections.

• Nucleid acid amplification tests (NAATs) for detection of virus particles.
• Serologic tests: IgM antibody testing is an important diagnostic tool. However, interpreting the results is complicated by cross-reactivity with other flaviviruses, like Zika virus or yellow fever virus.

Please refer to the appropriate local or international guidelines for clinical management. All clinical management including the administration of any treatment or vaccine should be conducted by health professionals.

Important therapy principles include following:

• There is no specific treatment to cure dengue fever, but supportive care is important and can prevent complications including death.
• For severe dengue, medical care by physicians and nurses experienced with the effects and progression of the disease can save lives, decreasing mortality rates from more than 20 per cent to less than one per cent. Maintenance of the patient's body fluid volume is critical to severe dengue care.
• Care should be taken to avoid certain medications, such as aspirin or other nonsteroidal anti-inflammatory drugs (e.g. Ibuprofen, Naproxen), which may increase the risk of bleeding.

Dengue vaccine is available (three dose series given six months apart, 9—45 years). However, recent evidence indicates potential long-term safety issues in seronegative individuals when vaccine is used. The current Strategic Advisory Group of Experts’ (SAGE) recommendation is that for countries considering vaccination as part of their dengue control programme, a “pre-vaccination screening strategy” would be the preferred option, in which only dengue-seropositive persons are vaccinated. This will require careful assessment at the country level, including sensitivity and specificity of a screening, dengue hospitalization rates, and affordability of pre-vaccination screening. If vaccines are used, it should be considered as part of an integrated dengue prevention and control strategy together with effective vector control and clinical care.

• Recovery from infection by one dengue virus provides lifelong immunity against that particular virus serotype. However, this immunity gives only partial and transient protection against new infection by the other three serotypes of the virus. The efficacy of the vaccine against laboratory confirmed dengue, measured for 12 months after the last dose, was 59 per cent in the year following the primary series, and 79 per cent against severe dengue fever.