Dengue is a mosquito-borne viral disease that has rapidly spread in recent years around the world.
Dengue virus is transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, Ae. albopictus.
These mosquitoes are also vectors of chikungunya, yellow fever and Zika viruses. Dengue is widespread throughout the tropics, with local variations in risk influenced by rainfall, temperature, relative humidity and unplanned rapid urbanization.
Dengue causes a wide spectrum of disease. This can range from subclinical disease (people may not know they are even infected) to severe flu-like symptoms in those infected. Although less common, some people develop severe dengue, which can be any number of complications associated with severe bleeding, organ impairment and/or plasma leakage. Severe dengue has a higher risk of death when not managed appropriately. Severe dengue was first recognized in the 1950s during dengue epidemics in the Philippines and Thailand. Today, severe dengue affects most Asian and Latin American countries and has become a leading cause of hospitalization and death among children and adults in these regions.
Dengue is caused by a virus of the Flaviviridae family and there are four distinct, but closely related, serotypes of the virus that cause dengue (DENV-1, DENV-2, DENV-3 and DENV-4). Recovery from infection is believed to provide lifelong immunity against that serotype. However, cross-immunity to the other serotypes after recovery is only partial, and temporary. Subsequent infections (secondary infection) by other serotypes increase the risk of developing severe dengue.
Dengue has distinct epidemiological patterns, associated with the four serotypes of the virus. These can co-circulate within a region, and indeed many countries are hyper-endemic for all four serotypes. Dengue has an alarming impact on both human health and the global and national economies. DENV is frequently transported from one place to another by infected travellers; when susceptible vectors are present in these new areas, there is the potential for local transmission to be established.
SYMPTOMS
Dengue should be suspected when a high fever (40°C/104°F) is accompanied by 2 of the following symptoms during the febrile phase:
- severe headache
- pain behind the eyes
- muscle and joint pains
- nausea
- vomiting
- swollen glands
- rash.
Severe dengue
A patient enters what is called the critical phase normally about 3-7 days after illness onset. It is at this time, when the fever is dropping (below 38°C/100°F) in the patient, that warning signs associated with severe dengue can manifest. Severe dengue is a potentially fatal complication, due to plasma leaking, fluid accumulation, respiratory distress, severe bleeding, or organ impairment.
Warning signs that doctors should look for include:
- severe abdominal pain
- persistent vomiting
- rapid breathing
- bleeding gums
- fatigue
- restlessness
- blood in vomit.
If patients manifest these symptoms during the critical phase, close observation for the next 24–48 hours is essential so that proper medical care can be provided, to avoid complications and risk of death.
TREATMENT
There is no specific treatment for dengue fever.
Fever reducers and pain killers can be taken to control the symptoms of muscle aches and pains, and fever.
The best options to treat these symptoms are acetaminophen or paracetamol.
NSAIDs (non-steroidal anti-inflammatory drugs), such as ibuprofen and aspirin should be avoided. These anti-inflammatory drugs act by thinning the blood, and in a disease with risk of hemorrhage, blood thinners may exacerbate the prognosis.
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% to less than 1%. Maintenance of the patient’s body fluid volume is critical to severe dengue care. Patients with dengue should seek medical advice upon the appearance of warning signs.
Vaccination against dengue
The first dengue vaccine, Dengvaxia® (CYD-TDV) developed by Sanofi Pasteur was licensed in December 2015 and has now been approved by regulatory authorities in ~20 countries. In November 2017, the results of an additional analysis to retrospectively determine serostatus at the time of vaccination were released. The analysis showed that the subset of trial participants who were inferred to be seronegative at time of first vaccination had a higher risk of more severe dengue and hospitalizations from dengue compared to unvaccinated participants. As such, use of the vaccine is targeted for persons living in endemic areas, ranging from 9-45 years of age, who have had at least 1 documented dengue virus infection previously.
WHO position on the CYD-TDV vaccine
The live attenuated dengue vaccine CYD-TDV has been shown in clinical trials to be efficacious and safe in persons who have had a previous dengue virus infection (seropositive individuals).
However, it carries an increased risk of severe dengue in those who experience their first natural dengue infection after vaccination (those who were seronegative at the time of vaccination).
For countries considering vaccination as part of their dengue control programme, pre-vaccination screening is the recommended strategy. With this strategy, only persons with evidence of a past dengue infection would be vaccinated (based on an antibody test, or on a documented laboratory confirmed dengue infection in the past).
Decisions about implementing a pre-vaccination screening strategy will require careful assessment at the country level, including consideration of the sensitivity and specificity of available tests and of local priorities, dengue epidemiology, country-specific dengue hospitalization rates, and affordability of both CYD-TDV and screening tests.
Vaccination should be considered as part of an integrated dengue prevention and control strategy. There is an ongoing need to adhere to other disease preventive measures such as well-executed and sustained vector control. Individuals, whether vaccinated or not, should seek prompt medical care if dengue-like symptoms occur.
PREVENTION AND CONTROL
If you know you have dengue, avoid getting further mosquito bites during the first week of illness. Virus may be circulating in the blood during this time, and therefore you may transmit the virus to new uninfected mosquitoes, who may in turn infect other people.
The proximity of mosquito vector breeding sites to human habitation is a significant risk factor for dengue as well as for other diseases that Aedes mosquito transmit. At present, the main method to control or prevent the transmission of dengue virus is to combat the mosquito vectors. This is achieved through:
Prevention of mosquito breeding
Preventing mosquitoes from accessing egg-laying habitats by environmental management and modification;
Disposing of solid waste properly and removing artificial man-made habitats that can hold water;
Covering, emptying and cleaning of domestic water storage containers on a weekly basis;
Applying appropriate insecticides to water storage outdoor containers;
Personal protection from mosquito bites:
Using of personal household protection measures, such as window screens, repellents, insecticide treated materials, coils and vaporizers. These measures must be observed during the day both inside and outside of the home (e.g.: at work/school) because the primary mosquito vectors bites throughout the day;
Wearing clothing that minimises skin exposure to mosquitoes is advised;
Community engagement:
Educating the community on the risks of mosquito-borne diseases;
Engaging with the community to improve participation and mobilization for sustained vector control;
Reactive vector control:
Emergency vector control measures such as applying insecticides as space spraying during outbreaks may be used by health authorities;
Active mosquito and virus surveillance:
Active monitoring and surveillance of vector abundance and species composition should be carried out to determine effectiveness of control interventions;
Prospectively monitor prevalence of virus in the mosquito population, with active screening of sentinel mosquito collections;
In addition, there is ongoing research amongst many groups of international collaborators in search of novel tools and innovative strategies that will contribute in global efforts to interrupt transmission of dengue, as well as other mosquito-borne diseases.
The integration of vector management approaches is encouraged by WHO to achieve sustainable, effective locally adapted vector control interventions.
SOURCE: WHO
