What is ... Dengue?
Dengue is a mosquito-borne viral infection. It is caused by any one of four closely related dengue viruses. The viruses are transmitted to humans by the bite of an infected mosquito.
Dengue is the most rapidly spreading mosquito-borne viral disease, with a 30-fold increase in global incidence over the past 50 years.
Please find more information on this disease in the text below or watch expert interview:
What is the disease?
What is dengue hemorrhagic fever (DHF)?
DHF is a more severe form of dengue infection. It can be fatal if unrecognized and not properly treated. DHF is caused by infection with the same viruses that cause dengue fever.
How dangerous is Dengue?
With good medical management, mortality due to DHF can be less than 1%.
Infection with one serotype does not protect against the others, and sequential infections put people at greater risk for dengue hemorraghic fever (DHF) and dengue shock syndrome (DSS).
Who is at risk?
All people living in or traveling to the tropics or subtropics. With about 2.5 billion people, or 40% of the world’s population, living in areas where there is a risk of dengue transmission, dengue virus is a leading cause of illness and death in the tropics and subtropics.
How many people are affected by Dengue?
According to the WHO 50 to 100 million infections occur yearly, including 500,000 DHF cases and 22,000 deaths, mostly among children.
Where is Dengue found?
Dengue is endemic in at least 100 countries in Asia, the Pacific, the Americas, Africa, and the Caribbean. It is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas but close to 75% of the global population exposed to dengue are in the Asia-Pacific region.
Outbreaks of dengue occur primarily in areas where Ae. aegypti and sometimes also Ae. albopictus mosquitoes live. This includes most tropical urban areas of the world.
How do people get Dengue?
Dengue cannot be spread directly from person to person.
It is transmitted to people by the bite of an Aedes mosquito that is infected with a dengue virus. The adult mosquitoes bite inside as well as around homes, during the day and at night when the lights are on.
SYMPTOMS AND COURSE
What are the signs and symptoms of Dengue?
Symptoms of infection usually begin 4 – 7 days after the mosquito bite and typically last 3 – 10 days.
The principal symptoms of dengue are:
- high fever and at least two of the following:
- severe headache
- severe eye pain behind the eyes
- joint pain
- muscle and/or bone pain
- mild bleeding manifestation e.g., nose or gum bleed, petechiae, or easy bruising
- low white cell count
Generally, younger children and those with their first dengue infection have a milder illness than older children and adults.
How is the disease developing?
The infection causes flu-like illness, and occasionally develops into a potentially lethal complication called severe dengue or dengue hemorrhagic fever (DHF).
Dengue hemorrhagic fever is characterized by a fever that lasts from 2 to 7 days, with general signs and symptoms consistent with dengue fever.
When the fever declines, symptoms including
- persistent vomiting
- severe abdominal pain
- difficulty breathing
may develop. This marks the beginning of a 24- to 48-hour period when the smallest blood vessels (capillaries) become excessively permeable (“leaky”), allowing the fluid component to escape from the blood vessels into the peritoneum causing ascites and pleural cavity leading to pleural effusions.
This may lead to failure of the circulatory system and shock, followed by death, if circulatory failure is not corrected.
In addition, the patient with DHF has
- a low platelet count and hemorrhagic manifestations
- a tendency to bruise easily
- other types of skin hemorrhages
- bleeding nose or gums
- possibly internal bleeding.
Go immediately to an emergency room or the closest health care provider if any of the following warning signs appear:
- severe abdominal pain or persistent vomiting
- red spots or patches on the skin
- bleeding from nose or gums
- vomiting blood
- black, tarry stools (feces, excrement)
- drowsiness or irritability
- pale, cold, or clammy skin
- difficulty breathing
DIAGNOSIS AND TREATMENT
How is Dengue diagnosed?
Dengue should be suspected when a high fever of 40°C/104°F is accompanied by two of the following symptoms:
- severe headache
- pain behind the eyes
- muscle and joint pains
- swollen glands or rash
Symptoms usually last for 2–7 days, after an incubation period of 4–10 days after the bite from an infected mosquito.
Severe dengue or dengue hemorrhagic fever (DHF) is a potentially deadly complication due to
- plasma leaking
- fluid accumulation
- respiratory distress
- severe bleeding
- organ impairment.
Warning signs occur 3–7 days after the first symptoms in conjunction with a decrease in temperature below 38°C/100°F and include:
- severe abdominal pain
- persistent vomiting
- rapid breathing
- bleeding gums
- restlessness and blood in vomit
The next 24–48 hours of the critical stage can be lethal. Proper medical care is needed to avoid complications and risk of death.
How is Dengue treated?
There is no specific medication for treatment of a dengue infection.
When infected, early recognition and prompt supportive treatment can substantially lower the risk of medical complications and death.
- Persons who think they have dengue should use analgesics (pain relievers) with acetaminophen and avoid those containing aspirin.
- They should also rest, drink plenty of fluids, and consult a physician
- If they feel worse e.g., develop vomiting and severe abdominal pain in the first 24 hours after the fever declines, they should go immediately to the hospital for evaluation
Recovery from infection by one of the four distinct, but closely related, serotypes of the virus provides lifelong immunity against that particular serotype.
However, cross-immunity to the other serotypes after recovery is only partial and temporary.
Subsequent infections by other serotypes increase the risk of developing dengue hemorrhagic fever (DHF).
Is there an effective treatment for dengue hemorrhagic fever (DHF)?
As with dengue fever, there is no specific medication for DHF. It can however be effectively treated by fluid replacement therapy if an early clinical diagnosis is made.
DHF management frequently requires hospitalization.
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.
PREVENTION, CONTROL AND EDUCATION
How can I prevent infection?
Infection with one serotype does not protect against the others, and sequential infections put people at greater risk for dengue hemor-raghic fever (DHF) and dengue shock syndrome (DSS).
Please follow these recommendations:
- prevent mosquito bites
- eliminate places where the mosquito lays her eggs, primarily arti-ficial containers that hold water
- cover or properly discard items that collect rainwater or store wa-ter
- empty and clean pet and animal watering containers and vases with fresh flowers at least once a week to eliminate mosquito eggs and larvae and reduce the number of mosquitoes present
- use insect repellent in strict accordance with product label instructions. (Repellents should contain 20% to 30% DEET as the active ingredient)
- wear long sleeves and pants, and stay in places with air conditioning or window and door screens
- treat items, such as boots, pants, socks, and tents, with permethrin or buy permethrin-treated clothing and gear
- dress children in clothing that covers arms and legs
- cover crib, stroller, and baby carrier with mosquito netting
- use screens on windows and doors
- repair holes in screens to keep mosquitoes outside
- use air conditioning when available
- sleep under a mosquito bed net if air conditioned or screened rooms are not available
The risk of dengue infection for international travelers appears to be small. There is increased risk if an epidemic is in progress.
In late 2015 and early 2016, the first dengue vaccine, Dengvaxia (CYD- TDV) was registered in several countries for use in individuals 9-45 years of age living in endemic areas. The vaccine is effective against all four variants of the virus and provides 93% vaccine protection.
Other tetravalent live-attenuated vaccines are under development in phase III clinical trials, and other vaccine candidates based on subunit, DNA and purified inactivated virus platforms are at earlier stages of clinical development.
WHO provides technical advice and guidance to countries and pri-vate partners to support vaccine research and evaluation.
TRANSMISSION, VECTOR AND VECTOR CONTROL
How is Dengue transmitted?
Infected symptomatic or asymptomatic humans are the main carriers and multipliers of the virus. Patients who are already infected with the dengue virus can usually transmit the infection for 4–5 days via Aedes mosquitoes after their first symptoms appear.
In order for transmission to occur a mosquito must feed on a person during a 5- day period when large amounts of virus are in the blood. This period usually begins a little before the person becomes symptomatic. Some people never have significant symptoms but can still infect mosquitoes.
After entering the mosquito in the blood meal, the virus will require an additional 8-12 days incubation before it can then be transmitted to another human.
The mosquito remains infected for the remainder of its life.
In rare cases dengue can be transmitted in organ transplants or blood transfusions from infected donors, and there is evidence of transmission from an infected pregnant mother to her fetus.
Dengue epidemics require a coincidence of large numbers of vector mosquitoes, large numbers of people with no immunity to one of the four virus types and the opportunity for contact between the two.
How can the vector be controlled?
Prevention and control relies heavily on reducing the number of natural and artificial water-filled container habitats that support breeding of the mosquitoes.
During outbreaks, insecticides may be sprayed to kill flying mosquitoes, applied to surfaces in and around containers where the mosquitoes land, and used to treat water in containers to kill the immature larvae.
At present, the main method to control or prevent the transmission of dengue virus is to combat vector mosquitoes through:
- preventing mosquitoes from accessing egg-laying habitats
- disposing of solid waste properly and removing artificial man-made habitats
- covering, emptying and cleaning of domestic water storage containers on a weekly basis
- applying appropriate insecticides to water storage outdoor containers
- using of personal household protection such as window screens, long-sleeved clothes, insecticide treated materials, coils and vaporizers
- improving community participation and mobilization for sustained vector control
- applying insecticides as space spraying during outbreaks as one of the emergency vector-control measures
In Vietnam, rudder foot cancers of the genus Mesocyclops have been used for several years to combat dengue fever, with the implementation of the measures being checked on a monthly basis. As a result, there was no case of dengue fever in the affected areas between 2002 and 2005.
Other approaches are still in testing / development phase and not yet available on large scale:
- the spread of mosquitoes immunized against the virus by wMel-Wolbachia (bacteria of the genus Wolbachia)
- the release of genetically modified males of yellow fever mosquitoes. (There were and still are numerous concerns about the release of about 10 million genetically modified male mosquitoes in Brazil.)
- a parasitic fungus (Beauveria bassiana) that kills or weakens the mosquitoes
Active monitoring and surveillance of vectors should be carried out to determine effectiveness of control interventions.
Careful clinical detection and management of dengue patients can significantly reduce mortality rates from severe dengue.
How can we prevent epidemics of dengue hemorrhagic fever (DHF)?
The emphasis for dengue prevention is on sustainable, community-based, integrated mosquito control, with limited reliance on insecticides.
Preventing epidemic disease requires a coordinated community effort to increase awareness about dengue fever/DHF, how to recognize it, and how to control the mosquito that transmits it.
Residents are responsible for keeping their yards and patios free of standing water where mosquitoes can be produced.
What are the difficulties and challenges in combating Dengue?
The proximity of mosquito vector breeding sites to human habitation is a significant risk factor for Dengue as well as for other diseases that these species transmit.
It is very difficult to control or eliminate Ae. aegypti mosquitoes because of adaptations to the environment that make them highly resilient. Additionally they have the ability to rapidly bounce back to initial numbers after natural phenomena like droughts or human control measures.
One such adaptation is the ability of the eggs to withstand desiccation (drying) and to survive without water for several months. If, for instance, all larvae, pupae, and adult Ae. aegypti were eliminated at once from a site, its population could recover two weeks later as a result of egg hatching following rainfall or the addition of water to containers harboring eggs.
Ae..aegypti seems to continually adapt to environmental change. For example, it was recently found that Ae. aegypti is able to undergo immature development in broken or open septic tanks, resulting in the production of hundreds or thousands of Ae..aegypti adults per day.
In general, it is expected that control interventions will change the spatial and temporal dispersal of Ae. aegypti and perhaps the pattern of habitat utilization.
For these reasons, entomological studies should be included to give support before and throughout vector control operations.
Aedes albopictus, a secondary dengue vector in Asia, has spread to North America and more than 25 countries in the European Region, largely due to the international trade in used tires, which are a breeding habitat, and other goods e.g. lucky bamboo.
Ae. albopictus is highly adaptive and, therefore, can survive in cooler temperate regions of Europe. Its spread is due to its tolerance to temperatures below freezing, hibernation, and ability to shelter in microhabitats.
INITIATIVES AND PARTNERS
What programs exist against Dengue?
Besides many initiatives by affected countries, universities, NGOs and other organizations in 2012 the WHO initiated the 2012–2020 Global Strategy For Dengue Prevention And Control
The goal of the global strategy is to reduce the burden of dengue. The specific objectives are to reduce mortality and morbidity from dengue by 2020 by at least 50% and 25% respectively using 2010 as the baseline. It is unlikely that these ambitious goal will be reached in the proposed time frame.
Dengue mortality can be reduced by
- implementing early case detection and appropriate management of severe cases
- reorienting health services to identify early cases and manage dengue outbreaks effectively
Dengue morbidity can be reduced by
- implementing improved outbreak prediction and detection through coordinated epidemiological and entomological surveillance
- promoting the principles of integrated vector management and deploying locally-adapted vector control measures including effective urban and household water management
Effective communication can augment prevention programs.
Research should improve methods and systems for surveillance, prevention and control.
Reversing the trend requires commitments and obligations from partners, organizations and countries, as well as leadership by WHO and increased funding.
WHO responds to dengue in the following ways:
- supports countries in the confirmation of outbreaks through its collaborating network of laboratories
- provides technical support and guidance to countries for the effective management of dengue outbreaks
- supports countries to improve their reporting systems and capture the true burden of the disease
- provides training on clinical management, diagnosis and vector control at the regional level with some of its collaborating centers
- formulates evidence-based strategies and policies
- develops new tools, including insecticide products and application technologies
- gathers official records of dengue and severe dengue from over 100 Member States
- publishes guidelines and handbooks for case management, diagnosis, dengue prevention and control for Member States
➞ link to for instance: „Prevention and Control Strategies to Counter Dengue Virus Infection“ published: 25 July 2017 doi: 10.3389/fcimb.2017.00336 in Frontiers in Cellular and Infection Microbiology |
What does Bayer contribute to the fight against Dengue?
Bayer has been successfully developing vector control products for decades (see below).
- Currently, the two most relevant Vector Control methods for fighting mosquito-borne diseases are Space Spray applications and breeding sites management. Bayer is a major supplier of Space Spray products since decades.
- A major issue is the build-up of mosquito resistance to the different active ingredient they have been exposed to. Most products used since many years are now facing this situation.
During the last six years Bayer researchers have developed an innovative approach for fighting resistance build-up. They are bringing to market a range of mosquito insecticides that combine two different modes of action, In particular, the new Fludora™ Co-Max Space Spray includes also a new chemistry family. This solution will associate robustness to resistance build up as well as excellent efficacy.
- Thanks to an innovative polymere formulation, Bayer has also launched a totally new type of intervention, Targeted Outdoor Residual Spray (TORS) . This type of application rolled out is South East Asia id particularly adapted to urban environment where Chikungunya, dengue and Zika strive. The product is marketed under the brand KOthrne™ Polyzone.
Additionally Bayer has devised an education tool – Mosquito Control Learning Lab – an online learning platform that explains which diseases are transmitted by mosquitos, how they spread and how individuals can protect themselves against mosquito bites. The platform is interactive, testing users in their knowledge and skills in real life scenarios.
Bayer Mosquito Control Learning Lab can be accessed on any computer or tablet and is found here: https://www.environmentalscience.bayer.ph/Fight-Dengue
Besides this Bayer can look back on products that are still supplied in many parts of the world where resistance to pyrethroid insecticides is not yet established:
- Since 1990s: Aqua K-Othrine™ and Aqua Reslin™ Super are launched. These are the first space sprays to employ a new technology, Film Forming Aqueous Spray Technology (FFAST), and are used to combat adult mosquitos in flight outdoors without releasing volatile hydrocarbons.
- Since 2015: DeltaGard™ launched in the United States. The space spray can be used at 80 times lower doses than comparable products. DeltaGard™ is currently the only product in its class that does not contain volatile organic compounds (VOCs) and is water-based. It was awarded the rarely conferred reduced-risk product classification by the U.S. Environmental Protection Agency (EPA).
What is the societal burden of Dengue?
In 2012, dengue ranked as the most important mosquito-borne viral disease in the world.
Outbreaks exert a huge burden on populations, health systems and economies in most tropical countries of the world. The emergence and spread of all four dengue viruses from Asia to the Americas, Africa and the Eastern Mediterranean regions represent a global pandemic threat. During the past five decades, the incidence of dengue has increased 30-fold.
Some 50–100 million new infections are estimated to occur annually in more than 100 endemic countries, with a documented further spread to previously unaffected areas.
Every year hundreds of thousands of severe cases arise, including 20 000 deaths (Gubler DJ, Meltzer MI, 1999)
264 disability-adjusted life years per million population per year are lost (Cattand P et al, 2006), at an estimated cost for ambulatory and hospitalized cases of US$ 514–1394 (Suaya J et al, 2009), often affecting very poor populations. The true numbers are probably far worse, since severe underreporting and misclassification of dengue cases have been documented (Suaya J et al., 2007; Beatty ME et al. 2011).
Member States in three WHO regions regularly report the annual number of cases. The number of cases reported increased from 2.2 million in 2010 to 3.2 million in 2015.
Before 1970, only 9 countries had experienced severe dengue epidemics. The disease is now endemic in more than 100 countries in the WHO regions of Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific. The America, South-East Asia and Western Pacific regions are the most seriously affected.
In 2015, 2.35 million cases of dengue were reported in the Americas alone, of which 10 200 cases were diagnosed as severe dengue causing 1 181 deaths.
Not only is the number of cases increasing as the disease spreads to new areas, but explosive outbreaks are occurring. The threat of a possible outbreak of dengue fever now exists in Europe as local transmission was reported for the first time in France and Croatia in 2010 and imported cases were detected in three other European countries.
In 2012, an outbreak of dengue on the Madeira islands of Portugal resulted in over 2 000 cases and imported cases were detected in mainland Portugal and 10 other countries in Europe.
In 2015, Delhi, India, recorded its worst outbreak since 2006 with over 15 000 cases.
The year 2016 was characterized by large dengue outbreaks world-wide. The Region of the Americas reported more than 2.38 million cases in 2016, where Brazil alone contributed slightly less than 1.5 million cases, approximately 3 times higher than in 2014. 1 032 dengue deaths were also reported in the region. The Western Pacific Region reported more than 375 000 suspected cases of dengue in 2016, of which the Philippines reported 176 411 and Malaysia 100 028 cases, representing a similar burden to the previous year for both countries. The Solomon Islands declared an outbreak with more than 7 000 suspected. In the African Region, Burkina Faso reported a localized outbreak of dengue with 1 061 probable cases.
Epidemics of dengue result in human suffering, strained health services and massive economic losses. In some countries, the burden of dengue is comparable to that of tuberculosis and other communicable diseases with high disease burdens; unexpected surges in cases and the challenge to health systems of triaging thousands of cases without knowing which severe cases will require hospital care are additional challenges.
➞ link to for instance:
Disease and economic burdens of dengue Marcia C Castro, Mary E Wilson, David E Bloom
How did the history of the disease proceed?
- between 100 and 800 years ago the four dengue viruses originated in monkeys and independently jumped to humans in Africa or Southeast Asia
- until the middle of the 20th century Dengue remained a relatively minor, geographically restricted disease
- during the second world war in particular the coincidental transport of Aedes mosquitoes around the world in cargo is thought to have played a crucial role in the dissemination of the viruses
- in the 1950s DHF was first documented only during epidemics in the Philippines and Thailand
- until the early 1970s highly effective Aedes control programs had been in installed
- in 1981 large numbers of DHF cases began to appear in the Carribean and Latin America
- in recent decades the incidence of dengue has grown dramatically around the world, while the actual numbers of dengue cases are underreported and many cases are misclassified