Dengue and severe dengue
Key facts
- Dengue is a mosquito-borne viral infection.
- The infection causes flu-like illness, and occasionally develops
into a potentially lethal complication called severe dengue.
- The global incidence of dengue has grown dramatically in recent
decades. About half of the world's population is now at risk.
- Dengue is found in tropical and sub-tropical climates worldwide,
mostly in urban and semi-urban areas.
- Severe dengue is a leading cause of serious illness and death
among children in some Asian and Latin American countries.
- There is no specific treatment for dengue/ severe dengue, but
early detection and access to proper medical care lowers fatality
rates below 1%.
- Dengue prevention and control depends on effective vector control
measures.
- A dengue vaccine has been licensed by several National Regulatory
Authorities for use in people 9-45 years of age living in endemic
settings.
Dengue is a mosquito-borne viral disease that has rapidly spread
in all regions of WHO in recent years. Dengue virus is transmitted
by female mosquitoes mainly of the species Aedes aegypti and, to
a lesser extent, Ae. albopictus. This mosquito also transmits chikungunya,
yellow fever and Zika infection. Dengue is widespread throughout
the tropics, with local variations in risk influenced by rainfall,
temperature and unplanned rapid urbanization.
Severe dengue (also known as Dengue Haemorrhagic Fever) 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.
There are 4 distinct, but closely related, serotypes of the virus
that cause dengue (DEN-1, DEN-2, DEN-3 and DEN-4). Recovery from
infection by one 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 severe dengue.
Global burden of dengue
The incidence of dengue has grown dramatically around the world
in recent decades. The actual numbers of dengue cases are underreported
and many cases are misclassified. One recent estimate indicates
390 million dengue infections per year (95% credible interval 284–528
million), of which 96 million (67–136 million) manifest clinically
(with any severity of disease).1 Another study, of the prevalence
of dengue, estimates that 3.9 billion people, in 128 countries,
are at risk of infection with dengue viruses.2
Member States in 3 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. Although the full global burden
of the disease is uncertain, the initiation of activities to record
all dengue cases partly explains the sharp increase in the number
of cases reported in recent years.
Other features of the disease include its epidemiological patterns,
including hyper-endemicity of multiple dengue virus serotypes in
many countries and the alarming impact on both human health and
the global and national economies.
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.
Cases across the Americas, South-East Asia and Western Pacific
exceeded 1.2 million in 2008 and over 3.2 million in 2015 (based
on official data submitted by Member States). Recently the number
of reported cases has continued to increase. 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 1181 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 3 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. Among travellers
returning from low- and middle-income countries, dengue is the second
most diagnosed cause of fever after malaria.
In 2013, cases have occurred in Florida (United States of America)
and Yunnan province of China. Dengue also continues to affect several
South American countries, notably Costa Rica, Honduras and Mexico.
In Asia, Singapore has reported an increase in cases after a lapse
of several years and outbreaks have also been reported in Laos.
In 2014, trends indicate increases in the number of cases in the
People's Republic of China, the Cook Islands, Fiji, Malaysia and
Vanuatu, with Dengue Type 3 (DEN 3) affecting the Pacific Island
countries after a lapse of over 10 years. Dengue was also reported
in Japan after a lapse of over 70 years.
In 2015, Delhi, India, recorded its worst outbreak since 2006 with
over 15 000 cases. The Island of Hawaii, United States of America,
was affected by an outbreak with 181 cases reported in 2015 and
ongoing transmission in 2016. The Pacific island countries of Fiji,
Tonga and French Polynesia have continued to record cases.
The year 2016 was characterized by large dengue outbreaks worldwide.
The Region of the Americas region 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. 1032
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 7000 suspected.
In the African Region, Burkina Faso reported a localized outbreak
of dengue with 1061 probable cases.
In 2017 (as of Epidemiological Week 11), the Region of Americas
have reported 50 172 cases of dengue fever, a reduction as compared
with corresponding periods in previous years. The Western Pacific
Region has reported dengue outbreaks in several Member States in
the Pacific, as well as the circulation of DENV-1 and DENV-2 serotypes.
Transmission
The Aedes aegypti mosquito is the primary vector of dengue. The
virus is transmitted to humans through the bites of infected female
mosquitoes. After virus incubation for 4–10 days, an infected mosquito
is capable of transmitting the virus for the rest of its life.
Infected symptomatic or asymptomatic humans are the main carriers
and multipliers of the virus, serving as a source of the virus for
uninfected mosquitoes. Patients who are already infected with the
dengue virus can transmit the infection (for 4–5 days; maximum 12)
via Aedes mosquitoes after their first symptoms appear.
The Aedes aegypti mosquito lives in urban habitats and breeds mostly
in man-made containers. Unlike other mosquitoes Ae. aegypti is a
day-time feeder; its peak biting periods are early in the morning
and in the evening before dusk. Female Ae. aegypti bites multiple
people during each feeding period.
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 tyres (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.
Characteristics
Dengue fever is a severe, flu-like illness that affects infants,
young children and adults, but seldom causes death.
Dengue should be suspected when a high fever (40°C/104°F) is accompanied
by 2 of the following symptoms: severe headache, pain behind the
eyes, muscle and joint pains, nausea, vomiting, 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 is a potentially deadly complication due to plasma
leaking, fluid accumulation, respiratory distress, severe bleeding,
or 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, fatigue, 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.
Treatment
There is no specific treatment for dengue fever.
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.
Immunization
In late 2015 and early 2016, the first dengue vaccine, Dengvaxia
(CYD-TDV) by Sanofi Pasteur, was registered in several countries
for use in individuals 9-45 years of age living in endemic areas.
Prevention and control
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 by
environmental management and modification;
- 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;
- active monitoring and surveillance of vectors should be carried
out to determine effectiveness of control interventions.
WHO response
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 centres;
- 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; and
- publishes guidelines and handbooks for case management, diagnosis,
dengue prevention and control for Member States.
|
