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| Dengue and Dengue
Haemorrhagic Fever (DHF) |
| Dengue is a mosquito-borne infection. It is an
infectious viral disease associated with fever and eruptions. Dengue is found in tropical
and subtropical regions around the world, predominately in urban and peri-urban areas.
Dengue haemorrhagic fever (DHF) which is a potentially lethal complication was first
recognized during the 1950s. Dengue has today become a leading cause of childhood
mortality in several Asian countries. There are four distinct, but closely related,
viruses that cause dengue. Recovery from infection by one provides lifelong immunity
against that virus but confers only partial and transient protection against subsequent
infection by the other three. |
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Epidemiology |
The global prevalence of dengue has grown
dramatically in recent decades. The disease is now endemic in more than 100 countries.
Before 1970 only nine countries had experienced DHF epidemics. But by 1955 this number
grew by more than fourfold. 2500 million people (i.e. about two fifths of the world's
population) are now at risk from dengue.
It is estimated that there may be 50 million cases of dengue infection worldwide every
year. This is greater than double the number of dengue cases recorded in the same region
in 1995. Not only is the number of cases increasing as the disease is spreading to new
areas, but explosive outbreaks are occurring. During epidemics of dengue, attack rates
among susceptible are often 40 - 50%, but may reach 80 - 90%. An estimated 500,000 cases
of DHF require hospitalization each year. A large proportion of these is children and
roughly 5% of them die. Without proper treatment, DHF case fatality rates can exceed 20%.
With modern intensive supportive therapy, this can be reduced to less than 1%. The spread
of dengue is attributed to expanding geographic distribution of the four dengue viruses
and of their mosquito vectors, the most important of which is the predominantly urban
species Aedes aegypti.
A rapid rise in urban populations is bringing ever greater numbers of people into contact
with this vector, especially in areas which are favorable for mosquito breeding e.g.,
where household water storage is common and where solid waste disposal services are
inadequate.
Dengue fever has been known in India for a very long time. There have been periodic
outbreaks of the disease. An explosive out break of DHF occurred in Delhi in october 1996
with 7247 cases and 297 deaths.
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Transmission |
| Dengue viruses are transmitted to humans through the
bites of infective female Aedes mosquitoes. When the mosquitoes feed on the blood of the
infected person, they acquire the virus. Once infective, a mosquito is capable of
transmitting the virus to susceptible individuals for the rest of its life, during probing
and blood feeding. Infected female mosquitoes may also transmit the virus to the next
generation of mosquitoes by transovarian transmission i.e. via its eggs.
Humans are the main amplifying host of the virus, although studies have shown that in some
parts of the world monkeys may become infected. These monkeys can serve as a source of
virus for uninfected mosquitoes. The virus circulates in the blood of infected humans for
2-7 days, at approximately the same time as they have fever.
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Clinical picture |
| Dengue fever is a severe, flu-like illness that
affects infants, young children and adults but rarely causes death. The clinical features
of dengue fever vary according to the age of the patient. Infants and young children may
have a nonspecific febrile illness with rash. Older children and adults may have either a
mild febrile illness or the classical disease. back to
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Classical Dengue Fever |
Sudden onset with chills and high fever, intense
headache, muscle and joint pains, which prevent all movement, characterize the disease.
Within 24 hours retro-orbital pain (pain at the back of the eye), particularly on eye
movements or eye pressure and photophobia develops.
Other common symptoms include extreme weakness, loss of appetite, constipation, altered
taste, colicky pain, dragging pain in the inguinal region, sore throat and general
depression. Fever is usually between 39-40 deg. C. Fever is followed by a phase of
remission lasting a few hours to a few days after which it reappears.
The skin eruptions usually appear either during the remission or on the reappearance of
fever. The rash starts on the body and then spreads to the limbs and rarely to the face.
Fever lasts for 5-7 days after which usually complete recovery occurs. Convalescence is
prolonged. back to top |
Dengue Haemorrhagic Fever (DHF) |
| DHF is a sever form of Dengue fever, caused by
infection with more than one type of dengue virus. The disease is much more common in
children below 15 years as compared to adults. The onset is abrupt with high fever
accompanied by facial flushing and headache. Loss of appetite, vomiting, abdominal pain
and discomfort are common. Patient has a bleeding tendency and spontaneous bleeding into
the skin may be apparent.
In sever cases there may be a collapse of the circulatory system characterized by a week
and rapid pulse, fall in blood pressure and a cold and clammy skin. If diagnosed and
treated early, death rate can be lower than 5%; otherwise it can be upto 30%.
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Treatment |
| There is no specific treatment for dengue fever.
However, careful clinical management by experienced physicians and nurses frequently save
the lives of DHF patients. With appropriate intensive supportive therapy, mortality may
be reduced to less than 1%. Bed rest is advisable during the febrile phase. Using
antipyretics and cold sponging reduces fever. Aspirin is usually avoided, especially in
areas where DHF is prevalent as it may cause bleeding.
Maintenance of the circulating fluid volume is the central feature of DHF case management.
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Prevention |
- Vaccine development for dengue and DHF is difficult because any of four different
viruses may cause disease. Moreover, protection against only one or two dengue viruses
could actually increase the risk of more serious disease. However, progress is gradually
being made in the development of vaccines that may protect against all four dengue
viruses.
- To combat the vector mosquitoes as preventive measure is the only method of controlling
or preventing dengue and DHF. In Asia and the Americas, Aedes aegypti breeds primarily in
containers like earthenware jars, metal drums and concrete cisterns used for domestic
water storage.
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