Once virus enters the host, it binds to cell lining and enters white blood cells, It reproduces inside the
cells while they move throughout the body. The white blood cells respond to
virus by producing a number of signaling proteins, such as interferon,
which are responsible for many of the general symptoms, such a fever, flu-like
symptoms and the severe pains. In severe infection occurs , the virus
multiplication inside the body is greatly increased, and many more organs can
be affected. Furthermore, dysfunction of the bone marrow leads to reduced
numbers of platelets, which are necessary for effective blood clotting; this
increases the risk of bleeding, the other major complication of dengue fever.
Once inside the skin, dengue
virus binds to Langerhans cells. (a population of dendritic
cells.). The dendritic cell moves
to the nearest lymph node. Meanwhile, the virus genome is
translated in membrane-bound vesicles on the cell's endoplasmic reticulum. Here cell's
protein synthesis apparatus produces new viral proteins that replicate the
viral RNA and begin to form viral particles. Immature virus particles are
transported to the Golgi apparatus and complete mature particle is formed. Mature new viruses bud on the surface of the infected cell and are
released through exocytosis.
The incubation period (time between exposure and onset of symptoms) ranges from 3–14 days. And therefore,
travelers returns from endemic areas show likely symptoms are unlikely to have
dengue. Children often experience symptoms similar to those of the common cold and gastroentritis and, though initial symptoms are generally mild but include high fever. Symptoms
ignored in children’s or old people can give rise to severe dengue infection
which can be life threatening and thus preliminary precautions has to be taken.
SIGNS AND SYMPTOMS:-
The general characteristic symptoms of
dengue are sudden-onset fever, headache muscle and joint pains, and a rash. The
alternative name for dengue, "break-bone fever", comes from the
associated muscle and joint pains. The
course of infection is divided into three phases: febrile, critical, and
recovery. Phases are associated with pain headache for 3 to 6 days while may a times vomiting is
seen due to abdominal discomfort. Measles like rashes are prominently visible,
this symptoms should be confused with measles. The fever itself is classically biphasic in nature, breaking and then returning
for one or two days, although there is wide variation in how often this pattern
actually happens.
In some people, the disease proceeds to
a critical phase. During this phase there may be
significant fluid accumulation in the chest and abdominal
cavity due to
increased capillary permeability and leakage. This leads to depletion of
fluid from the circulation and decreased
blood supply to vital organs. During this phase, organ dysfunction
and severe bleeding,
typically from the gastrointestinal tract, may occur. Shock (dengue
shock syndrome) and hemorrhage (dengue hemorrhagic fever) occur in less than 5%
of all cases of dengue, however those who have previously been
infected with other serotypes of dengue virus ("secondary
infection") are at an increased risk.
DIAGNOSIS:-
The diagnosis of dengue is typically
made clinically, on the basis of reported symptoms and physical examination; this kind of
diagnosis is especially carried in endemic areas. However, early disease can be
difficult to differentiate from other viral infections. General
diagnosis is based on the findings of fever nausea and vomiting, rash, generalized pains, low white blood cell count, positive tourniquet test, in someone who lives in anendemic area. The diagnosis should be
considered in anyone who develops a fever within two weeks of being in the tropics or subtropics. It
can be difficult to distinguish dengue fever and chikungunya, as both the viral infection shares many symptoms
and occurs in similar parts of the world to dengue. Often, investigations are performed to
exclude other conditions that cause similar symptoms, such as malaria, leptospirosis, viral hemorrhagic fever, typhoid fever, measles,
and influenza.
The earliest change detectable in laboratory testing is a low white
blood cell count, which may then be followed by low platelets and metabolic acidosis. A
moderately elevated level of aminotransferase from the liver
is commonly associated with low platelets and white blood cells.
Dengue fever may be
diagnosed by microbiological laboratory testing. This can be done by
virus isolation in cell cultures, nucleic acid detection by PCR, viral antigen detection or specific antibodies. Virus isolation and
nucleic acid detection are more accurate than antigen detection, but these
tests are not widely available due to their greater cost.
Tests for dengue virus-specific antibodies, types IgG and IgM, can be useful in confirming a diagnosis in the later stages of the
infection. Both IgG and IgM are produced after 5–7 days. The highest levels of
IgM are detected following a primary infection. After a
primary infection the IgG reaches peak levels in the blood after 14–21 days.
Both IgG and IgM provide protective immunity to the infecting serotype of the
virus.
PREVENTION AND CONTROL:-
- There are no approved vaccines for the dengue virus.
-Prevention thus depends on control and protection from the bites of the mosquito that transmits it.
-Elimination of
stagnant water at home, schools and work place to avoid breeding of mosquitoes.
-Using insect repellents over the exposed parts of the body.Using mosquito
screens or nets in non – air-conditioned rooms.
-Wearing the long sleeved
clothes like long trousers of a light shade for protection against mosquitoes.
-Properly
covering all water tanks so that mosquitoes cannot get in. Getting rid of any
container capable of retaining water in the outdoor surroundings (used tyres,
food cans, garbage, saucers under flower pots, etc).
- Renew water in flower
vases at least once a week. Aedes
species is the main target of control. Source reduction of breeding sites of mosquitoe.
-Requires
community involvement to keep the water storage containers free of mosquitoes.
Eliminate other breeding
places in and around houses.
-Introduction of larvivorous fish, namely Gambusia and Guppy in water
tanks and other water sources. -
-The organophosphorous insecticide ABATE is being used in a large scale.
ABATE can prevent breeding
upto 3 months when applied to sand granules. It does not affect man or the taste of water.
-Educate community about the
disease, mode of its transmission, availability of treatment and adoption of
control measures.
-Changes in practice of storage of water and personal
protection should be encouraged. They should also be reassured that this a preventable disease.
-Community should be advised to cooperate
in fogging. Take measures for eliminating breeding places. Special campaigns
may be carried out involving mass media including local vernacular
newspapers/magazines, radio and TV as well outdoor publicity like hoardings,
miking, drum beating, rallies etc.
-Health education materials should be developed and widely disseminated in
the form of posters, pamphlets, handbills.
-Interpersonal communication through
group meetings, traditional/folk media particularly must be optimally utilized.
EPIDEOMOLOGY :-
