Dengue fever can occur when a mosquito carrying
the arbovirus bites a human, passing the virus on to the new host.
Once in the body, the virus travels to various glands where it
multiplies. The virus can then enter the bloodstream. The presence
of the virus within the blood vessels, especially those feeding the
skin, causes changes to these blood vessels. The vessels swell and
leak. The spleen and lymph nodes become enlarged, and patches of
liver tissue die. A process called disseminated intravascular
coagulation (DIC) occurs, where chemicals responsible for clotting
are used up and lead to a risk of severe bleeding (hemorrhage).
After the virus has been transmitted to the human
host, a period of incubation occurs. During this time (lasting about
five-eight days) the virus multiplies. Symptoms of the disease
appear suddenly and include high fever, chills, headache, eye pain,
red eyes, enlarged lymph nodes, a red flush to the face, lower back
pain, extreme weakness, and severe aches in the legs and joints.
This initial period of illness lasts about two-three
days. After this time, the fever drops rapidly and the patient
sweats heavily. After about a day of feeling relatively well, the
patient's temperature increases again, although not as much as the
first time. A rash of small red bumps begins on the arms and legs,
spreading to the chest, abdomen, and back. It rarely affects the
face. The palms of the hands and the soles of the feet become
swollen and turn bright red. The characteristic combination of fever,
rash, and headache are called the "dengue triad." Most people
recover fully from dengue fever, although weakness and fatigue may
last for several weeks. Once a person has been infected with dengue
fever, his or her immune system keeps producing cells that prevent
reinfection for about a year.
More severe illness may occur in some people.
These people may be experiencing dengue fever for the first time.
However, in some cases a person may have already had dengue fever at
one time, recovered, and then is reinfected with the virus. In these
cases, the first infection teaches the immune system to recognize
the presence of the arbovirus. When the immune cells encounter the
virus during later infections, the immune system over-reacts. These
types of illnesses, called dengue hemorrhagic fever (DHF) or dengue
shock syndrome (DSS), involve more severe symptoms. Fever and
headache are the first symptoms, but the other initial symptoms of
dengue fever are absent. The patient develops a cough, followed by
the appearance of small purplish spots (petechiae) on the skin.
These petechiae are areas where blood is leaking out of the vessels.
Large bruised areas appear as the bleeding worsens and abdominal
pain may be severe. The patient may begin to vomit a substance that
looks like coffee grounds. This is actually a sign of bleeding into
the stomach. As the blood vessels become more damaged, they leak
more and continue to increase in diameter (dilate), causing a
decrease in blood flow to all tissues of the body. This state of low
blood flow is called shock. Shock can result in damage to the body's
organs (especially the heart and kidneys) because low blood flow
deprives them of oxygen.
