Yellow fever
Yellow fever is a viral disease that has caused large epidemics in Africa
and the Americas. It can be recognized from historic texts stretching back 400
years. Infection causes a wide spectrum of disease, from mild symptoms to
severe illness and death. The "yellow" in the name is explained by the
jaundice that affects some patients.
Yellow fever is a viral disease that has caused large epidemics in Africa
and the Americas. It can be recognized from historic texts stretching back 400
years. Infection causes a wide spectrum of disease, from mild symptoms to
severe illness and death. The "yellow" in the name is explained by the
jaundice that affects some patients. Although an effective vaccine has been
available for 60 years, the number of people infected over the last two
decades has increased and yellow fever is now a serious public health issue
again.
In mild cases, yellow fever causes fever, headache, nausea and vomiting. But
yellow fever can become more serious, causing bleeding (hemorrhaging), heart,
liver and kidney problems. Up to 50 percent of those with the more severe form
of yellow fever die of the disease.
Symptoms of Yellow Fever
Many yellow fever infections are mild, but the disease can cause severe,
life-threatening illness. Symptoms of severe infection are high fever, chills,
headache, muscle aches, vomiting, and backache. After a brief recovery period,
the infection can lead to shock, bleeding, and kidney and liver failure. Liver
failure causes jaundice (yellowing of the skin and the whites of the eyes),
which gives yellow fever its name.
Chest congestion develops in many patients, and abdominal pain and discomfort
are common. The fever becomes constant. Improvement occurs in the third and
fourth week in those without complications. About 10% of patients have
recurrent symptoms (relapse) after feeling better for one to two weeks.
Relapses are actually more common in individuals treated with antibiotics.
The illness may progress to liver and renal failure, and hemorrhagic symptoms
and signs caused by thrombocytopenia and abnormal clotting and coagulation may
occur. The case-fatality rate of yellow fever varies widely in different
studies and may be different for Africa compared to South America, but is
typically 20% or higher. Jaundice or other gross evidence of severe liver
disease is associated with higher mortality rates.
The fever pattern is biphasic and is called a dromedary pattern, reflecting
the 3 phases of the illness described above. In the acute phase, fevers may be
high, with relative bradycardia. The saddle occurs during the secondary stage,
when temperatures normalize. In the intoxication phase, fevers recur.
Infection ranges from asymptomatic (in 5 to 50% of cases) to a hemorrhagic
fever with 50% mortality. Incubation lasts 3 to 6 days. Onset is sudden, with
fever of 39 to 40° C, chills, headache, dizziness, and maligns. The pulse,
usually rapid initially, by the 2nd day becomes slow for the degree of fever (Faget''s
sign). The face is flushed and the eyes are injected. Nausea, vomiting,
constipation, severe prostration, restlessness, and irritability are common.
When a person becomes infected with the yellow fever virus, the virus begins
to multiply. After three to six days, the symptoms of yellow fever can begin
to appear. The period between becoming infected with virus and the appearance
of yellow fever symptoms is called the incubation period.
The virus remains silent in the body during an incubation period of three to
six days. There are then two disease phases. While some infections have no
symptoms whatsoever, the first, "acute", phase is normally characterized by
fever, muscle pain (with prominent backache), headache, shivers, loss of
appetite, nausea and/or vomiting. Often, the high fever is paradoxically
associated with a slow pulse. After three to four days most patients improve
and their symptoms disappear.
