(See the World
Health Organization's (WHO)web site for
a map of countries with moderate to high risk
Yellow fever is found in sub-Saharan Africa
and areas of Central and South America. According
to the WHO, yellow fever epidemics have increased
in number since the 1980s.
Mosquitoes that bite during the day, most notably
the species Aedes aegypti, spread the disease.
The risk of infection increases in rural and forested
or jungle areas, but risk does exist in urban areas.
The virus that causes yellow fever infects humans
and monkeys. For that reason, countries where the
right mosquito species exists in proximity to monkeys
are considered at risk for yellow fever, even if
no human cases have been recorded there (many parts
of Asia fall into this category).
Yellow fever causes initial symptoms that resemble
the flu, with fever, vomiting, headaches, slow
pulse and muscle aches. According to the WHO,
about 15 percent of patients progress to a second
phase of the disease, developing jaundice and
uncontrolled internal bleeding. Half of the patients
who progress that far die within two weeks after
the initial symptoms appear.
Prevention, as with any other disease, is the
best medicine. Follow the guidelines for avoiding
mosquito bite. People who travel to areas
where yellow fever is common should be vaccinated
against the disease. Certain countries require
the vaccine for all entering visitors, unless
a medical waiver was obtained before the trip.
It is important to remember that countries that
do not require the vaccine are not necessarily
free of yellow fever. Countries that are at risk
of yellow fever but had no cases of the disease
(as explained above) will require that travelers
get the vaccine to protect the country itself
from the disease.
Yellow fever vaccine should not be administered
to children younger than 9 months. The vaccine
is considered otherwise safe for most healthy people.
Because some data suggest that the vaccine may
cause infection in a developing fetus, and not
enough information is available on the possible
consequences of such an infection, the current
recommendation is not to vaccinate pregnant women.
People sensitive to eggs or egg products should
not receive this vaccine because it is produced
in chick embryos. Immunosuppressed individuals,
such as people with AIDS or leukemia, should not
receive the vaccine. A person who falls into any
of these categories should carefully consider the
necessity of their trip, and discuss alternatives
with their travel medicine specialist. The yellow
fever vaccine provides protection for 10 years.