Penn Travel Medicine






Insect-borne Diseases


Yellow Fever

Traveler's Diarrhea

Yellow Fever

(See the World Health Organization's (WHO)web site for a map of countries with moderate to high risk of infection)

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.


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