Yellow fever is a viral disease transmitted to humans by infected mosquitoes. It has caused large epidemics in tropical areas of Africa and the Americas.
Symptoms occur within three to six days after infection. Initial symptoms include fever, loss of appetite, headache, vomiting, and backache. As the disease progresses, the pulse slows and weakens. After three to four days, most patients improve and their symptoms disappear. However, about 15% of cases enter a "toxic phase within 24 hours. This phase is characterized by bleeding of the gums and bloody urine, and can progress to delirium, seizures, and coma. Jaundice can also occur relatively early in the disease, thus the name "yellow fever."
Every year about 200,000 cases of yellow fever are recorded worldwide, and 30,000 of these die, but the figures are underestimated because of faulty record keeping.
Only a handful of cases have been documented in the U.S. in the past 80 years, all unvaccinated people that traveled to or came from high-risk areas. People are at risk if they travel to an area where yellow fever is seen in humans or monkeys (endemic areas) and there are mosquitoes to spread the virus. Even so, the risk for illness when traveling to these areas is considered small.
Yellow fever is spread mostly in two different cycles:
Jungle yellow fever is mainly a disease of monkeys. It is spread from infected mosquitoes to monkeys in the tropical rain forest. Jungle yellow fever is rare and occurs mostly in persons who work in tropical rain forests who are bitten by mosquitoes infected by monkeys.
Urban yellow fever is a disease of humans and the cause of most yellow fever outbreaks. Aedes aegyptiis the type of mosquito that usually carries yellow fever from human to human. These mosquitoes breed in discarded tires, flowerpots, oil drums, and water storage containers close to human dwellings.
Yellow fever is preventable by a relatively safe, effective vaccine. The single-dose 'live' vaccine is recommended for people 9 months of age and older. The vaccine becomes protective after 10 days, and provides immunity to a vaccinated individual for 10 years or more.
Describe your symptoms to your health care provider, and do not forget to mention your travel history.
Yellow fever is difficult to recognize, especially during the early stages. It can be easily confused with malaria, typhoid, rickettsial diseases, hemorrhagic viral fevers (e.g. Ebola), dengue, leptospirosis, and viral hepatitis. A laboratory analysis is required to confirm a suspect case. Blood tests can detect antibodies that are produced in response to the infection.
There is no specific treatment for yellow fever. Treatment for symptoms may include intravenous fluids, blood products for severe bleeding, and dialysis for renal failure.
The risk for a traveler of acquiring yellow fever depends in part on the destination, season, outdoor activities while traveling, and the rate of transmission at the time of travel. For example, in West Africa, the most dangerous time of year is during the late rainy and early dry seasons (July to October), while virus transmission is highest during the rainy season (January to March) in Brazil.
Travelers should get vaccinated for yellow fever before visiting areas where yellow fever is found.