Yellow fever is a viral disease found only in the forests of South America and the wet savanna areas of West and Central Africa. It is passed between people (and other primates) by mosquitoes. Hundreds of thousands of people become infected during epidemics in Africa—unfortunately, these epidemics have grown increasingly more common in both Africa and South America over the past 20 years.
There are two types of yellow fever. Jungle yellow fever is primarily a disease passed between mosquitoes and monkeys. It is rare in people, but occasionally affects workers in tropical rain forests.
Urban yellow fever is carried from person to person by mosquitoes. Found in cities and villages, it is the cause of most yellow fever outbreaks and epidemics.
Yellow fever infection can cause a mild flu-like illness, but symptoms can be more severe, including high fever, chills, headache, muscle aches, vomiting and backache. Severe hepatitis, hemorrhagic fever, as well as kidney and liver failure can also result—in fact, the disease was named for the jaundice (yellowing of the skin) caused by this liver failure.
Most mosquitoes that carry the disease pose more of a threat in the evening—yet the mosquitoes that spread yellow fever usually bite during the day. While this viral disease rarely affects travelers, daytime protection against mosquitoes is more important when visiting areas where there is a threat of yellow fever exposure.
Yellow fever vaccinations are necessary before gaining entry to many countries. According to the Centers for Disease Control and Prevention (CDC), yellow fever vaccination recommendations changed in 2002. For more information about yellow fever, visit www.cdc.gov/ncidod/dvbid/yellowfever/index.htm.
What is yellow fever and how is it transmitted?
Yellow fever is caused by a virus that is transmitted by mosquitoes, and occurs in Africa and South America. The disease vectors in Africa are Aedes aegypti, Aedes simpsaloni and Aedes africanus. In South America, the vectors are of the Haemagogus genus. The virus is a member of the Flaviviridae family, which also includes the West Nile virus, as well as the viruses that cause dengue, hepatitis C and several other insect-borne viruses.
Yellow fever endemic zones in Africa, 2007 (Source: CDC)
Yellow fever endemic zones in South America, 2007 (Source: CDC)
Over 200,000 cases of yellow fever are reported annually—90% of which are in Africa.
There are three transmission cycles for yellow fever: sylvatic, intermediate and urban. All three cycles exist in Africa; in South America, only sylvatic and urban cycles occur.
In the sylvatic, or jungle cycle, the yellow fever virus is transmitted between primates. People are infected when they interrupt this cycle by entering jungle habitats.
The intermediate cycle occurs in humid or semi-humid savannas of Africa. Small-scale epidemics occur in many separate villages at the same time, but few people die. Mosquitoes infect both primates and people.
The urban cycle occurs when the virus is introduced into urban areas by migrants from endemic areas. In this cycle, the virus is transmitted from person to person, and no primate hosts are involved.
After infection, an incubation period of 3 to 6 days occurs, during which the patient experiences no symptoms. In some infections, no symptoms ever develop. In others, the patient suffers high fever, muscle pain with backache, headache, nausea, vomiting and loss of appetite. In most cases, symptoms abate after 3 to 4 days, and the patient returns to normal. In approximately 15% of cases, the patient progresses to a toxic phase 24 hours after apparent recovery, experiencing jaundice, severe abdominal pain, vomiting, bleeding from the mouth, nose, eyes and stomach—even kidney failure. Of the patients that progress to this stage, 50% die within 14 days; the remainder recover.
Is there yellow fever in the United States?
Yellow fever has been eradicated in the United States.
How is yellow fever treated?
As it is a viral disease, there is no specific treatment for yellow fever. Patients may receive supportive care such as rehydration and antibiotics for secondary infections.
Is there a vaccine for yellow fever?
Yes, a highly effective and safe vaccine is available for children over nine months old and adults. It confers immunity against the yellow fever virus for ten years. Unfortunately this vaccine is not available for the majority of the people who need it in developing countries. In the few countries that have been able to institute mass vaccination programs, yellow fever has been eradicated.
I’m traveling to an area where there is yellow fever. How can I protect myself?
You may be required to present proof of yellow fever vaccination prior to entering the country you're visiting. For more information, visit the U.S.Centers for Disease Control and Prevention online, http://wwwn.cdc.gov/travel/default.aspx
Additionally, you should take measures to prevent mosquito bites. Insect Shield® Repellent Apparel is proven and registered to repel mosquitoes—as well as ticks, ants, flies and chiggers. The U.S. Environmental Protection Agency (EPA) requires extensive effectiveness data to prove a product's ability to repel insects. Many species and varieties of these insects have been tested, including those that carry dangerous diseases such as yellow fever. Travelers across the globe have experienced the benefits of wearing Insect Shield apparel in areas where insect-borne diseases are endemic.