Yellow fever is a viral disease that is transmitted to humans through the bite of infected mosquitoes. Yellow fever occurs in tropical regions of Africa and in parts of South America. Yellow fever is a very rare cause of illness in U.S. travelers. The last epidemic of yellow fever in North America occurred in New Orleans in 1905.
Cause
Yellow fever is caused by infection with yellow fever virus, which is transmitted by the bite of infected mosquitoes.
Symptoms
Patients with yellow fever may be viremic (have virus in their blood) for 3 to 6 days before demonstrating symptoms. Initial symptoms include fever and chills, severe headache, back pain, general muscle aches, nausea, fatigue, and weakness. This phase may be followed by a short period of symptom remission.
The toxic phase develops as the fever returns, with clinical symptoms including high fever, headache, back pain, nausea, vomiting, abdominal pain, and fatigue. Hepatic coagulopathy produces hemorrhagic symptoms, including hematemesis (black vomit), epistaxis (nose bleed), gum bleeding, and petechial and purpuric hemorrhages (bruising). Deepening jaundice and proteinuria frequently occur in severe cases.
In the late stages of disease, patients can develop hypotension, shock, metabolic acidosis, acute tubular necrosis, myocardial dysfunction, and cardiac arrhythmia. Confusion, seizures, and coma can also occur. When epidemics occur in unvaccinated populations, case-fatality rates range from 15% to more than 50%. Secondary bacterial infections and kidney failure are complications. Symptoms of weakness and fatigue may last several months in people who recover.
Those who recover from yellow fever generally have lasting immunity against subsequent infection.
Yellow Fever Virus Prevention
Yellow fever can be prevented by vaccination. Travelers should also take precautions against mosquito bites when in areas with yellow fever transmission.
Travelers should get vaccinated for yellow fever before visiting areas where yellow fever occurs. In the United States, the vaccine is given only at designated yellow fever vaccination centers. International regulations require proof of yellow fever vaccination for travel to and from certain countries. People who get vaccinated should be given an International Certificate of Vaccination.
Avoid mosquito bites when traveling in tropical areas. Mosquitoes that spread yellow fever usually bite during the day, especially at dusk and dawn.
- When outside:
- Wear long-sleeved clothing and long pants. For extra protection, treat clothing with the insecticide permethrin.
- Use insect repellent on exposed skin. Repellents containing DEET (N,N-diethylmetatoluamide), Picaridin (KBR 3023), IR 3535, p-Menthane 3,8-diole (PMD or oil of lemon eucalyptus) are effective. Follow application instructions carefully.
- When inside:
- Stay in well-screened areas as much as possible.
- Spray living and sleeping areas with insecticide.
Transmission Cycle
There are two kinds of yellow fever, spread by two different cycles of infection.
Jungle yellow fever is mainly a disease of monkeys. It is spread from infected mosquitoes to monkeys in the tropical rain forest. People get jungle yellow fever when they are bitten by mosquitoes that have been infected after feeding on infected monkeys. Jungle yellow fever is rare and occurs mainly in persons who live or work in tropical rain forests.
Urban yellow fever is a disease of humans. It is spread by mosquitoes that have been infected by other people. Aedes aegypti is the type of mosquito that usually carries yellow fever from human to human. These mosquitoes have adapted to living among humans in cities, towns, and villages. Their larvae grow in discarded tires, flower pots, oil drums, and water storage containers close to human dwellings. Urban yellow fever is the cause of most yellow fever outbreaks and epidemics.
What type of illness does yellow fever virus cause?
Illness ranges in severity from a self-limited febrile illness to severe hepatitis and hemorrhagic 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. Severe yellow fever infections can be fatal.
What is the incubation period for yellow fever?
The incubation period (time from infection to illness) is usually 3-6 days.
What is the mortality rate of yellow fever?
Case-fatality rates from severe disease range from 15% to more than 50%.
How is yellow fever treated?
There is no specific treatment for yellow fever. Treatment is symptomatic-rest, fluids, and ibuprofen, naproxen, acetaminophen, or paracetamol may relieve symptoms of fever and aching. Aspirin should be avoided. Infected persons should be protected from further mosquito exposure (staying indoors and/or under a mosquito net during the first few days of illness) so that they can't contribute to the transmission cycle.
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