Yellow fever is a viral disease of typically short duration. In most cases, symptoms include fever, chills, loss of appetite, nausea, muscle pains particularly in the back, and headaches. Symptoms typically improve within five days.
In about 15% of people, within a day of improving the fever comes back, abdominal pain occurs, and liver damage begins causing yellow skin. If this occurs, the risk of bleeding and kidney problemsis increased.
The disease is caused by yellow fever virus and is spread by the bite of an infected female mosquito. It infects only humans, other primates, and several types of mosquitoes. In cities, it is spread primarily by Aedes aegypti, a type of mosquito found throughout the tropics and subtropics.
The virus is an RNA virus of the genus Flavivirus. The disease may be difficult to tell apart from other illnesses, especially in the early stages. To confirm a suspected case, blood-sample testing with polymerase chain reaction is required.
Signs and symptoms
Yellow fever begins after an incubation period of three to six days. Most cases only cause a mild infection with fever, headache, chills, back pain, fatigue, loss of appetite, muscle pain, nausea, and vomiting. In these cases, the infection lasts only three to four days.
In 15% of cases, though, people enter a second, toxic phase of the disease with recurring fever, this time accompanied by jaundice due to liver damage, as well as abdominal pain.
Bleeding in the mouth, the eyes, and the gastrointestinal tract cause vomit containing blood, hence the Spanish name for yellow fever, vómito negro (“black vomit”). There may also be kidney failure, hiccups, and delirium.
Among those who develop jaundice, the fatality rate is 20 to 50%, while the overall fatality rate is about 5%. Severe cases may have a mortality greater than 50%.
Surviving the infection provides lifelong immunity, and normally no permanent organ damage results.
Tips for prevention
Stay away from mosquito-infested areas. mosquitoes are found on every continent except Antarctica, If possible, avoid jungles, forests, and other tropical and sub-tropical zones, especially sub-Saharan/West Africa and South America.
Get vaccinated. If you plan to be in a dangerous area, talk to your doctor about getting the vaccine. The yellow fever vaccine is called the 17D vaccine; it’s a live, attenuated vaccine that causes the body to produce antibodies against yellow fever. It is generally safe and gives maximum immunity against yellow fever within 7-10 days of vaccination. Your immunity will last up to ten years.
- Some people should not get the vaccine. People with weakened immune systems, people with allergies to eggs or to the vaccine itself, and children under nine months old should not be vaccinated. Pregnant women should not be vaccinated until there is a yellow fever outbreak. Extra care should be given when people older than 60 get the vaccine.
- Once you get the yellow fever vaccine, you will be issued an International Certificate of Vaccination (or “yellow card”).
- Side effects of the vaccine include headaches, muscle pain, fever, and chills, and, in a small number of people, severe and more dangerous problems, including allergic reactions, neurological diseases, and organ failure.