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Yellow fever is a serious, potentially deadly flu-like disease spread by mosquitoes. Characterized by a high fever and jaundice, it is most prevalent in certain parts of Africa and South America. The disease is not curable, but is preventable with the yellow fever vaccine.
Yellow fever is caused by the yellow fever virus (YFV), also called Flavivirus. The virus is transmitted by female mosquitos, who pick it up from monkeys or other humans, then delivers it to a new human when they bite and suck blood. The disease cannot be spread from person to person.
Mosquitoes breed in tropical rainforests, humid and semi-humid environments, and around bodies of still water. Increased contact between humans and infected mosquitoes, particularly in areas where people have not been vaccinated for yellow fever, can create small-scale epidemics.
Those who haven’t been vaccinated for yellow fever and who live in areas populated by infected mosquitoes are at risk. According to the World Health Organization, an estimated 200,000 people become infected each year (WHO). Most cases occur in 32 countries in Africa, including Rwanda and Sierra, and in 13 countries in Latin America, including Bolivia, Brazil, Colombia, Ecuador, and Peru (WHO).
Cases of yellow fever can also be transmitted to other countries that aren’t normally affected, if conditions allow.
However, for one reason or another, the disease has never been reported in Asia.
Yellow fever comes on quickly, with symptoms occurring three to six days after exposure. The initial signs of the infection are similar to those of the influenza virus, and include headaches, muscle and joint aches, and fever. After that, the disease proceeds in three stages, which are described below.
Called the “acute” stage, the first phase usually lasts for three to four days. In addition to the headaches and fever, victims may experience flushing, loss of appetite, shivers, and backache.
Called the “remission” stage, this is the period when symptoms go away. The person gradually starts to feel better. Many people recover fully at this stage. Others, however, will get worse within about 24 hours.
Called the “toxic” phase, this is the most serious of the three phases. Symptoms will return, along with new symptoms, including decreased urination, abdominal pain, and vomiting (sometimes with blood). Other symptoms occurring at this phase include heart rhythm problems, liver failure (which may show up as jaundice — a yellowing of the skin and eyes), kidney failure, seizures, delirium, and possibly bleeding from the nose, mouth, and eyes. This phase of the disease is often fatal.
If you have been traveling recently, and you experience flu-like symptoms, check with your doctor right away. If the doctor notices signs that indicate yellow fever, you will likely be advised to undergo a blood test. The doctor will also ask you about your recent travel experiences, and determine whether or not you traveled to an area of the world known to harbor yellow fever mosquitoes.
The results of the blood test will confirm whether or not you may have the disease. Laboratory technicians look for signs of the virus itself, or of the immune system’s antibodies that build up in response to the presence of the virus.
There is no cure for yellow fever, so doctors treat only the symptoms, and do their best to support the body’s own ability to fight off the infection. This effort may include:
According to WHO, half of patients who enter the toxic phase of the disease will die within 10 to 14 days, while the rest will recover fully (WHO). The Centers for Disease Control and Prevention estimates that serious cases of the disease will result in death about 20 to 50 percent of the time (CDC). Older adults and those with compromised immune systems are most at risk for serious complications.
Vaccination is the only way to prevent yellow fever. Given as a single shot, the vaccine contains a live, weakened version of the virus that helps your body create immunity. The CDC suggests that all persons 9 months old through 59 years of age traveling to or living in an area where the risk of yellow fever is present be vaccinated. (You can find areas of potential infection by going to www.cdc.gov/travel.)
Those with severe allergies to eggs, chicken proteins, or gelatin should not get the vaccine. Neither should infants younger than 6 months old, or people who have HIV/AIDS or other immune-compromising conditions. Individuals older than 60 who are considering traveling to an area that may contain the virus should discuss vaccination with their doctors. Infants 6 to 8 months old and nursing mothers should postpone travel to these areas if possible, or talk to their doctors about vaccination.
The vaccine is considered extremely safe, with a single dose providing protection for at least 10 years. Side effects may include mild headache, muscle pain, fatigue, and low-grade fevers.
Other methods of prevention include using insect repellant, wearing clothing to reduce mosquito bites, and staying inside during peak biting times.
Written by: Colleen Story
Medically reviewed by George Krucik, MD
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