Yellow Fever

What is yellow fever?

Yellow fever is a tropical disease caused by the yellow fever virus. It is spread by certain types of mosquitoes.

There was a time when yellow fever was one of the most feared diseases in America. In the 1700s and 1800s, yellow fever killed more than 100,000 Americans from New Orleans to Boston. The last epidemic in this country ended in 1905, but yellow fever continues to be a scourge of tropical South America and Sub-Saharan Africa. According to the World Health Organization (WHO), there are roughly 200,000 new cases of yellow fever each year, resulting in 30,000 deaths. However, few cases are ever positively identified, so the true toll could be even higher.

As more people flock to mosquito-infested cities — and as a warming climate encourages the spread of infected mosquitoes — cases of yellow fever could soar in the near future. In fact, the disease may already be on the rise: In February 2008, Paraguay recorded its first outbreak since 1974. As the WHO reports, it’s even possible that the disease could once again return to the United States.

How do people catch yellow fever?

People develop yellow fever when they’re bitten by mosquitoes infected with the yellow fever virus. The mosquitoes pick up the germ by biting infected humans or monkeys (in rural or remote jungle areas). In this way, the disease can move quickly through a neighborhood, village, or city. The mosquitoes that carry yellow fever are a different type than the ones that carry malaria, so if you’re going someplace with mosquitoes you don’t necessarily need to be worried about yellow fever.

Where do people get it?

Yellow fever can occur over large swaths of South America, including Bolivia, Venezuela, Peru, Colombia and the interior of Brazil. But Africa is the real hot zone. The WHO estimates that up to 508 million Africans in 33 countries are at risk for the disease. Several recent epidemics have struck West African countries such as Burkina Faso, Guinea, and Senegal.

Mosquitoes breed in standing water, like puddles and ponds. The illness is especially common in slums and shantytowns where people live close together and where mosquitoes can breed in water storage containers, garbage piles, abandoned cars, and shacks. In rural areas in West Africa, yellow fever is seasonal, with most cases occurring between the end of the rainy season and the dry season (July to October). In South America, cases are highest from January to March.

What are the symptoms of yellow fever?

Some people in areas with yellow fever have developed immunity to the virus, so they may not get sick when bitten by an infected mosquito. For most, symptoms start three to six days after being bitten by an infected mosquito. Early symptoms include high fever, backache and other muscle pain, headache, chills, loss of appetite, nausea, and vomiting. In most cases, the illness lasts three or four days and the patient recovers completely.

But for about 15 percent of cases, the illness doesn’t stop there. The fever returns, and the liver starts to fail, causing a yellowing of the skin and eyes (jaundice) that gives the disease its name. Victims suffer stomach pain and vomiting, and blood can start running from their mouths, eyes, or noses. This is why yellow fever is sometimes described as a hemorrhagic fever, similar to Dengue and Ebola. Kidneys can fail, too, which can completely shut down the production of urine. About half of people who reach this stage of the illness die within a couple of weeks.

How is yellow fever diagnosed?

The symptoms of yellow fever make it very easy to confuse with other illnesses. The only way to make a definitive diagnosis is to run a blood test that checks for antibodies to the yellow fever virus. This can only be done in a sophisticated lab by experienced personnel, which largely explains why the WHO can only guess at the true extent of the disease.

How is it treated?

There’s no cure for yellow fever. Some patients need extra fluids to treat dehydration, and acetaminophen, ibuprofen, or similar medicines to ease pain and lower the fever.

How can yellow fever be prevented?

A vaccine against yellow fever has been available for 60 years. In areas with yellow fever, the WHO recommends routine childhood immunizations and catch-up shots for the general population.

Visitors to South America or Africa very rarely catch yellow fever. All six reported cases among American and European travelers from 1996-2002 have been among people who were not vaccinated. If your travel plans include spending time outdoors in places where the disease is active, you should receive a yellow fever vaccine — at a certified yellow fever vaccination clinic — at least 10 days before leaving the U.S. The vaccine and is safe and effective for most people, and it only takes a single shot. Up to 25 percent of people report mild reactions including low fever, mild headache, and muscle pain. In rare cases, there have been reports of severe, even fatal, reactions to the vaccine. Researchers are working on developing even safer vaccines.

Because of the potential for serious side effects, babies younger than 9 months of age should not get the vaccine, and people over age 60 should consult their doctors first. If you have an egg allergy or thymus problem, you may be more likely to react to the vaccine. If you are pregnant or nursing, it’s best to avoid traveling to areas with yellow fever; pregnant and nursing women are advised to decline the vaccine unless the benefits are greater than the risks. For example, pregnant women may choose to be vaccinated during an epidemic, but not otherwise.

Even if you’ve been immunized, try to minimize your chances of getting mosquito bites in the tropics. Yellow fever is just one of many diseases that mosquitoes can carry.

Here are some tips:

  • Stay indoors whenever possible.
  • Wear long sleeves and long pants to cover as much skin as you can. Keep in mind mosquitoes can bite through very thin material.
  • Spray your clothing with insect repellent. Brands containing the insecticide DEET are the most effective. The spray will last until you wash your clothes. Once you’re out of the yellow fever zone, wash your clothes before wearing them again. (If you’re pregnant, DEET appears to be safe but it’s still a good idea to limit your exposure.)
  • Consider wearing insect-repellent sprays or lotions on exposed skin. When using DEET sprays, lotions, or wipes, follow all directions and minimize your contact. Don’t use on broken skin, near the mouth or eyes, or on infants under two months of age. After you come back inside, wash off the sprayed areas with soap and water. DEET isn’t meant for long-term use, as it can cause agitation, disorientation, jerkiness (ataxia), seizures, and coma. The risk may be higher for children.
  • If you’d rather not use chemical sprays, there are natural options available with citronella, rosemary, and other insect-repellent essential oils. However, these are not as effective and wear off faster.
  • When possible, sleep only in places that are air-conditioned or at least breezy and well-screened from the outside.
  • Cover your bed with mosquito netting. You can also spray the netting with repellents containing DEET or permethrin for added protection.
  • In many parts of the world it’s common to burn incense-like coils of mosquito repellent containing citronella, but beware — many brands contain toxic, cancer-causing chemicals banned in the United States.


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