Yellow Fever

This article was written by Dr. Oscar Bernal, M.D., Ph.D.. Dr. Bernal has extensive experience in tropical medicine in Africa, Asia and the Americas, most of this with the international medical humanitarian organization, Doctors Without Borders.

What is Yellow fever?

Yellow fever is a viral disease, characterized by fever and by a yellow color in the skin and eyes. This disease has not affected people in the United States for 50 years, but the increased presence of Aedes aegypti mosquitoes in the United States, especially during the summer months, means it is possible for yellow fever to make a comeback. Yellow fever currently produces outbreaks in Africa and the Americas. Each year, there are an estimated 200,000 cases of yellow fever, with 30,000 deaths. Fortunately, there is a vaccine that protects against yellow fever for 10 years and the yellow fever vaccine is an entry requirement for some countries.

What Causes Yellow Fever?

Yellow fever is produced by a flavivirus with two different genotypes, associated with East and West Africa. South America has two different types, but since 1974, only one has been identified as the cause of disease outbreaks.

What Spreads Yellow Fever?

The mosquito Aedes aegypti is the most important vector. This mosquito can host yellow fever, Chikungunya and dengue fever. This is an urban mosquito, it is silent, bites by day and night, outside as well as inside the house. Urbanization in tropical countries has been increasing the number of Aedes aegypti and people infected. Aedes aegypti has been invading new countries, like Spain in 2004, and they are very good at surviving; they arrive to stay. Another mosquito that transmits yellow fever is the Haemogogus mosquito.

Where is Yellow Fever Found?

Yellow fever is present in west and central Africa and South America. The tropical areas of Bolivia, Brazil, Colombia, Ecuador and Peru are considered at greatest risk. If you are traveling only to the capital cities of Bolivia and Colombia, La Paz and Bogotá, there is no risk of getting yellow fever. There is no yellow fever reported in Asia. The complete list of yellow fever information is available from the World Health Organization.

Symptoms of Yellow Fever

Yellow fever has two different phases:

• The acute phase is normally characterized by:
  • fever
  • muscle pain,
  • headache
  • shivers
  • loss of appetite
  • nausea and/or vomiting
  • Pulse may be slow and weak in spite of the presence of fever (This is called Faget sign.)
  After three to four days most patients improve and their symptoms disappear.

• However, 15% of patients enter a "toxic phase" within 24 hours.
  • Fever reappears and several body systems are affected
  • The patient rapidly develops jaundice and complains of abdominal pain with vomiting
  • Bleeding can occur from the mouth, nose, eyes and/or stomach.
  Fatality from the toxic phase of yellow fever is 50%.

Diagnosis of Yellow Fever

The symptoms may be confused with other diseases. A blood test can detect yellow fever antibodies that are produced in response to the infection. Cultures and PCR can be done from blood or liver biopsies but require specialized laboratories.

How Is It Treated?

• There are no specific medications for yellow fever.
• Good hydration is a key point in yellow fever management and may include oral therapy and intravenous fluids.
• Management of fever and pain using acetaminophen (known to many people from the United States as Tylenol and to Europeans and Latin Americans as paracetamol). Aspirin and non-steroidal anti-inflammatory medications like ibuprofen are off limits since they may make bleeding worse.
• Any bacterial infections should be treated with an appropriate antibiotic.
• If a patient goes into the toxic phase, he or she would be hospitalized in the intensive care unit and could need a blood transfusion.

Do Not Dodge the Shot

Yellow fever is a serious disease. When I was working in Liberia, near a health center run by Doctors Without Borders, six soldiers from an international force died from yellow fever. It turns out they bought a fake vaccination card because they were too afraid to get a shot. If you are traveling, go to the World Health Organization’s page for the latest country by country update on yellow fever vaccination requirements and the malaria situation.