What is yellow fever?
Yellow fever is a mosquito borne virus that once caused major epidemics in large cities of this country like Philadelphia and New Orleans. Due to good mosquito control and public health practice, the last epidemic in the US was seen over 100 years ago.
There are three transmission cycles to yellow fever:
• Jungle cycle- This cycle involves the mosquitoes Aedes and Haemagogus and primates. This transmission is restricted to tropical areas of Africa and South America. A few hundred cases occur annually; mostly among young males working in forested areas.
• Intermediate cycle- This cycle occurs in savannah regions of Africa and involves humans and the Aedes mosquito.
• Urban cycle- This involves humans and the Aedes aegypti mosquito. This is the cycle where human epidemics occur.
Yellow fever is found in 33 countries in Africa and 9 in South America and the Caribbean islands.
After being bit by an infected mosquito, the incubation time is 3-6 days. It is typically of short duration and various severities.
Mild cases are characterized by sudden onset of fever, chills, headache, backache, muscle pain and nausea and vomiting. This stage lasts about 48 hours. Most infections resolve at this stage.
About 15% of the time, the disease may progress to a severe hemorrhagic fever. There is a “period of calm” of a few hours to a day.
This stage of the disease is characterized by jaundice and hemorrhagic symptoms like bleeding out the nose, gingival bleeding, and vomiting blood (may be black and look like coffee grounds).
Abnormalities in clotting factors and liver enzymes may be the result of kidney and liver failure.
Yellow fever can be laboratory diagnosed by growing the virus in cell culture, by demonstrating viral antigens, and by molecular methods like PCR.
There is no treatment for yellow fever itself, just treating the symptoms.
What can you do to prevent getting yellow fever when traveling to one of these endemic areas?
The Centers for Disease Control and Prevention (CDC) recommend the following:
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 are 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.
- 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.
- Stay in well-screened areas as much as possible.
- Spray living and sleeping areas with insecticide.
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