Yellow fever is a viral infection transmitted by a bite from infected mosquitoes most commonly found in parts of South America and Africa. When transmitted to humans, the yellow fever virus can damage the liver and other internal organs and be potentially fatal.
The World Health Organization estimates there are 200,000 cases of yellow fever worldwide each year, resulting in 30,000 deaths. Yellow fever appears to be on the rise internationally, due to a decreased immunity to infection among local populations, deforestation, climate change, and high-density urbanization.
Public health scientists verified that a common virus -- a coronavirus -- that has become more severe as the likely cause of severe acute respiratory syndrome (SARS). Many people wonder just how scientists know that the cause is a virus and, more importantly, this particular virus.
In 1890, Robert Koch described the basis rules that scientists use to determine if an infectious organism causes a specific disease. These four rules are called "Koch's postulates."
The organism must be found in...
The CDC has identified 44 counties with a risk of yellow fever transmission, many of them with tropical climates. While the actual number of yellow fever cases among U.S. and European travelers to these at-risk countries is low, vaccination is advised for most international travelers to these countries, because yellow fever has no cure and can be deadly.
How Does Yellow Fever Spread?
Yellow fever is typically spread to humans from bites by infected mosquitoes. People cannot spread yellow fever among themselves through casual contact, although the infection can be transmitted directly into the blood through contaminated needles.
A few different species of mosquitoes transmit the yellow fever virus; some breed in urban areas, others in jungles. Mosquitoes that breed in the jungle also transmit yelllow fever to monkeys, who, in addition to humans, are a host for the disease.
Yellow Fever Symptoms
Yellow fever gets its name from two of its most obvious symptoms: fever and yellowing of the skin. The yellowing occurs because the disease causes liver damage, hepatitis. For some people, yellow fever has no initial symptoms, while for others, the first symptoms appear from three to six days after exposure to the virus from a mosquito bite.
An infection with yellow fever typically has three phases. The first phase of symptoms can last for three to four days and then, for most people, disappears. The first phase is generally non-specific and cannot be distinguished from other viral infections.