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Jumat, 21 Desember 2012

Yellow fever

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Yellow fever

Yellow fever
Definition:

Yellow fever is a viral infection spread by a particular species of mosquito. It's most common in areas of Africa and South America, affecting travelers to and residents of those areas.

In mild cases, yellow fever causes fever, headache, nausea and vomiting. But yellow fever can become more serious, causing heart, liver and kidney problems along with bleeding (hemorrhaging). Up to 50 percent of people with the more severe form of yellow fever die of the disease.

There's no specific treatment for yellow fever. But getting a yellow fever vaccine before traveling to an area in which the virus is known to exist can protect you from the disease.

Symptoms:

During the first three to six days after you've contracted yellow fever — the incubation period — you won't experience any signs or symptoms. After this, the virus enters an acute phase and then, in some cases, a toxic phase that can be life-threatening.
Acute phase
Once the yellow fever virus enters the acute phase, you may experience signs and symptoms including:
  • Fever
  • Headache
  • Muscle aches, particularly in your back and knees
  • Nausea, vomiting or both
  • Loss of appetite
  • Dizziness
  • Red eyes, face or tongue
These signs and symptoms usually improve and are gone within several days.
Toxic phase
Although signs and symptoms may disappear for a day or two following the acute phase, some people with acute yellow fever then enter a toxic phase. During the toxic phase, acute signs and symptoms return and more-severe and life-threatening ones also appear. These can include:
  • Yellowing of your skin and the whites of your eyes (jaundice)
  • Abdominal pain and vomiting, sometimes of blood
  • Decreased urination
  • Bleeding from your nose, mouth and eyes
  • Heart dysfunction (arrhythmia)
  • Liver and kidney failure
  • Brain dysfunction, including delirium, seizures and coma
The toxic phase of yellow fever can be fatal.
When to see a doctor
Make an appointment to see your doctor four to six weeks before traveling to an area in which yellow fever is known to occur. If you don't have that much time to prepare, call your doctor anyway. Your doctor will help you determine whether you need vaccinations and can provide general guidance on protecting your health while abroad.
Seek emergency medical care if you've recently traveled to a region where yellow fever is known to occur and you develop severe signs or symptoms of the disease. If you develop mild symptoms, call your doctor.

Causes:

Yellow fever is caused by a virus that is spread by the Aedes aegypti mosquito. These mosquitoes thrive in and near human habitations where they breed in even the cleanest water. Most cases of yellow fever occur in sub-Saharan Africa and tropical South America.
Humans and monkeys are most commonly infected with the yellow fever virus. Mosquitoes transmit the virus back and forth between monkeys, humans or both. When a mosquito bites a human or monkey infected with yellow fever, the virus enters the mosquito's bloodstream and circulates before settling in the salivary glands. When the infected mosquito bites another monkey or human, the virus then enters the host's bloodstream, where it may cause illness.

Complications:

Yellow fever results in death for 20 to 50 percent of those who develop severe disease. Death usually occurs within two weeks from the start of infection. Complications during the toxic phase of a yellow fever infection include kidney and liver failure, jaundice, delirium and coma.
People who survive the infection recover gradually over a period of several weeks to months, usually without significant organ damage. During this time a person may experience fatigue and jaundice. Other complications include secondary bacterial infections, such as pneumonia or blood infections.

Treatments and drugs:
 
No antiviral medications have proved helpful in treating yellow fever. As a result, treatment consists primarily of supportive care in a hospital. This includes providing fluids and oxygen, maintaining adequate blood pressure, replacing blood loss, providing dialysis for kidney failure, and treating any other infections that develop. Some people receive transfusions of plasma to replace blood proteins that improve clotting.
If you have yellow fever, you may also be kept away from mosquitoes, to avoid transmitting the disease to others.

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