Yellow Fever

 (Survival manual/6. Medical/b) Disease/Yellow Fever)

  A.  Background
From 1793-1822, yellow fever was one of the most dreaded diseases in US port cities. Yellow fever outbreaks in the United States shaped American history and influenced important national decisions. In the 1780s, yellow fever outbreaks in Philadelphia were responsible for killing one tenth of the city’s population. Benjamin Rush described the epidemic and, based on the science of the time, sought to contain the devastating illness. Yellow fever did not discriminate by gender, race, occupation, or socioeconomic status. Yellow fever may have played a part in shaping the decision to move the nation’s capital out of Philadelphia.1 The disease had such an impact on the local economies that, in 1803, Napoleon, with his troops decimated by yellow fever, had few reservations about selling the affected Louisiana and western territories to the US government.

Yellow fever is a hemorrhagic fever caused by a virus 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 bleeding (hemorrhaging), heart, liver and kidney problems. 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.

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 blood
  • Decreased urination
  • Bleeding from your nose, mouth and eyes
  • Heart dysfunction (arrhythmias)
  • 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.

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 then bites another monkey or human, the virus then enters the host’s bloodstream, where it may cause illness.

Risk factors: Traveling to Africa or South America
Traveling to an area in which the yellow fever virus is known to be present puts you at risk of the disease. These areas include sub-Saharan Africa and tropical South America.
Even if there aren’t current reports of infected humans in these areas, it doesn’t mean you’re risk-free. It’s possible that local populations have been vaccinated and are protected from the disease, or that cases of yellow fever just haven’t been detected and officially reported.

If you’re planning on traveling to these areas, you can protect yourself by getting a yellow fever vaccine at least 10 to 14 days prior to traveling.
Anyone can be infected with the yellow fever virus, but older adults are at greater risk of getting seriously ill.

Yellow fever results in death for 20 to 50 percent of those who develop severe disease. This 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.

Tests and diagnosis
Diagnosing yellow fever based on signs and symptoms can be difficult because its early signs and symptoms can be easily confused with those of other diseases, such as malaria, typhoid, dengue fever and other viral hemorrhagic fevers. To diagnose your condition, your doctor will likely ask about your medical and travel history and order blood tests.

If you have yellow fever, your blood may reveal the virus itself. If not, blood tests known as enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) also can detect antigens and antibodies specific to the virus. Results for these tests may take several days.

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.

Yellow Fever Treatment in Mild Cases
People who experience mild yellow fever symptoms usually have symptoms for a couple of days. During this time, treatment to relieve symptoms can include:

•  Resting in bed
•  Drinking plenty of fluids
•  Taking common medication such as acetaminophen (not aspirin) to relieve fever and discomfort.

Common medications used at home for pain and fever in children with yellow fever include:
•  Acetaminophen
•  Ibuprofen
•  Naproxen

Aspirin and most of the other nonsteroidal anti-inflammatory drugs (NSAIDS) are not used in children except under a doctor’s care.

_Acetaminophen (Tylenol and others)
•  Acetaminophen decreases fever and pain, but does not help inflammation.
•  Dosing is 10-15 mg per kilogram (5-7 mg per pound) of body weight every 4-6 hours, up to the adult dose.
•  Do not exceed the maximum daily dose.
•  Acetaminophen products come in various strengths. Always follow the package instructions.
•  Avoid this drug in children with liver disease or an allergy to acetaminophen.
•  Common acetaminophen products include Tylenol, Panadol and many others.

•  Ibuprofen decreases pain, fever and inflammation.
•  It is a nonsteroidal anti-inflammatory medication (NSAID).
•  Dosing for children over 6 months of age is 7-10 mg per kilogram (4-5 mg per pound) of body weight every 6 hours, up to the adult dose.
•  Do not exceed the maximum daily dose.
•  Always follow the package instructions.
•  Avoid this drug in children with liver, kidney, stomach or bleeding problems.
•  Brand names include Advil, Motrin and Nuprin.

•  Naproxen decreases pain, fever and inflammation.
•  It is a nonsteroidal anti-inflammatory medication (NSAID).
•  Dosing for 13 and older is 200 mg twice a day with food.
•  Do not exceed 500 mg per day.
•  Always follow the package instructions.
•  Avoid this drug in children with liver, kidney, stomach or bleeding problems.
•  The brand name for naproxen is Aleve.

The case-fatality rate of yellow fever has been reported at 5%-70%.
•  In recent outbreaks, the fatality rate was approximately 20% among patients with jaundice.
•  Up to 50% of patients who progress to the toxic phase die.


B.  Prevention
1.  Vaccine
A safe and highly effective vaccine prevents yellow fever. Yellow fever is known to be present in sub-Saharan Africa and parts of South America. Talk to your doctor about whether you need the yellow fever vaccine at least 10 to 14 days before traveling to these areas or if you are a resident of one of them. Some of these countries require a valid certificate of immunization in order to enter the country.

A single dose of the vaccine provides protection for at least 10 years. Side effects of the yellow fever vaccine are usually mild, lasting five to 10 days, and may include headaches, low-grade fevers, muscle pain, fatigue and soreness at the site of injection. More-significant reactions — such as developing a syndrome similar to actual yellow fever, inflammation of the brain (encephalitis) or death — can occur, most often in infants and older adults. The vaccine is considered safest for those between the ages of 9 months and 60 years. Talk to your doctor about whether the vaccine is appropriate if your child is younger than 9 months or you’re older than 60 years.

2.  Mosquito protection
In addition to getting the vaccine, you can help protect yourself against yellow fever by protecting yourself against mosquitoes.

To reduce your exposure to mosquitoes:

  • Avoid unnecessary outdoor activity when mosquitoes are most prevalent, such as at dawn, dusk and early evening.
  • Wear long-sleeved shirts and long pants when you go into mosquito-infested areas.
  • Stay in air-conditioned or well-screened housing.

To ward off mosquitoes with repellent, use both of the following:

  • Nonskin repellent. Apply permethrin-containing mosquito repellent to your clothing, shoes, and camping gear and bed netting. Some products pre-treated with permethrin are available to buy. Permethrin is not intended for use on your skin.
  • Skin repellent. Products with the active ingredients DEET or picaridin provide the longest lasting skin protection. Choose the concentration based on the hours of protection you need. In general, higher concentrations last longer. Keep in mind that chemical repellents can be toxic, and use only the amount needed for the time you’ll be outdoors. Don’t use DEET on the hands of young children or on infants under 2 months of age. Instead, cover your infant’s stroller or playpen with mosquito netting when outside.

According to the Centers for Disease Control and Prevention, oil of lemon eucalyptus, a more natural product, offers the same protection as DEET when used in similar concentrations. However, these products should not be used on children younger than age 3.

_United States
Reports of yellow fever in the United States are exceedingly rare, with the last outbreak reported in New Orleans in 1905. It is a rare cause of illness in returning travelers. In 1999, the Centers for Disease Control and Prevention (CDC) reported a case of fatal yellow fever in a previously healthy California man who had returned from a 10-day trip to Venezuela. A second case of fatal yellow fever was reported in 1996 in a US resident returning from South America. Prior to these reports, the last case was reported in 1924. Neither patient had received a yellow fever vaccine prior to travel.
•  World Health Organization (WHO) data suggest that the rate of yellow fever transmission is increasing, especially in sub-Saharan Africa. In addition, the number of US residents traveling to South America and Africa is also increasing. The WHO estimates that travelers from the United States to endemic areas has doubled since 1988.  Without proper precautions, including vaccination, these travelers are at risk of contracting yellow fever.
•  A aegypti mosquitoes are present in the southeastern United States, making the outbreak of yellow fever in that region a potential risk.

•  After adjustment for underreporting, an estimated 200,000 cases of yellow fever occur annually, with 30,000 deaths per year.
•  Thirty-three countries in Africa are at risk. Transmission in Africa is facilitated by the close proximity of vector mosquito populations to unvaccinated human populations.The case-fatality rate of yellow fever in Africa approximates 20%. Infants and children are at highest risk.
•  Yellow fever is endemic in 9 South American countries and several Caribbean islands. Bolivia, Brazil, Ecuador, and Peru are considered at highest risk.The incidence of yellow fever in South America is lower than in Africa because the infected monkeys in the rain forest canopy do not often come in contact with human populations. Indigenous human populations have immunity as a part of mass immunization campaigns.  Yellow fever occurs most frequently in young men through occupational exposure in forested areas.
•  Outbreaks of yellow fever have not been reported in Asia, but this region remains at risk because of the presence of competent vector mosquitoes and nonhuman primates.  

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