Yellow fever
What is yellow fever?
Yellow fever is an infectious viral disease transmitted by mosquitoes in tropical and sub-tropical climates. It is a serious health concern, particularly in sub-Saharan African and some South American countries.
An estimated 200,000 people contract yellow fever each year, the vast majority of them in Africa. Around 30,000 die annually as a result. [1] [2]
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Neilson A.A. and Mayer C.A. (2010) Yellow fever – prevention in travellers. Australian Family Physician 39:570-573.
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Barnett E.D. (2007) Yellow fever: epidemiology and prevention. Clinical Infectious Diseases 44:850–856.
Causes
Yellow fever is caused by a virus that mainly infects monkeys. However, mosquitoes can transmit the virus from an infected monkey to a human. The virus is not able to be spread directly from person to person.
When the virus enters a person's bloodstream from a mosquito bite, it is able to spread to multiple organs in the body. It is still not clear how the virus causes the characteristic bleeding observed in the toxic stage of the illness.
Mosquito bites transmit the yellow fever virus.
Risk factors
Risk factors for yellow fever include:
Season
In South America, the most prevalent season for yellow fever is the rainy season (January - May), whereas in Africa, the disease is most common between the rainy and dry seasons (July - October).
Age
Older people have a greater chance of developing the severe form of yellow fever and dying from it.
Signs and symptoms
Many people infected with the yellow fever virus suffer few or no symptoms.
If symptoms do appear, it is usually after a period of 3-6 days. The symptoms can appear over three separate stages: early, remission and toxic.
Early stage
The early stage of yellow fever appears 3-6 days after infection has occurred. Symptoms of early-stage yellow fever can include:
- Fever;
- Headache and back pain;
- Jaundice;
- Nausea and vomiting;
- Loss of appetite;
- Nosebleeds;
- Irritability, and;
- Weakness.
Remission stage
After about two days with symptoms, most people fight off the infection. However, in about 15-25% of people, the illness goes into remission. This is where the symptoms subside, but the virus is not completely removed from the body. Remission can last between a few hours to a whole day, before they reappear in a more serious form, known as toxic or intoxication stage. [3]
Toxic stage
At this stage, bleeding can occur from multiple internal organs, including the heart, kidneys, spleen, liver and stomach. Symptoms can include:
- High fever;
- Jaundice;
- Reddening of the eyes, face and tongue;
- Seizures;
- Bleeding from the eyes and nose;
- Bloody stools and black or 'coffee-ground' vomit (the result of bleeding in the stomach), and;
- Brain damage, coma and delirium.
Toxic stage symptoms of yellow fever include severe jaundice.
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Coma
A state of deep and prolonged unconsciousness.
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Delirium
A mental state caused by temporary disturbances in brain function and characterized by a host of symptoms that may include fluctuating confusion, restlessness, excitement, incoherence, illusions, anxiety, and attention deficit.
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Jaundice
A yellowing of the skin, the whites of the eyes and the mucous membranes, due to an accumulation of bilirubin in the blood. Often a symptom of liver problems.
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Remission
A partial or complete reversal of the course of illness, such as cancer or a chronic disease. Remission can be spontaneous or the result of therapy.
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Spleen
An organ in the abdominal cavity that is involved in filtering out old blood cells and fighting infection.
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Markoff L. (2013) Yellow fever outbreak in Sudan. New England Journal of Medicine 368:689–691.
Methods for diagnosis
If a yellow fever infection is suspected, your doctor may perform specific blood tests to identify the presence of the virus or antibodies to the virus. Other blood tests may be performed to assess your liver and kidney function.
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Antibodies
A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralize them or target them for destruction.
Types of treatment
There is no specific treatment for yellow fever. Antibiotics and existing antiviral medications have no effect on the virus. If you are suffering from yellow fever, treatment will focus on managing your symptoms and hydration.
Treatment measures can include:
- Rest;
- Drinking plenty of fluids - in severe cases, intravenous fluids may be required;
- Medication to relieve pain and fever, and;
- For people suffering severe kidney damage, kidney dialysis may be recommended.
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Dialysis
A mechanical blood-filtering treatment that mimics the function of your kidneys, which normally work as your body’s natural filtration system to remove the body's waste products from the blood.
Prognosis
Most people who contract yellow fever make a full recovery. However, people who reach the toxic stage of the disease have a 20-50% chance of dying within two weeks. [2] [3]
X
Barnett E.D. (2007) Yellow fever: epidemiology and prevention. Clinical Infectious Diseases 44:850–856.
X
Markoff L. (2013) Yellow fever outbreak in Sudan. New England Journal of Medicine 368:689–691.
Prevention
Vaccination
An effective yellow fever vaccine is available and is routinely given to people living in, or travelling to, areas where the virus is commonly found. Some countries require a certificate of vaccination against yellow fever before entering them. The vaccine is given as a single injection and is thought to give decades of protection to the disease.
A vaccination is an effective way of protecting yourself against yellow fever.
Bite prevention methods
A good way of reducing the chance of developing yellow fever is to avoid mosquito bites. In areas where the yellow fever virus is commonly found, you can protect yourself by taking the following measures:
- Wearing long-sleeved shirts and trousers, light-colored clothing, and;
- Applying tropical strength repellent, containing DEET (diethyltoluamide or diethylmethylbenzamide) or picaridin, every four hours during daylight hours.
The Aedes aegypti mosquitoes, which is mainly responsible for transmitting yellow fever, are mostly active during the day. Therefore, bed nets and other night-time bite prevention strategies are less useful against yellow fever than for other mosquito-borne diseases such as malaria.
Mosquito control methods
An effective way of controlling Aedes aegypti mosquito numbers is to prevent their access to standing water in which they lay eggs. This requires governments and citizens to be aware of sources of standing water in their environment (containers, puddles, old tires, pots, etc.) and to empty or seal them.
Activities to reduce mosquito breeding:
- Weekly removal of items that provide breeding areas (e.g. tires, pot plant bases, palm fronds);
- Weekly flushing of stagnant water sources (e.g. dog bowls), and;
- Application of repellent surface spray to areas that may harbor mosquitoes (e.g. under beds, behind furniture, within closets).
References
- Neilson A.A. and Mayer C.A. (2010) Yellow fever – prevention in travellers. Australian Family Physician 39:570-573.
- Barnett E.D. (2007) Yellow fever: epidemiology and prevention. Clinical Infectious Diseases 44:850–856.
- Markoff L. (2013) Yellow fever outbreak in Sudan. New England Journal of Medicine 368:689–691.
- Barnett ED. Yellow Fever: Epidemiology and Prevention. Clin Infect Dis. 2007 Mar 15;44(6):8506.
- Board ADAME. Yellow fever [Internet]. PubMed Health. 2013 [cited 2014 Jun 18]. Available from: link here
- Choices NHS. Yellow fever - NHS Choices [Internet]. 2013 [cited 2014 Jun 19]. Available from: link here
- link here
- Jonker EFF Visser LG Roukens AH. Advances and controversies in yellow fever vaccination. Ther Adv Vaccines. 2013 Nov;1(4):14452.
- Medline Plus. Yellow fever [Internet] link here
- Paulson T. Drug development: Searching for patterns. Nature. 2014 Mar 6;507(7490):S10S11.
- Protection AGD of HO of H. Yellow fever - general fact sheet [Internet]. Australian Government Department of Health; [cited 2014 Jun 19]. Available from: link here
- Nandini Shetty Julian W Tang Julie Andrews. (2009). Infectious Disease: Pathogenesis Prevention and Case Studies (1st ed.). Wiley-Blackwell.
- Weir E Haider S. Yellow fever: readily prevented but difficult to treat. CMAJ. 2004 Jun 22;170(13):190910.
- Yellow fever - Blue Book - Department of Health Victoria Australia [Internet]. [cited 2014 Jun 18]. Available from: link here
- Yellow Fever - Chapter 3 - 2014 Yellow Book | Travelers Health | CDC [Internet]. [cited 2014 Jun 19]. Available from: link here
- Yellow fever | Up to date | Accessed 27 July 2014 from link here
10 Most frequently asked questions (FAQs)
Yellow fever is an infectious disease caused by the yellow fever virus, which is transmitted by mosquitoes in tropical and sub-tropical climates. How common is yellow fever? Yellow fever is a common disease in Africa and South America. Every year, 200,000 cases of yellow fever occur, with 30,000 people dying of the disease. What are the symptoms of yellow fever? Many people who catch the yellow fever virus show no symptoms at all. Early symptoms of yellow fever include fever, headache, back pain, muscle and joint pain, jaundice, nausea and vomiting, loss of appetite, weakness, restlessness and irritability. In cases where the disease has progressed to its severe stage, internal bleeding from multiple organs can occur, which can cause death. Anyone can become infected by yellow fever if bitten by a mosquito that is carrying yellow fever virus. How is yellow fever diagnosed? If a yellow fever infection is suspected, your doctor may perform specific blood tests to identify the presence of the virus or antibodies to the virus. Other blood tests may be performed to assess your blood cell counts (usually a lowered white blood cell count is found), and your liver and kidney function. Other viruses may be tested for, depending on your symptoms and where you travelled to. How is yellow fever treated? There is no specific treatment for yellow fever. Antibiotics and existing antiviral medications have no effect on the virus. If you are suffering from yellow fever, treatment will focus on managing your symptoms, hydration, supporting your body's immune system as it handles the infection, and helping the body recover. Yellow fever is a very serious condition. People who reach the severe stage of the disease can suffer significant damage to the kidneys, liver and other internal organs and have a 20-50% chance of dying within two weeks. Can I prevent being infected with yellow fever? An effective yellow fever vaccine is available and is routinely given to people living in, or travelling to, areas where the virus is commonly found. The vaccine is given as a single injection and is thought to give decades of protection from the disease.
Related topics
Dengue fever is an infectious viral disease transmitted by mosquitoes in tropical and sub-tropical climates. Most people with dengue fever suffer unpleasant symptoms, such as fever, headache and vomiting, but will make a full recovery. However, repeated infections can result in a form of haemorrhagic fever. Mosquitoes can transmit a variety of disease-causing microorganisms, including many kinds of viruses and several kinds of parasites. Often, different species of mosquitoes, found in different locations, will transmit different diseases. Malaria is a parasitic blood infection acquired through the bite of certain infected mosquitos. Malaria destroys red blood cells in the body causing tiredness, fever and unwellness. Taking preventative measures when travelling to areas with malaria is recommended. Modern air travel is remarkably safe, and normally poses no significant challenges to your health. Overall, travelling can be fun, and most people don't get sick. However, travelling by air does come with an increase in some health risks. Knowing what to look out for, and following the advice given below, can help you avoid these risks. If you do get sick, rest up, keep up your fluids and consider