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]

1. Neilson A.A. and Mayer C.A. (2010) Yellow fever – prevention in travellers. Australian Family Physician 39:570-573.

2. 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.  

1. Neilson A.A. and Mayer C.A. (2010) Yellow fever – prevention in travellers. Australian Family Physician 39:570-573.

2. Barnett E.D. (2007) Yellow fever: epidemiology and prevention. Clinical Infectious Diseases 44:850–856.

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.

1. Neilson A.A. and Mayer C.A. (2010) Yellow fever – prevention in travellers. Australian Family Physician 39:570-573.

2. Barnett E.D. (2007) Yellow fever: epidemiology and prevention. Clinical Infectious Diseases 44:850–856.

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.

A healthy person and a person with jaundice.Toxic stage symptoms of yellow fever include severe jaundice. 

Coma

A state of deep and prolonged unconsciousness.

Delirium

A mental state caused by temporary disturbances in brain function and characterised by a host of symptoms that may include fluctuating confusion, restlessness, excitement, incoherence, illusions, anxiety, and attention deficit.

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.

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.

Seizures

A sudden, involuntary contraction of muscle groups caused by abnormal electrical activity in the brain.

Spleen

An organ in the abdominal cavity that is involved in filtering out old blood cells and fighting infection.

3. 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. 

Antibodies

A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralise them or target them for destruction.

3. Markoff L. (2013) Yellow fever outbreak in Sudan. New England Journal of Medicine 368:689–691.

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.

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.

Intravenous

Within a vein.

3. Markoff L. (2013) Yellow fever outbreak in Sudan. New England Journal of Medicine 368:689–691.

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]

2. Barnett E.D. (2007) Yellow fever: epidemiology and prevention. Clinical Infectious Diseases 44:850–856.

3. 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.

Vaccination.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-coloured 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 tyres, pots, etc.) and to empty or seal them.

Activities to reduce mosquito breeding:

  • Weekly removal of items that provide breeding areas (e.g. tyres, 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 harbour mosquitoes (e.g. under beds, behind furniture, within closets).

Vaccine

A preparation containing a microorganism (that causes a specific disease) in a dead or weakened state, or parts of it, for the purpose of inducing immunity in a person to that microorganism.

2. Barnett E.D. (2007) Yellow fever: epidemiology and prevention. Clinical Infectious Diseases 44:850–856.

3. Markoff L. (2013) Yellow fever outbreak in Sudan. New England Journal of Medicine 368:689–691.