Yellow Fever Disease: Symptoms, Causes, and Treatment;

Causes and Transmission

The primary cause of yellow fever is a virus belonging to the Flavivirus genus. This virus is primarily transmitted to humans through the bite of infected Aedes or Haemagogus mosquitoes. These mosquitoes typically breed in tropical and subtropical regions, thriving in humid environments and areas with standing water.

The transmission cycle of yellow fever involves three main scenarios:

1. Sylvatic (jungle) yellow fever:

In this cycle, the virus circulates between monkeys and mosquitoes in forest areas. Humans can become infected when they enter these regions and are bitten by infected mosquitoes.

2. Intermediate yellow fever:

This occurs in humid or semi-humid areas of Africa, where mosquitoes can infect both monkeys and humans. It’s the most common type of outbreak in African regions.

3. Urban yellow fever:

In this scenario, infected mosquitoes transmit the virus directly from human to human. This can lead to large epidemics, especially in areas with high population density and low vaccination coverage.

It's important to note that yellow fever cannot be transmitted directly from person to person. The mosquito acts as an essential vector in spreading the disease.

Symptoms and Complications

The symptoms of yellow fever virus can vary greatly in severity, ranging from mild flu-like symptoms to severe, life-threatening complications. The illness typically progresses through three stages —

1. Infection stage:

This initial phase usually begins 3-6 days after exposure to the virus. Common symptoms include —

• Sudden onset of fever

• Headache

• Muscle aches

• Back pain

• Nausea and vomiting

• Loss of appetite

• Fatigue

2. Remission stage:

For many individuals, symptoms improve after 3-4 days, and they recover fully. However, for some, the illness progresses to the toxic phase.

3. Toxic stage:

About 15-25% of patients enter this severe phase, which can be life-threatening. Symptoms may include —

• Recurrence of high fever

• Jaundice (yellowing of the skin and eyes)

• Abdominal pain

• Bleeding from various body parts (mouth, nose, eyes, or stomach)

• Kidney and liver failure

• Shock

• Brain dysfunction, including delirium and seizures

Complications of severe yellow fever can include heart, liver, and kidney problems. In the most severe cases, multi-organ failure can occur, leading to death in up to 50% of patients who reach this stage.

Vaccination and Treatment

Prevention is key when it comes to yellow fever, and vaccination remains the most effective method. The yellow fever vaccine offers lifelong protection for most people after a single dose. It's recommended for individuals aged 9 months and older who are travelling to or living in areas where the ailment is prevalent.

The vaccine should be administered at least 10 days before travel to allow for the development of protective antibodies. Some countries require proof of vaccination for entry, so travellers should check requirements well in advance.

As for yellow fever treatment, there is no specific antiviral medication available. Yellow fever treatment focuses on managing symptoms and providing supportive care. This may include:

• Rest and hydration

• Pain relief and managing fever

• Oxygen therapy, if needed

• Blood transfusions in cases of severe bleeding

• Dialysis for kidney failure

In severe cases, hospitalisation is often necessary to provide intensive supportive care.

FAQs

1. How long does the yellow fever vaccine provide protection?

The yellow fever vaccine typically provides lifelong protection for most individuals after a single dose.

2. Can yellow fever be transmitted from person to person?

No, yellow fever cannot be transmitted directly from person to person. It requires a mosquito vector for transmission.

3. Are there any side effects of the yellow fever vaccine?

Most people experience mild side effects such as low-grade fever, headache, and muscle aches. Severe side effects are rare but can occur.

4. How quickly do symptoms of yellow fever virus appear after infection?

Symptoms typically appear 3-6 days after being bitten by an infected mosquito.

5. Is yellow fever present in all tropical and subtropical regions?

No, yellow fever is primarily found in certain parts of Africa and South America. It is not present in Asia or the Pacific region, despite the presence of the mosquito vector in these regions.