Meaning

Yellow fever is an acute viral disease transmitted mainly by infected mosquitoes. It is called “yellow” fever because severe cases can cause jaundice, where the skin and eyes turn yellow due to liver involvement.

Causative Agent

Yellow fever is caused by the yellow fever virus, a flavivirus.

It belongs to the same broad virus family as:

• Dengue
• Zika
• West Nile fever
• Japanese encephalitis

Transmission

Yellow fever spreads through mosquito bites.

The main vectors are:

• Aedes mosquitoes
• Haemagogus mosquitoes in forest cycles

The disease does not usually spread directly from person to person.

Transmission Cycles

Yellow fever has three main transmission cycles.

Sylvatic or jungle cycle:
Virus circulates between monkeys and forest mosquitoes. Humans get infected when they enter forest areas.

Intermediate cycle:
Mosquitoes infect both monkeys and humans in areas near forests or rural settlements.

Urban cycle:
Virus spreads between humans and Aedes mosquitoes in urban areas. This can cause large outbreaks.

Symptoms

Many infections are mild or asymptomatic.

Common symptoms include:

• Fever
• Headache
• Muscle pain
• Back pain
• Nausea
• Vomiting
• Fatigue

Most people recover after this phase.

Severe Disease

A small proportion of patients develop severe yellow fever.

Severe disease may cause:

• Jaundice
• Liver damage
• Kidney failure
• Bleeding
• Shock
• Multi-organ failure

Severe yellow fever can be fatal.

Diagnosis

Yellow fever can resemble dengue, malaria, leptospirosis, viral hepatitis and other febrile illnesses.

Diagnosis may involve:

• RT-PCR in early infection
• Serological tests
• Liver function tests
• Travel and vaccination history
• Differentiation from other mosquito-borne diseases

Treatment

There is no specific antiviral treatment for yellow fever.

Treatment is mainly supportive:

• Rest
• Fluids
• Fever control
• Monitoring liver and kidney function
• Hospital care in severe cases
• Management of bleeding and shock

Aspirin and some anti-inflammatory drugs are avoided because they may increase bleeding risk.

Vaccine

Yellow fever is vaccine-preventable.

A single dose of yellow fever vaccine provides long-lasting protection for most people.

Vaccination is especially important for people travelling to or living in endemic areas.

Many countries require a yellow fever vaccination certificate for travellers coming from risk areas.

Distribution

Yellow fever is mainly found in parts of:

• Sub-Saharan Africa
• Tropical South America

It is not endemic in India, but India monitors it because international travel can bring imported cases and because Aedes mosquitoes are present in the country.

Prevention

Prevention depends on vaccination and mosquito control.

Important measures include:

• Yellow fever vaccination before travel to risk areas
• Avoiding mosquito bites
• Wearing full-sleeved clothing
• Using mosquito repellents
• Using bed nets and window screens
• Removing mosquito breeding sites
• Public health surveillance
• Rapid outbreak response

Public Health Importance

Yellow fever is important because it can cause explosive urban outbreaks if introduced into areas with Aedes mosquitoes and low vaccination coverage.

It is also important for international health regulations because proof of vaccination may be required for travel.

Conclusion

Yellow fever is a mosquito-borne viral disease that can range from mild fever to severe liver disease, bleeding and death.

It is not endemic in India, but remains important because of international travel, mosquito presence and global outbreak risk.

The most effective protection is vaccination, along with mosquito control and strong public health surveillance.