Yellow fever is a disease that can be prevented by vaccination and is transmitted to humans through infected mosquitoes. The disease is caused by a virus that is transmitted by the Aedes and Haemagogus mosquitoes, which can be found in domestic, wild, and semi-domestic environments. Yellow fever is a serious disease that can easily spread internationally, posing a risk to global health security.
There are three types of transmission cycles: sylvatic (jungle) yellow fever, intermediate yellow fever, and urban yellow fever. The sylvatic cycle involves monkeys being bitten by wild mosquitoes, which can then spread the virus to other monkeys and humans. The intermediate cycle is the most common in Africa, with semi-domestic mosquitoes infecting both monkeys and people. Urban yellow fever occurs in heavily populated areas with high mosquito density, and infected mosquitoes can transmit the virus from person to person.
To prevent the spread of yellow fever, it is important to have strong case-based surveillance and for travellers to high-risk areas to present yellow fever vaccination certificates. The International Health Regulations (2005) must be followed to prevent international spread of the disease. The Eliminate Yellow Fever Epidemics (EYE) strategy is a long-term plan developed by a coalition of partners to prevent the spread of yellow fever by building resilience in urban centres and preparedness in areas with potential for outbreaks while ensuring a reliable vaccine supply.
Symptoms
Yellow fever can have varying symptoms and severity, with an incubation period of 3-6 days after contracting the virus. Many people do not experience symptoms, but common symptoms include fever, muscle pain, backache, headache, loss of appetite, and nausea/vomiting, which typically resolve within 3-4 days.
A small percentage of patients may enter a more toxic phase within 24 hours of initial recovery, with high fever and organ failure, especially affecting the liver and kidneys. This phase is often characterized by jaundice, dark urine, abdominal pain, vomiting, and bleeding, and can result in death for half of those affected within 7-10 days.
Diagnosing yellow fever can be challenging, especially in the early stages, as symptoms can be similar to other diseases like malaria, viral hepatitis, and other hemorrhagic fevers. Polymerase chain reaction (PCR) testing in blood and urine can detect the virus in early stages, while later stages require testing for antibodies (IgM) to identify the disease.
Treatment
Yellow fever can be a serious and potentially fatal illness, but early and supportive treatment in hospitals can improve survival rates. While there is no specific antiviral medication for yellow fever, managing symptoms like dehydration, fever, and organ failure can help patients recover. Antibiotics can also be used to treat bacterial infections that may accompany the disease. Patients should stay protected from mosquitoes during the day to avoid spreading the virus.
Prevention of yellow fever outbreaks relies on vaccination. Immunizing the majority of the population is key to preventing the spread of the disease. The yellow fever vaccine is safe, affordable, and provides life-long immunity after a single dose. People who have recovered from yellow fever are also protected for life. In areas where vaccination coverage is low or unavailable, controlling the mosquito population through elimination of breeding sites and use of insecticides is essential. Community involvement in mosquito control efforts, such as cleaning up stagnant water sources, can also be effective.
