Yellow fever

Yellow fever is a life-threatening infection that is caused by an arbovirus of the flavivirus genus. The ‘yellow’ in the name refers to the jaundice that affects some patients.

Transmission

Vector

Mosquitoes belonging to the Aedes and Haemogogus species that primarily bite during the day. The virus is transmitted by these vector species in a forest or rural cycle, and by Aedes aegypti in an urban environment.

Reservoirs

Monkeys are the primary reservoirs. Humans are only infected occasionally (sporadic infection of forest yellow fever). Large epidemics of yellow fever occur when infected people introduce the virus into heavily populated areas with high mosquito density and where most people have little or no immunity, due to a lack of vaccination. In these conditions, infected mosquitoes of the Aedes aegypti species transmit the virus from person to person.

Incubation period 

Short, 3 to 6 days.

Symptoms 

Most infections (80-85%) are subclinical or have minor symptoms, like fever, muscle pain, headache, loss of appetite, nausea or vomiting, which disappear after three to four days. After a short remission of symptoms, lasting up to 48 hours, a smaller proportion (20-15%) will develop a severe life-threatening disease with fever, jaundice, renal failure and hemorrhage. Approximately half ( 20% -60%)  of those die within seven to ten days. 

Prevention 

Prevention is important, since there is no cure for yellow fever, and only supportive treatment to ease the symptoms is available. 
Travellers at risk for yellow fever should be advised on:

• Mosquito repellent measurements, especially during daytime.
• Yellow fever vaccine: the most effective prevention is vaccination . This vaccine  is only available in authorised centres.

Additional information

• International Health Regulations (2005), Third Edition (WHO 2016) 
  Yellow fever (CDC 2019)
• CDC Yellow Book: Travel-related Infectious Diseases- Yellow Fever (CDC 2020)
• Yellow fever factsheet (National Travel Health Network and Centre 2021)

References

• Medasso, gezondheidsadviezen voor reizigers, laatste update 2016-2017 
• The green book of immunisation- chapter 35 - yellow fever (UK, 2020)
• Mark D. Gershman, J. Erin Staples, 64 - Yellow Fever, editors: Elaine C. Jong, Dennis L. Stevens, Netter’s Infectious Diseases, W.B. Saunders, 2012, Pages 383-389