What is Yellow fever

Yellow fever is a viral infection transmitted by mosquitoes and characterized by fever, jaundice, kidney failure, and bleeding.

Statistics on Yellow fever

The disease is of widely varying severity and so is underreported. Cases occur mostly in Africa (90%) and in South America.

While yellow fever can affect individuals of all ages, the elderly have a higher risk of severe infection. If a person is bitten by an infected mosquito, symptoms usually develop three to six days later.

Risk Factors for Yellow fever

Yellow fever is an arbovirus (arthropod bourne) infection.

There are two forms:

  1. Urban form: in this form the vector (the transmitting organism) is the mosquito Aedes aegypti and the reservoir is humans – ie there is human to human transmission via mosquitos.
  2. Jungle (in the wild): This form is transmitted by various species of mosquito and the reservoir are tree dwelling monkeys. Hence it is usually transmitted from monkey to monkey via mosquitos, though humans can be infected if bitten by a mosquito carrying the virus.

The vaccine for yellow fever is moderately effective and mosquito control measures can be helpful.

Progression of Yellow fever

This is an arbovirus (arthropod-borne) infection.

Yellow fever can be divided into three stages:

  • Early stage: headache, muscle aches, fever, loss of appetite, vomiting, and jaundice are common.
  • Period of remission: fever and other symptoms resolve — most individuals will recover at this stage, yet up to 15% may move onto the third, most dangerous stage.
  • Period of intoxication: characterized by multi-organ dysfunction — liver and kidney failure, bleeding disorders/hemorrhage, brain dysfunction including delirium, seizures, coma, shock, and in up to 30% individuals, death.

How is Yellow fever Diagnosed?

A diagnosis is established by careful history of travel and vaccination status, and by isolation of the virus from blood during the first 3 days of illness.

Prognosis of Yellow fever

Mortality rate is up to 40% in severe cases.

How is Yellow fever Treated?

Treatment is supportive. Effective treatment includes bed rest (under mosquito nets), analgesics and maintenance of fluid and electrolyte balance.

Yellow fever is an internationally notifiable disease and is preventable by vaccination (which is valid for 10 years). However, vaccination is not recommended for children under 9 months and immunosupressed patients unless there are compelling reasons.

Yellow fever References

  1. Kumar P, Clark M. Clinical Medicine. Fourth Ed. WB Saunders, 2002.
  2. MEDLINE Plus.
  3. Timbury, MC., Notes on Medical Virology, 11th Ed. Churchill Livingstone 1997.