- Yellow Fever Epidemiology
- Clinical Manifestations of Yellow Fever
- Public Health Significance
- Approval for Vaccination Clinics or Providers
Yellow fever is caused by the yellow fever virus, which belongs in the genus Flavivirus.
Mode of Transmission
Yellow fever virus is mainly transmitted by the bite of several species of infected mosquitoes of the genus Aedes. In settled urban areas these mosquitoes transmit infection between humans, although animal to human transmission can also occur.
In South American rain forests, yellow fever is also transmitted between monkeys by the bite of several species of forest mosquitoes of the genus Haemagogus. Transmission from monkeys to humans occurs rarely (jungle Yellow Fever) and usually involves people working or living in the jungle.
Vector Presence in Australia
Aedes aegypti, a vector involved in the transmission of yellow fever virus is widely distributed in northern Queensland. The possibility of an urban outbreak of yellow fever exists if these mosquitoes acquire yellow fever from an infected traveller.
Period of Communicability
Human blood is infectious to mosquitoes shortly before the onset of fever and for the first 3–5 days of the illness. The disease spreads rapidly where there are susceptible populations and abundance of vector to transmit the virus. Aedes aegypti, after an incubation period of 9–12 days with this virus, is infectious to humans and remains so throughout its life span.
Yellow fever causes an acute viral illness which is usually mild. Early symptoms occur 3–6 days after a person is bitten and are relatively non-specific. They include:
- Lumbosacral and joint pain, particularly in the lower extremities
- Anorexia, nausea or vomiting
These symptoms last 3–5 days during which time the person is viraemic and potentially infectious.
About 15% of people infected with yellow fever will develop a severe clinical syndrome 3 to 6 days after initial symptoms develop. This may occur about 48 hours after the initial illness has recovered. This severe disease is characterised by the return of high fever, prostration, hepatic and renal dysfunction and haemorrhage. Between 15–50% of people with this severe disease die from shock, renal failure and/or cardiac dysfunction.
If a person survives the severe manifestations of infection, the infection terminates rapidly on about day 6 of symptoms. Convalescence from yellow fever can include several weeks of fatigue. Jaundice can persist for weeks to months.
Testing for yellow fever is not routinely performed in many Australian laboratories. Clinicians should consult their local public health unit if unsure about where testing can be obtained.
Laboratory diagnosis of yellow fever usually relies on;
- Demonstration of IgM in the blood by Enzyme Linked Immunosorbent Assays (ELISA) or liver tissue by use of labelled specific antibodies.
- Demonstration of viral genome in blood or liver tissue by nucleic acid amplification assays or hybridisation probes.
- Serological diagnosis with significant rise of IgG levels to yellow fever virus in a convalescent specimen.
The virus can be potentially cultured from blood by inoculation into suckling mice or amplification in cell cultures (mosquito cells).
Further information can be obtained from the Australian Immunisation Handbook.
Yellow fever is endemic in tropical areas of South America and Central Africa.
Outbreaks can occur in usually unaffected areas if mosquitoes become infected by infected people entering the area. In these areas the absence of endemic subclinical or mild infections in an unaffected population may mean it is vulnerable to high rates of infection if yellow fever is introduced.
Yellow fever is not endemic to Australia but potential mosquito vectors are prevalent in northern Queensland. It is therefore important for clinicians to rapidly diagnose cases of yellow fever in travellers returning to areas with Aedes mosquitoes and isolate them from contact with mosquitoes. Isolation of people with yellow fever from contact with other people is not necessary to avoid transmission of the virus.
Preventative and Control Measures
- Yellow fever vaccination is recommended for all travellers to endemic areas in Africa and South America.
- Travellers entering Australia from yellow fever endemic areas are required to produce evidence of yellow fever vaccination*.
- All those travelling to or living in yellow fever endemic countries are advised to take mosquito avoidance measures such as using insect repellents, coils and sprays; using mosquito nets (preferably those that have been treated with an insecticide); and ensuring adequate screening of residential premises.
*People arriving in Australia who are required to possess a yellow fever vaccination certificate but do not have one will be provided with a Yellow Fever Action Card by a biosecurity Officer from the Department of Agriculture and Water Resources. The Yellow Fever Action Card instructs the unvaccinated person to seek medical advice promptly if they develop any symptom of yellow fever in the six-day period following their departure from a yellow fever declared place. The card also provides information for doctors in the event that the unvaccinated person presents with the card.
In Australia, yellow fever vaccination clinics or providers are approved by state and territory health authorities. Please contact the health authority in your state or territory for approval criteria and procedures.
The approved yellow fever clinics or providers are supplied with the WHO-approved yellow fever vaccine (Stamaril brand manufactured by Sanofi-Pasteur).
While every care has been taken in preparing this fact sheet, the Commonwealth of Australia does not accept liability for any injury or loss or damage arising from the use of or reliance upon its contents.