Yellow fever

Notification requirement for yellow fever

Yellow fever is an ‘urgent’ notifiable condition. It must be notified by medical practitioners and pathology services to the Department of Health (the department) immediately by telephone upon initial diagnosis (suspected or confirmed). Pathology services must follow up with written notification as soon as practicable.

This is a Victorian statutory requirement.

Yellow fever is a listed human disease and is subject to Australian quarantine precautions at the international border to prevent the introduction to the virus into Australian mosquitoes. The Australian Government must report yellow fever to the World Health Organization (WHO) under the International Health Regulations (2005).

Primary school and children’s services centres exclusion for yellow fever

Not applicable.

Infectious agent of yellow fever

Yellow fever virus is a member of the flavivirus group.

Identification of yellow fever

Clinical features

Yellow fever is a viral disease of variable duration and severity. People usually develop symptoms 3 to 6 days after contracting the virus.

People often develop an initial “acute” phase with symptomatic illness. This may progress in some to a second “toxic” phase which is associated with high morbidity and mortality.

Initial ‘acute’ phase

During the initial ‘acute’ phase, symptoms may include:

• fever
• muscle pain with prominent backache
• headache
• shivers
• loss of appetite
• nausea or vomiting

Most people improve and their symptoms disappear after 3–4 days.

Second ‘toxic’ phase

15 to 25 per cent of people enter the second ‘toxic’ phase within 24 hours of the initial remission.

Symptoms may include:

• high fever
• multisystem organ failure
• jaundice
• abdominal pain with vomiting
• bleeding from the mouth, nose, eyes or stomach
• deteriorating kidney function

Half of the patients who enter the ‘toxic’ phase die within 10–14 days. The rest recover without significant organ damage.

Yellow fever is difficult to diagnose, especially during the early stages. It can be confused with malaria, typhoid, dengue, hepatitis and other diseases. Yellow fever is named after the yellow skin discolouration (or jaundice) that is usually observed in people with serious infection.

Diagnosis

Diagnosis is based on the presence of clinical, epidemiological and laboratory evidence.

• Clinical evidence refers to a clinically compatible illness.
• Epidemiological evidence includes history of travel to a yellow fever endemic country in the week preceding onset of illness.
• Laboratory definitive evidence includes one of the following:
  • isolation of yellow fever virus
  • detection of yellow fever virus by nucleic acid testing
  • seroconversion, or a fourfold or greater rise in yellow fever virus–specific serum IgM or IgG levels between acute and convalescent serum samples
  • detection of yellow fever virus antigen in tissues by immunohistochemistry.
• Laboratory suggestive evidence includes:
  • Yellow fever virus–specific IgM detected in the absence of IgM to other relevant flaviviruses is suggestive of yellow fever.

Yellow fever virus–specific IgG on a single specimen confirmed by neutralisation, where cross-reactions with other flaviviruses have been excluded, is suggestive of infection, and should be viewed in the context of clinical and epidemiological evidence.

All clinical specimens should be transferred immediately to the Victorian Infectious Diseases Reference Laboratory (VIDRL). Contact VIDRL to discuss requirements for sending specimens and for interpretation of laboratory results. Cross-reactivity with other flaviviruses can occur.

A person with a febrile illness who has been in a yellow fever area within the previous 6 days should be considered a suspected case and notified immediately.

Incubation period of yellow fever

The incubation period is 3–6 days.

Public health significance and occurrence of yellow fever

Yellow fever is endemic in tropical and subtropical areas of Central and South America and central Africa.

See links below for up-to-date countries of risk:

• Africa
• South America

People travelling to endemic areas are strongly recommended to be vaccinated against yellow fever. Several countries require documented evidence of yellow fever vaccination, or exemption if indicated.

Outbreaks may occur in unaffected areas if vector mosquitoes are exposed to migrating humans or monkeys that are infected with the virus.

While yellow fever virus is not known to circulate in Australian mosquitoes, the Aedes aegypti mosquito which are common in coastal regions of far north Queensland is capable of transmitting the virus. The potential introduction of yellow fever virus to local mosquito populations could theoretically result in localised spread and an outbreak of human disease.

Reservoir for yellow fever virus

In urban areas of endemic countries - humans and Aedes species mosquitoes.

In remote areas of endemic countries - vertebrates other than humans (mainly monkeys and possibly marsupials) and Aedes species mosquitoes.

Mode of transmission of yellow fever

Yellow fever virus is spread to humans by infected mosquitoes.

Mosquitoes become infected when they feed on a person or animal who has yellow fever virus in their blood during their infectious period. The virus multiplies inside the mosquito and can subsequently infect other people with future bites.

Human-to-human transmission has not been documented.

Period of communicability of yellow fever

Human blood is infective for mosquitoes shortly before the onset of fever and for 3–5 days after. Mosquitoes require 9–12 days after a blood meal to become infectious and remain so for life.

Susceptibility and resistance to yellow fever

Mild infections are common in endemic areas. Passive immunity in infants born to immune mothers may last for 6 months. Infection confers lifelong immunity.

Yellow fever vaccination is strongly recommended in people aged ≥9 months who are travelling to endemic countries. A single vaccine dose elicits protective levels of antibodies in most healthy adults and children. Some people are recommended a booster if their last dose was 10 years ago or more. Yellow fever vaccine is a live vaccine and may not be suitable for all people.

For more information on yellow fever vaccination, visit the Australian Immunisation Handbook.

Control measures for yellow fever

Preventive measures

People travelling to a yellow fever endemic area

People aged ≥9 months who are travelling to endemic areas in Africa and Central/South America are strongly recommended to be vaccinated for yellow fever. Travellers are advised to check their vaccination requirements.

People travelling to a yellow fever endemic area are advised to avoid mosquito bites by:

• Wear mosquito repellent containing DEET or picaridin
• Wear light coloured, long-sleeved, loose clothes when outdoors
• Ensure accommodation is mosquito-proof with fly screens over windows and doors and a mosquito net over the bed

People arriving in Australia from a yellow fever endemic area

Certification of yellow fever vaccination is requested from travellers over 1 year of age entering Australia within 6 days of leaving an infected country. A yellow fever vaccination certificate is valid for the duration of the life of the person vaccinated. Vaccine providers in Victoria must be accredited with the department.

People arriving in Australia, who are required to possess a yellow fever vaccination certificate but do not have one, will be interviewed on arrival by a Biosecurity Officer. Biosecurity Officers will permit unvaccinated people to enter Australia but will reinforce the seriousness of the disease to the person and provide them with a Yellow Fever Action Card.

The card provides instructions to the unvaccinated person such as to:

• avoid being bitten by mosquitoes by wearing insect repellents and staying indoors for the 6 days following their departure from a yellow fever risk country.
• if they develop any symptoms of yellow fever in the six-day period they should seek medical advice and notify the Department of Health.

Control of case

Sick travellers arriving to Australia are screened for yellow fever and other Listed Human Diseases under biosecurity arrangements. Travellers with compatible illness are assessed and managed by Biosecurity Officers and Human Biosecurity Officers at the international border.

In Victoria, suspected or confirmed cases that require inpatient treatment should be referred to the Victorian Infectious Diseases Service at the Royal Melbourne Hospital, where adequate facilities for isolation are available if required. This is of particular concern in suspected cases where the differential diagnosis may include other viral or haemorrhagic fevers with greater potential for person-to-person spread.

Cases should be protected from exposure to mosquitoes for five days after onset of infection. The case should be cared for in an isolation room, or in a screened room with use of an insecticide-treated mosquito net, if not in hospital.

Control of contacts

Travel contacts of a confirmed case are requested to self-monitor for symptoms of a febrile illness for six days since their last overnight stay in a country where yellow fever may be present. They should avoid being bitten by mosquitoes and must not travel to areas such as Queensland until 6 days after their return from an endemic area.

Control of environment

If a traveller to Australia is diagnosed with yellow fever and has been potentially exposed to Australian Aedes aegypti mosquitoes during the period of viraemia, or if the first recognised case has no history of overseas travel, environmental evaluation and control measures will be carried out by the department.

Environmental management is crucial for infection prevention and minimisation. Insect quarantine at airports and seaports should be maintained to prevent the introduction of Aedes aegypti and Aedes albopictus, species that are capable of transmitting yellow fever.

Outbreak measures for yellow fever

A single case of locally acquired transmission constitutes an outbreak. In the event of an epidemic of yellow fever in an urban area, all people living in the area infested with known vector mosquitoesshould be offered yellow fever vaccine, and a wider mosquito control program should be implemented.