Yellow Fever Virus

Testing Indications

Testing for Yellow Fever virus infection is indicated when a patient displays clinically compatible signs/symptoms of infection and has a relevant exposure history (e.g. travel to an endemic area, noted mosquito bites during travel, among others).

Most Yellow Fever virus infections are asymptomatic. In individuals that develop disease (e.g. those without prior immunization against Yellow Fever), symptoms may appear within 3 to 6 days of infection and can include, but are not limited to, fever, malaise, headache, photophobia, muscle pain, a rash or arthralgia. Some individuals may develop more severe disease characterized by jaundice, abdominal pain and hepatitis. Hemorrhagic manifestations may also occur.^1,4

Polymerase chain reaction (PCR) testing may be used to detect the virus during the acute viremic phase of the infection in individuals suspected of an active infection.⁵ Serologic testing is indicated for individuals with prolonged symptoms or those suspected of having a resolved infection.⁴ Testing is not recommended for asymptomatic individuals unless confirming titres for those that are at high-risk of infection (e.g. ongoing risk of exposure, among others).⁵

Acceptance/Rejection Criteria

Specimens received without the appropriate forms or approvals (See: Submission and Collection Notes) will not be tested.

Timing of Specimen Collection

Serologic testing for Yellow Fever virus:
Acute and convalescent sera should be collected for serologic testing, where applicable. The convalescent serum specimen should be collected at least 2 to 3 weeks after the initial acute specimen.

Molecular (real-time RT-PCR) testing for Yellow Fever virus:
Collect specimens for molecular testing early in the course of illness. A negative PCR result does not rule out infection. See acceptance/rejection criteria above.

Limitations

Haemolysed, icteric, lipemic or microbial contaminated sera or plasma are not recommended for testing.

Storage and Transport

All clinical specimens must be shipped in accordance with the Transportation of Dangerous Goods Act/Regulations.

For serum separator tubes: centrifuge specimen prior to placing in biohazard bag.
Place each specimen type in an individual biohazard bag and seal. Insert the corresponding requisition in the pocket on the outside of each sealed biohazard bag.

All specimens submitted for molecular testing should be stored at 2-8°C following collection and shipped to PHO’s laboratory on ice packs. If a delay in transport to PHO’s laboratory is anticipated (more than 72 hours), specimens should be frozen (at -80°C if possible) and shipped on dry ice.

Special Instructions

Each specimen submitted for testing must be accompanied by a separate PHO General Test Requisition. All fields on each requisition must be completed.

It is MANDATORY to submit the Arbovirus (Non-Zika) Testing Intake Form. where specified, with all fields completed. If all of the requested information from the Intake Form has been provided on the PHO General Test Requisition, we do not require an additional Arbovirus (Non-Zika) Testing Intake Form. Specimens submitted with this mandatory information missing will not be tested until that information is provided.

Test Frequency and Turnaround Time (TAT)

All Yellow Fever virus testing is considered a Referred Out Test. Specimens are sent to the NML in Winnipeg for testing.

The TAT for serology and molecular testing is up to 28 days from receipt at PHO’s laboratory.

Serology is performed at the NML by Plaque Reduction Neutralization Test (PRNT).

Molecular testing is performed by RT-PCR at the NML. This test requires prior approval by the PHO Microbiologist.

Interpretation

All results should be interpreted in the context of the specific clinical scenario. Given the overlap in distribution of disease vectors, testing for other potential pathogens should be considered, where applicable.

Serologic testing for Yellow Fever virus:
A ≥4 fold increase in neutralizing antibody titre between acute and convalescent sera (collected 2 to 3 weeks apart) tested by PRNT is considered indicative of seropositivity. (Detection of Antibodies Directed Towards Yellow Fever Virus by PRNT - Guide to Services - CNPHI (canada.ca))

Cross reactions (a reactive test result) may occur with other Flaviviruses such as Dengue virus, West Nile virus; therefore, submitting both acute and convalescent sera is recommended. Testing for other arboviruses may be added to assist with interpretation.

Molecular testing for Yellow Fever virus:
A positive PCR result indicates that Yellow Fever virus nucleic acids were detected in the specimen and an acute/recent infection. (Molecular Detection of Yellow Fever Virus by Real-Time Reverse Transcriptase PCR (RT-PCR) - Guide to Services - CNPHI (canada.ca))

A negative PCR result indicates that Yellow Fever virus nucleic acids were not detected in the specimen. This does not exclude Yellow Fever virus infection.

Reporting

Results received from the National Microbiology Laboratory (NML) are reported to the physician, authorized health care provider or submitter as indicated on the requisition.

References

1. Public Health Agency of Canada. Yellow Fever [Internet]. Ottawa: Public Health Agency of Canada; [cited 2023]. Available from: https://www.canada.ca/en/public-health/services/diseases/yellow-fever.html
2. City of Toronto. Public Health Reportable Diseases – Department of Public Health Sciences. Toronto: City of Toronto; 2023. [cited 2023]. Available from: https://www.toronto.ca/wp-content/uploads/2023/06/989f-PublicHealthReportable-DoPHSJuly2023.pdf
3. Thunder Bay District Health Unit. Disease of Public Health Significance – Reportable Diseases [internet]. Thunder Bay; [cited 2023]. Available from: https://www.tbdhu.com/professionals/health-care-providers/diseases-of-public-health-significance-reportable-diseases 
4. World Health Organization. Yellow fever [Internet]. Geneva: World Health Organization [cited 2023]. Available from: https://www.who.int/news-room/fact-sheets/detail/yellow-fever (Yellow fever (who.int))
5. Public Health Agency of Canada. Canadian Immunization Guide – Part 4: Active Vaccines [Internet]. Ottawa: Public Health Agency of Canada; [cited 2023]. Available from: https://www.canada.ca/en/public-health/services/publications/healthy-living/canadian-immunization-guide-part-4-active-vaccines/page-25-yellow-fever-vaccine.html