California Serogroup (CSG) Viruses - Serology and PCR

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

Background
This page provides information on the testing available through Public Health Ontario (PHO) for viruses within the California serogroup (CSG).

Viruses in the CSG are mosquito-borne RNA viruses in the Peribunyaviridae family (genus Orthobunyavirus) that can cause encephalitis in humans¹.
There are two known CSG viruses found in Canada, the Jamestown Canyon (JTC) and Snowshoe Hare (SSH) viruses. Clinical cases have been documented across the country, including Ontario, Québec, British Columbia, Yukon and Northwest Territories^1,2.
Testing for CSG viruses involves serology and/or PCR depending on the clinical scenario.

Testing for the JTC and SSH CSG viruses is performed at the National Microbiology Laboratory (NML)³.

Updates
Effective July 2, 2025, submission of the new Vector-borne and Zoonotic Virus Testing Intake Form is mandatory, along with the General Test Requisition when requesting specific vector-borne or zoonotic virus tests. The new intake form replaces both the Arbovirus (Non-Zika) Testing Intake Form and the Mandatory Intake Form for Zika Virus Testing.

*Uncontrolled print copy. Valid only on day of print: 29 July 2025.

Testing Indications

Testing for CSG infection may be considered in individuals with:

clinically compatible signs/symptoms of infection
relevant exposures (e.g. travel to or residence in endemic areas or areas with ongoing transmission, outdoor activities in endemic areas, noted mosquito bites, among others).

Many individuals exposed to JTC or SSH viruses remain asymptomatic. Others may develop an acute febrile illness like other vector-borne viral diseases, which can progress to neuroinvasive disease.

Serology is the preferred method for CSG virus testing¹. Test requests with insufficient justification based on the indications above may be cancelled. This includes requests for CSG PCR without an accompanying request for CSG serology. Testing by PCR is not routinely recommended and should be considered only for individuals that are immune compromised and during active mosquito season. Testing is not recommended for asymptomatic individuals.

Due to the overlap in geographic distribution of the corresponding vectors², infection with other vector-borne pathogens, such as West Nile Virus, should be considered if suspecting CSG virus infection during active mosquito season.

Acceptance/Rejection Criteria

Specimens received without the appropriate forms (See: Submission and Collection Notes) are subject to cancellation.

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
California Group Serology	General Test Requisition Vector-borne and Zoonotic Virus Testing Intake Form	Paired serum specimens (acute AND convalescent) collected 2-3 weeks apart from patients with clinical illness³	1.0 mL	Red top or Serum separator tubes (SST)
California Group Serology	General Test Requisition Vector-borne and Zoonotic Virus Testing Intake Form	Cerebrospinal fluid (CSF) paired with single serum from patients with clinical illness³	500 µL	CSF: Sterile tube/container And Serum: Red top or Serum separator tubes (SST)
California Serogroup PCR⁵	General Test Requisition Vector-borne and Zoonotic Virus Testing Intake Form	Serum	250 µL	Red top or Serum separator tubes (serum)
California Serogroup PCR⁵	General Test Requisition Vector-borne and Zoonotic Virus Testing Intake Form	CSF	250 µL	Sterile tube/container

Submission and Collection Notes

Label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay.

Each specimen submitted for testing must be accompanied by a separate PHO General Test Requisition, with all fields completed.

It is MANDATORY to provide the clinical information, relevant travel(s), and relevant exposures for Vector-borne viruses requested on the Vector-borne and Zoonotic Virus Testing Intake Form. Test requests that are submitted without the appropriate mandatory information are subject to cancellation.

NML will not accept unpaired specimens for CSG testing. See Timing of specimen collection for details on paired specimen requirements.

Testing for California Serogroup PCR is not routinely performed and must be approved by a PHO Microbiologist. Submission of the completed Vector-borne and Zoonotic Virus Testing Intake Form will initiate the review process at PHO provided the form contains all necessary information. Requests received without the form, forms submitted with insufficient information or insufficient justification for testing are subject to cancellation.

Timing of Specimen Collection

Serology:
The following paired specimens are accepted for CSG serology³:

Paired serum specimens (acute and convalescent) collected 2-3 weeks apart from patients with clinical illness.
CSF paired with single serum from patients with clinical illness.

Molecular (real-time PCR):
Clotted blood, serum or CSF specimens for PCR testing should be collected as soon as possible after symptom onset.

Limitations

Hemolysed, icteric, lipemic or microbially 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 sample 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.
Clotted blood/serum /CSF specimens should be stored at 2-8°C following collection and shipped to PHO on ice packs.

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.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

All CSG viruses testing is considered a Referred Out Test. Specimens are sent to the NML in Winnipeg to be tested.

Serology:
The TAT for IgM Enzyme Linked Immunosorbent Assay (ELISA) is 14 days from receipt at NML. The TAT for the confirmatory Plaque Reduction Neutralization Test (PRNT) is 28 days from receipt at NML.

Molecular (real-time RT-PCR):
RT-PCR (if performed at NML) is 14 days TAT following the ELISA.

Test Methods

Screening test: IgM ELISA only; IgG ELISA is not performed.
Confirmatory test: PRNT
Optional test: molecular detection by RT-PCR

PCR is not routinely recommended for CSG viruses as it is not a sensitive test.

Algorithm

Submitted specimens will first be analyzed by the IgM ELISA to determine if the patient has developed anti-CSG antibodies. IgM-reactive specimens will undergo PRNT confirmation.

Note: IgG serology is not available/not performed at NML.

PCR testing will be considered on a case-by-case basis.

Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

Positive CSG results for encephalitis cases are reported to the Medical Officer of Health as per the Ontario Health Protection and Promotion Act.

References

Emerging mosquito-borne bunyaviruses in Canada. Available from: https://www.canada.ca/content/dam/phac-aspc/migration/phac-aspc/publicat/ccdr-rmtc/15vol41/dr-rm41-06/assets/pdf/ccdrv41i06a01-eng.pdf
Public Health Agency of Canada. 2024. West Nile virus and other mosquito-borne diseases surveillance in Canada: Annual edition 2022. Available from: https://www.canada.ca/content/dam/phac-aspc/documents/services/publications/diseases-conditions/west-nile-virus-surveillance/2022/annual-edition/annual-edition.pdf
National Microbiology Laboratory. 2022. Diagnostic and sample submission considerations for California serogroup viruses. Available from: https://cnphi.canada.ca/gts/downloadFile?source=reqForm&id=13000&lang=en