Risk Group and Containment Level Requirements for Single Stranded, Positive Sense RNA

The Centre for Biosecurity recently completed a risk assessment on single-stranded positive sense RNA. Single-stranded positive sense RNA viruses have genomes that function like messenger RNA and can be directly translated after entering a host cell. Examples of single-stranded positive sense RNA viruses include West Nile virus, Enterovirus C (Poliovirus), and Eastern equine encephalitis virus.

Intact full-length viral single-stranded positive sense RNA can cause infection by serving as the template for the synthesis of viral RNAs. This results in replication of the parental virus. However, the infectivity of purified or chemically synthesized single-stranded positive sense RNA is much lower than that of the parental virus, because exogenous RNA is unstable and not readily taken up by cells. Under favourable conditions, efficient transfection can occur.

Risk group and containment level requirements for single-stranded positive sense RNA

Under favourable conditions for cellular uptake of full length viral single-stranded positive sense RNA (for example, transfection protocols, in vivo injection), the infectivity of single-stranded positive sense RNA may be similar to that of the source parental intact virus.

•         The risk group of the full length viral single-stranded positive sense RNA is classified the same as the risk group of the parental virus.
•         Activities with the full length viral single-stranded positive sense RNA should be performed at the same containment level as the parental virus.

Under unfavourable conditions for cellular uptake of full length viral single-stranded positive sense RNA (for example, laboratory analyses, polymerase chain reaction, viral heat inactivation) the infectivity of single-stranded positive sense RNA is very low. However, it does remain potentially infectious.

•         Full length viral single-stranded positive sense RNA from regulated viruses (Risk Group 2, 3, or 4) is classified as human and animal Risk Group 2
•         Activities can be safely performed at Containment Level 1, as determined by a local risk assessment.

Fragmented or chemically or radiologically altered full length viral single-stranded positive sense RNA aren't considered infectious. They are classified as Risk Group 1 and can be safely handled at Containment Level 1.

Diagnostic laboratory activities with material containing single-stranded positive sense RNA may be exempt from licensing under Section 27(1) of the Human Pathogens and Toxins Regulations. The importation of single-stranded positive sense RNA however, is regulated under the Health of Animals Act and Regulations and a permit to import may be required.

You can find information on full length viral single-stranded positive sense RNA in:

• Section 4.3.9 of the Canadian Biosafety Handbook
• the ePATHogen database which is a comprehensive listing of all biological agents, risk groups, and containment levels, including single-stranded positive sense RNA
• the SARS-CoV-2 Biosafety Advisory, which contains requirements and recommendations for working with SARS-CoV-2 single-stranded positive sense RNA.

For questions or concerns, please contact the Biosafety Risk Assessment team at pathogens.pathogenes@phac-aspc.gc.ca.