Tracing the Virus by Mutation
• SARS coronavirus does not have enough similarity to any known virus to identify its origin in another species.
• RNA viruses have high frequencies of mutation, but the selection of mutations is more important. SARS coronaviruses isolated have shown very few mutations and these are more likely to be epidemiological markers than biologically significant.
• We do not have the information to correlate point mutations with effects on functionality or phenotypes.
Stability and Reservoirs of Virus
• TGEV is stable in frozen fecal material, but is inactivated by UV radiation in summer; infections show seasonality.
• Birds and flies may serve as reservoirs of TGEV mechanically or by ingesting and shedding viruses.
• Possible fomites for SARS should be considered.
• There is some stability to the virus when dried, and it lasts for probably a few days.
• If fecal shedding occurs, it could cause sewage contamination.
• There is some evidence to suggest coronavirus can persist noninfectiously in chickens and that cats shed feline enteric CoV for months.
• Super-spreader phenomenon does not appear to be virus-specific.
• There is no correlation seen in Hong Kong between mortality and seroconversion, as seen with IFA.
• PRCV is shown to elicit high levels of alpha-interferon.
• NK cells play a role in TGEV infection, and there is evidence of antibody-dependent enhancement of immune response.
Virus Detection and Culture
• SARS coronavirus has been grown in Vero, Vero E6, LLCMK2, primary monkey kidney, and PK15 cell lines.
• PCR shows RNA copies in stool, sometimes at higher levels than respiratory secretions.
• In some cases SARS virus has been amplified from plasma but not consistently.
• In animals, peak viremia usually correlates with peak shedding; correlates are better with ELISA for viral antigen because PCR methods detect virus before symptoms appear.
• In feline models, certain types of vaccine-introduced antibodies can enhance infection, primarily including monoclonals against epitopes of the spike protein; one epitope did not.
• Factors could be involved in exacerbating respiratory infections.