Unexpected thermal stability of two enveloped megaviruses, Emiliania huxleyi virus and African swine fever virus, as measured by viability PCR (preprint)

ABSTRACT

Background: The particle structure of Emiliania huxleyi virus (EhV), an algal infecting member of nucleocytoplasmic large DNA viruses (NCLDVs), contains an outer lipid membrane envelope similar to that found in animal viruses such as African swine fever virus (ASFV). Despite both being enveloped NCLDVs, EhV and ASFV are known for their stability in the environment. Method: Here we report for the first time, the application of a viability PCR method to describe the unprecedented and similar virion thermal stability of both EhV and ASFV. This result contradicts the bioassay method that suggests that virus “infectivity” is lost in a matter of seconds (EhV) and minutes (ASFV) at temperature greater than 50 °C. Confocal microscopy and analytical flow cytometry methods was used to validate the viability PCR data for EhV. Results: We observed that both EhV and ASFV particles has unprecedented thermal tolerances. These two NCLDVs are exceptions to the rule that having an enveloped virion anatomy is a predicted weakness, as is often observed in enveloped RNA viruses (i.e., the viruses causing Porcine Reproductive and Respiratory Syndrome (PRRS), COVID-19, Ebola, or seasonal influenza). Using the viability PCR method, we confirm that no PRRSV particles remain after 20 minutes of exposure to temperatures up to 100 °C. Conclusions: This observation has practical implications for industries involved in animal health and food security. Finally, we propose that EhV could be used as a surrogate for ASFV under certain circumstances.