African swine fever is heat resistant
Editor’s Note: This article is based on a webinar presented in March 2023 that is copyrighted by Informa Markets and the University of Minnesota. The individual speakers are solely responsible for their content and opinions.
Dr. Declan Schroeder is an Associate Professor of Virology, College of Veterinary Medicine, University of Minnesota. He said that to research the African swine fever (ASF) virus, very tight biosecurity is needed; and not every laboratory can do this. Researchers must be extremely careful when investigating the ASF virus with live pigs. Because of the biosecurity needed, these studies are very limited, and the information generated is limited, he noted.
Therefore, different alternatives are commonly used to develop in vitro cell culture assays in the ASF field, he said.
Surrogate: Emiliana huxleyi
“We know that ASF is the only virus in its family, and it's unique to swine. There is nothing else out there like it, especially when it comes to swine. But it's not an isolated virus, it hasn't just appeared by magic, it has a good evolutionary history,” Schroder noted.
He pointed out that a surrogate virus used is a relative of ASF called Emiliana huxleyi, which infects algae and only one specific species of algae. This surrogate virus presents no risk to the swine industry or to any other animals or plants.
Schroeder explained that enough work has been done with the surrogate to understand how closely related it is to ASF.
The ASF virus is an envelope virus with capsules and inner membranes — it’s a large double stranded DNA virus, 200 nanometers in diameter. The algal virus shares the same features as the ASF virus because these two viruses co-evolved. They have a common origin many, many years back, but they evolved and diverged, he said.
What makes this algal virus very similar to the ASF virus is that it infects cells in the same way, using micropinocytosis. It just needs to have an intact particle for the virus to be taken up, he said.
ASF thermal stability
The surrogate virus has been helpful in studying ASF as the two viruses have a similar thermal stability. Research was done exposing the two viruses to heat ranging from 60 to 100° C (140 to 212° F), Schroeder said.
The research demonstrated, using standard PCR with 5 logs of virus, that ASF is stable until 100° C (212° F) at which point there was a 2-log virus reduction.
The algal virus has similar features. Starting with 6 logs of virus and the same temperature exposure, the algal virus has thermal stability until the 80° C (176° F) mark, and like ASF, there was 2-to-3-log virus reduction at 100° C (212° F).
The virus similarity between ASF and Emiliana huxleyi has allowed the use of a technique called viability PCR, which only monitors viable viruses and can be modified to make it quantitative. With viability PCR, research on Emiliana huxleyi is generating unique data about the ASF virus, Schroeder concluded.