When African Swine Fever virus (ASFV) surged through China, Russia, and other parts of Europe, producers, veterinarians, and researchers hustled to curb its impact. Food security experts across the globe identified feed as one possible avenue for ASFV to enter swine herds. But when importing feed into the U.S. was highlighted as the highest risk, Jennifer van de Ligt, PhD, director of the Food Protection and Defense Institute at the University of Minnesota College of Veterinary Medicine (CVM), was skeptical.

“Because of past experience in the food industry, I evaluate issues from a global supply chain and food systems perspective—how food makes it from primary agricultural regions into feed and into animals,” van de Ligt says. For example, in order to prepare soybeans for swine feed, she says, the soybeans are exposed to specific temperatures for a certain period of time in order to improve their usefulness to the animals. According to van de Ligt, this process should be enough to destroy ASFV. But there was no published scientific literature specifically focused on this.

With this in mind, van de Ligt noticed a fairly new CVM faculty member, Declan Schroeder, PhD, associate professor in the Department of Veterinary Population Medicine, had the perfect expertise to help answer unresolved questions about how ASFV hitchhikes in feed. For 20 years, Schroeder has researched Emiliania huxleyi virus (EhV), which often infects algae and belongs to the same phylum—or category—of viruses as ASFV. So, the researchers decided to pursue investigating EhV as a surrogate virus, meaning modeling strategies for destroying ASFV by working with EhV. 

Algal answers

Previously, the surrogate viruses scientists researched to understand potential ASFV transmission through feed were non-related swine viruses, atypical of ASFV. Since ASFV is a double-stranded DNA virus, a closer surrogate would ideally be a double-stranded DNA virus from the same phylum (commonly referred to as giant viruses). Enter, EhV.  

“My first post-doc job was to characterize a new giant virus,” Schroeder says. He was the first to describe EhV and give it a new family name in a paper published in 2002. He also sequenced the virus in a paper published in 2005.

Most virologists focus on curing disease, either identifying a pathogen based on how it manifests in a host or assessing how it spreads in order to contain it. “Those two disciplines dominate human, animal, and plant virology,” Schroeder says. “But now, there is a third field emerging because life on earth is more than just plants, humans, and animals.” In this tier of virology, called viral ecology, scientists try to classify all the viruses on earth, where they come from, and what their hosts are. Schroeder’s work falls into this category.

Usually, algae blooms are bad news, so many researchers at the time of Schroeder’s post-doc were investigating ways to control them. But algae isn’t simply the bad guy. Schroeder says 50 percent of our oxygen comes from algae in the oceans. So, studying them to understand what makes them tick, through a field of discovery called algal ecology, helps scientists understand the distribution of algae in the sea.

“When we studied EhV in the big context of life and the way algal blooms work, we realized viruses were important for the survival of algae,” says Schroeder. Every alga has its own virus and different algae work together to keep the oceans balanced and healthy. In the world of algae, viruses act as an important check on the surrounding ecosystem. “Killing EhV never entered our minds. The mindset for us as algal virologists was understanding the virus in its natural context and identifying how it worked.” 

Same concept, new context

When van de Ligt approached Schroeder about collaborating to identify and confirm an ASFV surrogate virus scientists could use more easily, Schroeder says he had to do a “mental switch.” But as he and his team looked closer at EhV in this new way, they noticed it had a similar sensitivity to heat as ASFV. 

Scientists recommend exposing ASFV to 50–60 degrees Celcius for at least 20 minutes to destroy it. “The idea was to determine whether the surrogate behaved similarly,” Schroeder says, “and it appears to have done so.” It’s likely the two viruses respond to temperature similarly because of overlapping physical features. 

The team used a slightly different approach to expose EhV to heat than previous studies have, so their next step will apply this refined methodology to ASFV directly. “We have applied to bring ASFV here to the U of M,” Schroeder says. But doing so requires stringent biosecurity measures. At time of publication, only two labs in the United States have such capabilities. Hence the need for a solid surrogate virus to begin with. 

The power of partnership

With support from Archer Daniels Midland, BASF, Buhler, Cargill, the Fats and Protein Research Foundation, Kemin, Land O’ Lakes, and the United Soybean Foundation, this project spanned three different colleges within the University. Gerald C. Shurson, PhD, and Pedro Urriola, DVM, PhD, professor and associate professor respectively of swine nutrition in the College of Food, Agricultural and Natural Resource Sciences, provided essential context, interpretation, and connections within the feed and pork industries. And Fernando SampedroParra, PhD, a researcher in the School of Public Health, wrangled key data and trends for the research, using state-of-the-art data analysis approaches for understanding virus behavior under various heat treatment conditions. Shurson, Urriola, and Parra also bring several years of previous experiences to this new research initiative from working with industry collaborators to conduct risk assessments and evaluate mitigation strategies to inactivate porcine epidemic diarrhea virus in feed ingredients.

Thanks to these varied perspectives, the team approached this virus in a new way. “It’s the mindset of veterinarians and medical doctors that viruses are bad,” Schroeder says. “We, as a society, mess with our own system. Our populations are large, our interactions with animals have changed—these are all unnatural situations that select for unnatural problems.”

For Schroeder, analyzing similarities between and across different viruses can help identify the unique solutions necessary for this multifaceted context we humans have created here on Earth. 
 

An added bonus, according to Schroeder, is that this collaborative team discovered killing this algal virus requires a temperature it would never encounter in its environment—around 48 degrees Celsius—for a prolonged period of time. His team also discovered that while the temperature is effective, it does not destroy all the virus particles, leaving behind viable viruses that, if left unchecked, could continue to spread. So, EhV should be set to continue its key job of balancing algal ecosystems and keeping blooms under control. 

But when it comes to pork, the reverberations COVID-19 had on production plants reminded us all just how much our diets rely on the essential protein. According to van de Ligt, if ASFV came to the US, the disruption could be much, much worse and the consumer impact is only the tip of the iceberg. The entire pork economy would struggle, starting with hog farmers, as the export market would close due to global regulations. 

“The devastation ASFV would cause across the pork supply chain from farm-to-fork is why I’m passionate about finding and promoting incredible research collaborations like this,”van de Ligt says. “The power of our public-private partnership to develop this innovative approach is the key to understanding, controlling, and preventing ASFV from entering the U.S.”