Stopping ASF spread by wild boars

Monday, May 13, 2024

Gene editing could avert 'existential crisis'

By Lilian Schaer, for Livestock Research Innovation Corporation

It's been more than five years since African Swine Fever (ASF) first broke out in China. Since then, hog farmers around the world have been on high alert and the world has watched with bated breath as the virus continues its relentless spread across Asia, into Europe and in the Caribbean.

The disease has yet to reach North America, and experts warn of the dramatic impact on the industry if or when it does, particularly in Canada where 70 per cent of hogs are exported as pork or live animals and a confirmed case of ASF will quickly close those export markets.

There is no vaccine or treatment currently available for ASF, and the virus is incredibly robust with the ability to remain in the environment for days, in meat products for months, and in vector or virus-transmitting insects for years.

The wild pig problem

A complicating factor is that wild boars are a reservoir for ASF as well as other pig and human diseases, and ASF can spread rapidly from the wild population into domestic swine production herds. In fact, wild boars are the most prolific invasive mammal in Canada.

Populations have developed rapidly across the country in the past 15 years, the largest of which are in Alberta, Saskatchewan and Manitoba. In areas where they've settled, they cause extensive crop and property damage, contribute to soil erosion and water contamination, and create ecosystem disruption.

But it's their disease-spreading potential that is particularly concerning.

"It would be a crisis if we got a case of African Swine Fever in a hog barn, but eventually, we would recover as a smaller, tightly-controlled industry. However, if it is found in wild pigs in Canada it means we would have a permanent reservoir for the disease, leaving the industry in a permanent existential crisis," says Ted Bilyea, an agri-food consultant specializing in innovation who spent 35 years working for Maple Leaf Foods.

Only a few pork operations with highly compartmentalized systems, solid domestic brands, and extensive processed pork lines would survive, he adds, leading to massive industry contraction that would have a falling domino effect on many related industries that service the pork industry from genetics and feed to veterinary services and transportation.

New solutions from new technology

It's a problem that led Dr. John Webb, a swine industry consultant specializing in genetics and former colleague of Bilyea's at Maple Leaf Foods, to wonder about the potential of finding a genetic solution that could help suppress the wild boar population.

Gene editing has been used successfully in mosquitos, for example, to suppress populations by making the insects sterile and to reduce the spread of malaria by modifying how they harbour and spread the parasite causing the disease.

This is done using something called a gene drive, a self-propagating mechanism that scientists can insert into an organism through a gene editing tool called CRISPR. The organism passes the edited gene to its offspring and the offspring do the same.

Gene editing is the technology behind the development of pigs resistant to Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), where scientists have used the tool to disrupt a cell surface viral receptor.

Webb approached Ray Lu, an associate professor in molecular and cellular biology at the University of Guelph, for help.

"This type of work has not been done in farm animals, but I have a lot of experience working with mice," says Lu. "I found this to be a very interesting problem and wanted to do something about it."

Feasibility modelling points to success potential

Gene editing, he believes, could help address the ASF challenge by making the boars resistant to the virus, but could also solve the other problems they pose by slowing down the speed at which they reproduce.

With support from Swine Innovation Porc, Lu was able to secure a Mitacs grant to fund a gene-drive feasibility study using computer modelling to demonstrate the effectiveness of gene editing solutions. The project confirmed that a gene-drive strategy could be successful and brought forward various safety considerations that will be needed should such an approach move forward.

These include making sure edited gene variants can only spread by mating, building in an "off-switch" to turn off the spread of edited genes if needed, and implementing tracing or identification strategies for pigs with edited genes.

Lu is now working on the next step, which is research to create the molecular design of an edited gene to insert into cells and evaluate how it behaves inside cell cultures.

Ultimately, this will lead to development of gene-edited pigs in a research setting to further evaluate the success of the technology.

It's going well, he says, but what is really needed now is funding to keep the work moving forward in a more substantial way – and so far, those efforts have been without success.

Funding roadblocks

In 2022, Health Canada announced it no longer requires additional risk assessments on gene-edited crops, but Canada does not yet have a regulatory framework for gene-edited animals.

In the United States, for example, the Food and Drug Administration has approved meat from gene-edited pigs from Washington State University for human consumption, but in Canada, the uncertainty around a regulatory framework is a major contributing factor to a reluctance to support research in this field.

There's also the challenge of public perception. The ongoing pushback against GM (genetic modification) technology is another contributing factor, even though the two approaches are not the same. GM technology involves inserting genes from another organism, whereas gene editing focuses on editing an organism's existing genes, and there is hope that public opinion will evolve as more people come to understand the gene editing technology.

"Gene editing and gene-drive is quite new and different but offers a potential solution to a tremendous problem in a practical and economic way," Lu says. "The concern is around regulatory approval and when we would be able to actually use this type of solution."

Regulatory approval processes take time, however, but so does research and development. Given the urgency of the threat posed by wild boars, Lu and other industry experts like Bilyea believe strongly in the need for ongoing funding from government and industry to help the industry be ready to act once regulatory approvals are in place.

"Invasive wild pigs not only present an existential threat to the hog and pork industry, but indeed to human health as they can become a reservoir for zoonotic diseases," says Bilyea. "Given the similarity in human and pig genomes, inaction on removal of this risk is needlessly endangering human health as well." BP

This article is provided by Livestock Research Innovation Corporation as part of LRIC's ongoing efforts to report on research, innovation, and issues affecting the Canadian livestock industry. LRIC is funded in part by the Sustainable Canadian Agricultural Partnership (Sustainable CAP), a five-year, federal-provincial-territorial initiative.