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Quirks and Quarks

New cat contraception method using gene therapy could help manage feral populations

Controlling feral cat populations is controversial and often involves capturing, surgically sterilizing and releasing the animals, which is complex and expensive. U.S. scientists have developed a new method for cat contraception that involves a single injection of a gene that prevents cat eggs from maturing.

An alternative to resource-intensive spay surgery has the potential to permanently sterilize female cats

CBC Radio ·
Four cats sit on a bench in a lab
U.S. scientists developed a contraception method for cats that's significantly less invasive and expensive than current approaches to managing feral populations. (Cincinnati Zoo & Botanical Garden)

Managing feral cats has been a complex, costly and controversial challenge for animal welfare organizations, but scientists in the U.S. have developed a new method of contraception that is simpler and less invasive than existing methods — and requires just a single injection.

The U.S. Department of Agriculture estimates there are  between 30 and 80 million unowned, or feral, cats in the U.S. North America, and Canada could have another 1.4 to 4.5 million. They pose a risk to wildlife, people, pets and often have a poor quality of life themselves compared to domestic cats.

And according to a study from 2013, free-ranging cats kill an estimated 2.4 billion birds annually across the continent, making cats the number one cause of bird mortality.

Communities often deal with feral cats by capturing and then surgically sterilizing them. 

Conservation biologist Bill Swanson from the Cincinnati Zoo & Botanical Garden was part of a team that developed and tested a new and simpler method of contraception using gene therapy. 

It led to a The single injection that causes the cats to overproduce a naturally occurring hormone called anti-müllerian hormone (AMH). It prevents the eggs from maturing, and in some instances, prevents the cats from ovulating altogether.

"We're inserting that gene [AMH] into the muscle cells of the cat. So the muscles, not the ovaries, are making very high levels of this protein, about 100 to 1,000 times the normal levels that they would produce," Swanson told Quirks & Quarks host Bob McDonald.

A cat sits on the ground near a railing.
A cat from the feral colony living on the Cranbrook, B.C., campus of the College of the Rockies. Managing feral cat populations has posed challenges in many communities across Canada. (EKCARES)

The study was published in the journal Nature Communications.

The gene is delivered to the cat's cells by a non-reproducing virus, a technology known in biomedicine as a "viral vector."

"It's really important to note that the gene isn't incorporated into the DNA of the cat. It's not incorporated into the genome. So the gene isn't passed on to offspring. It basically floats in the nucleus of the muscle cell and the normal machinery of the nucleus makes the protein that we need at very high levels," Swanson said. 

The advantage of this new technology is its simplicity – and, if widely adopted — its lower cost, to Swanson he said.

Current management, promising future

The Toronto Humane Society estimated in 2017 that there are about 17,000 unowned cats in the city proper. Last year, the Toronto Humane Society spayed and neutered more than 1,000 cats in a practice known as "trap, neuter, release" or TNR. 

Grey cat stands by tree on dry grass
Lower costs for controlling feral populations would decrease the risk of the animals spreading disease and attacking wildlife. (Taylor Holmes)

Jackie Ellis, doctor of animal behaviour and director of behaviour at the Toronto Humane Society, said the TNR method relies on volunteers who — while passionate about their work — are under-resourced. Additionally, there aren't enough veterinary doctors, especially in remote areas, to meet the demand for spay and neuter surgeries for feral cats. 

Swanson said the gene therapy he and his colleagues developed will, they hope, mean an easier, less stressful, process for both animals and local animal welfare groups.

"It's really exciting to think that as we learn more about the efficacy of this drug that we might have a more permanent method of helping these populations of unowned cats," said Ellis. 

This new technology also has potential to prevent other animals, including feral dogs as well as invasive species, from reproducing. 

"You would have to have the gene for that species, because it does seem to be species specific," said Swanson. "But once you've worked out the gene sequence, you could use basically the same approach, we think, and pretty much any other animal species that you want to sterilize."

The technology is new and will have to be commercialized before it can be used widely to manage cat populations. But Ellis thinks it could have potential as a humane way to manage unowned cat populations.

"As I see it, nothing jumps out at me as concerning or a red flag … nothing that says 'here's a big problem with it.' It's just exciting," she said. 

Written by Taylor Holmes. Produced by Jim Lebans.