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In this Aug. 26, 2019, file photo, Salt Lake City Mosquito Abatement District biologist Nadja Reissen examines a mosquito in Salt Lake City. The potentially fatal West Nile Virus is popping up more around the U.S. Southwest following a rainier winter. There are a record number of cases in Maricopa County and nine deaths for the entire state of Arizona so far this year. (AP Photo/Rick Bowmer, File)

Brian Foy just wants to get this out of the way: This is not a story that has anything to do with COVID.

Sure, this story is about a novel use of ivermectin, the common deworming medicine that is now the subject of rapturous internet theories — all unproven — that it is a magic bullet against the SARS-CoV-2 coronavirus. And, yes, Foy, a professor at Colorado State University who specializes in infectious diseases, is talking about a new way of using ivermectin to battle a potentially lethal virus.

But, to repeat: This. Is. Not. A. Story. About. COVID.

This is a story about how to murder mosquitoes.

And Foy, who has studied mosquito-borne diseases the world over, thinks he and his colleagues may have hit upon a way to dramatically reduce the spread of West Nile virus by using ivermectin to turn hungry birds into passive assassins.

“We’re looking for better ways to potentially offer control,” he said.

But let’s back up.

Before the pandemic, before podcasters and YouTubers and Facebook physicians, heck even before the internet, ivermectin was being used to fight infectious disease. Its primary purpose, in humans and other animals, is to battle internal parasites — things like heartworms in dogs or the worm Onchocerca volvulus, which causes a disease in humans called river blindness.

Colorado State University Microbiology, Immunology and Pathology professor Brian Foy poses in his lab, October 11, 2018. (Provided by CSU)

But scientists had long noticed something about ivermectin, Foy said. In addition to killing parasites inside of people and other animals, it was also pretty good at killing blood-sucking parasites that bite people and other animals.

Ivermectin works by blocking nerve pulses in worms and other invertebrates, causing paralysis. So when those blood-sucking beasts get a meal full of ivermectin, their bodies shut down. And that is handy because if those parasites are capable of transmitting diseases, their ivermectin-fueled deaths mean they can’t infect anyone else.

“People learned a long time ago that mosquitoes can die pretty efficiently when they take up blood after an animal or humans have been treated with ivermectin,” Foy said.

Foy has a long-running research interest in trying to use mass administration of ivermectin to reduce transmission of malaria. That work has taken him to the African nation of Burkina Faso, where he has conducted studies giving ivermectin to entire villages of people to see if it cuts local malaria spread.

But he and others also began to think about an application closer to home.

Between 1999 and 2019, more than 5,600 people were infected with West Nile virus in Colorado, making it one of the hardest-hit states in the country. In 2019, the most recent year for which finalized data are available, Colorado saw 122 cases of West Nile virus and eight deaths.

Northern Colorado, with its abundance of agricultural land making it the perfect breeding ground for West Nile-carrying mosquitoes, is especially vulnerable to the disease. Because of that, when West Nile seasons get bad enough, communities in Boulder, Larimer and Weld counties will conduct mass-spraying to kill mosquitoes.

West Nile ivermectin Colorado photo for The Temperature 12/08/21
Delta County environmental health officer Keith Lucy, left, and mosquito control officer Jim Terrazas look for mosquito larvae at Escalante Wildlife Area near Delta, Colo, April 8, 2004. (AP Photo/Chris Froese)

But Foy wondered, what if there was another way to target the transmission chain? And that’s when he began eyeing backyard bird feeders.

Birds — especially the songbirds that frequent bird feeders — are a key reservoir for West Nile virus, Foy said. While most do not get very sick from the virus, they can often harbor it, like little, feathered West Nile vending machines. Mosquitoes that bite them pick up the virus and then carry it to humans.

Birds dosed with ivermectin that kills the mosquitoes that bite them could potentially provide a break in the chain.

“You could get presumably a zone of protection around your property,” Foy said.

Foy worked with a recent doctoral graduate of the University of California Davis named Karen Holcomb to assess the potential effectiveness of the strategy, using preliminary tests with outdoor chicken coops and also a mathematical model. The result?

“We found that widespread use of ivermectin in backyard bird feeders could reduce neighborhood transmission of West Nile virus by about 60%,” Holcomb said in a news release announcing the findings.

But Foy said there’s a lot more work that needs to be done before the approach can be rolled out.

Colorado State University professor Brian Foy works in an outdoor “mesocosm” used to study the biting behavior of mosquitoes on chickens. The research is part of Foy’s effort to understand whether feeding ivermectin to birds can help kill mosquitoes and reduce the spread of West Nile virus. (Provided by Brian Foy)

Researchers need to figure out how much ivermectin various species of birds can tolerate. They need to make sure ivermectin is safe for squirrels, too, since those furry ninjas will inevitably eat whatever is put into a feeder.

They need to figure out how many feeders in a neighborhood must be loaded with ivermectin-infused bird seed and how far apart those feeders should be placed. They need to develop a method for spraying ivermectin onto bird seed that won’t cause birds to reject it but will allow the coating to withstand sun and rain. (Foy is working with a company in Golden on that one.)

They need to learn how fast birds clear ivermectin from their systems and how often they need to be fed the medication to keep up their killing prowess and how often neighborhood birds get their food from a feeder versus elsewhere.

“Birds are pretty fast metabolizers, so it doesn’t stay in their system very long,” Foy said. “They’re going to have to keep self-medicating.”

And researchers are going to need to find a reliable source of ivermectin — something that has become more complicated now that people are scooping it up to treat coronavirus infections. OK, so this story has a little bit to do with COVID.

Foy said he has had more trouble finding an ivermectin lately, as has another researcher he knows. But, ever the cautious scientist, he said he can’t state definitively that COVID hoarding is causing a supply crunch for ivermectin. 

“I’m worried that it’s all going to be anecdotal, and I don’t want to push it too much,” he said.

Then he laughed. “It seems to be that it’s hard to get these days.”

John Ingold

John Ingold is a co-founder of The Colorado Sun and a reporter currently specializing in health care coverage. Born and raised in Colorado Springs, John spent 18 years working at The Denver Post. Prior to that, he held internships at the Rocky Ford Daily Gazette, the Colorado Springs...