The scent of sickness: 5 questions answered about using dogs – and mice and ferrets – to detect disease

Could medical detection animals smell coronavirus?

Can medical detection dogs smell coronavirus?
Leon Neal/Getty Images
As COVID-19 continues to spread worldwide, scientists are analyzing new ways to track it.

One promising approach is training dogs to detect people who are infected by smelling samples of human urine or sweat. Research scientist Glen Golden, who has trained dogs and ferrets to detect avian flu in birds, explains why certain animals are well suited to sniff out sickness.

1. Which species have a nose for disease?

Some animals have highly developed senses of smell. They include rodents; dogs and their wild relatives, like wolves and coyotes; and mustelids – carnivorous mammals such as weasels, otters and ferrets. These species' brains have three or more times more functional olfactory receptor neurons – nerve cells that respond to odors – than species with less keen smelling abilities, including humans and other primates.

These neurons are responsible for detecting and identifying volatile olfactory compounds that send meaningful signals, like smoke from a fire or the aroma of fresh meat. A substance is volatile if it changes readily from liquid to gas at low temperatures, like the acetone that gives nail polish remover its fruity smell. Once it vaporizes, it can spread rapidly through the air.

When one of these animals detects a meaningful odor, the chemical signal is translated into messages and transported throughout its brain. The messages go simultaneously to the olfactory cortex, which is responsible for identifying, localizing and remembering odor, and to other brain regions responsible for decision-making and emotion. So these animals can detect many chemical signals over great distances and can make rapid and accurate mental associations about them.

2. How do researchers choose a target scent?

In most studies that have used dogs to detect cancer, the dogs have identified physical samples, such as skin, urine or breath, from patients who either have been diagnosed with cancer or have undiagnosed cancer at an early stage. Scientists don't know what odor cue the dogs use or whether it varies by type of cancer.

The U.S. Department of Agriculture's National Wildlife Research Center in Colorado and the Monell Chemical Senses Center in Pennsylvania have trained mice to detect avian influenza in fecal samples from infected ducks. Bird flu is hard to detect in wild flocks, and it can spread to humans, so this work is designed to help wildlife biologists monitor for outbreaks.

The Kimball lab at Monell taught the mice to get a reward when they smelled a confirmed positive sample from an infected animal. For example, mice would get a drink of water when they traveled down the arm of a Y-shaped maze that contained feces from a duck infected with avian influenza virus.

By chemically analyzing the fecal samples, researchers found that the concentration of volatile chemical compounds in them changed when a duck became infected with bird flu. So they inferred that this altered smell profile was what the mice recognized.

Members of the mustelid family, such as ferrets, badgers and otters, have highly developed senses of smell. Here a wolverine sniffs out frozen meat buried deep in the snow.

Building on that work, we've trained ferrets and dogs to detect avian influenza in fowl, such as wild ducks and domestic chickens, in a collaborative study between Colorado State University and the National Wildlife Research Center that is currently under review for publication.

With ferrets, we started by training them to alert, or signal that they had detected the target odor, by scratching on a box that contained high ratios of those volatile compounds and to ignore boxes that contained low ratios. Next we showed the ferrets fecal samples from both infected and noninfected ducks, and the ferrets immediately began alerting to the box containing the fecal sample from an infected duck.

This approach is similar to the way that dogs are trained to detect known volatile odors in explosives or illegal drugs. Sometimes, though, we have to let the detector animal determine the odor profile that it will respond to.

3. Can animals be trained to detect more than one target?

Yes. To avoid confusion about what a trained animal is detecting, we can teach it a different behavioral response for each target odor.

For example, the dogs in the U.S. Department of Agriculture's Wildlife Services Canine Disease Detection Program respond with an aggressive alert, such as scratching, when they detect a sample from a duck infected with bird flu. When they detect a sample from a white-tailed deer infected by the prion that causes chronic wasting disease, they respond with a passive alert such as sitting down.

Research at the University of Auburn has shown that dogs can remember and respond to 72 odors during an odor memory task. The only limitation is how many ways a dog can communicate about different odor cues.

4. What kinds of factors can complicate this process?

First, any organization that trains animals to detect disease needs the right type of laboratory and equipment. Depending on the disease, that could include personal protection equipment and air filtering.

Another concern is whether the pathogen might infect the detection animals. If that's a risk, researchers may need to inactivate the samples before they expose the animals. Then they need to see whether that process has altered the volatiles that they are teaching the animals to associate with infection.

Finally, handlers have to think about how to reinforce the desired response from detection animals in the field. If they are working in a population of mostly noninfected people – for example, in an airport – and an animal doesn't get a chance to earn a reward, it may lose interest and stop working. We look for animals that have a strong drive to work without stopping, but working for a long time without reward can be challenging for even the most motivated animal.

5. Why not build a machine that can do this?

Right now we don't have devices that are as sensitive as animals with well-developed senses of smell. For example, a dog's sense of smell is at least 1,000 times more sensitive than any mechanical device. This could explain why dogs have detected cancer in tissue samples that have been medically cleared as not cancerous

We also know that ferrets can detect avian flu infection in fecal samples before and after laboratory analysis shows that the virus has stopped shedding. This suggests that for some pathogens, there may be changes in volatiles in individuals who are infected but are asymptomatic.

As scientists learn more about how mammals' sense of smell works, they'll have a better chance of creating devices that are as sensitive and reliable in sniffing out disease.The Conversation

Glen J. Golden, Research Scientist/Scholar I, Colorado State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

A landslide is imminent and so is its tsunami

An open letter predicts that a massive wall of rock is about to plunge into Barry Arm Fjord in Alaska.

Image source: Christian Zimmerman/USGS/Big Think
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  • A remote area visited by tourists and cruises, and home to fishing villages, is about to be visited by a devastating tsunami.
  • A wall of rock exposed by a receding glacier is about crash into the waters below.
  • Glaciers hold such areas together — and when they're gone, bad stuff can be left behind.

The Barry Glacier gives its name to Alaska's Barry Arm Fjord, and a new open letter forecasts trouble ahead.

Thanks to global warming, the glacier has been retreating, so far removing two-thirds of its support for a steep mile-long slope, or scarp, containing perhaps 500 million cubic meters of material. (Think the Hoover Dam times several hundred.) The slope has been moving slowly since 1957, but scientists say it's become an avalanche waiting to happen, maybe within the next year, and likely within 20. When it does come crashing down into the fjord, it could set in motion a frightening tsunami overwhelming the fjord's normally peaceful waters .

"It could happen anytime, but the risk just goes way up as this glacier recedes," says hydrologist Anna Liljedahl of Woods Hole, one of the signatories to the letter.

The Barry Arm Fjord

Camping on the fjord's Black Sand Beach

Image source: Matt Zimmerman

The Barry Arm Fjord is a stretch of water between the Harriman Fjord and the Port Wills Fjord, located at the northwest corner of the well-known Prince William Sound. It's a beautiful area, home to a few hundred people supporting the local fishing industry, and it's also a popular destination for tourists — its Black Sand Beach is one of Alaska's most scenic — and cruise ships.

Not Alaska’s first watery rodeo, but likely the biggest

Image source: whrc.org

There have been at least two similar events in the state's recent history, though not on such a massive scale. On July 9, 1958, an earthquake nearby caused 40 million cubic yards of rock to suddenly slide 2,000 feet down into Lituya Bay, producing a tsunami whose peak waves reportedly reached 1,720 feet in height. By the time the wall of water reached the mouth of the bay, it was still 75 feet high. At Taan Fjord in 2015, a landslide caused a tsunami that crested at 600 feet. Both of these events thankfully occurred in sparsely populated areas, so few fatalities occurred.

The Barry Arm event will be larger than either of these by far.

"This is an enormous slope — the mass that could fail weighs over a billion tonnes," said geologist Dave Petley, speaking to Earther. "The internal structure of that rock mass, which will determine whether it collapses, is very complex. At the moment we don't know enough about it to be able to forecast its future behavior."

Outside of Alaska, on the west coast of Greenland, a landslide-produced tsunami towered 300 feet high, obliterating a fishing village in its path.

What the letter predicts for Barry Arm Fjord

Moving slowly at first...

Image source: whrc.org

"The effects would be especially severe near where the landslide enters the water at the head of Barry Arm. Additionally, areas of shallow water, or low-lying land near the shore, would be in danger even further from the source. A minor failure may not produce significant impacts beyond the inner parts of the fiord, while a complete failure could be destructive throughout Barry Arm, Harriman Fiord, and parts of Port Wells. Our initial results show complex impacts further from the landslide than Barry Arm, with over 30 foot waves in some distant bays, including Whittier."

The discovery of the impeding landslide began with an observation by the sister of geologist Hig Higman of Ground Truth, an organization in Seldovia, Alaska. Artist Valisa Higman was vacationing in the area and sent her brother some photos of worrying fractures she noticed in the slope, taken while she was on a boat cruising the fjord.

Higman confirmed his sister's hunch via available satellite imagery and, digging deeper, found that between 2009 and 2015 the slope had moved 600 feet downhill, leaving a prominent scar.

Ohio State's Chunli Dai unearthed a connection between the movement and the receding of the Barry Glacier. Comparison of the Barry Arm slope with other similar areas, combined with computer modeling of the possible resulting tsunamis, led to the publication of the group's letter.

While the full group of signatories from 14 organizations and institutions has only been working on the situation for a month, the implications were immediately clear. The signers include experts from Ohio State University, the University of Southern California, and the Anchorage and Fairbanks campuses of the University of Alaska.

Once informed of the open letter's contents, the Alaska's Department of Natural Resources immediately released a warning that "an increasingly likely landslide could generate a wave with devastating effects on fishermen and recreationalists."

How do you prepare for something like this?

Image source: whrc.org

The obvious question is what can be done to prepare for the landslide and tsunami? For one thing, there's more to understand about the upcoming event, and the researchers lay out their plan in the letter:

"To inform and refine hazard mitigation efforts, we would like to pursue several lines of investigation: Detect changes in the slope that might forewarn of a landslide, better understand what could trigger a landslide, and refine tsunami model projections. By mapping the landslide and nearby terrain, both above and below sea level, we can more accurately determine the basic physical dimensions of the landslide. This can be paired with GPS and seismic measurements made over time to see how the slope responds to changes in the glacier and to events like rainstorms and earthquakes. Field and satellite data can support near-real time hazard monitoring, while computer models of landslide and tsunami scenarios can help identify specific places that are most at risk."

In the letter, the authors reached out to those living in and visiting the area, asking, "What specific questions are most important to you?" and "What could be done to reduce the danger to people who want to visit or work in Barry Arm?" They also invited locals to let them know about any changes, including even small rock-falls and landslides.

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