Something in the Air

Via Gizmodo

My recent inquiries from online journalists are beginning to form a pattern and it’s not good.

First came an email from Eric Spitznagel at Vice Tonic asking about the science behind the age-old saying “he who smelt it dealt it.” His starting point was the idea that laws of gas diffusion and the concentration gradient of odor dispersion would invariably indict the smeller as the dealer. (From the published piece it appears he got this working hypothesis from an engineering professor at the University of Colorado.) My response was to distinguish between models that describe the behavior of ideal gases, and the more complicated turbulent currents and plumes found in real life. The non-ideal distribution of scented air streams is the basis for the “casting” behavior which many animals species use to localize the source of a smell (they zig-zag back and forth through the odor plume in ever-shorter tacks until they reach it). Given these atmospheric vagaries it is entirely possible that an emission from the guilty party might curl up an innocent person’s nostrils first.

Next heard from was Daniel Kolitz at Gizmodo who was putting together a “GIZ Asks” installment on the legitimate if somewhat feculent question “Why does dog poop smell bad to us but good to dogs?” Kolitz collates answers from a crack team of dog specialists and smell researchers including, beside yours truly, Alexandra Horowitz, Don Wilson, Peter Hepper, Cat Warren, and Charles “I’m publishing as fast as I can” Spence (I kid, I kid). What’s interesting is that several of the experts blithely assume that all human odor responses are cultural, while other take the (correct) view that certain smells or categories of smell are inherently (biologically) offensive. Click over to read the whole thing, but here here’s the pungent part of my answer:

Dogs don’t approach shit as an aesthetic experience—they treat it as a source of social information, like an olfactory Instagram. It answers a lot of questions: Who left it? How recently? Is the pooper healthy? We are able to extract similar information. The lingering cloud in the office restroom tells you who had lunch at P.F. Chang’s. Plumbing and ventilation rob us of the social signals in feces and leave us with mere disgust.

So where is this latest journo-trend heading? What follows farts and dog poop? I could make an educated guess, but I’ll take the lazy way out and just wait for the next email from an inquiring mind.

Stepping in It: How Journalists Perpetuate the Myth that Dogs' Sense of Smell is Superior to Our Own

We’ve been hearing a lot about dog noses recently and how they are far more sensitive than ours. Liz Bestic kicked things off with a July 1 story in New Scientist called “The cancer sniffers: Dogs could be the best tool for diagnosis.” She covers some studies showing that dogs are able to sniff out specimens from patients with various types of cancer. An infographic accompanying her story states

“A dog’s sense of smell is between 1000 and 100,000 times more sensitive than that of humans.”

Next up was Rachel Pannett, the Sydney-based Deputy Bureau Chief for The Wall Street Journal in Australia and New Zealand. Her story appeared on the front page of the July 16, 2015 edition: “Forget drugs, these dogs sniff out a different kind of evil weed: Australia tries using spaniels to hunt for invasive plants called orange hawkweed, a.k.a ‘Grim the Collier’.” Pannett’s story includes this line:

A dog’s nose can be over 10,000 times more sensitive than humans, according to academic studies.

Zounds! Those are some impressive numbers. No wonder those dogs can sniff out cancer—their sense of smell is soooo much more sensitive than ours.

But wait. What’s that beeping sound in the distance? Why, it’s the alarm on the FirstNerve Bogosity Meter (hooked up to the battery of a rusty Ford F150 behind the tool shed). It seems there might be something dodgy about these doggy claims.

First off, let’s assume for the sake of argument that all the experimental results are correct and dogs can reliably sniff out a variety of human cancers. What does that prove about the relative sensitivity of dog noses and human noses? The answer is: nothing at all. Relative sensitivity is logically irrelevant to these results. But for some reason, journalists feel compelled to assert that dogs have more sensitive noses than we do. A competitive sniff-off between dogs and humans would address the point directly. It would be nice if a Deputy Bureau Chief or a “health journalist” asked cancer study researchers whether they had, you know, let human panelists evaluate the scent samples the same way the dogs did. Wouldn’t it be interesting if a bunch of orderlies, interns, and maintenance people could sniff out cancer? (Bestic mentions that doctors since Hippocrates have used smell as a diagnostic tool. She doesn’t explain why 21st century physicians have suddenly ceded the game to dogs.)

Hey! Will someone please turn down the alarm on the Bogosity Meter? It’s getting on my nerves.

The next fishy thing about these stories is the beautiful, quote-tastic simplicity of the numbers: dogs are 1,000 or 10,000 or 100,000 thousand times more sensitive than humans. Not 27,000 times more sensitive. Not 1,450 times. But more sensitive by nice fat powers of ten.

Bestic and Pannett are merely the latest journalists to run with these numbers. Here is Mary Bates, PhD, writing on the Animal Minds blog at PsychologyToday.com in 2012 (“Cancer-detecting canines sniff out a diagnosis”):

Canines’ sense of smell is generally 10,000 -100,000 times superior to that of humans.

Stefan Lovgren (“Dogs smell cancer in patients’ breath, study shows,” National Geographic News, 2006) and Peter Tyson (“Dogs’ dazzling sense of smell,” scienceNOW blog at PBS.org, 2012) use the same comparisons.

So where are journalists getting these numbers? Unlike their colleagues, Lovgren and Tyson attribute them to a specific person. Here’s Lovgren:

According to James Walker, director of the Sensory Research Institute at Florida State University in Tallahassee, canines’ sense of smell is generally 10,000 to 100,000 times superior to that of humans.

And here’s Tyson:

Dogs’ sense of smell overpowers our own by orders of magnitude—it’s 10,000 to 100,000 times as acute, scientists say. “Let’s suppose they’re just 10,000 times better,” says James Walker, former director of the Sensory Research Institute at Florida State University, who, with several colleagues, came up with that jaw-dropping estimate during a rigorously designed, oft-cited study.”

Now we’re getting somewhere—the 10,000 to 100,000 claim was made by a smell scientist. [Full disclosure: I met Jim Walker numerous times at the AChemS meetings long ago.] Walker and his colleagues were once active in designing new ways to measure olfactory sensitivity. In 2003, they published a paper in Chemical Senses called “Human odor detectability: new methodology used to determine threshold and variation.” Using their new technique, they estimated a value for human sensitivity to amyl acetate, a chemical that smells like bananas and is something of a standard odor in studies on olfactory thresholds. So far, so good.

In 2006, Walker and colleagues published “Naturalistic quantification of canine olfactory sensitivity” in Applied Animal Behaviour Science. They tested two dogs (a Rottweiler and Standard Schnauzer) for sensitivity to amyl acetate. The threshold value they found was lower than that reported previously by other dog researchers, presumably reflecting the more precise experimental methods used.

In discussing the results, the researchers wrote

Our recent investigation of human odor detectability (Walker et al., 2003) yielded thresholds approximately 10,000- to 100,000-fold higher than those we report here for the dog.

Again, so far, so good. But note: the “10,000- to 100,000-fold higher” statement applies only to amyl acetate (i.e., one specific chemical) and only to two studies (i.e., those coauthored by Walker). Yet Lovgren and Tyson quote Walker with the clear implication that dogs are 10,000 to 100,000 time more sensitive to smells in general. Either Walker did not mention these limitations when he was interviewed by them, or he mentioned the caveat and they chose to ignore it. In any case, journalists are now on notice that they should be cautious in how they quote Walker and/or his 10K/100K claims of canine smell superiority.

Still, there exists a strong presumption that dogs have a sense of smell that is more sensitive than ours in general, i.e., for the vast majority of odors. Surely there are other studies on other odor chemicals that support the claim, no? Enter Matthias Laska, a professor at Linköping University in Sweden. Laska is far and away the current authority of olfactory sensitivity in mammals—he has conducted smell experiments with mice, spider monkeys, squirrel monkeys, pigtail macaques, elephants, and fur seals. At this year’s AChemS meeting in April, Laska gave a talk titled “Busting a myth: humans are not generally less sensitive to odors than nonhuman mammals.” (Abstract here.) I attended his presentation and found it compelling.

Laska put together a data base of all published odor thresholds for humans and nonhuman mammals (17 species tested across a total of 138 odors). This let him compare the relative performance of humans and other species on a chemical-by-chemical basis.

I found that human subjects have lower olfactory detection thresholds, that is, a higher sensitivity with the majority of odorants tested so far compared to most of the nonhuman mammal species tested so far. This includes species traditionally considered to have a highly developed sense of smell such as mice, hedgehogs, shrews, pigs and rabbits. Humans outperform rats with 31 of the 41 odorants tested with both species. Humans even outperform the dog, often considered as the undisputed super-nose of the animal kingdom, with 5 of the 15 odorants tested with both species. Based on these comparisons, and contrary to traditional textbook wisdom, humans are not generally inferior in their olfactory sensitivity compared to nonhuman mammals.

So according to the most recent, most comprehensive review of the topic, humans outperform dogs on 5 of the 15 odorants tested. Does that sound like total, across-the-board, doggy nose superiority to you? No, not really.

After the recent flurry of dog superiority claims, I checked in with Laska by email. He confirms that the canine odor threshold for amyl acetate (-5.94 log ppm) reported in Walker’s 2006 study is the lowest on record. However, he points out that the lowest reported human threshold for amyl acetate in his database is -7.02 log ppm. In other words, when it comes to amyl acetate humans are more sensitive than dogs.

Let me repeat that: According to all the available scientific evidence, humans are more sensitive to amyl acetate than are dogs.

Where does this leave us? With three take-home messages:

#1: James Walker’s narrow claim that dogs are 10,000 to 100,000 times more sensitive to amyl acetate than humans is simply incorrect. The fact is that humans, not dogs, are more sensitive to amyl acetate.

#2: The broader, and much-cited claim that dogs are 10,000 to 100,000 times more sensitive to smells in general is unsubstantiated. The fact is that dogs outperform humans on some but not all of the smells tested to date.

#3: The media ought to take a healthily skeptical approach to claims about the incredible superiority of the canine sense of smell. Some of us have expressed reservations about this before, and have noted that undue deference to the dog nose leads to some dubious outcomes in the criminal justice system. Even assuming that all the studies to date are valid and replicable, the practicality and cost-benefit ratio of cancer detection with sniffer dogs is not that impressive.

P.S. Don’t even bother coming back at me with the claim by one Dr. Lawrence Myers. “Dr. Myers has been quoted as saying dogs can smell a million times better than humans. He says that was a speculative (but possible) number he used in an interview to illustrate a narrow point. The reporter picked up the figure as science and quoted it out of proper context.”

P.P.S. Und danke schön, German dog fans, but don’t bother digging up this old bone from 1953: “The olfactory sensitivity of the dog is 1,000,000 to 100,000,000 times better than humans.” [My translation.] It’s a hand-waving, one-line summary of results, now superseded, that dates back to the dawn of olfactory psychophysics.

The studies discussed here are “Human odor detectability: new methodology used to determine threshold and variation,” by James C. Walker, Sandra B. Hall, Dianne B. Walker, Martin S. Kendal-Reed, Alison F. Hood & Xu-Feng Niu. Chemical Senses 28, 817–826, 2003; “Naturalistic quantification of canine olfactory sensitivity,” by Dianne Beidler Walker, James Cornelius Walker, Peter James Cavnar, Jennifer Leigh Taylor, Duane Howard Pickel, Sandra Biddle Hall & Joseph Carlos Suarez. Applied Animal Behaviour Science 97, 241–254, 2006; and “Über die Riechschärfe des Hundes für Fettsäuren,” by Walter Neuhaus. Zeitschrift für vergleichende Physiologie 35, 527-552, 1953.

Amazing Human Tricks: Dundowran Beach Edition

A woman named Sandy Fletcher loses her watch while taking her daily walk on Dundowran Beach, about 160 miles north of Brisbane, Australia. An 11-year-old kid finds it, and his 9-year-old dog sister recognizes the owner—by smell.

Call Off the Dogs

The space between the lost clinical art of olfactory diagnosis and Dr. McCoy’s tricorder of the future is filled with canine scent detection studies. These prove, ad nauseum, that a disease may have a distinctive scent signature. But to put this principle to work in a way that doesn’t involve teams of trained dogs we need a precise, chemically defined profile of each disease’s scent. Some new studies suggest we’re finally getting some traction on the problem.

My former Monell Center colleague George Preti, along with others at Monell and UPenn, has found a small set of volatile molecules that distinguish melanoma cells from normal melanocytes. The usual cautions apply—e.g., the volatiles were collected over cell cultures and not over the skin of actual patients—but the work is a significant step toward a device that can “smell” skin cancer. Preti et al. used sophisticated scent capture (solid-phase micro-extraction for GC-MS) supplemented by nanotubes coated with single-stranded DNA. Strictly speaking this isn’t an e-nose but an e-nose with nanosensors. The team then did a lot of heavy lifting to screen out volatiles not endogenous to the melanoma cells. (Earlier studies picked up traces of antiseptics and anesthetics from the hospital environs.)

The result: key differentiating compounds included isovaleric acid, 2-methylbutyric acid, and isoamyl alcohol, plus the sulfur containing compounds dimethylsulfone, dimethyldi- and trisulfide. None are exotic but the pattern allows discrimination of healthy and cancerous cells. Heightened production of these molecules is presumably to metabolic differences between the two cell types.

Meanwhile, researchers in the UK reported pilot data on detection of bladder cancer using a GC-sensor device that samples urine headspace. Using statistical algorithms the device correctly separates urine from cancer patients and that of healthy matched controls. Nice.

A leading member of the team is Professor Norman Ratcliffe, pictured below.



With necktie and fresh, unwrinkled lab coat he’s quite well dressed for an engineering professor. [Especially a British one!—Ed.] He appears to be holding a urine sample. Honestly, dude, glove up!

Prof. Ratcliffe presumably knows better than to bare-hand biofluids. He and his colleagues have previously done a lot of shitty work [Phrasing!—Ed.] using fecal volatiles to diagnose diarrhea, cholera, necrotizing enterocolitis, and irritable bowel syndrome.

From the Competing Interests statement of the PLoS ONE paper, it appears that team Ratcliffe has been granted one patent and has applied for another. To my inexpert eye, the granted patent seems rather broad—it covers the idea of a headspace collector and analyzer that can diagnose disease via odors. I don’t see how it would hold up in litigation, but then I’m not a patent attorney. [Or a patent troll.—Ed.] By publishing in PLoS ONE they certainly achieved plenty of free publicity for their patented device.

While human cancer studies make the headlines, olfactory diagnosis is advancing down on the farm. In Germany, a group of veterinarians and vet students was matched against an e-nose. The task: sniff post-partum vaginal discharge from a cow and judge whether or not the animal suffers from acute puerperal metritis. The humans performed adequately but they were completely dusted by the DiagNose device. The researchers note, however, that the e-nose is yet suitable for use in the field, er, barn.

The studies discussed here are “Volatile biomarkers from human melanoma cells,” by Jae Kwak, Michelle Gallagher, Mehmet H. Ozdener, Charles J. Wysocki, Brett R. Goldsmith, Amaka Isamah, Adam Faranda, Steven S. Fakharzadeh, Meenhard Herlyn, A.T. Charlie Johnson, and George Preti, published in Journal of Chromatography B 15:90-6, 2013,

“A pilot study combining a GC-sensor device with a statistical model for the identification of bladder cancer from urine headspace,” by Tanzeela Khalid, Paul White, Ben De Lacy Costello, Raj Persad, Richard Ewen, Emmanuel Johnson, Chris S. Probert, & Norman Ratcliffe, published in PLoS One, 8(7):e69602, 2013,

“An investigation of fecal volatile organic metabolites in irritable bowel syndrome,” by Iftikhar Ahmed, Rosemary Greenwood, Ben De Lacy Costello, Norman M. Ratcliffe, & Chris S. Probert, published in PLoS One, 8(3):e58204, 2013, and

“Evaluation of odor from vaginal discharge of cows in the first 10 days after calving by olfactory cognition and an electronic device,” by I. Sannmann, O. Burfeind, V. Suthar, A. Bos, M. Bruins, & W. Heuwieser, published online in Journal of Dairy Science, June 27, 2013.

Good Dog! . . . Uh, Bad Dog?

Image via TheWeedBlog.

Washington’s recent decriminalization of pot creates problems for the state’s drug-sniffing dogs and their handlers. The big question: Can a drug-sniffing dog be selectively untrained?

Talking Odor Perception on Huff Post Live

I’ve been on the road and am just now getting around to posting a link to this smelly panel discussion hosted on Tuesday by Josh Zepps. It’s me, Stuart Firestein, Bonnie Blodgett, and Sissel Tolaas.

Supreme Court: Drug-Sniffing Dog on Your Porch Needs a Warrant

Today’s Florida v. Jardines decision in a nutshell (by Kevin Russell at ScotusBlog):

The Court held a dog sniff at the front door of a house where the police suspected drugs where being grown constitutes a search for purposes of the Fourth Amendment.

The case involved a marijuana grow house and the smell in question was that of pot plants, not pot smoke. (FN and WTNK readers understand that the former scent is much more difficult to detect and has been the subject of over-reaching claims by various police departments.)

The case hinges on expectations of privacy in and around one’s home, on whether a drug-sniffing dog is like thermal-imaging technology, and on the Founder’s view of the legal status of scent-tracking dogs.

Interesting split decision: conservative justices Scalia and Thomas joined by liberals Kagen, Ginsburg, and Sotomayor for the majority; conservatives Alito and Roberts joined by liberals Kennedy and Breyer in dissent.

Dog owner and constitutional law prof Ann Althouse finds Alito’s opinion more “dog positive.”

Clinical Medicine Goes to the Dogs: Poop of Principle

Cliff, the Clostridium Sniffing Beagle

In WTNK, I was skeptical that trained dogs would be of much practical use in sniffing out disease. Since then, a steady trickle of studies has claimed that dogs can smell cancer of the lung, colon, ovary and prostate. This doesn’t strike me as far fetched. However, the elaborate training and housing of cancer dogs along with laborious preparation of test samples make it an expensive and cumbersome proposition. A recent review of the scientific literature found additional reasons why cancer dogs might not yet be ready for grand rounds.

Now, using a male beagle named Cliff, a Dutch research team has staked out new territory in canine diagnostics. They trained Cliff to recognize the smell of Clostridium difficile, a nasty intestinal bacterium that can cause life-threatening diarrhea, especially in hospital settings.

Cliff’s training took a relatively quick two months, after which he displayed near perfect performance judging a series of positive and negative stool samples. (Cliff responds to the C. difficile scent by sitting or lying down.) For the crucial clinical tests he was walked on a leash past an actual patient in a hospital bed—no stool sample, no prep, no contact, just an open-air sniff.

Cliff alerted to 25 out of 30 C. difficile patients, and correctly rejected 265 out of 270 control cases. That’s some pretty good sniffing. There are, however, some caveats. His trainer did not know the patients’ status but he knew there would be only one positive case out of the ten presented that day, i.e., enough information to possibly communicate an unconscious bias to Cliff. The authors also note Cliff had a harder time making the right call when they had him sniff residents in a nursing home lounge, i.e., away from their (smelly?) beds.

I’m willing to give Cliff the benefit of the doubt. But that still leaves me with a question I’ve asked before: why not run a straight-up sniff test with human odor judges? After all, C. difficile is said to smell like horse manure and it should not be difficult for most people to detect.

In fact, a 2002 study examined the various clinical features nurses use to recognize C. difficile infections in their patients. Along with fever and recent use of antibiotics, “characteristic odor” was a statistically significant predictor of the infection. In a 2007 study, nurses without any odor-training recognized the odor of C. difficile in 55% of cases, and correctly ruled it out in 83% of controls.

This suggests to me that with a few training sessions any nurse or doctor should be able to make a highly reliable olfactory diagnosis of C. difficile infection. They could begin treatment before the confirming lab results—a real benefit for the patient.

I’m all for bringing smell back to the practice of medicine. Let’s start with our own noses.

The study discussed here is “Using a dog’s superior olfactory sensitivity to identify Clostridium difficile in stools and patients: proof of principle study,” by Marije K. Bomers, Michiel A. van Agtmael, Hotsche Luik, Merk C. van Veen, Vandenbroucke-Christina M.J.E. Vandenbroucke-Grauls, and Yvo M. Smulders, published in BMJ 345:7396, 2012.

Is Lassie the Answer?

In Los Angeles, KABC’s Denise Dador supplies another heartwarming story about olfactory service dogs: “Type 1 diabetes patients get help with blood sugar from scent-detection dogs.”

Let’s stipulate that there are odor cues associated with diabetes (and skin and lung and prostate cancer). Let’s also stipulate that dogs can be trained to recognize these odors. For me, the question remains: Is this a practical and cost-effective way of dealing with the problem?

Dador quotes the anxious mother of a diabetic child: “She could die of a low blood sugar during the night.” So . . . the alert dog never sleeps?

According to Dador, fully trained diabetic alert dogs cost about $20,000. She also notes that about 3 million Americans take insulin for their diabetes. What Dador doesn’t do is the math: a fully implemented diabetic dog solution would cost $60 billion dollars.

Meanwhile, a pair of Italian researchers has just published a mini-review titled “Canine olfactory detection of cancer versus laboratory testing: myth or opportunity?” Giuseppe Lippi and Gianfranco Cervellin reviewed the scientific studies in which dogs were used to detect the scent of bladder, ovary, breast, prostate and skin cancer. While the sensitivity and specificity of disease detection were impressive in some studies, they were less so in others.

In fact, Lippi and Cervellin find that “the most problematic issue” in these studies is “the large heterogeneity of performance” by the canine sniffers. They attribute this variability to differences in dog breeds, training methods, tissue sample preparation, as well as intrinsic smellability of different cancers. Of course, these are hurdles that can be cleared with further research and refinement of methods.

Lippi and Cervellin raise another, more substantial issue: confounding comorbidities.

Another important drawback is that the animals were tested to distinguish between normal and cancer samples (either being cancer tissue, blood or urine), but they have not been tested so far to differentiate cancer patients from those suffering from other comorbidities. A variety of non-cancerous diseases (e.g., those characterized by inflammation, infection, or necrosis) might produce confounding or even overlapping biochemical signals that might confuse the animal, decreasing its detecting performance. At best, additional and more specific training might be required for the animals to distinguish between confounding diseases and cancers.

To me, this fair-minded analysis shows there is still a long way to go before scent detection dogs become a routine part of medical diagnosis and care.

The study discussed here is “Canine olfactory detection of cancer versus laboratory testing: myth or opportunity?” by Giuseppe Lippi and Gianfranco Cervellin, published in Clinical Chemistry and Laboratory Medicine 50:435-439, 2012.

A Boy and His Rat

It seems like every few months we’re treated to another heart-warming story about scent-detecting service dogs. Lately it’s been dogs for diabetics. You know the drill: Fido alerts one way when Johnnie’s blood sugar is too low, and another way when it’s too high.

The latest entry is Ben Ownby, a middle-schooler from San Antonio, Texas, and his Labradoodle Dakota. Before them it was another Texan, Katie Jane Brashier, and her Labrador Retriever mix named Shots.

This is the adorable public face of the scientific enthusiasm for training dogs to detect various human diseases by odor. I was skeptical of it in What the Nose Knows:

So, yes, dogs can smell odors associated with bladder-cancer. But this is a far cry from “What’s that Lassie? Timmy has bladder cancer?” To make use of this canine talent, your local hospital would have to maintain a half dozen dogs and their trainers, supply copious medically-certified human urine samples, and provide ongoing statistical support and chemical analysis. At which point 6 out of 10 bladder cancers would go undetected.

Recently published studies report more impressive success rates. A French group used a Belgian Malinois shepard to sniff urine sample from patients with prostate cancer. The dog correctly chose cancer samples in 30 of 33 cases, for a detection sensitivity of 91%. Detection specificity was also 91%. (In other words the dog correctly identified 91% of cancer samples, and correctly rejected 91% of non-cancer samples.)

This is a pretty impressive performance, but keep in mind that it came after 16 months of training, and that “training was a full-time job for the team, who worked with the dog 5 d/wk over the study period.” No wonder the authors caution that

the present work is a proof-of-principle study, and the use of these dogs is not supposed to be generalized. We tested a limited number of subjects in a costly, long study that makes it difficult to conceive of an extended use for this test in clinical practice.

Meanwhile, a German research group claims 71% sensitivity and 93% specificity for dogs trained to detect odors associated with lung cancer.

If you’re going to use animals for routine disease detection in the clinic, you need a species that is less expensive and less demanding that the dog. And now, thanks to a multi-national research team led by Georgies F. Mgode, we have a candidate—a rodent, less. Allow us to present Cricetomys gambianus, the African giant pouched rat. (It weighs in slightly more than one of Paris Hilton’s dogs.)

Mgode et al. have previously trained the giant rats to detect odor associated with tuberculosis. Now they use lab culture samples to ask whether the animals can discriminate TB samples from non-TB bacterial samples using artificial laboratory cultures. Which brings us to this classic line from their methods section:

Negative sputum samples from TB clinics in Dar es Salaam, Tanzanai, were used for spiking test microorganisms.

Mmmmmm . . . make mine a Rhodococcus!

Having obtained the necessary sputum, the next step was to train the animals.

during training sessions, rats were rewarded with food (mashed banana mixed with crushed commercial rat food) when they paused for 5 s at known TB-positive sputum samples. They did not receive food for pausing at known TB-negative samples. With extensive training the rats learnt to consistently pause at TB-positive samples but not at TB-negative samples.

Here’s a photo of co-author Maureen Jubitana, two trainers, and the study animals.

Mgode and colleagues tested the trained rats on sputum samples containing either TB culture or cultures of other, nontuberculosis mycobacteria. The rats responded only to the TB-spiked samples, indicating that there is an odor profile specific to TB, and not to other pulmonary bacterial infections. Interestingly, the detection rate for the TB-spiked sputum samples was lower than that for naturally occurring TB-positive sputum. And the spiked samples were more detectable when the spiking dose was taken from certain growth phases of the bacterial culture. Evidently, the exact character and intensity of the TB-associated scent depends on the biological context and growing condition of the bacteria.

Dogs, African giant pouched rats, whatever. What I want to know is, why don’t any of the labs just straight-out run a sniff test with human odor judges?

The articles discussed here are “Olfactory detection of prostate cancer by dogs sniffing urine: a step forward in early diagnosis,” by Jean-Nicolas Cornu, Géraldine Cancel-Tassin, Valérie Ondet, Caroline Girardet, and Olivier Cussenot, which appeared in European Urology 59:197-201, 2011, and “Ability of Cricetomys rats to detect Mycobacterium tuberculosis and discriminate it from other microorganisms,” by Georgies F. Mgode, Bart J. Weetjens, Christophe Cox, Maureen Jubitana, Robert S. Machang’u, Doris Lazar, January Weiner, Jean-Pierre Van Geertruyden, and Stefan H.E. Kaufmann, which appeared in Tuberculosis (Edinb), 92:182-186, 2012.

Steer Clear of the Chickenshit Jurisdiction of Collinsville, Illinois

In WTNK, I questioned whether the olfactory abilities of police officers live up to the deference shown them by courts in search-and-seizure drug cases. Empirical work by Richard Doty and others casts serious doubt on one typically extravagant claim: that unburned marijuana is detectable by nose when wrapped and stashed in a car trunk.

Nevertheless, the “in plain smell” doctrine is now law in many states: the odor of pot, as perceived by a police officer, is sufficient to establish probable cause for a warrantless search of a vehicle. Thanks to a U.S. Supreme Court ruling, an “alert” behavior by a trained drug detection dog also suffices.

Bringing dogs into the equation doesn’t help matters. A recent study suggests that dogs respond to subtle, unintended cues from their handlers that can result in “false alarm” alerts.

Radley Balko now examines some data from the Illinois State Police K-9 Unit and comes to a disturbing conclusion.

Even giving this dog credit for the cases in which the officer found only [drug] residue, over this 11-month period, the dog had about a 28 percent failure rate. Which means that nearly three of the 10 times the dogs alerted provided probable cause for a warrantless search of a motorist’s car without a warrant, the motorist was completely innocent.

What’s that, Lassie? It gets worse?

Include the “residue” stops, which didn’t produce a large enough quantity of illicit drugs to be measured, and the dog’s error rate climbs to 74 percent. And these are all cases in which the dog’s handler presumably was suspicious enough to conduct a sniff search in the first place.

Bad girl!

Before you smack Lassie on the snout with a rolled-up newspaper, consider the tactics employed by officer Michael Reichert of the Collinsville (Illinois) Police Department, and his canine sidekick. Radley Balko has the story here, but you really should watch the nifty little video by Terrance Huff that accompanies the story. It gives you the full gamey flavor of what happens when questionable legal doctrine combines with questionable use of scent dogs and questionable policing in a chickenshit town like Collinsville, Illinois.

[Via Instapundit.]

A Dog’s Life: Canine Olfaction Put to the Test

In What the Nose Knows, as well as here on FirstNerve, I’ve questioned the conventional wisdom about the dog’s sense of smell, namely that it is amazingly better than our own. Recent evidence suggests that the human nose, in terms of its sensitivity as an odor detector, is quite competitive with the canine nose. The dog’s ease in odor tracking may have more to do with differences in sniffing behavior, nostril design and the amount of brain devoted to analyzing olfactory information.

Still, the conventional narrative gets a boost with every report of dogs smelling termites, bedbugs, abnormal glucose levels in diabetics, bowel cancer, ovarian cancer, and so on. Just because a trained scent dog is handy in a pilot study (“does disease X have a smell?”) doesn’t prove that dogs alone are able to make this discrimination. And unless tight controls are built into the experimental design, we still have to rule out that subtle, unintended cues from the dog’s handler are giving us a false result.

This was brought home by a new study that examined the role of human handlers in the response of working scent dogs. Conducted by Lisa Lit and her colleagues at the University of California at Davis, the experiment looked at canine scent-tracking behavior without using any scent at all. It’s a trans-species examination of what social psychologists call “demand characteristics”, i.e., cues that study participants use to glean the aim of an experiment and behave accordingly.

In this case, 18 dog-plus-handler teams—all trained, certified, and experienced in the detection of drugs or explosives—search four rooms in a church for contraband. In view of the teams, an experimenter set down a metal box of gunpowder or marijuana samples. The samples, however, were never opened; this was a ruse to make the room searches believable.

Each dog/handler team searched the four rooms twice. An observer noted when and where the dog signaled an “alert.” Of course the correct response in every trial was “no alert,” as there were not drugs or explosives present. What were present, on some trials, were decoys: a red sheet of paper (for the handlers to notice) or a new tennis ball and a couple of Slim Jims (for the dog to notice), or both. Lit and her team were interested in how alerts by the scent dog (i.e., false alarms) were distributed across the experimental conditions.

The great majority of false alarms happened in rooms with a red sheet of paper; this included trials with and without a scent decoy. To Lit and her team,

this suggests that human influence on handler beliefs affects alerts to a greater degree than dog influence on handler beliefs.

Lit et al., consider and dismiss the possibility that handlers were calling alerts in the absence of corresponding behavior from the dog. Instead, they suspect that the dogs were responding to subtle cues from the handler, who in turn was influenced by the apparent location cue of the red paper. This would be an instance of the Clever Hans Effect. (Dig up your Psych 1 notes, people.)

Even without formal training, dogs respond to human cues such as pointing, nodding, head turning and gazing. The mental pull of these cues is powerful, to the point that a companion dog looking for food will ignore a bowl full of food and head to an empty bowl if directed there by his owner. Highly trained scent-detection dogs don’t fall for obvious distractions; clearly, however, they are not immune from subtle, even unintended, influence from their handlers.

Scent-tracking dogs have proven useful in search and rescue missions, detection of contraband, and tracking of criminal suspects. Whether the results of so-called scent lineups conducted by police dogs should be admitted as courtroom evidence is another question altogether. Radley Balko wrote about a recent case in Texas that brought these issues to the forefront.

Research on the olfactory ability of dogs are becoming increasingly sophisticated. While some results, like Lit’s, raise important cautions, another new study adds to the positive side of the ledger. It involved a rigorous and well-designed assessment of the dog’s ability to distinguish identical human twins (aka monozyogtic or MZ twins) by smell. Previous studies (in 1955, 1988, 1990 and 2006) have been a mixed bag. It has been claimed that MZ twins can be distinguished, cannot be distinguished, cannot be distinguished when they share a similar diet, and can be distinguished by some dogs but only if the twins don’t live together.

The new study, by researchers in the Czech Republic, starts on a strong note by using a single breed of dog with similar levels of training, namely ten German Shepherds, each a trained and proven scent-detection animal employed by the Czech Republic Police. The key body scents were provided by pairs of kids living together: two sets of MZ twins and two sets of DZ twins. Their MZ/DZ status was confirmed by DNA testing. BO was collected according to Czech Police forensic protocols (cotton pads in glass jars) and presented to the dogs in a seven-jar “lineup.” The dog signaled a scent match by lying down next to the jar that smelled like the target his handler gave him at the start of each trial. Various combinations of target and lineup scents were used; on trials when the target scent was not in the lineup, the correct response for the dog was to not lie down.

Remarkably, every dog made the correct judgment in every trial (10 dogs, 60 trials each). It seems the mixed results of earlier studies were due to variable skill levels among the dogs tested. Still, not one single incorrect response in 600 trials? (Experimental data with zero statistical variance is, uh, a little unusual.) On the other hand, if it’s this easy for dogs, I bet that humans are able to smell the difference between MZ twins living together.

The studies discussed here are “Handler beliefs affect scent detection dog outcomes.” by Lisa Lit, Julie B. Schweitzer, & Anita M. Oberbauer, published in Animal Cognition 14:387-394, 2011, and “Dogs discriminate identical twins,” by Ludvik Pinc, Luděk Bartoš, Alice Reslová, & Radim Kotrba, published in PLoS One, 6(6):e20704, 2011.

The dog days of August: How humans have shaped the canine sense of smell

One of the most unshakeable bits of conventional wisdom about smell is that the nose of the dog is vastly superior to our own. In my book, I took a few potshots at this shibboleth; I pointed out that (a) molecule for molecule, the sensitivity of the human nose is competitive with that of the dog, and (b) plenty of human nasal talents sound amazing if given equal hoopla. (Amazing human ability: people can identify the geographical origin of the wood in a popsicle stick by the flavor it leaves in the ice cream!)If we are on a par with dogs when it comes to odor detection under lab conditions, why don’t we outperform them on a daily basis? What dogs have going for them is that they devote more of their brain to analyzing and interpreting scent signals than we do. To a far greater degree, their life revolves around odors.

In What the Nose Knows, I proposed that human odorant receptors evolved to track our biological traits of cooking and seasoning food. I cited evidence that “in the last 5,000 to 10,000 years, genes for smell receptors, along with genes related to diet and metabolism, have been evolving faster than those in any other physiological system.” I speculated that this may have had consequences for our long friendship with dogs.

I also suspect that dogs are part of the whole story. Dogs were first domesticated by man somewhere in Siberia about 15,000 years ago, just as humans populations were shifting from a hunter-gatherer existence to sedentary village life. Increasingly preoccupied with the complex man-made aromas of the cooking pot, our ancestors began to rely on hunting dogs to locate the telltale scent of game. Having co-opted the canine nose, our own scent-tracking ability began to fade. Dogs became, in effect, our long-distance noses, while we specialized in the close-in smelling of food in the mouth.

Two recent studies on canine evolution got me thinking again about human-canine co-evolution. The first was a comparative analysis of cranial and brain anatomy of thirteen different dog breeds. It was conducted by a trio of Australian scientists led by Taryn Roberts at the University of Sydney. Her team notes that the grey wolf, the immediate ancestor of the domestic dog, is dolichocephalic; that is to say it is has a long, relatively narrow skull. Some breeds of domestic dog, such as greyhounds and Russian wolfhounds, still display this trait. Many other breeds are bradycephalic (short-skulled); they retain the flat-faced, snub-nosed look of puppies. (Think Maltese or Staffordshire bull terrier.) As the authors say, “canine bradycephaly is purely a human invention,” the result of selective breeding over the past few thousand years.

Using MRI images of skull and brain, the Roberts team calculated a Cephalic Index (skull width / skull length x 100) for each breed. They also charted the anatomy of the olfactory bulbs—the first processing point in the brain for odor information from the nose. As in humans, the dog’s olfactory bulbs are located just below the frontal lobes of the brain. It turns out that as one moves from long-skulled to short-skulled breeds, the brain tilts downward and the olfactory bulbs change their relative position—they move further below and to the rear of the frontal lobes. This remarkable rotation depends entirely on the Cephalic Index; a breed’s overall body size or weight have nothing to do with it.

How does this human-induced change in olfactory neuroanatomy affect each breed’s sense of smell? That’s the big question, one the authors say is “of intense interest for future research.” I hope we’ll be hearing more soon.

The other dog paper that caught my eye is called “Tracking footprints of artificial selection in the dog genome.” It’s a highly mathematical analysis of a large-scale DNA dataset: more than 21,000 gene loci taken from 275 dogs from 10 breeds. The researchers—from four different institutions across the United States—combed through this enormous pile of data using statistical filters that picked up genetic variation consistent with artificial selection, i.e., evidence of selective breeding. They found 155 genetic regions that met the criteria, including all five genes linked to breed-specific traits in previous, smaller scale studies. (One gene, for example, is associated with skin-wrinkling in the Shar-Pei.)

Although they don’t specifically mention olfactory gene regions that might vary between breeds, the authors raise another, rather provocative, possibility. They note that for many gene locations associated with positive selection in the dog, there are analogous locations in humans.

Although this result should be interpreted with caution, as the specific targets of selection are generally not known with certainty in either dogs or humans, it does raise the intriguing possibility that recent selection has influenced common loci in both the human and dog lineages.

Translation: to some extent dogs and humans have coevolved at the genetic level.

Would it be too big a stretch to think this might have to do with our shared food? Every cooked and spiced scrap tossed to the dogs might have helped shape their olfactory ability. And every gazelle felled by an arrow after being scented by hound would just keep the feedback loop going.

Necessary?

The English have a long and honorable tradition of tolerating eccentrics, but the Baltesz family of Bristol is really pushing the envelope. Together with their teenage children, Mr. and Mrs. Baltesz are peeing into bottles and spritzing the neighborhood with their urine. Why, you ask? To help their lost dog Simon find his way home, of course. They hope he’ll follow the scent trail.

Unlike their less fastidious contemporaries, however, members of the Baltesz family dilute their urine before leaving it in public places. Why, you ask? (What, are you dense?)

Because Jane Hayes, their finder-of-lost-dogs consultant, says that

A dog’s sense of smell is 3,000 times more potent than ours . . .

Three thousand times more potent? Ms. Hayes clearly hasn’t read What the Nose Knows, or she'd know that controlled studies find the human and canine nose are close to parity. In fact, I’ll bet her a warm bottle of recycled Sierra Nevada Pale Ale that she can’t come up with scientific evidence to support her claim.

British Healthcare Going to the Dogs

Take your diabetic grandmother to the clinic and they’ll tell you she can be seen by the corgi in five weeks or by the Yorkshire terrier in eight. But it’s the National Health Service, so it’s free!