E-Noses Detect Disease in Plants, Animals & Humans

Every living organism emits volatile organic compounds. CC0 photo

The fragrance of a rose comes from volatile organic compounds. Living plants, animals, humans, and even inanimate objects emit complex mixtures of VOCs. VOC mixtures are so distinctive that new words are used to describe them: volatilome, breathprint, and smellprint.

“There are over 2,000 VOCs in a person’s breath,” says USDA Forest Service scientist Dan Wilson.“If you have a disease, you release abnormal compounds in your breath. This allows pathologists to non-invasively detect many different diseases in the body by simply analyzing the breath.”

Similarly, sick bats can be diagnosed by their smellprints. Every bat species has a distinctive smellprint. Bats infected with the fungal pathogen Pseudogymnoascus destructans (Pd) have different smellprints than healthy bats. Pd causes white-nose syndrome, a disease that has killed more than six million bats since 2006.

Electronic noses can differentiate Pd from related fungal species that grow on bat skins but are not pathogenic, as Wilson and his colleagues recently reported in the journal Sensors & Transducers.

Identifying the Pd smellprint signature is just the beginning. Molecule by molecule, Wilson and his colleagues are identifying the VOCs associated with different cave types, the Pd pathogen, white-nose syndrome, and at least eight WNS-susceptible bat species. The scientists are also looking for VOC disease biomarkers.

Every bat species has a distinctive smellprint, as does the fungus that causes white-nose syndrome. Image courtesy of Anna Doty.

Anna Doty, a post-doctoral research associate at Arkansas State University, is integral to this work. Doty’s winter field work includes riding to remote caves on a four-wheeler, collecting air samples with VOCs from bats, and shipping the air samples to Wilson’s WNS lab in Mississippi. Their collaboration is featured in a recent Untamed Science video.

Air samples must be collected without disturbing the bats while they hibernate in caves. “Keeping the bats in a state of torpor is essential for their winter survival,” says Wilson.

Wilson and his colleagues aim to differentiate between healthy and sick bats of different species by their e-nose smellprint signatures. E-noses could also help detect WNS early, which would greatly improve treatment effectiveness.

Wilson has not always studied wildlife diseases. He is a research plant pathologist who pioneered the use of e-noses for diagnosing plant diseases in the 1990s, especially root- and bole-rot fungi of hardwood trees.

In 2014, SRS station director Rob Doudrick appointed Wilson to the National FS WNS Research Team, asking him to focus on new methods for the early detection and control of WNS. This research is crucial, as the deadly fungal disease had reached the South and was affecting southern bat species.

Doty and a colleague collect air samples from a bat hibernaculum. Photo by Mike Slay, courtesy of Anna Doty. 

It was a huge shift in Wilson’s research focus that required thorough understanding of mammalian biology and physiology. “I studied human diseases as a key model,” says Wilson, who has since made major contributions to the biomedical field, publishing on everything from forensic science to gastrointestinal disease and biomarker metabolite signatures. Medical professionals have requested Wilson’s expertise in producing such synthesis papers, as few biomedical researchers have the extensive e-nose experience necessary.

“The medical papers are creating the scientific basis for applying e-nose tools to wildlife early disease-detection research,” says Wilson. “The biochemical mechanisms for diagnosing diseases in humans can be applied to wildlife diseases – but the theories and approaches behind it are brand new.”

E-noses can detect disease in a wide range of hosts – plants, animals, and humans. Wilson’s recent review paper, published in the journal Chemosensors, shows how modified e-nose technologies, theories, and methodologies can be applied to such varied hosts.

“E-nose technologies are advancing at an explosive rate,” says Wilson. New sensors, algorithms, methods, and VOC-biomarkers are identified and developed every year. New smellprint databases are constantly being developed. Smellprint patterns are so precise that false negatives and false positives can be largely eliminated, especially when used with application-specific reference databases and disease biomarker detection.

Wilson also reviews dual-technology e-noses. These instruments contain e-nose sensor arrays plus analytical chemistry capabilities (such as gas chromatography). Wilson uses this type of e-nose in his research on Pd and WNS.

e-nose
Wilson uses a dual-technology e-nose system in his WNS research. Photo by Dan Wilson, USFS.

“We’re always trying to expand on e-nose capabilities,” says Wilson. “We’re laying the foundation for applying this technology to early detection of many wildlife diseases, particularly mammals – including bats and cervids.”

Wilson and his research team have won numerous awards, including Sensors Best Paper Award for their 2009 review.

Read the full text of the Chemosensors article.

Read the full text of the Sensors & Transducers article.

For more information, email Dan Wilson at dwilson02@usda.gov.

Access the latest publications by SRS scientists.

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