Olfaction in the canine cognitive and emotional processes: From behavioral and neural viewpoints to measurement possibilities

Domestic dogs (Canis familiaris) have excellent olfactory processing capabilities that are utilized widely in human society e.g., working with customs, police, and army; their scent detection is also used in guarding, hunting, mold-sniffing, searching for missing people or animals, and facilitating the life of the disabled. Sniffing and searching for odors is a natural, species-typical behavior and essential for the dog's welfare. While taking advantage of this canine ability widely, we understand its foundations and implications quite poorly. We can improve animal welfare by better understanding their olfactory world. In this review, we outline the olfactory processing of dogs in the nervous system, summarize the current knowledge of scent detection and differentiation; the effect of odors on the dogs' cognitive and emotional processes and the dog-human bond; and consider the methodological advancements that could be developed further to aid in our understanding of the canine world of odors.

Scent detection of Brucella abortus by African giant pouched rats (Cricetomys ansorgei)

BACKGROUND

Brucellosis is a contagious zoonosis caused by bacteria of the genus Brucella. While the disease has been eradicated in most developed countries, it remains endemic in sub-Saharan Africa where access to reliable diagnostics is limited. African giant pouched rats (Cricetomys ansorgei) have been trained to detect the scent of Mycobacterium tuberculosis to increase case detection in sub-Saharan Africa. Given the similar diagnostic challenges facing brucellosis and tuberculosis, we explored the feasibility of training African giant pouched rats to detect Brucella.

RESULTS

After 3 months of training, rats reliably identified cultured Brucella, achieving an average sensitivity of 93.56% (SD = 0.650) and specificity of 97.65% (SD = 0.016). Rats readily generalized to novel, younger Brucella cultures that presumably generated a weaker volatile signal and correctly identified at least one out of three fecal samples spiked with Brucella culture during a final test of feasibility.

DISCUSSION

To our knowledge, these experiments are the first to demonstrate Brucella emits a unique odor profile that scent detection animals can be trained to identify. Importantly, cultured E. coli samples were included throughout training and test to ensure the rats learned to specifically identify Brucella bacteria rather than any bacteria in comparison to bacteria-free culture medium. E. coli controls therefore served a crucial function in determining to what extent Brucella abortus emits a unique odor signature. Further research is needed to determine if a Brucella-specific volatile signature is present within clinical samples. If confirmed, the present results suggest trained rats could serve as a valuable, novel method for the detection of Brucella infection.

Rapidly training African giant pouched rats (Cricetomys ansorgei) with multiple targets for scent detection

Since 1997, APOPO, a non-profit organization based in Tanzania, has deployed African giant pouched rats (Cricetomys ansorgei) to detect landmines in post-conflict areas. More recent research suggests the pouched rats can also be trained to detect tuberculosis in human sputum samples. Despite proven success on both tasks, the potential impact of each rat is limited by the required training time and constraint to a single target odor. The aim of this project was to establish a technique to rapidly train pouched rats to detect multiple odor targets. Eight pouched rats were trained to detect five unrelated target odors in Experiment 1. In addition to training duration, we measured maintenance of all odor targets. In Experiment 2, we examined response persistence under conditions of extinction. Experiment 3 investigated whether refresher sessions before tests would maintain detection accuracy. The animals mastered all odor targets in significantly fewer sessions than APOPO's operational rats require to master a single target odor. Importantly, rats demonstrated strong discrimination between targets and non-targets despite the potential for interference and forgetting, suggesting pouched rats can be trained to detect at least five targets simultaneously. These results have the potential to increase the impact of each detection rat by both decreasing training time and expanding operational versatility, e.g., a single rat could be trained to detect multiple diseases.

A detection dog to identify patients with Clostridium difficile infection during a hospital outbreak

OBJECTIVES

Early and rapid identification of Clostridium difficile infections (CDI) is important to prevent transmission. In this study we assessed the diagnostic accuracy of a trained detection dog for detecting CDI cases on hospital wards in an outbreak setting.

METHODS

During a CDI outbreak in a large Dutch university hospital, we screened affected hospital wards repeatedly with a trained detection dog. The dog's response was compared to the clinical diagnosis, supported by laboratory results.

RESULTS

During a total of 9 hospital visits, the dog performed 651 screenings involving 371 participants. The dog correctly identified 12 out of 14 CDI cases [sensitivity 86% (95% confidence interval (CI): 56-97%)] and 346 out of 357 CDI negative participants [specificity of 97% (95% CI: 94-98%)]. Interestingly, of the 11 CDI negative participants that were 'falsely' indicated by the dog as positive, 2 (18%) did actually developed CDI during the 3 months of follow-up after the detection period; compared to only 12 of the 346 participants (3.5%) that the dog identified as C. difficile negative (p = 0.06).

CONCLUSION

A trained detection dog can accurately detect CDI in hospitalized patients during an outbreak. A (repeated) positive dog response is a strong indication of a CDI episode coming, be it the next day or possibly up to a month.