Canine Olfactory Detection of a Non-Systemic Phytobacterial Citrus Pathogen of International Quarantine Significance

Abstract

For millennia humans have benefitted from application of the acute canine sense of smell to hunt, track and find targets of importance. In this report, canines were evaluated for their ability to detect the severe exotic phytobacterial arboreal pathogen Xanthomonas citri pv. citri (Xcc), which is the causal agent of Asiatic citrus canker (Acc). Since Xcc causes only local lesions, infections are non-systemic, limiting the use of serological and molecular diagnostic tools for field-level detection. This necessitates reliance on human visual surveys for Acc symptoms, which is highly inefficient at low disease incidence, and thus for early detection. In simulated orchards the overall combined performance metrics for a pair of canines were 0.9856, 0.9974, 0.9257 and 0.9970, for sensitivity, specificity, precision, and accuracy, respectively, with 1–2 s/tree detection time. Detection of trace Xcc infections on commercial packinghouse fruit resulted in 0.7313, 0.9947, 0.8750, and 0.9821 for the same performance metrics across a range of cartons with 0–10% Xcc-infected fruit despite the noisy, hot and potentially distracting environment. In orchards, the sensitivity of canines increased with lesion incidence, whereas the specificity and overall accuracy was >0.99 across all incidence levels; i.e., false positive rates were uniformly low. Canines also alerted to a range of 1–12-week-old infections with equal accuracy. When trained to either Xcc-infected trees or Xcc axenic cultures, canines inherently detected the homologous and heterologous targets, suggesting they can detect Xcc directly rather than only volatiles produced by the host following infection. Canines were able to detect the Xcc scent signature at very low concentrations (10,000× less than 1 bacterial cell per sample), which implies that the scent signature is composed of bacterial cell volatile organic compound constituents or exudates that occur at concentrations many fold that of the bacterial cells. The results imply that canines can be trained as viable early detectors of Xcc and deployed across citrus orchards, packinghouses, and nurseries.

Highly sensitive scent-detection of COVID-19 patients in vivo by trained dogs

“…In the field of medical diagnosis, dogs are known to detect specific conditions [ 16 ], but most are anecdotal reports instead of formal protocols designed to validate a diagnostic test for clinical use [ 17 ]. However, at least one study demonstrated that appropriate training, coupled with strict adherence to the scientific method, lead to consistent diagnosis of Clostridioides difficile infection in humans [ 18 ], and, more recently, a comprehensive method was published validating canine diagnosis of two plant pathogens of international concern [ 19 , 20 ]. Dogs detect and differentiate unique odors that result from the emission of volatile organic compounds (VOC) that constitute the “smell print” of the target [ 21 ].…”

Plant Disease Detection Technology Assessment

“…Eleven dogs detected Asian citrus canker caused by X. citri pv. citri in seedlings, fruit orchards, packing houses, and even isolated bacterial cultures [73]. The dogs detected X. citri infections with a good sensitivity (73%) and specificity (99%).…”

Preliminary accuracy of COVID-19 odor detection by canines and HS-SPME-GC-MS using exhaled breath samples

“…Other studies have also demonstrated high rates of success in detection of plant pathogens causing laurel wilt disease in avocado trees [ 39 , 40 ]. Other researchers have demonstrated success with a citrus pathogen [ 41 , 42 ]. The current hypothesis assumes that, as with other diseased individuals, persons suffering from COVID-19 will exhibit a physiological change that manifests as a disease state related VOC profile, thereby allowing detection by a well-trained scent detection canine.…”