Detection of Symptomatic and Asymptomatic SARS-CoV-2 by Naïve Dogs: Feasible in Controlled Tasks but Envisioned as Limited for Public Screening

Dogs can detect volatile organic compounds (VOCs) associated with infectious diseases, but their ability to distinguish between symptomatic and asymptomatic SARS-CoV-2 infections has not been fully established. In this study, eight naïve dogs began training with either symptomatic or asymptomatic Delta samples; seven reached the testing phase and were then evaluated on the alternate group to assess cross-generalization. Training initially used a yes/no protocol but was adapted to a line-up design after poor performance. When presented with novel Delta samples, dogs significantly discriminated them from controls, achieving a mean sensitivity of 71% and specificity of 51%, with no difference between training groups. In contrast, performance dropped when dogs were tested with asymptomatic Omicron samples from vaccinated individuals, with a mean sensitivity of 55%. These results show that dogs can generalize across symptomatic and asymptomatic COVID-19 cases for the Delta variant but fail to detect Omicron reliably, likely due to altered VOC profiles in vaccinated individuals. While proof-of-concept feasibility was demonstrated with a line up protocol for detecting asymptomatic scent, detection dogs should not currently be recommended for large-scale screening, but findings underscore the need for standardized protocols and variant-specific retraining.