Identification of Adult Ixodid Tick Species by Raman Spectroscopy of Their Feces

Abstract

Background: Ticks and tick-borne diseases pose significant challenges to cattle production, necessitating effective control measures based on understanding tick presence, identification, abundance, and dispersal. The standard method for inspection is visual and physical examination of restrained animals, but the limitations of human sight and touch can allow for larval, nymphal, and unfed adult ticks to remain undetected due to their small size and attachment sites. However, Raman spectroscopy, an analytical tool widely used in agriculture, shows promise for tick-species identification of tick-infested cattle. Raman spectroscopy provides a non-invasive and efficient method for acquiring data by leveraging the interaction between molecules and light, allowing for the identification of molecular constituents within specimens. Methods: Raman spectroscopy was employed to analyze the structure and composition of tick feces deposited on host skin and hair during blood-feeding. Feces from 12 ixodid tick species spanning five genera were scanned. Spectral data were subjected to a machine-learning model called partial least squares discriminant analysis. In addition, we compared and evaluated feces of the horn fly, Haematobia irritans, after feeding on cattle, using Raman spectroscopy and the same analytical procedures. Results: Raman spectroscopy of tick feces identified six genus/sub-genus taxonomic groups at overall true prediction rates ranging from 92.3 to 100. At the species level, Raman spectroscopy identified Dermacentor albipictus, D. andersoni and D. variabilis at the overall true prediction rates of 100, 99.28 and 100, respectively. There were distinct differences between horn fly and tick feces in blood and guanine vibrational features. The overall true prediction rate for separating tick and horn fly feces was 98%. Conclusions: Our findings highlight the proficiency of Raman spectroscopy in reliably identifying tick species through their feces and its potential for practical field-based applications to identify tick infested cattle.