Detection of winter tick, Dermacentor albipictus, infestations using near infrared reflectance spectroscopy of bovine feces

Abstract

The objective of this study was to determine whether artificial infestations of D. albipictus could be detected in cattle using near infrared reflectance spectroscopy of bovine feces (fNIRS) and if detection capability was sensitive to size of tick infestation and phase of on-host stage-specific tick development. Fecal samples were collected daily from six non-infested then later tick-infested Bos taurus yearling heifers who each served as their own control. Cattle with D. albipictus infestations arising from as few as 1000 larvae were identified by fecal chemistry changes using fNIRS technology. In two separate trials, three animal pairs were infested with one of three treatment levels (low: ∼ 1000, medium: ∼ 4000, and high: ∼ 8000) of D. albipictus larvae in a repeated measures experimental design. Trial 1 consisted of tick naïve cattle while Trial 2 consisted of prior tick exposed cattle. Date of drop and daily sum of engorged female ticks were tabulated to characterize each infestation. Cluster, common factor, principal component and MANOVA analyses were used to define and assess fecal spectra changes associated with experimental stages of infestation. Cluster analyses found significant differences in fecal samples for heifer pairs in each treatment level group (low, medium, and high) in Trial 1 and then in Trial 2 from two pre-infestation control periods (outside and inside), three stages of tick development (larval feeding, nymphal feeding, adult feeding), and post-tick recovery periods. Five shifts in fecal chemistry of non-infested and tick-infested periods were identified by six clusters of NIRS fecal spectra measured between 576 and 1126 nm. The PCA’s resulted in 97.56% and 97.77% for Trials 1 and 2 respectively of the total variation in the 1050 frequencies being explained by the first three principal components (P1, P2, P3). Results from the MANOVA and the Wilk’s Lambda test for both trials showed highly significant evidence (p-values < 0.0001) of a difference in the means of the three principal components across the six Stages. There was significant evidence in Trial 1 (p-values = 0.0067) and Trial 2 (p-values < 0.0001) of a difference between the means of the three principal components across the three levels of tick infestation. These significant pair-wise comparisons reflect developmental phases of tick attachment and blood-feeding that define periods of increasing, peak and declining stress identified in five fecal chemistry shifts defined by six fecal spectral clusters.