Immunological response of lame sheep to clinical interdigital dermatitis and footrot: Procalcitonin, acute phase proteins, and pro-inflammatory cytokines

Abstract

In many countries, sheep lameness is a cause of economic concern and a contributing factor to a declining economy. This study aimed to investigate changes in procalcitonin (PCT), acute phase proteins (APPs), and cytokines (CYTs) in response to interdigital dermatitis and footrot in sheep under field conditions, to emphasize their role in the disease pathogenesis, diagnosis, as well as monitoring treatment response. Fifty-three sheep with foot diseases (26 clinical cases with interdigital dermatitis and 27 clinical cases with footrot) and 20 clinically healthy naemi sheep were used in this study. Real time PCR for detection of Fusobacterium necrophorum (F. necrophorum) and Dichelobacter nodosus (D. nodosus) revealed that, all samples collected from lame sheep (N = 53) were positive for D. nodosus (100 %), whereas F. necrophorum was detected in 19 out of 53 samples (35.84 %). The virulent D. nodosus was detected in 48 lameness cases where non-virulent D. nodosus were identified in 5 cases (in concurrent with F. necrophorum). The mean serum levels of PCT, C-reactive protein (CRP), serum amyloid A (SAA), haptoglobin (HP), fibrinogen (Fg) and CYTs (IL1-β, IL-1α, IFN-γ, IL-6 and TNF-α) in sheep with clinical interdigital dermatitis and footrot were remarkably higher than those detected in control healthy sheep. The serum levels of PCT, CRP, SAA, HP, Fg, and CYTs markers in lame sheep pre- and post-treatment were measured. A substantial decline was detected in serum levels of tested biomarkers of lame sheep after 14 days of treatment. The ROC curves were created. The AUC was assessed to evaluate the accuracy of each variable in distinguishing diseased and healthy sheep. Based on the ROC curves and AUCs; PCT, CRP, SAA, HP, and CYTs were highly diagnostic and predictive for the treatment response of sheep with clinical interdigital dermatitis and footrot. Moreover, all tested biomarkers had a noteworthy role in disease immuno-pathogenesis. Nevertheless, PCT and CRP are better than other tested APPs and CYTs as diagnostic markers for interdigital dermatitis and footrot. However, PCT only has the ability to differentiate sheep with different lameness score.

Keywords: C. reactive protein; Haptoglobin; Lameness; Procalcitonin; Serum amyloid A.