E09 - Plasma Inflammatory Cytokine Profiles in Colitis Cases with and Without Equine Neorickettsiosis (Potomac Horse Fever)

Abstract: Background: Laminitis appears to be a more common complication of Potomac Horse Fever (PHF) compared with colitis of other etiologies. Differences in the severity of the systemic inflammatory response may be responsible for this and warrant investigation.

Hypothesis/objectives: The objective was to compare plasma inflammatory cytokine profiles between horses with PHF colitis (PHF[+]) and colitis due to other causes (PHF[-]). We hypothesized that PHF[+] horses would have increased proinflammatory cytokine concentrations in plasma at hospital admission compared to PHF[-].

Animals: 21 client-owned mixed breed adult horses diagnosed with colitis

Methods: In a prospective case-control study, plasma samples were collected from horses diagnosed with colitis at admission to hospital and analyzed using a multiplex ELISA for inflammatory cytokines including IL-1β, IL-6, IL-8 and TNF-α. Cytokine concentrations were compared between PHF[+] (n=6) and PHF[-] (n=15) cases using Mann-Whitney tests.

Results: Laminitis was more frequent in PHF[+] (4/6) compared to PHF[-] (0/15) cases (p = 0.003). Median (IQR) plasma cytokine concentrations were not different between PHF[+] and PHF[-] cases: IL-1β (PHF[+] 37.4 [0-98] pg/ml vs PHF[-] 59.8 [0-142.8] pg/ml), p = 0.6; IL-6 (PHF[+] 22.8 [4-51.1] pg/ml vs PHF[-] 19.5 [0-134] pg/ml), p = 0.8; IL-8 (PHF[+] 95.3 [60-138.3] pg/ml vs PHF[-] 104 [69-173.5] pg/ml), p = 0.8; TNF-α (PHF[+] 17.8 [10.4-46.9] pg/ml vs PHF[-] 18 [1-128] pg/ml), p > 0.99.

Conclusions and clinical importance: The results do not indicate that more profound systemic inflammation was responsible for the higher incidence of laminitis in PHF[+] cases in this study.