Seroprevalence and Risk Factors Associated With Corynebacterium pseudotuberculosis Detectable Antibodies in Equids in Alabama

•Although never reported in Alabama, 50% of horses had low detectable synergistic hemolysis inhibition (SHI) titers (1:8 to 1:64) and 2.6% of horses had titers ≥1:128.•Increasing SHI titers in horses was associated with contact with ruminants.•Further evaluation of cross-reaction with phospholipase D exotoxin from C. p. biovar ovis is warranted.•Additional research regarding the serological diagnosis of pigeon fever is needed.

A cross-sectional serological survey was carried out to screen the equine population of the nonendemic state of Alabama for the presence of detectable antibody titers against Corynebacterium pseudotuberculosis. A second objective was to determine the association of detectable titers with risk factors such as exposure to ruminants or previous travel to endemic states. A total of 342 equine serum samples from 40 Alabama counties were analyzed using the synergistic hemolysis inhibition test (SHI). The prevalence of detectable antibody titers (≥1:8) was 52.5% (95% confidence interval [CI], 47%-57.9%). Titers ≥1:128 were detected in 2.63% (95% CI, 1.2%-4.9%), and titers ≥1:512 were detected in 0.3% (95% CI, 0%-1.6%) of the sampled population. In the final generalized linear model, age (P < .001), breed (P = .023), and contact with cattle (P = .05) were associated with increasing SHI titers. Contact with goats was associated in the initial but not in the final analysis (P = .19). Previous travel was not associated with increasing SHI titer (P = .97). The results demonstrated a high prevalence of low detectable titers and low prevalence of titers ≥ 1:128 in a nonendemic population. Further evaluation of SHI cutoff titers and accuracy is warranted to reduce the risk of a false positive diagnosis.