key: cord-0691409-99tajtoc
authors: Kopper, Jamie J.; Willette, Jaclyn A.; Kogan, Clark J.; Seguin, Alexis; Bolin, Steven R.; Schott, Harold C.
title: Detection of pathogens in blood or feces of adult horses with enteric disease and association with outcome of colitis
date: 2021-08-12
journal: J Vet Intern Med
DOI: 10.1111/jvim.16238
sha: 6893dc1fda35893840f0a178e72dea776e6a0e5c
doc_id: 691409
cord_uid: 99tajtoc

BACKGROUND: Rates of detecting ≥1 potential enteric pathogens (PEP) or toxins (PEP‐T) in feces, blood, or both of horses ≥6 months of age with enteric disease and impact of multiple detections on outcome of horses with colitis has not been reported. OBJECTIVE: To determine detection rates of PEP/PEP‐T in feces, blood, or both of horses with enteric disease and effect of detecting multiple agents on outcome of horses with colitis. ANIMALS: Thirty‐seven hundred fifty‐three fecal samples submitted to IDEXX Laboratories and 239 fecal and blood samples submitted to Michigan State University's Veterinary Diagnostic Laboratory (MSUVDL). METHODS: Retrospective evaluation of PEP/PEP‐T testing results was performed to determine rates of detection of 1 or more PEP/PEP‐T. Impact of detecting multiple agents on outcome was assessed in 239 horses hospitalized for colitis. RESULTS: One or more PEP/PEP‐T was detected in 1175/3753 (31.3%) and 145/239 (60.7%) of samples submitted to IDEXX Laboratories and MSUVDL, respectively. In a hospitalized cohort, survival to discharge was lower (76%) in horses with 1 agent, compared to horses with either no (88%) or multiple (89%) agents. There was no difference (P = .78) in days of hospitalization between horses with 0 (1–17), 1 (1–33), and > 1 positive (1–20) result. There was no difference in cost of hospitalization (P = .25) between horses with 0 ($2357, $1110‐15 553), 1 ($2742, $788‐11 005), and >1 positive ($2560, $1091‐10 895) result. CONCLUSIONS AND CLINICAL IMPORTANCE: Detection rates of PEP/PEP‐T in horses with colitis vary with cohorts and tests performed. Detection of more than 1 PEP or PEP‐T did not affect outcome.

Colitis, often manifested as an acute onset of diarrhea, is a lifethreatening disease in horses and determining the cause of colitis can be challenging. [1] [2] [3] As an example, an etiologic diagnosis was established in only 7.7% of horses with colitis at a veterinary teaching hospital in 1 report. 4 Determining a microbial cause of colitis and other enteric diseases is desirable to institute therapies directed against specific pathogens and to allow appropriate biosafety measures to be instituted, based on pathogen-specific concerns for disease transmission to other horses, contamination of the environment, and zoonotic potential.

Pathogens including Salmonella spp., 2, 5 Neorickettsia risticii, 2,5 toxin producing strains of Clostridiodes difficile and Clostridium perfringens, 4, [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] and more recently coronavirus [17] [18] [19] are well-recognized agents of acute colitis in adult horses. Infection with other pathogens, including rotavirus, 10, 20 Lawsonia intracellularis, [21] [22] [23] Rhodococcus equi, 24 Aeromonas spp., 25 Eimeria spp., 26 and Cryptosporidium parvum 27, 28 as well as infestation with internal parasites 29, 30 can also cause enteric disease in equids, with some pathogens more commonly causing disease in younger equids.

Isolation of any of these agents from feces of equids with enteric disease leads to establishment of a definitive etiologic diagnosis by many clinicians.

Although this conclusion can be accurate for some pathogens (ie, N. risticii), cause and effect when 1 or more potential enteric pathogens (PEP) or their toxins (PEP-T) is detected is not always clear. As molecular diagnostic tools (ie, real-time PCR) have progressed to allow more economic screening for multiple PEP and PEP-T in fecal samples, higher rates of PEP and PEP-T detection have been achieved and, in some samples, multiple positive results provide support for infection by more than 1 PEP. 31, 32 However, multiple positive results can also cause confusion when developing treatment and biosecurity plans. As an example, a recent systematic review of 23 studies comparing PCR fecal diagnostic panels to conventional fecal testing in humans with diarrhea found that molecular tests consistently yielded a higher percentage of positive results than conventional tests; however, the study concluded that it was unclear whether or not the additional positive test results were clinically relevant. 33 The objective of this retrospective study was to determine the rate of detecting 1 or more PEP or PEP-T in horse fecal and blood samples. Table 1) . Detection of both C. difficile toxin A and B genes (tcdA and tcdB) from the same sample was the most strongly correlated result. Additional pairwise comparisons were also significantly associated but correlation coefficients were low (.11 or less; Table 2 ).

T A B L E 1 Detection rates (%) for each potential enteric pathogen (PEP) or potential enteric pathogen toxins (PEP-T), rate of detection of multiple agents, and total number of fecal samples collected from horses ≥6 months of age by year for samples submitted to IDEXX Laboratories 

Overall, 197 of 239 (82%) horses survived to hospital discharge.

Survival was lowest for horses from which 1 PEP or PEP-T was detected, as compared to horses from which either no pathogen or multiple pathogens were detected ( PEP and PEP-T, codetection would be a more appropriate term than coinfection. At MSUVMC we have found a number of horses with colitis due to N. risticii to also have positive ELISA results for C. difficile or C. perfringens toxins. This finding led to speculation that disruption of normal enteric flora during infection with N. risticii could lead to upregulation of toxin production by Clostridium spp. Further, if resident Clostridium spp. started to produce toxins during clinical disease due to N. risticii, these toxins could pose a further insult to the intestinal barrier, prolonging disease course and increasing case fatality rate.

Codetection of N. risticii and Clostridium spp. toxins also raised the question of whether addition of metronidazole to the treatment regimen should be considered, although the latter drug could also have adverse effects. Although neither a significant association of detecting both N. risiticii and Clostridium spp. toxins nor an increased risk of death with detection of more than 1 PEP or PEP-T was found in our cohort of horses with colitis, these questions remain unanswered.

When clinicians submit samples for enteric disease panels, which is typically a more economic approach than a barrage of individual tests, it is important to understand the information that might be ret- 49, 50 Finally, our review of medical records of horses with colitis at MSUVMC did not clearly reveal whether nonsurvival was due to ongoing enteric disease or development of complications. Consequently, whether detection of more than 1 PEP and PEP-T affected the severity of colitis was unable to be accurately determined.

In conclusion, we found substantially different detection rates for PEP and PEP-T between the 2 enteric disease panels, most likely due to different study populations tested. Finding both C. difficile toxins A and B was the most common codetection with enteric disease testing of horses ≥6 months of age; however, this finding likely indicated dual toxin production by the same organism, rather than infection with separate organisms. Contrary to our hypothesis, detection of more than 1 PEP or PEP-T was not associated with 

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Detection of pathogens in blood or feces of adult horses with enteric disease and association with outcome of colitis

Authors declare no off-label use of antimicrobials.

Authors declare no IACUC or other approval was needed.

Authors declare human ethics approval was not needed for this study.ORCID Jamie J. Kopper https://orcid.org/0000-0001-6829-7224Harold C. Schott II https://orcid.org/0000-0002-7728-5409