Successful treatment of a chronic oroantral fistula infected with extensively drug resistant bacteria using long-term oesophageal tube feeding and several non-conventional treatments in a horse.

BACKGROUND: Chronic oroantral fistulae (OAF) with secondary sinusitis can occur following repulsion of cheek teeth in horses. CASE REPORT: An 8-year-old Andalusian cross gelding presented with an iatrogenic clinical crown fracture of tooth 209, which underwent repulsion of its apical portion (day 0). The horse was treated with intramuscular penicillin and intravenous gentamicin (5 days), followed by oral trimethoprim-sulphonamide (10 days) and then oral doxycycline (14 days). The acute iatrogenic OAF created during the initial repulsion persisted; a chronic OAF was identified on day 24. On day 48, septic sinusitis with multidrug-resistant (MDR) Escherichia coli was confirmed. Although susceptible to enrofloxacin in vitro, 30 days of therapy was unsuccessful. Subsequent serial cultures grew multiple MDR and extensively drug-resistant (XDR) gram-negative microorganisms. Whole-genome sequencing (WGS) revealed multiple sequence types of E. coli, with a range of resistance and virulence genes. The orientation of the OAF, regional osteomyelitis and septic sinusitis were confirmed with computed tomography on day 70. On day 74, enteral nutrition was provided through a cervical oesophagostomy tube for 3 months for prevention of oral feed contamination. The OAF was treated with various alternative therapeutics, including apple cider vinegar, propolis and amikacin impregnated products, until resolution on day 116. CONCLUSION: These non-conventional therapeutics, antimicrobials and long-term oesophagostomy contributed to the successful treatment of a complicated OAF. In the future, WGS may be useful to inform antimicrobial selection when MDR or XDR organisms are identified.

The effect of regional hypothermia on mechanical nociceptive thresholds in the equine distal forelimb.

Regional hypothermia has shown promise as analgesic in horses when used to manage painful conditions of the distal limb such as laminitis. In this prospective study, the analgesic effects of regional hypothermia were assessed using mechanical nociceptive thresholds during distal limb cooling. The study population consisted of eight healthy adult Standardbred horses, selected from a teaching herd. A distal forelimb of each horse was cooled using water immersion at the following sequential target water temperatures: 34 °C, 20 °C, 10 °C, 5 °C, 1 °C, 5 °C, 10 °C, 20 °C. Limb surface temperature was measured after 30 min at each target water temperature and the mechanical force required to elicit a response (mechanical nociceptive threshold) was determined using a pneumatic actuator. Both forelimbs of each horse were tested one week apart. At skin surface temperatures above 7 °C, there was little association between skin surface temperature and the mechanical force required to elicit a response. As the skin surface temperature decreased below 7 °C, there was a rapid increase in the force required to elicit a response (P = 0.036). Skin surface temperatures of <7 °C required water temperatures below 2 °C. The results of this study suggest that hypothermia has potential to provide distal limb analgesia in horses at skin surface temperatures below 7 °C. Further evaluation of the technique is warranted.

Essential oil spray reduces clinical signs of insect bite hypersensitivity in horses.

OBJECTIVE: To assess the efficacy of an herbal spray combining various essential oils, with a claim of mast cell stabilisation, antipruritic, anti-inflammatory, and insect repellent effects on the clinical presentation of insect bite hypersensitivity (IBH) in horses. DESIGN: Double-blinded, placebo-controlled, randomised, cross-over clinical trial. METHODS: Twenty adult horses with clinical IBH were treated with a daily application of herbal spray or placebo for 28 days in a randomised, cross-over fashion, separated by a>28-day washout period. Horses were examined and scored prior to and after the completion of each treatment. Histopathology was performed on four horses. Owners kept daily diaries of observations. RESULTS: The herbal spray significantly reduced the severity of all assessed parameters (pruritus, excoriations, lichenification and alopecia; P < 0.05) compared with baseline values (pretreatment) and with placebo. Owners reported improvement of pruritus in 19/20 horses (95%) with complete resolution in 17 horses (85%) following treatment. Skin biopsies showed resolution of orthokeratosis in 4/4 horses, reduced thickness of the stratum spinosum in 2/4 horses and complete resolution of histopathological abnormalities in 1/4 horses after treatment, compared with either no change or deterioration of histopathologic lesions after placebo. No side effects were observed. CONCLUSIONS: The tested herbal spray may be an effective treatment for the management of equine IBH.

Continuous digital hypothermia prevents lamellar failure in the euglycaemic hyperinsulinaemic clamp model of equine laminitis.

BACKGROUND: Continuous digital hypothermia can prevent the development and progression of laminitis associated with sepsis but its effects on laminitis due to hyperinsulinaemia are unknown. OBJECTIVES: To determine the effects of continuous digital hypothermia on laminitis development in the euglycaemic hyperinsulinaemic clamp model. STUDY DESIGN: Randomised, controlled (within subject), blinded, experiment. METHODS: Eight clinically normal Standardbred horses underwent laminitis induction using the euglycaemic hyperinsulinaemic clamp model (EHC). At initiation of the EHC, one forelimb was continuously cooled (ICE), with the other maintained at ambient temperature (AMB). Dorsal lamellar sections (proximal, middle, distal) were harvested 48 h after initiation of the EHC and were analysed using histological scoring (0-3) and histomorphometry. Cellular proliferation was quantified by counting epidermal cell nuclei staining positive with an immunohistochemical proliferation marker (TPX2). RESULTS: Severe elongation and disruption of SEL with dermo-epidermal separation (score of 3) was observed in all AMB feet at one or more section locations, but was not observed in any ICE sections. Overall 92% of the AMB sections received the most severe histological score (grade 3) and 8% were grade 2, whereas ICE sections were classified as either grade 1 (50%) or grade 2 (50%). Relative to AMB feet, ICE sections were 98% less likely to exhibit grades 2 or 3 (OR: 0.02, 95% CI 0.001, 0.365; P<0.01). Histomorphometry measurements of total and nonkeratinised primary epidermal lamellar length were significantly increased (P<0.01) in AMB limbs compared with ICE. TPX2 positive cell counts were significantly increased (P<0.01) in AMB limbs compared with ICE. MAIN LIMITATIONS: Continuous digital hypothermia was initiated before recognition of laminitis and therefore the clinical applicability requires further investigation. CONCLUSIONS: Continuous digital hypothermia reduced the severity of laminitis in the EHC model and prevented histological lesions compatible with lamellar structural failure.

Microdialysis measurements of lamellar perfusion and energy metabolism during the development of laminitis in the oligofructose model.

REASONS FOR PERFORMING STUDY: Failure of lamellar energy metabolism, with or without ischaemia, may be important in the pathophysiology of sepsis-associated laminitis. OBJECTIVES: To examine lamellar perfusion and energy balance during laminitis development in the oligofructose model using tissue microdialysis. STUDY DESIGN: In vivo experiment. METHODS: Six Standardbred horses underwent laminitis induction using the oligofructose model (OFT group) and 6 horses were untreated controls (CON group). Microdialysis probes were placed in the lamellar tissue of one forelimb (all horses) as well as the skin dermis of the tail in OFT horses. Dialysate and plasma samples were collected every 2 h for 24 h and concentrations of energy metabolites (glucose, lactate, pyruvate) and standard indices of energy metabolism (lactate to glucose ratio [L:G] and lactate to pyruvate ratio [L:P]) determined. Microdialysis urea clearance was used to estimate changes in tissue perfusion. Data were analysed nonparametrically. RESULTS: Median glucose concentration decreased to <30% of baseline by 8 h in OFT lamellar (P = <0.01) and skin (P<0.01) dialysate. Lactate increased mildly in skin dialysate (P = 0.04) and plasma (P = 0.05) but not lamellar dialysate in OFT horses. Median pyruvate concentration decreased to <50% of baseline in OFT lamellar dialysate (P = 0.03). A >5-fold increase in median L:G compared with baseline occurred in OFT lamellar and skin dialysate (P<0.03). From a baseline of <20, median L:P increased to a peak of 80 in OFT skin and 38.7 in OFT lamellar dialysates (P<0.02); however, OFT lamellar dialysate L:P was not significantly different from CON. Urea concentration decreased significantly in OFT lamellar dialysate (increased urea clearance) but not in OFT skin or CON lamellar dialysate. CONCLUSIONS: Increased lamellar perfusion occurred during the development of sepsis-associated laminitis in the oligofructose model. Glucose concentrations in the lamellar interstitium decreased, suggesting increased glucose consumption but there was no definitive evidence of lamellar energy failure.

The effect of weightbearing and limb load cycling on equine lamellar perfusion and energy metabolism measured using tissue microdialysis.

REASONS FOR PERFORMING STUDY: Lamellar perfusion is thought to be affected by weightbearing and limb load cycling; this may be critical in the development of supporting limb laminitis. OBJECTIVES: To document the effects of unilateral weightbearing and altered limb load cycling on lamellar energy metabolism and perfusion. STUDY DESIGN: Randomised, controlled (within subject), experimental trial. METHODS: Nine Standardbred horses were instrumented with microdialysis probes in the foot lamellar tissue and skin (over the tail base). Urea (20 mmol/l) was added to the perfusate. Samples were collected every 15 min for a 1 h control period, then during periods of unilateral weightbearing (opposite limb held off the ground for 1 h); enhanced static limb load cycling (instrumented limb lifted every 10 s for 30 min); reduced limb load cycling activity (i.v. detomidine sedation) and continuous walking (30 min). Dialysate concentrations of glucose, lactate, pyruvate and urea were measured and lactate:glucose (L:G) and lactate:pyruvate (L:P) ratios were calculated. For each intervention, values were compared with baseline using nonparametric statistical testing. RESULTS: Lamellar dialysate glucose increased and L:G decreased significantly during enhanced static limb load cycling. Glucose and pyruvate increased, and L:G, L:P and urea decreased significantly during walking. Simultaneous skin dialysate values did not change significantly. There were no significant dialysate changes during unilateral weightbearing or after detomidine administration, but only the latter resulted in a significant decrease in limb load cycling frequency. CONCLUSIONS: Increases in limb load cycling frequency (particularly walking) caused dialysate changes consistent with increased lamellar perfusion. Unilateral weightbearing (1 h) and a sedation-induced reduction in limb load cycling frequency did not have a detectable effect on lamellar perfusion. More research is needed to confirm the role of hypoperfusion in supporting limb laminitis, but strategies to increase limb load cycling may be important for prevention.

Microdialysis measurements of equine lamellar perfusion and energy metabolism in response to physical and pharmacological manipulations of blood flow.

REASONS FOR PERFORMING STUDY: A suitable method for evaluating lamellar perfusion changes and their metabolic consequences is currently lacking. OBJECTIVES: To examine perfusion changes in lamellar tissue using serial microdialysis measurements of urea clearance and energy metabolites. STUDY DESIGN: Randomised, controlled (within subject) experimental trial. METHODS: Nine Standardbred horses were instrumented with microdialysis probes in the foot lamellar tissue and skin (over the tail base). Urea (20 mmol/l) was added to the perfusate and its clearance was used to estimate local perfusion. Samples were collected every 15 min for a 1 h control period, then during application of a distal limb tourniquet, during periods when norepinephrine or potassium chloride (KCl) were included in both skin and lamellar perfusates, and after systemic (intravenous) acetylpromazine. Dialysate concentrations of glucose, lactate, pyruvate and urea were measured and lactate:glucose (L:G) and lactate:pyruvate (L:P) ratios calculated. Values were compared with pre-intervention baseline and also between simultaneous skin and lamellar samples using nonparametric statistical methods. RESULTS: Lamellar glucose decreased and lactate, urea, L:G and L:P increased significantly with tourniquet application, without significant changes in skin dialysate values. Lamellar and skin glucose decreased and L:G increased significantly during norepinephrine infusion, but mild increases in urea were not significant at either site. KCl caused significant decreases in lamellar and skin L:G, and an increase in skin glucose, but did not affect urea clearance. Acetylpromazine caused profound decreases in lamellar glucose and L:P, with increased L:G and pyruvate, but did not affect urea clearance or any skin dialysate values. CONCLUSIONS: Significant changes in microdialysis urea clearance only occurred with severe lamellar hypoperfusion. However, changes in dialysate metabolite concentrations reflected less profound fluctuations in perfusion. This method may be useful for examining lamellar perfusion and energy balance during laminitis development and for the evaluation of vasoactive therapeutics.

A liquid chromatography-tandem mass spectrometry-based investigation of the lamellar interstitial metabolome in healthy horses and during experimental laminitis induction.

Lamellar bioenergetic failure is thought to contribute to laminitis pathogenesis but current knowledge of lamellar bioenergetic physiology is limited. Metabolomic analysis (MA) can systematically profile multiple metabolites. Applied to lamellar microdialysis samples (dialysate), lamellar bioenergetic changes during laminitis (the laminitis metabolome) can be characterised. The objectives of this study were to develop a technique for targeted MA of lamellar and skin dialysates in normal horses, and to compare the lamellar and plasma metabolomic profiles of normal horses with those from horses developing experimentally induced laminitis. Archived lamellar and skin dialysates (n = 7) and tissues (n = 6) from normal horses, and lamellar dialysate and plasma from horses given either 10 g/kg oligofructose (treatment group, OFT; n = 4) or sham (control group, CON; n = 4) were analysed. The concentrations of 44 intermediates of central carbon metabolism (CCM) were determined using liquid chromatography-tandem mass spectrometry. Data were analysed using multivariate (MVA) and univariate (UVA) analysis methods. The plasma metabolome appeared to be more variable than the lamellar metabolome by MVA, driven by malate, pyruvate, aconitate and glycolate. In lamellar dialysate, these metabolites decreased in OFT horses at the later time points. Plasma malate was markedly increased after 6 h in OFT horses. Plasma malate concentrations between OFT and CON at this time point were significantly different by UVA. MA of lamellar CCM was capable of differentiating horses developing experimental laminitis from controls. Lamellar malate, pyruvate, aconitate and glycolate, and plasma malate alone were identified as the source of differentiation between OFT and CON groups. These results highlighted clear discriminators between OFT and CON horses, suggesting that changes in energy metabolism occur locally in the lamellar tissue during laminitis development. The biological significance of these alterations requires further investigation.

Regional intravenous limb perfusion compared to systemic intravenous administration for marimastat delivery to equine lamellar tissue.

Pharmaceutical agents with potential for laminitis prevention have been identified. Many of these, including the MMP inhibitor marimastat, are impractical for systemic administration. This study compared local delivery of marimastat by regional limb perfusion (RLP) to systemic intravenous bolus dosing (SIVB), and established whether RLP results in local lamellar drug delivery. Six adult horses received 0.23 mg/kg of marimastat by RLP followed by 0.23 mg/kg marimastat by SIVB, with a 24-h washout period. Lamellar ultrafiltration probes sampled lamellar interstitial fluid as lamellar ultrafiltrate (LUF). LUF and plasma marimastat concentrations (LUF[M] and P[M] respectively) were measured for 24 h after each treatment. Regional pharmacokinetic parameters were calculated using noncompartmental analyses. The LUF C(max) following RLP was 232 [34-457] times that following SIVB. LUF[M] after RLP were higher than those obtained after SIVB for 18 h (P < 0.03). Median LUF[M] were > IC(90) of equine lamellar MMP-2 and MMP-9 for 9 h after tourniquet removal. RLP appeared superior to SIVB for lamellar marimastat delivery (higher LUF C(max),, AUC and T > IC(90) of lamellar MMPs). However, frequent dosing is necessary to achieve therapeutic lamellar concentrations. RLP could be used to investigate whether marimastat prevents experimentally induced laminitis. Further refinement of the technique and dosing interval is necessary before clinical application.

Equine lamellar energy metabolism studied using tissue microdialysis.

Failure of lamellar energy metabolism may contribute to the pathophysiology of equine laminitis. Tissue microdialysis has the potential to dynamically monitor lamellar energy balance over time. The objectives of this study were to develop a minimally invasive lamellar microdialysis technique and use it to measure normal lamellar energy metabolite concentrations over 24 h. Microdialysis probes were placed (through the white line) into either the lamellar dermis (LAM) (n = 6) or the sublamellar dermis (SUBLAM) (n = 6) and perfused continuously over a 24 h study period. Probes were placed in the skin dermis (SKIN) for simultaneous comparison to LAM (n = 6). Samples were collected every 2 h and analysed for glucose, lactate, pyruvate, urea and glycerol concentrations. LAM was further compared with SUBLAM by simultaneous placement and sampling in four feet from two horses over 4 h. Horses were monitored for lameness, and either clinically evaluated for 1 month after probe removal (n = 4) or subjected to histological evaluation of the probe site (n = 10). There were no deleterious clinical effects of probe placement and the histological response was mild. Sample fluid recovery and metabolite concentrations were stable for 24 h. Glucose was lower (and lactate:glucose ratio higher) in LAM compared with SUBLAM and SKIN (P < 0.05). Pyruvate was lower in SUBLAM than SKIN and urea was lower in LAM than SKIN (P < 0.05). These differences suggest lower perfusion and increased glucose consumption in LAM compared with SUBLAM and SKIN. In conclusion, lamellar tissue microdialysis was well tolerated and may be useful for determining the contribution of energy failure in laminitis pathogenesis.

Continuous digital hypothermia initiated after the onset of lameness prevents lamellar failure in the oligofructose laminitis model.

REASONS FOR PERFORMING STUDY: Prophylactic digital hypothermia reduces the severity of acute laminitis experimentally but there is no evidence for its efficacy as a treatment once lameness has already developed. OBJECTIVES: To investigate the therapeutic effects of digital hypothermia, applied after the onset of lameness, in an experimental acute laminitis model. STUDY DESIGN: Randomised, controlled (within subject), blinded, experimental trial. METHODS: Eight Standardbred horses underwent laminitis induction using the oligofructose model. Once lameness was detected at the walk, one forelimb was continuously cooled (CRYO), with the other forelimb maintained at ambient temperature (NON-RX). Dorsal lamellar sections (proximal, middle and distal) harvested 36 h after the onset of lameness/initiation of cryotherapy were analysed by 2 blinded observers: laminitis pathology was scored (0 [normal] to 4 [severe]) and morphometric analyses performed. RESULTS: Median (interquartile range) histological scores were greater (P<0.05) in NON-RX (proximal 2.8 [2.5-4]; middle 3.5 [2-4]; distal 2.5 [2-3.8]) compared with CRYO limbs (proximal 0.5 [0.5-1.4]; middle 1 [0.6-1]; distal 0.75 [0.5-1]). There was complete physical separation of lamellar dermis from epidermis (score of 4) in 4 of the NON-RX feet at one or more section level(s), which was not observed in any CRYO sections. Histomorphometry was thus limited to sections that remained intact; there was a trend of increased total (TELL) and secondary (SELL) epidermal lamellar length and decreased secondary epidermal lamellar width (SELW) in NON-RX limbs compared with CRYO at all 3 levels; differences were significant (P<0.05) for SELL and SELW in the distal sections. CONCLUSIONS: Digital hypothermia reduced the severity of lamellar injury and prevented lamellar structural failure (complete dermoepidermal separation) when initiated at the detection of lameness in an acute laminitis model. This study provides the first evidence to support the use of therapeutic digital hypothermia as a treatment for acute laminitis.

Validation of a commercial enzyme immunoassay for detection of Clostridium difficile toxins in feces of horses with acute diarrhea.

BACKGROUND: Clostridium difficile infection (CDI) is a recognized cause of colitis in the horse. Identification of its toxins is important for management of individual cases and for prevention of transmission and zoonosis. In humans, CDI diagnosis is performed with enzyme immunoassays, none of which have been validated for horses. HYPOTHESIS/OBJECTIVES: (1) Establish which test for CDI diagnosis was more frequently used by diagnostic laboratories, (2) determine the identified test's performance, sensitivity, and specificity, and (3) validate its use in diarrheic horses. ANIMALS: Samples were obtained from 72 horses presented with acute diarrhea and hospitalized at the Ontario Veterinary College, University of Guelph. METHODS: A survey was conducted to establish which of the tests for CDI diagnosis in horses is most commonly used throughout North America. A questionnaire was sent to all laboratories registered in the Veterinary Infection Control Society and the American Association of Veterinary Laboratory Diagnosticians. The performance of the test was evaluated by comparison to a cell cytotoxicity assay (CTA), the accepted Gold Standard for C. difficile toxin detection. RESULTS: The Techlab C. difficile Tox A/B II ELISA was the most frequently used test. Compared with the CTA, no significant difference was observed, and a good level of agreement (93%) was obtained. The diagnostic performance of the ELISA test was adequate (84% sensitivity and 96% specificity). CONCLUSIONS AND CLINICAL IMPORTANCE: Results demonstrate that the Techlab C. difficile Tox A/B II ELISA is a reliable, adequate, and practical tool for identification of C. difficile toxins in horse feces.