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EQUINE VETERINARY EDUCATION / AE / SEPTEMBER 2017


Highlights of recent clinically relevant papers


Geneti. c basis for atrial fibrillation This retrospective study by Megan Kraus and colleagues in


Canada set out to investigate the heritability of atrial fibrillation in Standardbred racehorses. A population of 204 atrial fibrillation cases were compared


to unaffected controls selected randomly from a group of racing peers competing within the 6 months prior to the case being admitted, giving a population of 1221 horses for heritability analysis. The overall heritability for atrial fibrillation


was 0.30 (0.04) on the underlying scale and 0.14 on the observed scale. Similar values were obtained when male


horses were assessed. Lower values of 0.24 (0.09) on the underlying scale and 0.09 on the observed scale were found in the female population. The overall heritability in pacers was


0.32 (0.05) on the underlying scale and 0.15 on the observed scale. Within the pacer group, the heritability values in males were again higher than in females. The low numbers of trotters in the study precluded estimates being given for this group. A small number of sires were found to have contributed


significantly to disease incidence over time. Five stallions in particular had six or more offspring in the affected population


and were themselves relatively closely related. Atrial fibrillation is moderately heritable in Standardbreds, with greater heritability in males and pacing horses.


Toxoplasmosis


In this case–control study, K. James and colleagues in the USA evaluated possible associations between Toxoplasma gondii seroprevalence and clinical signs of equine protozoal myeloencephalitis (EPM) in horses. Toxoplasmosis is not commonly considered a clinical


disease of equines, although previous seroprevalence studies have reported differing background rates of T. gondii infection in horses globally. In this study, 720 Californian horses with neurological signs compatible with EPM were compared to healthy, non-neurologic horses for the presence of T. gondii antibodies (using indirect fluorescent antibody tests). T. gondii seroprevalence among cases and controls was determined at standard serum cut-offs: 40, 80, 160, 320 and 640. At a T. gondii titre cut-off of 320, horses with clinical signs


compatible with EPM had 3.55 times the odds of a seropositive test compared to those without clinical signs when adjusted for covariates. When restricted to the autumn season and at the same titre cut-off, an EPM suspect horse had 6.4 times the odds of testing seropositive to T. gondii, compared to non-neurologic horses. The association between high T. gondii titres and clinical signs compatible with EPM is potentially reflective of toxoplasmosis in equines.


The authors suggest that serological testing of cerebrospinal fluid and isolation of T. gondii in EPM suspect cases should be considered and that future studies investigating the relationship between T. gondii and EPM are warranted.


Detection of pneumothorax


In this prospective, experimental study Jessica Partlow and colleagues compared the results of thoracic ultrasonography and radiography for the detection of induced small volume pneumothorax.


© 2017 EVJ Ltd Small volume pneumothorax can be challenging to


diagnose in horses. Standing thoracic radiography is currently the standard method for diagnosis. The authors hypothesised that thoracic ultrasonography would be more sensitive and aimed to describe a thoracic ultrasound method for detection of small volume pneumothorax in horses, comparing results of radiography and ultrasound in a sample of horses with induced small volume pneumothorax. Six mature healthy horses were recruited. Five 50 mL air boluses were sequentially introduced via a teat cannula into the pleural space of each horse. Lateral thoracic radiographs and standardised ultrasound (2D and M-mode) examinations of both hemithoraces were performed following administration of each 50 mL air bolus. Four independent investigators who were unaware of treatment status analysed radiographs and ultrasound images/videos for detection of pneumothorax. Sensitivity, specificity, positive predictive values, negative predictive values, and agreement among investigators (Kappa test, j) were calculated for radiography, 2D and M-mode ultrasound. Comparisons were made using a chi-squared exact test with significance set at P<0.05. Two- dimensional (84%) and M-mode (80%) ultrasound were more sensitive than radiography (48%) for pneumothorax detection (P = 0.02 and P = 0.04, respectively). Specificity and positive predictive values were similar for all three imaging modalities (P = 1). Agreement between investigators for pneumothorax detection was excellent for 2D ultrasound (j = 1), very good for M-mode ultrasound (j = 0.87), and good for radiography (j = 0.79). Findings from this study supported the use of thoracic ultrasonography as a diagnostic method for detecting pneumothorax in horses.


Septic arthritis of the coxofemoral joint In this retrospective clinical study Francina Barcel


o Oliver and


colleagues in the UK and Australia described the clinical signs, surgical treatment and outcome of septic arthritis of the coxofemoral joint in 12 foals. Lameness was localised to the coxofemoral joint based


on physical examination. Sepsis was confirmed by cytological analysis of synovial fluid obtained under ultrasonographic guidance, during general anaesthesia or standing sedation. Intra-articular analgesia was used as an additional diagnostic modality in two foals. Surgical lavage of the affected joint was performed via arthroscopy or needle lavage. Seven foals underwent repeated lavage. Synovial fluid contained 4.4 to 173 9 109/L white blood cells


(WBCs), and 38–63 g/L total protein. Cultures were positive in 10/12 foals. Isolated organisms included Salmonella spp., Streptococcus spp., Rhodococcus spp., Enterococcus spp., Escherichia spp., Staphylococcus spp., Acinetobacter spp., Methicillin-resistant Staphylococcus aureus and Bacillus spp. Ten foals were discharged from hospital (83%): one was subjected to euthanasia 15 days later due to chronic intestinal salmonellosis and renal failure, and nine foals survived with no residual lameness detected 1 year after hospital discharge. The authors concluded that a combination of arthroscopic


lavage and the use of systemic and local antimicrobials is an effective treatment for sepsis of the coxofermoral joint.

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