Airway Hyperresponsiveness, but Not Bronchoalveolar Inflammatory Cytokines Profiles, Is Modified at the Subclinical Onset of Severe Equine Asthma

Airway hyperresponsiveness (AHR) and inflammation are both observed in human and equine asthma. The aim of this study was to assess the timeline and relationship of both features at the subclinical onset of severe equine asthma (SEA). First, the repeatability of the pulmonary function test (PFT) using impulse oscillometry system, and the methacholine bronchoprovocation test (BPT) were assessed at a 1-day interval on six SEA horses in clinical remission and six control horses. Then, clinical and ancillary tests were performed before and after a 1-week low-dust environmental challenge, including weighted clinical score, respiratory endoscopy, bronchoalveolar fluid cytology, PFT, and BPT. Both PFT and BPT showed acceptable repeatability. No test allowed SEA horses in clinical remission to be distinguished from control, unlike in human patients. Because of the low-dust environment, no significant difference was observed in the results of clinical and conventional ancillary examinations after the challenge. However, SEA horses showed increased AHR after the environmental challenge. At that stage, no signs of inflammation or changes in pro-inflammatory cytokines profiles (quantification and gene expression) were observed, suggesting AHR is present at an earlier stage of equine asthma than airway inflammation. This feature indicates SEA could present in a different disease pathway than neutrophilic human asthma.

In vitro virucidal activity of nebulized citrate-complexed silver nanoparticles against equine herpesvirus-1 and murine norovirus

Viruses can be involved in respiratory disorders in horses, with limited therapeutic options. Citrate-complexed silver nanoparticles (C-AgNP) have shown bactericidal properties after in vitro nebulization. The aim of the present study was to assess the virucidal activity of C-AgNP after in vitro instillation or nebulization on equine herpesvirus-1 (EHV-1) and murine norovirus (MNV), the latter used as surrogate for small non-enveloped viruses. Both viruses were instilled or nebulized with C-AgNP of increasing concentrations, and titres were determined via TCID₅₀ method. We demonstrated efficient inactivation of enveloped EHV-1 following instillation and nebulization of C-AgNP (infectivity losses of ≥ three orders of magnitude). While tenacious MNV was inactivated via 2000 ppm C-AgNP instillation, nebulized C-AgNP did not lead to reduction in MNV titres. Nebulization of C-AgNP may represent a novel virucidal therapeutic approach in horses. Further investigations are needed to assess its safety and effective concentrations for in vivo use.

Measuring heart rate variability using a heart rate monitor in horses (Equus caballus) during groundwork

Measuring physiological parameters of stress in horses during groundwork, for example when involved in equine-assisted interventions, is important to gain insight into the stress levels of the horses. Heart rate and heart rate variability can be used as physiological indicators of stress in horses. Heart rate monitors could be easily incorporated into practice, as they are not expensive and easy to use. However, it is questionable whether heart rate monitors present accurate heart rate variability results in exercising horses, similar to electrocardiograms. The aim of this study was to determine the accuracy of heart rate monitors for the assessment of heart rate variability in horses during groundwork exercise. Simultaneous telemetric electrocardiograms (Televet) and heart rate monitor (Polar H10 transmitter and M430 receiver, Hylofit electrodes) recordings were performed on 28 horses (15 mares and 13 geldings). Results indicate that the heart rate monitor accurately determined heart rate and time-domain heart rate variability parameters when compared to electrocardiograms during both baseline and groundwork conditions. As expected, heart rate significantly increased and the heart rate variability significantly decreased during groundwork compared to baseline conditions. This indicates that the heart rate monitor can be used to accurately determine heart rate variability during groundwork.

Accuracy of a heart rate monitor for calculating heart rate variability parameters in exercising horses

Heart rate is evaluated in exercising horses to monitor the level of fitness to exercise, and it is usually acquired using heart rate monitors (HRM) or telemetric electrocardiograms (ECG). While HRM are commonly available and easy-to-use for horse's owners, ECG is a more expensive equipment requiring user's experience. Interest for heart rate variability (HRV) in horses is increasing for both research and clinical purposes. HRV is usually calculated from interbeat intervals (IBI) obtained by ECG. The aim of this study was to determine the accuracy of an HRM to detect IBI for the calculation of HRV in both resting and exercising horses. Simultaneous ECG and HRM recordings were performed on 13 horses and ponies under normal training conditions for at least 45 minutes. IBI from ECG were corrected using a dedicated software. IBI from HRM were exported without correction. Two HRV-parameters were calculated on both recordings for resting and exercising periods: the standard deviation of R-R intervals (SDRR) and the root mean square of successive differences (RMSSD). Agreement and concordance between the two systems were determined using Bland-Altman plot and Lin's correlation coefficient, respectively. Effects of variables were consequently assessed. For both HRV-parameters during resting and exercising periods, the means of the differences between the two systems were lower than 0.47 ms with a correlation coefficient higher than 0.999. Height, weight and body condition score had no effect on the results. The studied HRM could be of interest as easy-to-use device for obtaining HRV-parameters SDRR and RMSSD in resting and exercising horses.

Evaluation of the Bactericidal Effect of Nebulized Silver Nanoparticles on Common Respiratory Bacteria in Horses- In Vitro Studies

Antimicrobial resistance is increasing in both human and veterinary medicine. Bacteria can be part of the etiology of respiratory disorders in horses. Bactericidal activity of silver has been largely described and silver is currently used in veterinary therapeutic applications such as wound dressings. The aim of this study was to assess the in vitro bactericidal effects of nebulized silver nanoparticles (AgNP) on 2 common equine respiratory bacteria, Streptococcus equi subsp. zooepidemicus and Actinobacillus equuli subsp. equuli. Firstly, antimicrobial susceptibility of AgNP was determined over time by turbidity assessment in liquid broth. Secondly, bacterial growth inhibition was tested after instillation or after nebulization of low (100 ppm) and high (500, 1,000 and 2,000 ppm) concentrations of AgNP on agar plate. Both bacteria were susceptible to AgNP, even at dilution 1:4 for A. equuli and 1:8 for S. zooepidemicus after 8 hours of incubation, and 1:256 for both bacteria after 24 hours of incubation. The bacterial growth was partially inhibited at low concentration and completely inhibited at high concentrations of instilled AgNP. The bacterial growth was completely inhibited after nebulization of low concentrations of AgNP for A. equuli and high concentrations of AgNP for S. zooepidemicus. We concluded nebulized AgNP could be a candidate for innovative therapeutic way against bacterial respiratory disorders in horses. Nevertheless, further investigations are required to assess the in vivo potential and toxicity of nebulized AgNP.

Prevalence of respiratory pathogens in nasal swabs from horses with acute respiratory disease in Belgium

Contagious respiratory infections are an important cause of respiratory disease in horses, resulting in impaired pulmonary function, poor performance and sometimes severe illness. Although bacterial infections are often suspected to be involved, viruses are frequently overlooked and are an underestimated cause of respiratory disease outbreaks in horses. In this study, nasal swabs of 103 horses with acute symptoms of respiratory disease were analyzed for the presence of 13 different respiratory pathogens. Gamma herpesviruses were the most commonly detected, with 60% of the samples being positive, followed by streptococcus equi subsp. zooepidemicus infection (30%). Rhinovirus B, streptococcus equi subsp. equi, adenovirus 1 and EHV-4 were more rarely detected. Further research is necessary to correctly interpret the importance of gamma herpesviruses in horses, for example by screening a healthy control population. National surveillance of respiratory viruses in horses by PCR analysis on nasal swabs might be a useful, earlywarning system for viral epidemics.