Influenza A viruses (IAVs) have a main natural reservoir in wild birds. IAVs are highly contagious, continually evolve, and have a wide host range that includes various mammalian species including horses, pigs, and humans. Furthering our understanding of host-pathogen interactions and cross-species transmissions is therefore essential. This review focuses on what is known regarding equine influenza virus (EIV) virology, pathogenesis, immune responses, clinical aspects, epidemiology (including factors contributing to local, national, and international transmission), surveillance, and preventive measures such as vaccines. We compare EIV and human influenza viruses and discuss parallels that can be drawn between them. We highlight differences in evolutionary rates between EIV and human IAVs, their impact on antigenic drift, and vaccine strain updates. We also describe the approaches used for the control of equine influenza (EI), which originated from those used in the human field, including surveillance networks and virological analysis methods. Finally, as vaccination in both species remains the cornerstone of disease mitigation, vaccine technologies and vaccination strategies against influenza in horses and humans are compared and discussed.

Equine herpesvirus type 1 (EHV‐1) and type 4 (EHV‐4) have a worldwide distribution and cause respiratory disease, abortion, neonatal death and myeloencephalopathy in susceptible horses. Given the scarcity of serological EHV‐1/EHV‐4 data in Spain, the objective of this cross‐sectional study was to estimate the seroprevalence of EHV‐1/EHV‐4 and to identify potential horse‐level and stud farm‐level factors associated with EHV‐1/EHV‐4 in the breeding Spanish Purebred (SP) horse population in central Spain. Serum samples from 334 SP unvaccinated horses, collected between September 2011 and November 2013 at 30 stud farms, were tested using a commercially available EHV‐1/EHV‐4 antibody ELISA and seroneutralisation as the World Organisation for Animal Health reference confirmation test. Data on factors putatively associated with seropositivity to EHV‐1/EHV‐4 were collected via a questionnaire and examined using logistic regression analysis. EHV‐1/EHV‐4 seroprevalence in the SP breeding population in central Spain, standardised for the sex distribution of the reference horse population, was 53.9 per cent (95 per cent confidence interval 44.0 per cent to 63.8 per cent). Increasing age, southern location of the stud farm, temperate climate during the summer, and a smaller surface area used for breeding activities in the farm were associated with increased odds for EHV‐1/EHV‐4 seropositivity, whereas EHV‐1/EHV‐4 vaccination of other resident horses and separation of breeding mares from youngsters were protective factors.

Repeated exposure to water treadmill (WT) exercise could elicit kinematic responses reflecting adaptation to WT exercise. The study’s aim was to compare the responses of a group of sport horses to a standardised WT exercise test (WT_SET) carried out at three time points, week 0 (n = 48), week 20 (n = 38), and week 40 (n = 29), throughout a normal training programme incorporating WT exercise. Horses were recruited from the existing client populations of two commercial water treadmill venues for the purpose of this longitudinal, observational study. Limb, back, poll, wither, and pelvic kinematics were measured during the WT_SET using videography, optical motion capture, and inertial motion sensors. Forelimb and hindlimb protraction increased (p < 0.001 for both), and forelimb and hindlimb retraction decreased (p < 0.001 for both) at week 40 compared to week 0. Caudal thoracic flexion–extension and lateral bend ranges of movement were greater at week 40 compared to week 0 (p < 0.001 and p = 0.009, respectively). Increased training speed was associated with increased craniocaudal poll movement (p = 0.021), decreased forelimb protraction (p = 0.008), and increased forelimb retraction (p = 0.021). In addition to characteristic changes in kinematics due to increasing water depth, regular WT exercise resulted in kinematic adaptation to movement in water. Factors such as the frequency of WT sessions and the type of session used with respect to depth and speed were seen to influence the nature of the adaptation. The results suggest that WT exercise sessions could be designed in accordance with specific training goals when used within a normal sport horse training programme.

Equine influenza (EI) is a fast-spreading respiratory disease of equids caused by equine influenza A virus (EIV), often resulting in high morbidity and a huge economic impact on the equine industry globally. In this cross-sectional study to determine the seroprevalence of EI and its associated risk factors, sera from 830 horses bled on a single occasion in Northwest Nigeria between October 2019 and January 2020 were screened for antibodies to A/equine/Richmond/1/2007 (H3N8) using the single radial haemolysis (SRH) assay. Antibodies were detected in 71.3% (592/830, 95% CI: 68–74%) of horses (SRH area ≥ 0.5 mm²). Although there were statistically significant univariable associations between seropositivity and age, sex, breed, purpose and coat colour, only age remained significant when included with each of the other variables in bivariable analyses. There was a clear trend for increasing odds of seropositivity with increasing age: OR 1.6, 95% CI: 1.05–2.40 (p = 0.03) for 5–14-year-olds and OR 8.13, 95% CI: 2.75–24.1 (p < 0.001) for ≥15-year-olds compared to horses 150 mm², considered sufficient to protect against clinical disease and virus shedding. Comparative screening of a subset of the horses (n = 118) with a 2019 H3N8 virus (A/equine/Worcestershire/2019) revealed a significantly greater seropositivity (p = 0.0001) than A/equine/Richmond/1/2007 consistent with exposure of the population during a widespread outbreak of EI in the region in 2019. In conclusion, there was an insufficient level of protection against EI in the region and introduction of a vaccination programme with vaccines containing recently circulating virus is recommended to mitigate against further outbreaks of EI in Nigeria.

Background: Strangles ( Streptococcus equi infection) remains endemic in the UK, with ~300 laboratory diagnoses annually. Sub‐clinically infected long‐term carriers are considered a key driver of endemicity. Analysing genomes of circulating strains could provide valuable transmission insights of this pathogen. Objectives: To determine the population structure and diversity of UK S. equi isolates and to model transmission using epidemiological and whole genome sequencing data. Study Design: Retrospective cross‐sectional epidemiological and genomic surveillance. Methods: A dated phylogenetic tree derived from 511 S. equi isolates collected from UK horses between 2015 and 2022 was reconstructed. Bayesian Analysis of Population Structure (BAPS) identified clusters of related genomes, while iGRAPH identified clusters of sequences appropriate for transmission analysis, performed using Transphylo. Results: BAPS identified nine groups, with 82% of strains clustering into two (McG‐BAPS3, McG‐BAPS5). A statistically significant association ( p < 0.001) was found between the year of recovery and trends in the frequency of McG‐BAPS groups, with McG‐BAPS3 increasing and McG‐BAPS5 decreasing in prevalence over the study period. Eight transmission clusters encompassing 64% of total sequences ( n = 286/447) underwent analysis. Sixteen direct transmission pairs were identified; 10 were between horses from different UK regions. A transmission chain extending over a 6‐month period was inferred from isolates from nine horses. Main Limitations: Bacterial strains from sub‐clinically infected carrier horses may be underrepresented due to data collection via positive laboratory diagnoses. Furthermore, a low sampling proportion relative to overall UK cases provided only a snapshot of broader, unsampled transmission events. Conclusions: The rapid change in S. equi population structure indicates acutely infected/recently convalesced short‐term carrier horses play a more influential role in transmission than long‐term carriers. Our work provides novel insights to our understanding of S. equi transmission dynamics. Transmission of genetically related strains across diverse regions suggests a real‐time sequence‐based surveillance system could inform interventions to minimise transmission.

Water treadmill (WT) exercise has become a popular tool for equine training and rehabilitation. However, few studies describe the long-term effects of WT exercise in low water on muscle development (MD). This study’s objectives were to compare MD changes over a 40-week period in sport horses that regularly used WT in low water within training (Group WTH, n = 55) and a control group that did not (control, n = 28). Subjective MD assessments were undertaken using an adaptation of a previously published method at weeks 0, 20 and 40. For Group WTH, MD significantly increased in the neck, pelvis and hindlimb adductor and abductors between weeks 0 and 20. Neck, thoracic, thoracic trapezius, lumbar, pelvis, quadriceps, hindlimb adductor and abductor, and hamstring musculature increased between weeks 0 and 40. Thoracic musculature only increased between weeks 20 and 40 (p ≤ 0.001 for all). In the control horses, MD did not significantly change between weeks. Regular WT exercise appears to increase MD, particularly for musculature used to create movement patterns seen on the WT. WTs may be appropriate for use under veterinary guidance as part of a directed rehabilitation/training programme to increase core and hindlimb MD.