A case control study of factors and infections associated with clinically apparent respiratory disease in UK Thoroughbred racehorses.

This study was conducted to identify infections and other factors related to visible respiratory illness in young racehorses in the UK. The findings revealed that younger horses and those newer to training were at greater risk of visible respiratory disease, with various bacteria linked to higher risks of illness.

Overview of the Research Methodology

• This investigation was conducted using a matched case-control study, an observational method that analyzes two existing groups differing in outcome to identify factors associated with the variation.
• The study involved a total of 170 cases, defined as horses showing sudden coughing, nasal discharge, or fever. These cases were matched with 632 unaffected controls based on their trainer and time period.
• The parameters tested included age, sex, period since admission into the training yard, time since last race, and various tracheal and nasopharyngeal (NP) bacterial and viral infections.
• Advanced statistical techniques (multivariable conditional logistic regression modelling) were used to measure the risk of the studied variables after adjusting for other factors.

Key Outcomes and Findings

• Younger horses and those that started their training recently were found to be at higher risk of presenting with visible respiratory disease.
• Among infections, the number of Pasteurella/Actinobacillus spp. bacteria found in tracheal washes proportionally impacted the risk of clinical disease.
• The study noticed a relationship between Streptococcus zooepidemicus tracheal infection with both visible respiratory disease and latent Inflammatory Airway Disease (IAD). However, no correlation was observed between study cases and S. zooepidemicus when all controls were involved, due to the former connection.
• The presence of Mycoplasma felis was also associated with visible disease after adjusting for other parameters.

Infections & Disease Risk

• An inverse association was found between Staphylococcus and Acinetobacter spp., transient non-pathogenic bacteria, and the risk of clinically apparent disease.
• No significant association was observed between visible disease and equine herpesviruses-1 and -4, rhinoviruses-1 and -2 or adenovirus infections.
• Although equine influenza showed correlation with visible respiratory disease, it was seldom seen in this well-vaccinated population.

In summary, this research provides essential information regarding the conditions that increase the risk for developing respiratory diseases in racehorses, useful knowledge for trainers and handlers to manage and prevent outbreaks efficiently.