That’s why it’s crucial to determine whether a respiratory issue is infectious as early as possible once clinical signs are observed. And there’s good news on this front: Researchers from the University of California, Davis, recently determined that a simple stall-side test could help veterinarians determine whether a horse should be quarantined to prevent disease spread or if he’s suffering from a noninfectious disease.
Molly Viner, a veterinary student at the University of California, Davis, School of Veterinary Medicine, and colleagues set out to measure the inflammatory biological marker serum amyloid A (SAA) in horses with both kinds of illness to determine if a stall-side test could help practitioners differentiate between the two. She presented her findings at the 2016 American Association of Equine Practitioners Convention, held Dec. 3-7 in Orlando, Florida.
Inflammatory Markers and SAA 101
Many small biologic proteins in the body mediate the inflammatory process. These inflammatory proteins can be localized, such as at a site of injury, or they can be systemic—found throughout the body—as in the case of illness. As the name suggests, acute-phase proteins such as SAA increase or decrease acutely in response to inflammation. SAA is undetectable in healthy horses, but increases within six to 12 hours in response to inflammation. SAA can increase up to 1,000-fold in response to inflammation during peak response. Once SAA reaches its peak, it subsequently decreases in concentration by half within 30 minutes to two hours.
SAA in Infectious vs. Noninfectious Disease
Viner and colleagues set out to evaluate horses’ SAA response to infectious and noninfectious respiratory disease using a stall-side test. The common respiratory illnesses they studied included inflammatory airway disease, equine herpesvirus-4, equine influenza, and strangles. The team also tested healthy controls. They measured SAA in whole blood, serum, or plasma samples using a commercially available handheld reader.
They found that SAA was significantly higher in horses with viral and bacterial disease compared to healthy controls and horses with inflammatory airway disease, the latter of which is not caused by infection. However, there was no difference between horses with viral disease and bacterial disease.
Horses with IAD had much lower SAA concentrations than horses with infectious respiratory disease, the latter group having moderate to high SAA levels. The stall-side assay was reliable for differentiating between noninfectious and infectious respiratory disease, which should facilitate decisions regarding quarantining sick horses, said Viner.