Diagnosing, Treating Equine Infections with Serum Amyloid A

Horse owners, take a moment and consider the following two scenarios:

Your horse isn’t quite right after coming home from a show on the weekend. It could be nothing, or he could be brewing an infection that puts all other infections to shame. Which is it?

Your horse is sick, and your veterinarian is doing everything possible to help. Is the treatment working? Will your horse pull through?

These situations are not foreign to many horse owners and could raise important yet difficult questions about a horse’s health.

“A stall-side test is now available to detect and monitor inflammation which, in turn, will help answer lingering questions about a horse’s illness,” noted Laura Petroski, B.V.M.S., a veterinarian at Kentucky Equine Research.

The test involves measuring a protein in the blood called serum amyloid A or SAA. Produced by the liver, this protein usually cannot be measured in healthy horses. In the face of infection or inflammation, the liver rapidly increases the production of this “acute-phase protein,” which helps combat both conditions.

“In fact, circulating SAA levels reportedly increase 100 to 1,000 times in as little as six hours in response to inflammation or infection,” said Petroski.

According a recent study*, SAA testing was once challenging to perform because samples had to be sent to a laboratory, a long turnaround time often negated the benefits of SAA testing, and the procedure was expensive. Now, stall-side or point-of-care tests not only measure SAA immediately but also indicate the underlying cause of the horse’s ailment.

Point-of-care testing uses whole blood, serum, or plasma, and the test provides immediate results. “This test allows a veterinarian to monitor a sick horse’s response to treatment, as SAA decreases as quickly as it increases when infection and inflammation resolve,” Petroski explained. “Repeated SAA testing allows a veterinarian to continue successful treatment strategies or alter the course of treatment if a horses fails to respond to therapy.”

Veterinarians should use the same sample type, preferably serum or plasma, for repeated samples on a single patient.

Joint disease, respiratory conditions, gastrointestinal disease, and other maladies often cause rapid increases in SAA. In some cases of respiratory disease, SAA testing can distinguish between different causes. For example, horses diagnosed with the equine influenza virus (the flu), equine herpesvirus-4 (EHV-4), and strangles all had different levels of SAA.

“Musculoskeletal and respiratory conditions occur commonly in horses. To maximize joint health, offer your horses a research-proven joint supplement, such KER•Flex and Synovate HA (Glucos-A-Flex in Australia). For respiratory health, supplement with marine-derived omega-3 fatty acids, like those  found in EO•3,” recommended Petroski.

*Schwartz, D., N. Pusterla, S. Jacobsen, et al. Analytical validation of a new point-of-care assay for serum amyloid A in horses. Equine Veterinary Journal. In press.