Septic arthritis, a debilitating disease caused by a bacterial infection in a horse’s joint, requires immediate and aggressive treatment when diagnosed. Currently, the standard treatment is arthroscopic lavage, a procedure in which fluid is injected into the joint to wash out debris or infection.

But after the initial procedure, the course of treatment becomes less clear. The clinical team may need to flush the infected joint repeatedly or perform a procedure that delivers high concentrations of antibiotics to a horse’s leg (regional limb perfusion).

In most cases, aggressive antibiotic therapy is required. But these drugs can cause side effects, such as diarrhea, and long-term exposure can play a role in antibiotic resistance.

What makes therapy even more challenging is that there’s no reliable way to establish when the infection has been eliminated and when treatment can be stopped. “What we want to do is identify a marker that we can use in the monitoring process,” said Dr. Bracamonte, a specialist in large animal surgery at the Western College of Veterinary Medicine. “It could tell us whether our aggressive treatment is working and, ideally, tell us when the bacterial infection is gone.”

In previous research, Dr. Bracamonte has identified a potential protein marker called serum amyloid A (SAA). He and his research team demonstrated that this protein was not affected after arthroscopic lavage or after repeated through-and-through lavage. In comparison, the traditional markers used to diagnose and monitor the response to treatment of horses with septic joints all increased with these procedures. This means that SAA has the potential to be used as an ideal marker of joint infection.

In his new study, Dr. Bracamonte wants to take this concept one step further and monitor changes in SAA and other proteins in joint fluid over the course of treatment for septic arthritis. The ideal marker should increase with joint infection, but it should also decrease to normal levels as the infection resolves.

Ultimately, the team’s goal is to identify a protein that could be a reliable indicator of whether or not bacteria are present in the joint. “If we are able to find that protein, there would be benefits for not only the horse, but for the owner too,” said Dr. Bracamonte. “We could accurately know when the infection is eradicated, see if our treatment is actually working, adjust our treatment, and most importantly, we could reduce exposure to long-term antibiotics.”

Once a protein is identified, the next step is to develop a stall-side test for veterinarians. The test could detect the presence of the protein marker to help practitioners determine if there is infection present in the joint and then guide their therapy.