"Right now the gold standard treatment is when we get these horses they go for an arthroscopic lavage," says Dr. Joe Bracamonte, a specialist in large animal surgery at the WCVM. "They go into surgery under general anesthesia and we stick a camera into the joint and then profusely lavage the joint."
But after the initial arthroscopic lavage, 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, equine patients often require aggressive antibiotic therapy. 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," says Bracamonte. "It could tell us whether our aggressive treatment … is working and ideally tell us when the bacterial infection is gone."
During his surgical career, Bracamonte has worked on a number of septic arthritis cases and has experienced the frustration of not knowing when to stop treatment on his patients.
"Septic joints have always been an interest for me — probably because my case load when I was resident was huge on septic joints," says Bracamonte, who is leading a new septic arthritis investigation with financial support from the Mark and Pat DuMont Equine Orthopedics Research Fund.
In previous research, 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 diagnosis 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, 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.
To do this, Bracamonte's research team is comparing horses with experimentally-induced septic arthritis to healthy horses and those with joint inflammation without any infections. Each horse receives the gold standard treatment for septic arthritis: arthroscopic lavage, several regional limb perfusions and a four-week course of antibiotics.
At specific time points during treatment, the researchers take samples of joint fluid from the horses for analysis. Specifically, the WCVM team is using proteinomics analysis and mass spectrometry to identify a potential biomarker.
"It is cutting-edge technology [that] we will use to look at protein profiles," says Bracamonte, whose team includes researchers from the University of Saskatchewan and University of Liverpool as well as the Vaccine and Infectious Disease Organization-International Vaccine Centre (VIDO-InterVac).
In addition, the researchers will attempt to grow bacteria from the samples of joint fluid and perform real-time PCR (polymerase chain reaction), a method used to detect bacterial DNA. The team will use their results to follow the resolution of the infection in the joint and to determine when the infection has been eliminated.
Next, they will look for patterns in the protein profiles that correlate well with joint infection and resolution. 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," says 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.
Ultimately, Bracamonte hopes his research work will provide veterinarians with an accurate tool for determining when a horse's joint is finally infection-free — and some peace of mind for horse owners.
Hayley Kosolofski of Sherwood Park, Alta., is a fourth-year veterinary student at the Western College of Veterinary Medicine (WCVM).