Protein may help diagnose septic arthritis

Last summer, I was involved in researching a protein called serum amyloid A (SAA) that may help veterinarians reach a proper and early diagnosis of joint infection — a severe and potential life-threatening illness in horses.

Infected joints (septic arthritis) is a particular problem in Saskatchewan, mainly because of the widespread use of barbed wire that’s often the culprit behind puncture wounds and cuts.

This project is extremely interesting to me: as a longtime horseowner and former 4-H member, I know how important it is to have a sound, healthy horse.

Once I graduate from the Western College of Veterinary Medicine (WCVM) in 2014, I want to become a large animal veterinarian with a focus on horses. Throughout my career I expect to see a number of joint disease cases, and this project has helped me to understand what I will be facing.

When a joint makes communication with the outside world through a puncture wound or cut, bacteria have potential to enter and cause infection. Veterinarians currently diagnose infected joints by using unspecific markers such as total protein and cell counts.

But the problem is that these methods don’t allow the general practitioner to confirm if the joint is infected or simply inflamed.

Serum amyloid A is a main acute phase protein in the horse that might be more specific to sepsis when measured in synovial fluid. When veterinarians examine a horse with septic arthritis, they flush out and clean the joint with saline (arthroscopic lavage). But what no one knows is whether the lavage affects the SAA levels in the joint.

If SAA levels are not affected by this procedure, the protein could then be used as a diagnostic tool.

“SAA could then be used as a specific marker for the diagnosis of septic arthritis as total protein and cell counts do increase with lavage,” explains Dr. Andres Sanchez, a surgical resident at the WCVM.

I helped Sanchez test his theory during the summer of 2013 with the support of equine surgeon Dr. Joe Bracamonte, my supervisor. We took a fluid sample by inserting a needle in the middle knee joints of six horses and then collected a fluid sample once a day for five days.

The horses were split into two groups. Sanchez simply took a joint sample from horses in the control group, but for horses in the treatment group, he flushed out their joints with saline before collecting the samples. Afterwards, we measured SAA, total protein and the nucleated cell count (NCC) in all of the joint samples.

A 2009 graduate of the veterinary school at Argentina’s National University of Central Buenos Aires, Sanchez first became interested in SAA after reading a few scientific articles about the protein and its involvement in inflammation and infection.

During his Master of Science program at the University of Pretoria in South Africa, he and his colleagues examined if SAA levels in synovial (joint) fluid increased after repeated injections of amikacin in to the joint. Amikacin is a common antibiotic used to treat septic joints.

What they found was that although total protein and cell counts increased with these joint injections, SAA levels did not. This confirmed that SAA can still be used as a marker for septic arthritis even after antibiotics are used.

Through his current research on SAA levels with lavage, Sanchez hopes to make it that much easier for veterinarians to diagnose septic arthritis even after aggressive treatment.

If our research project confirms that SAA does not increase with lavage, “it could give us a definite answer to whether sepsis is present and a better idea of the prognosis,” says Sanchez.

Monica Schott of Warren, Man., is a fourth-year veterinary student who was the WCVM Equine Health Research Fund’s undergraduate summer research student in 2013. Visit WCVM Today to read more WCVM-related animal health news.