Evaluating Joint Infections Using SAA Levels (AAEP 2012)

Joint infections are a serious occurrence in horses with the potential to end an athletic career or even a life. Although survival rates are as high as 62% in foals and 85% in adults, only 48-66% of horses return to previous athletic activity after a joint infection.

“A successful outcome requires early and aggressive treatment, including the intra-articular injection of a suitable antibiotic such as amikacin,” said Andres Sanchez Teran, Vet MSc, of the University of Pretoria’s Department of Companion Animal Clinical Studies, in South Africa (though he’s currently at the Western College of Veterinary Medicine, University of Saskatchewan, Canada). Since there’s no reliable way to determine if treatment is working, Sanchez Teran and his colleagues in Pretoria set out to find one, and he presented the results during the 2012 American Association of Equine Practitioners’ Convention, held Dec 1-5 in Anaheim, Calif.

This inability to monitor joint infections negatively impacts a horse’s chance for survival or function. Scientists know that cells lining the inside of the joint produce a protein called serum amyloid A (SAA), and SAA levels increase in cases of infection. More importantly, SAA levels in synovial (joint) fluid do not increase following routine joint injections the way total protein and total nucleated cell counts (NCCs) do.

“This means that SAA could be a better marker of joint infection (than total protein and other cell counts that are currently used),” explained Sanchez Teran.

To test this hypothesis, Sanchez Teran and colleagues collected synovial fluid by inserting a needle into the middle knee joints of five horses every two days for a total of five times. In the control group the team simply collected a fluid sample, and in the treatment group they injected the antibiotic amikacin after collecting the fluid. They measured SAA, total protein, and NCC in all samples.

The team’s key findings were:

  • As expected, total protein and NCC increased significantly after the first joint injection;
  • In some cases, the protein and NCC levels were so elevated they reached the point that would be expected in infected joints; and
  • Synovial fluid SAA levels did not increase in either group of horses.

“Because SAA levels in synovial fluid are not affected by the process of inserting a needle or administering amikacin into a joint, SAA could potentially be used to monitor response to treatment following administration of amikacin into the joint,” concluded Sanchez Teran.

He added, “For example, this means that if SAA levels are elevated in infected joints, the SAA levels would be expected to drop as the infection resolves.”

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.