Naturally occurring inflammatory arthritis of the spondyloarthropathy variety in Cayo Santiago rhesus macaques (Macaca mulatta).

The establishment of an animal model is a major priority in the battle to control inflammatory arthritis. Exploration to date has not yet identified a viable model for rheumatoid arthritis (RA), while artificial (e.g., collagen-induced) models do not seem to accurately represent RA. They, at least superficially, resemble human spondyloarthropathy. This study assesses the evidence for a common naturally-occurring spondyloarthropathy in a colony of free-ranging rhesus macaques.Skeletal elements of 275 Macaca mulatta of known age and troop affiliation from the Cayo Santiago colony [Caribbean Primate Research Center (CPRC)] were surveyed for the presence of spondyloarthropathy and osteoarthritis. Fisher exact tests established the independence of each pathological condition, age, sex, troop and specific joint.Spondyloarthropathy was evident in 10% of females and 7% of males. In surviving troops, its frequency in 82 animals over 8 years of age was 20%. The skeletal distribution of spondyloarthropathy was independent of troop membership. Osteoarthritis affected 20% of females and 4% of males and was independent of their troop. Significant differences in the frequencies of specific joint involvement were found when the natural model, particularly in the polyarticular subgroup, was compared to the collagen-induced model.Naturally-occurring spondyloarthropathy afflicts 20% of susceptible-aged individuals in surviving macaque troops at the CPRC. This phenomenon appears to present a unique natural model for the characterization of the genetic, immunological and environmental contributions to this disease, which afflicts 0.5-5% of the human population. This natural model would appear to supplant the need for the collagen-induced large animal model.