# Incidence and Pathogenicity of Yersinia pseudotuberculosis and Yersinia enterocolitica in a Large Rhesus Macaque (Macaca mulatta) Colony (2000–2024)

## TL;DR

This study examines the occurrence and effects of two Yersinia species in a rhesus macaque colony over 24 years, finding Y. pseudotuberculosis to be more common and associated with severe disease.

## Contribution

The study provides the first long-term, comprehensive analysis of Yersinia infections in a large rhesus macaque colony.

## Key findings

- Y. pseudotuberculosis was the most common species, found in 75.2% of infected animals.
- Y. pseudotuberculosis was more frequently linked to systemic illness and clinical decline.
- Mortality rates were 23.7% for Y. pseudotuberculosis and 30.4% for Y. enterocolitica.

## Abstract

Comprehensive epidemiological reports on the incidence and pathogenicity of Yersinia spp., specifically Yersinia pseudotuberculosis and Yersinia enterocolitica, in rhesus macaques (Macaca mulatta) are not prevalent. Here we report findings from a retrospective analysis of microbial culture results, necropsy reports, and histology records collected over 24 years (2000–2024) in a large captive rhesus macaque colony at the Oregon National Primate Research Center (ONPRC). Findings are compared between animals infected with either Y. pseudotuberculosis or Y. enterocolitica to evaluate the prevalence of infection within the population and determine whether Y. pseudotuberculosis is more likely to be associated with systemic disease and higher mortality than Y. enterocolitica. Among 101 affected animals, Y. pseudotuberculosis was the predominant species (75.2%), followed by Y. enterocolitica (22.7%) and Y. kristensenii (2.0%). Overall mortality among animals with confirmed yersiniosis was 25.3%, with comparable mortality rates for Y. pseudotuberculosis (23.7%) and Y. enterocolitica (30.4%) infections. Y. pseudotuberculosis was most frequently associated with systemic illness, spontaneous death, or significant clinical decline. Overall, these findings emphasize the importance of continued surveillance and targeted management strategies to mitigate the impact of Yersinia infections in captive nonhuman primate colonies.