Re-emergence of equine glanders in Mongolia based on region-wide serosurveillance

Glanders, a zoonotic disease caused by <i>Burkholderia mallei</i>, has re-emerged in Mongolia after decades of control. We conducted nationwide serosurveillance from 2021 to 2024 to assess the prevalence and geographic distribution of glanders. Using random 3-stage cluster sampling, we collected 3,001 horse serum samples from 332 herds. Those herds were in 46 soums (administrative districts equivalent to counties) in 13 provinces and in 3 districts in Ulaanbaatar. Sera were tested using the complement fixation test, and positive results were confirmed by immunoblotting and ELISA. Overall seroprevalence was 1.03% (95% CI: [0.7, 1.5]), with positive cases detected in 69.2% of provinces, 34.8% of soums, and 7.2% of herds. The highest prevalence was in the eastern region (2.5%), particularly in Sukhbaatar province (4.5%). None of the seropositive horses had clinical signs of infection. Compared with the 0.19% seroprevalence found in the 2011 nationwide surveillance program, our finding of a 5-fold increase (1.03%) indicates a resurgence of glanders. The likely drivers include reduced veterinary oversight and unrestricted equid movement for racing and breeding. Geographic and environmental factors may also influence transmission. Our results underscore the need for continued surveillance, movement control based on laboratory testing, and increased awareness among herders to prevent the further spread of glanders in Mongolia.