Prevalence of Corynebacterium ulcerans in cynomolgus monkeys for experimental use in Japan: retrospective analysis

Cynomolgus monkeys play an important role as experimental animals in the quality control of biologicals and in various areas of life science. We retrospectively surveyed cynomolgus monkeys that arrived at the National Institute of Infectious Diseases (NIID) for evidence of Corynebacterium ulcerans infection by measuring serum anti-diphtheria toxin titres. Serum samples from 527 monkeys, collected between 1969 and 2022, were analysed. Seropositivity varied depending on the year of arrival. The positivity rate started to increase in 1985, reached 64% in 1990, and then decreased to 0% in 2022, during which time the isolation of C. ulcerans , although nontoxigenic, from throat swabs continued. The seropositivity rate shifted independently of the anti-measles seropositivity rate, the latter of which suggests contact with humans. Therefore, transmission of C. ulcerans between humans and monkeys may not have followed the same human-associated transmission pattern as that of the measles virus. Nevertheless, regarding the potential impact of C. ulcerans infection on experimental results, more intensive monitoring is desired.