Contagious equine metritis (CEM) in Icelandic horses
Contagious equine metritis (CEM) in Icelandic horses – results of a screening programme in 2021
In a project funded by the Horse Levy Foundation, University of Copenhagen and Statens Serum Institut (SSI) aimed to follow up an outbreak in 2020 of CEM in Icelandic horses. After having optimized methods for culture of samples, we encouraged owners of Icelandic horses used for breeding to screen their horses for the causative bacterium, Taylorella equigenitalis. This resulted in a total of 2703 samples from Icelandic horses being sent to the diagnostic laboratory at SSI during 2021. A total of 53 samples (2%) were PCR-positive for T. equigenitalis. Subsequent culture of these and follow-up samples from PCR-positive horses resulted in isolation of 38 T. equigenitalis isolates. Whole-genome sequencing revealed that the vast majority (n=34) of these isolates belonged to the genetic type ST74, which also caused the CEM outbreak in 2020. Remaining isolates belonged to two distinct genetic types, thus suggesting that T. equigenitalis has been introduced to the Danish population of Icelandic horses on at least three separate occasions.
In parallel with this project, SSI detected T. equigenitalis in 38 of 103 (37%) samples received in 2021 from Fjord horses. Isolates from these horses belonged to a genetic type distinct of that detected in Icelandic horses, thus witnessing independent introduction of T. equigenitalis to this specific horse population in Denmark.
Elaboration of project results can be obtained free of charge by contacting project responsible Peter Damborg (pedam@sund.ku.dk). Results have also been published in Danish in the journal Dansk Veterinær Tidsskrift, and a publication in an international scientific journal is under preparation. Following project termination at the end of 2021, the project consortium has communicated with relevant breeding organisations and the Danish Veterinary and Food Agency. We recommend that legislation and recommendations concerning screening, treatment and follow-up on CEM-infected horses are carefully considered, and in some places revised, to further reduce the spread of CEM in Denmark.