Genomic insights into the epidemiology of Contagious Equine Metritis in Germany.

Genomic analysis of Taylorella equigenitalis isolates from Germany revealed substantial genetic diversity and suggested undetected cases of Contagious Equine Metritis, highlighting the importance of molecular surveillance to control this disease.

Background and Problem Statement

• Contagious Equine Metritis (CEM) is caused by the bacterium Taylorella equigenitalis.
• CEM is a persistent issue in horse populations in Germany, especially affecting the breeding industry.
• The disease is often subclinical, meaning infected horses may show no obvious symptoms but can still spread the infection.
• There has been limited information about the genetic diversity of T. equigenitalis strains circulating in Germany due to the absence of genome-level studies.

Study Objective and Methodology

• The study aimed to explore the genomic diversity and epidemiology of T. equigenitalis in Germany.
• Researchers sequenced 63 isolates of T. equigenitalis, collected from both archived strains and contemporary clinical isolates spanning from before 2007 to 2024.
• Most isolates originated from Icelandic horses located in southern Germany, indicating a population focus.
• To analyze genetic relationships, two methods were employed:
  • Multilocus Sequence Typing (MLST), which examines variations in a set of housekeeping genes.
  • Core genome nucleotide difference analysis, comparing the sequences across conserved regions of the genome.

Key Findings

• Significant genetic diversity was observed among the isolates, particularly within the dominant MLST sequence type 46, which included most samples.
• Genomic data helped confirm epidemiological links, such as an incident where a single stallion was identified as the likely source of infection for several mares.
• There was evidence suggesting that many CEM cases in Germany remain undetected, indicating silent spread within the horse populations.
• Antibiotic resistance testing showed that most streptomycin-resistant isolates shared a common mutation in the rpsL gene, suggesting a genetic basis for resistance.

Implications and Recommendations

• The study highlights the importance of molecular surveillance in detecting and controlling CEM, especially since infected horses might not exhibit symptoms yet still carry and transmit T. equigenitalis.
• Screening should include apparently healthy horses, as they might act as carriers contributing to unnoticed disease transmission.
• Understanding the genetic diversity of strains can help track outbreaks and identify risk factors associated with infection spread.
• Future control strategies may benefit from targeted genomic monitoring and antibiotic susceptibility testing to mitigate the disease’s impact on the breeding industry in Germany.