Diagnosis of Equine Genital Leptospirosis (EGL) in mares with poor reproductive performance.

Overview

• This study investigated the presence of equine genital leptospirosis (EGL) in mares with poor reproductive performance and genetically characterized the Leptospira bacteria involved.
• It confirmed that Leptospira infection is common in these mares, especially involving the Australis serogroup, and highlighted the usefulness of molecular diagnostic methods.

Background

• Leptospirosis is a zoonotic disease caused by bacteria of the genus Leptospira, which can infect various animal species including horses.
• Equine genital leptospirosis (EGL) is a chronic and often silent infection affecting the reproductive system of mares, linked to reproductive issues such as abortion, stillbirth, placentitis, embryonic loss, repeat breeding syndrome, and subfertility.
• Diagnosing EGL is challenging because symptoms can be subtle or non-specific, necessitating sensitive laboratory tests.

Objectives

• To detect and confirm genital Leptospira infection in naturally infected mares with poor reproductive history.
• To genetically characterize the Leptospira strains involved in these infections using molecular methods.

Methods

• Sample population: 41 mares exhibiting poor reproductive performance were selected for the study.
• Sample collection:
  • Blood serum samples for serological testing (Microscopic Agglutination Test – MAT).
  • Urine samples, uterine mucus, and uterine tissue biopsies were collected for molecular detection.
• Serology: MAT was used to detect antibodies against various Leptospira serogroups.
• Molecular detection:
  • LipL32-PCR screening was performed on urine, uterine mucus, and uterine tissue samples to detect the presence of pathogenic Leptospira DNA.
  • Samples positive by lipL32-PCR underwent further testing by secY gene nested-PCR amplification to genetically characterize the infecting strains.
  • Sequencing of the secY gene was done for identification and comparison with known Leptospira isolates.

Key Findings

• Serology findings:
  • 41.5% (17 out of 41) of the mares were seropositive by MAT, indicating exposure to Leptospira.
  • The most prevalent serogroup was Australis, detected in 76.5% of the seropositive mares (13 animals), consistent with a known common pathogen in equine infections.
• Molecular detection:
  • 61.0% (25 out of 41) of mares were positive for Leptospira DNA by lipL32-PCR in at least one tested sample.
  • 84.0% (21 out of 25) of positive mares had DNA detected specifically in genital samples (uterine mucus or uterine tissue), reinforcing the localized genital infection.
  • Only uterine tissue samples were successfully amplified by secY nested-PCR (6 samples), suggesting the importance of tissue sampling for genetic studies.
• Genetic characterization:
  • Sequencing revealed that all characterized samples were Leptospira interrogans.
  • Sequence similarity was ≥ 99% with serovar Bratislava strains, belonging to the Australis serogroup, confirming the serological findings.

Conclusions

• The study confirms that equine genital leptospirosis is present in mares suffering from poor reproductive outcomes.
• Genital samples (especially uterine tissues) are highly valuable for the detection of Leptospira DNA and molecular diagnosis of EGL.
• The predominance of the Australis serogroup, particularly serovar Bratislava, suggests it is a key pathogen in equine reproductive infections in this population.
• Combining serology and molecular methods enhances diagnostic accuracy for EGL, aiding better disease management.

Implications and Future Directions

• Veterinarians and equine reproductive specialists should consider leptospirosis in mares presenting with unexplained reproductive failures.
• Molecular diagnostic tools, especially PCR of genital tissues, should be integrated into routine diagnostic protocols for better identification of EGL.
• Further studies could investigate treatment options and preventive measures targeting the Australis serogroup to improve reproductive performance in affected herds.
• Understanding epidemiology and transmission dynamics of Leptospira interrogans serovar Bratislava in horse populations can help in designing control strategies.