Molecular detection of pathogenic Leptospira spp. in mares with reproductive disorders enrolled in embryo transfer programs.

Overview

• This study investigated the presence of pathogenic Leptospira bacteria in mares with reproductive problems involved in embryo transfer (ET) programs in Brazil.
• Using blood and reproductive tract samples, the researchers tested for signs of exposure and active infection, highlighting significant infection rates that suggest Leptospira plays a role in reproductive failures within ET programs.

Introduction to the Research Topic

• Equine genital leptospirosis (EGL): A bacterial infection caused by pathogenic Leptospira species linked to reproductive issues in mares such as infertility, abortion, or embryo loss.
• Embryo transfer (ET) programs: Breeding techniques used to transfer embryos from donor mares to recipient mares to increase reproduction efficiency.
• Knowledge gap: While EGL is known to cause reproductive problems, its impact on mares within ET programs and the prevalence of infection in these settings are not well understood.

Objectives

• To determine how often mares enrolled in ET programs show evidence of exposure or infection by pathogenic Leptospira bacteria.
• To use both serological (blood antibody testing) and molecular (DNA detection) methods to assess infection status in mares with a history of reproductive disorders.
• To analyze associations between infection presence and mare functional status (donor vs recipient in ET).

Methods

• Study population: 70 unvaccinated mares from 13 stud farms in Brazil, all with reproductive disorder histories.
• Sample collection: Serum samples for serology and endometrial cytobrush samples (ECS) to collect cells from the reproductive tract for DNA testing.
• Serological testing: Microscopic agglutination test (MAT) that detects antibodies against Leptospira, with titers ≥1:100 considered reactive indicating past or present exposure.
• Molecular testing: PCR assay targeting the lipL32 gene, a gene specific to pathogenic Leptospira, to detect bacterial DNA in the reproductive tract samples, indicating active infection.
• Sequencing: Confirmatory sequencing of PCR-positive samples to identify the specific Leptospira species.
• Statistical analysis: Comparison of infection detection rates between donor and recipient mares, calculation of odds ratios (OR), and significance testing.

Results

• Serological findings: 68.6% of mares showed positive antibody titers by MAT, indicating high exposure to Leptospira.
• Molecular findings: 45.7% of mares had PCR-positive endometrial samples, meaning almost half had detectable pathogenic Leptospira DNA in their reproductive tract.
• Farm-wide presence: Nearly all farms (12 out of 13) had at least one PCR-positive mare, suggesting widespread infection across stud farms.
• Species identification: Sequencing of one sample confirmed ≥99% identity with Leptospira interrogans, a well-known pathogenic species.
• Functional differences: Recipient mares showed significantly higher odds (OR = 3.15) of PCR positivity compared to donor mares, implying recipient mares might be more prone to active infection.

Conclusions and Implications

• The study demonstrates both a high rate of exposure to and active infection with pathogenic Leptospira spp. in mares involved in ET programs who have reproductive disorders.
• Molecular testing of reproductive tract samples is crucial for detecting active infections that could contribute to fertility problems in these breeding operations.
• Recipient mares appear at greater risk of infection, which may inform breeding management and health monitoring strategies.
• These findings emphasize the need for regular leptospirosis surveillance and possibly preventive measures in embryo transfer programs to safeguard reproductive success.