Equine leptospirosis: Experimental challenge of Leptospira interrogans serovar Bratislava fails to establish infection in naïve horses.
Authors: Zilch Tiago J, Lee Jen-Jie, Saleem Muhammad Zain, Zhang Hui, Cortese Victor, Voris Nathan, McDonough Sean P, Divers Thomas J, Chang Yung-Fu
Journal: Equine veterinary journal
Summary
# Editorial Summary: Leptospira interrogans serovar Bratislava Challenge in Horses Despite widespread concern about leptospirosis in equine populations, little experimental evidence exists regarding how horses respond to infection with *Leptospira interrogans* serovar Bratislava, a serovar commonly isolated from other species. Researchers inoculated six seronegative foals with 10⁹ leptospires via ocular and intraperitoneal routes, whilst four control foals received no challenge, then monitored all animals for 9 weeks using serological testing (microscopic agglutination), haematology, biochemistry, culture and histopathology. Despite developing a measurable antibody response, the challenged foals showed no fever, and neither PCR nor bacterial culture yielded positive results from any tissue or fluid samples; however, the blood work and differential counts indicated an inflammatory response had occurred. The findings suggest that serovar Bratislava, at least in this particular strain, may lack pathogenicity or host adaptation in equines—a finding that could reshape how clinicians interpret seropositivity in horses and reassess the significance of this serovar in equine disease. However, practitioners should interpret these results cautiously, as alternative strains of the same serovar, higher bacterial doses or different infection routes might produce different outcomes, leaving questions about clinical relevance unresolved.
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Practical Takeaways
- •L. interrogans serovar Bratislava appears to have low or no pathogenicity in horses, suggesting this serovar is not host-adapted to equines despite causing disease in other species
- •Horses may be resistant to this serovar infection or require different infection routes/doses than tested; field cases of equine leptospirosis should be investigated for other serovars
- •Serological testing (MAT) can confirm leptospiral exposure in horses but cross-reactivity between serovars occurs; genomic analysis may be needed for definitive serovar identification
Key Findings
- •Experimental challenge with 1×10⁹ leptospires via ocular and intraperitoneal routes failed to establish clinical infection in seronegative foals
- •All 6 challenged foals developed humoral antibody response detectable by MAT despite absence of bacteremia, pyrexia, or histopathological lesions
- •PCR and culture were negative from all sampled tissues (blood, urine, liver, kidney, reproductive tract, vitreous humour) in challenged animals
- •Haematological and serum biochemistry changes in challenged group suggest leptospiral exposure triggered inflammatory response without causing established infection