Serological Surveillance of Equine Leptospirosis in Croatia in the Period From 2012 to 2022: A Key Insight Into the Changing Epizootiology.

The article discusses a ten-year (2012-2022) Leptospirosis surveillance study on horses in Croatia, revealing a high percentage of seemingly healthy horses carrying the bacterium, particularly the serovar Pomona.

Introduction to Leptospirosis

• Leptospirosis is a significant bacterial zoonotic disease.
• The disease affects both wild and domestic animals, including horses and humans.
• Its re-emerging global prevalence has catalyzed disease control efforts in countries like Croatia, where monitoring of equine leptospirosis is enforced by law.

Study Methodology

• In the span of a decade, from 2012 to 2022, the study analyzed 61,724 serum samples from seemingly healthy horses in Croatia.
• These serum samples were tested for the presence of antibodies against various Leptospira serovars using the microscopic agglutination test (MAT).
• The threshold for seropositivity differed according to the serovar. For instance, a cut-off titre of 1:200 was deemed significant for the Bratislava serovar, while for others it was 1:400.

Findings of the Study

• Of all the samples tested, 10.80% or 6,665 serum samples exhibited seropositivity for at least one Leptospira serovar.
• The annual seroprevalence rates ranged between 5.00% and 15.94% during the study period.
• The most frequently found serovars were Pomona (41.98%) and Grippotyphosa (31.34%), trailed by Sejroe (8.03%), Icterohaemorrhagiae (7.05%), and Bratislava (6.47%).

Implications of the Findings

• The data revealed considerable exposure of the Croatian horse population to Leptospira infections.
• The highest prevalence was attributed to the Pomona serovar.
• Despite being outwardly healthy, many investigated horses carried an anamnestic titre, indicating a past infection.
• Notably, the high seropositivity for the Pomona serovar in this seemingly healthy horse population was unprecedented in European studies.
• The increasing prevalence of the Pomona serovar within the horse population raised questions about the potential dominant evolutionary adaptation of this pathogenic serovar in horses.