Seroprevalence of Borrelia burgdorferi sensu lato in horses in Spain.

Overview

• This study investigates the prevalence of antibodies against Borrelia burgdorferi sensu lato—the bacteria responsible for Lyme disease—in horses across Spain, aiming to understand how widespread exposure is and what factors increase risk.

Background and Purpose

• Borrelia burgdorferi sensu lato is a group of bacteria transmitted by ticks and causes Lyme borreliosis, affecting humans and animals, including horses.
• In horses, infection often shows no obvious symptoms, making diagnosis challenging due to varied clinical signs and limits in test accuracy.
• Prior to this study, epidemiological data on Borrelia exposure in horses were limited in Spain.
• The study aimed to:
  • Determine nationwide seroprevalence (the proportion of horses with antibodies indicating exposure to Borrelia).
  • Identify risk factors associated with seropositivity in horses across Spain.

Methodology

• Sample Collection: 716 serum samples were collected from clinically healthy horses distributed across 17 autonomous communities in Spain.
• Testing Approach:
  • Initial screening was done using ELISA (enzyme-linked immunosorbent assay) to detect antibodies.
  • Positive ELISA results were confirmed with Western blot for specificity.
  • Seropositive horses had further testing using real-time PCR on whole blood to detect the presence of bacterial DNA.
• Risk Factor Analysis:
  • A mixed-effects logistic regression model was applied to assess associations between seropositivity and horse-related or management-related variables.
  • Included prior data on serology for equine piroplasmosis (caused by Babesia caballi), another tick-borne disease, to examine co-exposure effects.

Key Findings

• Seroprevalence:
  • Overall crude seroprevalence was 9.6% (69 of 716 horses tested positive for Borrelia antibodies).
  • When adjusted based on the national equine census, seroprevalence increased to 11.5%.
  • A notable geographic variation: northern regions of Spain showed higher seroprevalence rates compared to other areas.
• PCR Results:
  • Only 3% of blood samples tested positive by PCR, indicating low detection of active infection or the limitations of PCR sensitivity in blood samples for Borrelia.
• Risk Factors Identified:
  • Horses used for sport had higher chances of being seropositive, possibly due to increased exposure to tick habitats.
  • Living in northern regions correlated with higher seropositivity.
  • Horses both exposed to ticks and seropositive for Babesia caballi had an increased likelihood of Borrelia exposure, indicating common vector pathways (ticks transmitting multiple pathogens).
  • There was a strong farm-level effect, meaning that horses on the same farm tended to have similar risks, showing clustering of infection within holdings.

Implications and Conclusions

• This study provides the first comprehensive, nationwide evidence of Borrelia burgdorferi s.l. exposure among horses in Spain.
• The uneven geographical distribution suggests environmental conditions and management practices influence risk, with northern Spain being a higher-risk area.
• The association with Babesia caballi exposure supports the role of shared tick vectors in driving infections.
• Findings highlight the need for:
  • Improved surveillance and diagnostic approaches in horses.
  • Targeted tick control and management strategies, especially in higher-risk areas.
  • Consideration of co-infections when diagnosing and managing tick-borne diseases in horses.