Tick-borne bacterial and protozoal pathogens in horses in Austria – A cross-sectional study on current and past infections and potential risk factors.

Tick-borne pathogens, including bacteria and protozoa, are a risk to horses in Austria, but nationwide studies are limited. This study tested blood from 588 horses across Austria for DNA and antibodies of key tick-borne pathogens to assess infection rates and identify risk factors.

Background and Purpose

• Tick-borne diseases caused by bacterial and protozoal pathogens threaten horse health globally.
• In Austria, there is a lack of comprehensive, nationwide data on infections with pathogens like Theileria equi, Babesia caballi, Anaplasma phagocytophilum, and Borrelia burgdorferi in horses.
• The study aims to fill this gap by assessing both current and past infections in a large sample of horses without prior records of tick-borne infections.

Methodology

• Blood samples were collected from 588 horses across Austria.
• Polymerase Chain Reaction (PCR) was used to detect DNA of Theileria equi, Babesia caballi, Babesia canis, and Anaplasma phagocytophilum, indicating active infection.
• Serological assays (ELISA and IFAT) tested for antibodies against these pathogens and Borrelia burgdorferi, signaling past or active exposure.
• The horses selected had no prior documented infections with tick-borne pathogens to better reflect natural exposure.

Key Findings

• Babesia caballi: No DNA was detected in any horse, but specific antibodies were found in 1.9% of horses, suggesting past exposure or infection.
• Theileria equi: DNA detected in 12 horses, indicating active infections; anti-T. equi antibodies were present in these and more horses, confirming exposure.
• Babesia canis: DNA was unexpectedly found in two horses, indicating possible tick transmission or cross-species infection.
• Anaplasma phagocytophilum: No DNA detected, but a high percentage had antibodies (approximately 43% by IFAT and 57% by ELISA), indicating widespread exposure rather than active infection at sampling.
• Borrelia burgdorferi: Approximately 44% of horses had antibodies, showing significant exposure to Lyme disease bacteria.
• More than a quarter (28%) of horses tested positive for two or three different pathogens, suggesting co-exposure is common.

Risk Factors and Associations

• Horses that were pastured or housed outdoors had higher rates of infection, emphasizing grazing and outdoor management as risk factors.
• For Theileria equi, place of birth or import status influenced infection risk, suggesting geographic or origin-related exposure differences.
• High rates of co-infections with A. phagocytophilum and B. burgdorferi hint at overlapping ecological niches and tick vectors.

Implications and Conclusions

• The study reveals a high level of exposure of Austrian horses to important tick-borne pathogens, particularly Anaplasma phagocytophilum and Borrelia burgdorferi.
• The presence of Theileria equi infections across the country suggests ongoing transmission risk.
• Co-infections are common and may complicate clinical diagnosis and treatment.
• Veterinarians should consider these pathogens as possible causes when diagnosing equine clinical cases consistent with tick-borne diseases.
• Management practices such as housing and grazing need to be evaluated to reduce tick exposure and transmission risks.
• Awareness and monitoring are essential to prevent disease outbreaks and ensure horse health in Austria’s tick-prevalent environments.