Herd-level occurrence and spread of Theileria equi and its associated ticks on an Austrian horse farm.

Overview

• This study investigated the presence, prevalence, and spread of the blood parasite Theileria equi, which causes equine piroplasmosis, on a single horse farm in eastern Austria over two years.
• Researchers tested horses and ticks on the farm to understand infection dynamics, confirm vectors, and evaluate the risk of disease persistence and spread in a region not traditionally considered endemic for this parasite.

Background

• Equine piroplasmosis (EP) is a disease of horses caused by blood parasites, primarily Theileria equi, Theileria haneyi, and Babesia caballi.
• The parasites are mainly transmitted through hard tick species (Ixodidae family).
• EP can range clinically from no noticeable symptoms (asymptomatic) to severe illness, and infected horses may carry the parasite for years, facilitating transmission.
• Austria is generally not considered endemic for EP, but there have been occasional case reports.

Study Objectives and Methods

• Goal: Monitor the infection status and dynamics of T. equi in horses and ticks on one Austrian farm to understand herd-level occurrence and potential spread.
• Sample collection:
  • Blood and fecal samples from 18 horses over two years, beginning with discovery of the first clinical T. equi case on this farm.
  • Hard ticks (a total of 1525, including Ixodes ricinus, Dermacentor reticulatus, and Haemaphysalis concinna) from horse pastures collected by flagging.
• Diagnostics:
  • Polymerase chain reaction (PCR) testing targeting 18S rRNA gene of piroplasms for detecting parasite DNA.
  • Sequence analysis of PCR products to confirm parasite species and genotype.
  • Commercial competitive ELISA (cELISA) for antibody detection to assess exposure/infection status.

Key Findings

• Initial detection:
  • Two horses showed clinical symptoms and tested positive for T. equi initially.
  • Among the other 16 horses, 12 were positive by PCR and serology but were asymptomatic.
• One year later:
  • Of 14 horses tested, 12 remained positive, indicating persistent infection.
  • Two previously negative horses became positive, showing ongoing spread.
  • One horse remained negative; it was kept separate from other animals, suggesting isolation limited spread.
• Fecal samples were all negative, implying no gastrointestinal shedding of the parasite.
• Tick findings:
  • Six ticks collected from pastures tested positive by PCR for T. equi: four Haemaphysalis concinna, one Ixodes ricinus, one Dermacentor reticulatus.
  • Eight Dermacentor reticulatus ticks removed directly from infected horses were also positive.
  • All parasite genetic sequences belonged to genotype E of T. equi.

Conclusions and Implications

• This is the first report documenting the occurrence and spread of T. equi on an Austrian horse farm, highlighting potential endemic presence despite Austria’s prior classification as non-endemic.
• The persistence of infection within the herd suggests the parasite can remain long-term, allowing continued risk for transmission.
• The presence of multiple tick species carrying the parasite supports the possibility of multiple local vectors facilitating spread.
• Recommendations include:
  • Raising awareness among horse owners and veterinarians in Austria about the risk of equine piroplasmosis.
  • Testing horses for T. equi before importation into the country to prevent introduction of infected animals.
  • Further research to:
    • Identify geographic risk areas within Austria.
    • Clarify the role and vector competence of the different tick species found on the farm.
    • Develop and implement control measures to reduce risk of widespread establishment (endemisation) of this disease.