A study of the epidemiology of Anoplocephala perfoliata infection in horses and the oribatid mite vector in southern England.

Overview

• This study investigated the seasonal patterns and epidemiology of the equine tapeworm Anoplocephala perfoliata and its oribatid mite intermediate hosts on horse pastures in southern England.
• The research aimed to better understand factors affecting tapeworm presence in mites and horses, contributing to improved parasite control strategies.

Background

• Parasite: Anoplocephala perfoliata is the most common tapeworm infecting horses, residing at the junction of the small and large intestine.
• Health impact: Infection has been linked to colic, a serious digestive condition in horses.
• Lifecycle: This cestode has an indirect lifecycle requiring oribatid mites as intermediate hosts, which ingest tapeworm eggs and later transmit infection to horses when grazed upon.
• Knowledge gap: Despite its importance, little was known about the detailed epidemiology of this parasite and its mite vector in the UK.

Study Objectives

• To monitor seasonal changes in numbers of oribatid mites on horse pastures.
• To detect the presence of Anoplocephala tapeworm DNA in mite populations using molecular techniques.
• To assess the exposure of horses to tapeworm infection by measuring specific antibodies in their saliva.
• To identify management and environmental factors linked to the presence of mites, infected mites, and tapeworm exposure in horses.

Methods

• Sample sites: Three equine premises in southern England were studied from June 2016 to August 2017.
• Sampling schedule: Each yard was visited approximately every four weeks.
• Mite collection:
  • Samples were collected from three pastures per yard via vacuum sampling.
  • Sampling targeted three 1-square meter sections (tetrads) and grass around 10 fecal pats per pasture.
  • Mites were counted and identified by family group.
• Molecular testing: Pools of mites grouped by family were tested for Anoplocephala DNA using polymerase chain reaction (PCR) to detect infection.
• Horse exposure assessment: 10-23 horses per yard had saliva samples taken every 2-3 weeks and tested with the EquiSal® Tapeworm ELISA for specific antibodies indicating recent or past infection.
• Data analysis: Mixed-effects regression models examined risk factors influencing:
  • Presence of different oribatid mite families on pasture.
  • Detection of tapeworm DNA in mite samples.
  • Intermediate or high antibody levels in horse saliva tests.

Key Findings

• Some oribatid mite families, previously not known to harbor tapeworm larvae, were identified as potential intermediate hosts for Anoplocephala spp.
• Oribatid mites persisted on pastures throughout the year, but specific families (Damaeolidae and Oribatidae) were significantly less common in winter compared to summer, decreasing by 81% and 64% respectively.
• Mites infected with tapeworms were primarily found from March to September — aligning with periods of higher mite abundance on paddocks.
• Horses showed the lowest prevalence of tapeworm-specific antibodies in autumn, suggesting a seasonal pattern in infection or exposure.
• Horses grazed for shorter periods (half a day) had a lower likelihood of testing positive by saliva ELISA compared to horses grazing full days, indicating grazing duration influences exposure risk.

Implications

• The study provided novel insights into the ecology and epidemiology of equine tapeworm infection in the UK, especially concerning the role of various oribatid mite families.
• It highlighted seasonal risks for tapeworm transmission, which can inform timing of parasite control measures, such as anthelmintic treatment or pasture management.
• Management practices that reduce grazing time or monitor mite populations seasonally could contribute to lower exposure and infection rates in horses.
• Results support evidence-based parasite control programs, potentially reducing incidence of colic associated with tapeworm infection.

Conclusion

• This comprehensive field and laboratory study advanced understanding of the complex interactions between Anoplocephala perfoliata, oribatid mites, and horses under UK pasture conditions.
• Identifying intermediate hosts, seasonal patterns, and horse exposure risk factors allows for better targeted and more effective control strategies against equine tapeworm infections.