Diagnostic challenges and alternatives for difficult-to-detect equine gastrointestinal parasites

Gastrointestinal parasites pose a significant threat to equine health and welfare worldwide. Effective parasite control relies heavily on accurate detection and monitoring, with faecal worm egg counts being the most commonly used diagnostic tool. Faecal worm egg counts provide valuable insights into parasite shedding and guide targeted anthelmintic treatments, which are essential for minimising drug resistance. However, this approach has limitations, including variability in egg shedding, failure to detect immature or hypobiotic larvae and a weak correlation between faecal worm egg count results and actual parasite burden. Furthermore, the commonly used cutoff values for treatment decisions are often arbitrary and not universally evidence-based, raising concerns about their reliability in determining true infection levels. Diagnostic challenges and alternatives for difficult-to-detect equine gastrointestinal parasites Routine faecal examinations are essential in equine parasitology, providing critical information on the presence of many gastrointestinal parasites. However, their effectiveness is limited for certain parasites that are not reliably detected through standard faecal analysis. This article examines the diagnostic challenges associated with equine parasites, including Oxyuris equi, Strongyloides westeri, Habronema spp., Anoplocephala spp., Fascioloides magna and Gasterophilus spp. O. equi eggs are typically laid in the perianal region and are often not present in faeces, making routine faecal examination methods ineffective. S. westeri larvae, particularly in older horses, may not be present in detectable numbers in faeces, reducing the utility of faecal examinations. Habronema spp. larvae, which cause gastritis, are not easily identified in faecal samples and may require alternative diagnostic methods such as stomach lavage or endoscopy. Tapeworms (Anoplocephala spp.) shed eggs intermittently, necessitating specialised tests such as enzyme-linked immunosorbent assay or coproantigen assays for accurate detection. Diagnosing F. magna is challenging because of its encapsulated nature, while botfly larvae (Gasterophilus spp.) attach to the stomach lining and are often missed in faecal analysis, requiring clinical evaluation and endoscopy for diagnosis. This article highlights the limitations of faecal examinations for detecting certain equine gastrointestinal parasites and discusses alternative diagnostic strategies that can improve detection accuracy. It also explores the role of various diagnostic methods in shaping treatment plans and management changes for equine health. By incorporating advanced diagnostic tools and maintaining a comprehensive diagnostic approach, equine clinicians can enhance parasite management and optimise treatment outcomes for affected horses.