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Parasites & vectors2026; 19(1); 65; doi: 10.1186/s13071-025-07192-1

Characterizing mixed strongyle infections in foals and broodmares using cytochrome c oxidase subunit I deep amplicon sequencing.

Abstract: Mixed strongyle infections represent the most prevalent equine parasitosis and can result in life-threatening disease, especially in young horses. Species involvement and pathogenesis of this parasitosis are poorly understood, and data on foals and broodmares are notably lacking. Methods: In a longitudinal study undertaken in 2022 in Germany, individual faecal samples (n = 497) and metadata were collected for naturally infected foals and broodmares (n = 48) kept under conventional husbandry conditions. Nematode infections were detected coproscopically via the Mini-FLOTAC method. In a subset of strongyle egg-positive samples (n = 46), species were identified using cytochrome c oxidase subunit I deep amplicon sequencing. Species prevalence, richness, and alpha and beta diversity were compared between foals and mares. Results: Overall, 22.2% of the foal samples and 10.2% of the mare samples were strongyle egg positive (eggs per gram > 5). Parascaris spp. were only detected in foals (15.1%). Strongyloides westeri was detected in one foal sample. Strongyle egg detection increased in likelihood with each additional sample timepoint (OR = 1.42, P < 0.001) and with ascarid egg detection (OR = 6.49, P < 0.001), while last anthelmintic treatment with pyrantel decreased the odds of detecting eggs (OR = 0.12, P = 0.002). Deep amplicon sequencing detected 16 species of small strongyles but no large strongyle species. Cylicostephanus goldi, Cylicostephanus minutus operational taxonomic unit II and Cylicocyclus ashworthi were significantly more prevalent in mares (P < 0.05), while Cylicostephanus calicatus operational taxonomic unit II was more prevalent in foals (P < 0.01). Mares showed a significantly higher amplicon sequence-variant-based richness (Chao 1 index, P < 0.001) and diversity (inverse Simpson index, P < 0.01) than foals. Group (foals vs. mares) explained some of the variance in beta diversity, according to permutational multivariate ANOVA. Co-infection with Parascaris spp. did not affect strongyle community composition in the foals. Bray-Curtis and Jaccard distance (dissimilarity) plots showed separate clusters for mares and foals, with some overlap and a moderate model fit. Conclusions: Cytochrome oxidase-based characterization of mixed strongyle infections revealed strongyle community differences between broodmares and foals. Possible age associations were identified for four species of small strongyles, including two cryptic species. Low overall strongyle prevalence and egg-shedding intensity, non-random sampling and differences in anthelmintic treatment schemes limited the statistical power of this study.
© 2025. The Author(s).
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Publication Date: 2026-01-03 PubMed ID: 41484633PubMed Central: PMC12866475DOI: 10.1186/s13071-025-07192-1Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigated the types and diversity of strongyle parasite infections in foals and broodmares using advanced DNA sequencing methods on fecal samples.
  • It identified differences in parasite species composition and diversity between young horses (foals) and adult females (mares), improving understanding of equine parasitic infections.

Background

  • Strongyles are parasitic nematodes commonly infecting horses and can cause serious health issues, especially in young horses.
  • Understanding which specific strongyle species infect horses and how their communities differ by age is important but previously limited.
  • The study focuses on foals and broodmares under conventional horse-keeping conditions in Germany, aiming to fill knowledge gaps.

Methods

  • Collected 497 individual fecal samples from 48 horses (foals and broodmares) in 2022.
  • Used the Mini-FLOTAC method, a microscopic technique, to detect nematode eggs in feces.
  • Selected 46 samples positive for strongyle eggs for further analysis using cytochrome c oxidase subunit I (COI) deep amplicon sequencing, a DNA-based method enabling precise identification of parasite species.
  • Analyzed species prevalence, richness (number of species), and diversity within (alpha diversity) and between (beta diversity) horse groups.

Key Results

  • Prevalence of infection: 22.2% of foal samples and 10.2% of mare samples had detectable strongyle eggs.
  • Other parasites: Parascaris species eggs found only in foals (15.1%); Strongyloides westeri detected in one foal.
  • Likelihood of strongyle egg detection increased with multiple sampling times and presence of ascarid eggs, but decreased following treatment with the anthelmintic pyrantel.
  • Species diversity: Identified 16 small strongyle species; no large strongyle species detected.
  • Some species were more prevalent in mares (e.g., Cylicostephanus goldi, Cylicostephanus minutus OTU II, Cylicocyclus ashworthi), while Cylicostephanus calicatus OTU II was more common in foals.
  • Mares had significantly higher parasite species richness and diversity compared to foals, suggesting differences in infection complexity with age.
  • Statistical analyses showed group membership (foals vs. mares) partially explained differences in parasite community composition.
  • Presence of Parascaris spp. co-infection did not significantly alter strongyle community structure in foals.

Interpretation

  • DNA sequencing of the COI gene effectively characterized mixed strongyle infections, revealing species-specific and age-related infection patterns.
  • Higher diversity in mares likely results from longer exposure and accumulation of multiple strongyle species.
  • Age-related differences in prevalence of certain small strongyle species suggest possible species-specific host preferences or immune interactions.
  • Lack of large strongyle species may reflect current management or anthelmintic practices reducing these historically important parasites.

Limitations

  • Low overall prevalence and intensity of strongyle egg shedding limited the amount of data available for robust statistical conclusions.
  • Sampling was not random and differences in timing and types of anthelmintic treatments between foals and mares may have influenced results.
  • Study focused on a single geographic region and limited number of horses, requiring broader studies to confirm findings.

Conclusions and Implications

  • The study advances knowledge about the composition and diversity of strongyle infections in horses, highlighting differences between young and adult animals.
  • Identification of cryptic and age-associated species suggests the need for tailored parasite control strategies.
  • Deep amplicon sequencing is a valuable tool for detailed parasite community profiling in equine health research and management.

Cite This Article

APA
Klass LG, Krücken J, Mbedi S, Sparmann S, Schenk T, Andreotti S, von Samson-Himmelstjerna G. (2026). Characterizing mixed strongyle infections in foals and broodmares using cytochrome c oxidase subunit I deep amplicon sequencing. Parasit Vectors, 19(1), 65. https://doi.org/10.1186/s13071-025-07192-1

Publication

Parasites & vectors
ISSN: 1756-3305
NlmUniqueID: 101462774
Country: England
Language: English
Volume: 19
Issue: 1
Pages: 65
PII: 65

Researcher Affiliations

Klass, Luise Grace
  • Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
  • Veterinary Centre for Resistance Research, Freie Universität Berlin, Berlin, Germany.
  • Institute of Veterinary Anatomy, Freie Universität Berlin, Berlin, Germany.
Krücken, Jürgen
  • Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
  • Veterinary Centre for Resistance Research, Freie Universität Berlin, Berlin, Germany.
Mbedi, Susan
  • Berlin Center for Genomics in Biodiversity Research (BeGenDiv), Berlin, Germany.
  • Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany.
Sparmann, Sarah
  • Berlin Center for Genomics in Biodiversity Research (BeGenDiv), Berlin, Germany.
  • Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.
Schenk, Thore
  • Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
  • Veterinary Centre for Resistance Research, Freie Universität Berlin, Berlin, Germany.
Andreotti, Sandro
  • Bioinformatics Solutions Center, Institute of Computer Science, Freie Universität Berlin, Berlin, Germany.
von Samson-Himmelstjerna, Georg
  • Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany. samson.georg@fu-berlin.de.
  • Veterinary Centre for Resistance Research, Freie Universität Berlin, Berlin, Germany. samson.georg@fu-berlin.de.

MeSH Terms

  • Animals
  • Horses
  • Electron Transport Complex IV / genetics
  • Feces / parasitology
  • Germany / epidemiology
  • Strongyle Infections, Equine / parasitology
  • Strongyle Infections, Equine / epidemiology
  • Female
  • Longitudinal Studies
  • Horse Diseases / parasitology
  • Horse Diseases / epidemiology
  • High-Throughput Nucleotide Sequencing
  • Prevalence
  • Coinfection / veterinary
  • Coinfection / parasitology
  • Coinfection / epidemiology
  • Parasite Egg Count
  • Male

Grant Funding

  • 033W034A / German Federal Ministry of Education and Research (BMBF)
  • RTG 2046, 251133687 / Deutsche Forschungsgemeinschaft

Conflict of Interest Statement

Declarations. Ethics approval and consent to participate: In accordance with established guidelines, ethical approval was not required for this study, as the research exclusively used environmental samples. All of the owners voluntarily allowed participation of their animals in this study, were informed about all of the procedures and further processing of the collected data, and gave their consent for the data to be published. Competing interests: GvSH declares that he has worked repeatedly as a consultant for different veterinary pharmaceutical and diagnostic companies. He currently has several ongoing research collaborations with various companies. All of the other authors declare that they have no competing interests.

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