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Parasitology research2024; 123(12); 410; doi: 10.1007/s00436-024-08438-0

Prevalence, risk factors, and species diversity of strongylid nematodes in domesticated Thai horses: insights from ITS-2 rDNA metabarcoding.

Abstract: Strongylid nematodes represent a major health and performance concern for equids globally. However, the epidemiology of strongylid infections in horse populations remains largely unexplored in Thailand. This study investigated the prevalence of strongylid parasites and the associated risk factors in domesticated horses in Thailand. Additionally, the study utilized ITS-2 rDNA metabarcoding to characterize the diversity and co-occurrence patterns of strongylid species. Of the 408 horses examined, 50.98% tested positive for strongyle infection, with an average intensity of 445.67 ± 639.58 eggs. Notably, only 25.74% exhibited fecal egg counts of ≥ 200 eggs per gram (EPG), highlighting the need for targeted deworming protocols. Significantly higher EPG values were observed in yearling horses (p = 0.001) and those kept in outdoor pastures (p = 0.0001). Metabarcoding identified 15 strongylid species, with Cylicostephanus longibursatus being the most abundant (mean relative abundance: 37.30%, SD = 31.16%). No Strongylus species were detected. Alpha diversity analysis revealed no significant differences in species richness and evenness across horse groups, while beta diversity analysis showed significant dissimilarities (p = 0.004), primarily driven by Cylicostephanus longibursatus, Cyathostomum pateratum, and Cylicostephanus calicatus, which contributed to over 60% of the variation. Species co-occurrence patterns were largely random, with a limited number of positive (n = 5) and negative (n = 2) species pair associations. These findings provide essential insights into the current state of strongylid infections in Thai horses and offer a foundation for future research and management strategies.
© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
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Publication Date: 2024-12-17 PubMed ID: 39688721PubMed Central: 4668017DOI: 10.1007/s00436-024-08438-0Google Scholar: Lookup
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  • Journal Article

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 examined how common strongylid nematode infections are in domesticated horses in Thailand and identified the main risk factors for infection.
  • It also used a genetic metabarcoding technique (ITS-2 rDNA) to analyze the diversity and relationships of different strongylid species found in these horses.

Background

  • Strongylid nematodes are parasitic worms that infect horses worldwide, affecting their health and performance.
  • The epidemiology—meaning the patterns, causes, and effects—of these infections in Thailand’s horse populations had been largely unknown before this study.

Study Objectives

  • Determine the prevalence (how common) strongylid infections are in domesticated Thai horses.
  • Identify risk factors associated with higher infection levels.
  • Use molecular metabarcoding to characterize the variety and relationships of strongylid species present.

Methods

  • Sampled feces from 408 domesticated horses across Thailand to test for strongylid eggs.
  • Measured fecal egg counts (FEC) to estimate intensity of infection—the number of parasite eggs per gram of feces.
  • Applied ITS-2 rDNA metabarcoding, a DNA-based technique that sequences a specific genetic marker, to identify and differentiate strongylid species present in fecal samples.

Results – Prevalence and Infection Intensity

  • About half (50.98%) of the sampled horses were infected with strongylid nematodes.
  • The average fecal egg count was 445.67 eggs per gram (EPG), but with high variability (standard deviation of 639.58 EPG).
  • Only approximately one-quarter (25.74%) had fecal egg counts ≥ 200 EPG, indicating these horses might need targeted deworming.

Risk Factors

  • Yearling horses (young horses around one year old) had significantly higher fecal egg counts (p = 0.001), suggesting they are more susceptible or have higher worm burdens.
  • Horses kept in outdoor pasture environments also had significantly higher infection intensities (p = 0.0001), likely due to increased exposure to infective larvae.

Species Diversity and Composition

  • Metabarcoding identified 15 different strongylid species circulating among these horses.
  • The most abundant species was Cylicostephanus longibursatus, comprising about 37.3% of the nematode community on average.
  • No Strongylus species were detected, which is notable as Strongylus had traditionally been major equine parasites but may be less prevalent today.

Diversity Analysis

  • Alpha diversity (species richness and evenness within individual horses or groups) did not differ significantly between horse groups, suggesting similar species variety and distribution across samples.
  • Beta diversity (differences in community composition between groups) showed significant differences (p = 0.004), driven primarily by variations in three species: Cylicostephanus longibursatus, Cyathostomum pateratum, and Cylicostephanus calicatus.
  • These three species together accounted for over 60% of the variation observed between horse groups.

Species Co-occurrence Patterns

  • Analysis of species co-occurrence suggested mostly random associations—meaning the presence of one species did not strongly predict the presence or absence of another.
  • There were a few significant positive associations (5 species pairs), indicating some species may co-exist or benefit from similar conditions.
  • There were very few negative associations (2 species pairs), suggesting competitive exclusion or antagonism was rare among strongylid species in these horses.

Implications and Conclusions

  • This research provides valuable baseline data on the prevalence, risk factors, and species diversity of strongylid infections in Thai horses, a previously under-studied population.
  • The finding that yearlings and pasture-kept horses have higher parasite loads can help inform targeted parasite control strategies, such as selective deworming focused on high-risk groups.
  • The use of ITS-2 rDNA metabarcoding offers a powerful tool for precise species identification and understanding parasite community structure, which is important for effective management and monitoring.
  • The absence of Strongylus species suggests shifts in species composition; control programs may need to adapt to these changes.
  • Overall, this study lays the groundwork for future research into parasite epidemiology, resistance, and effective control in horses in Thailand and similar settings.

Cite This Article

APA
Hamad MH, Jitsamai W, Chinkangsadarn T, Ngangam TS, Wattanapornpilom T, Naraporn D, Ouisuwan S, Taweethavonsawat P. (2024). Prevalence, risk factors, and species diversity of strongylid nematodes in domesticated Thai horses: insights from ITS-2 rDNA metabarcoding. Parasitol Res, 123(12), 410. https://doi.org/10.1007/s00436-024-08438-0

Publication

Parasitology research
ISSN: 1432-1955
NlmUniqueID: 8703571
Country: Germany
Language: English
Volume: 123
Issue: 12
Pages: 410

Researcher Affiliations

Hamad, Mohamed H
  • The International Graduate Program of Veterinary Science and Technology (VST), Faculty of Veterinary Science, Chulalongkorn University, Bangkok-10330, Thailand.
  • Infectious Diseases, Department of Animal Medicine, Faculty of Veterinary Medicine, Zagazig University, Zagazig-44511, Egypt.
  • Department of Veterinary Pathology, Faculty of Veterinary Science, Parasitology Unit, Chulalongkorn University, Bangkok, 10330, Thailand.
Jitsamai, Wanarit
  • Department of Parasitology and Entomology, Faculty of Public Health, Mahidol University, Bangkok, Thailand.
Chinkangsadarn, Teerapol
  • Department of Surgery, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, 10330, Thailand.
Ngangam, Tasorn Sa
  • Faculty of Veterinary Science, Equine Clinic, Animal Hospital-Student Training Center, Chulalongkorn University, Nakorn Pathom, 73000, Thailand.
Wattanapornpilom, Tanakorn
  • Veterinary and Agriculture Division 1, Veterinary and Remount Department, The Royal Thai Army, Kanchanaburi, 71000, Thailand.
Naraporn, Darm
  • Horse Farm and Laboratory Animal Breeding Center, Queen Saovabha Memorial Institute, The Thai Red Cross Society, Prachuap Khiri Khan, 77110, Thailand.
Ouisuwan, Suraseha
  • Horse Farm and Laboratory Animal Breeding Center, Queen Saovabha Memorial Institute, The Thai Red Cross Society, Prachuap Khiri Khan, 77110, Thailand.
Taweethavonsawat, Piyanan
  • Department of Veterinary Pathology, Faculty of Veterinary Science, Parasitology Unit, Chulalongkorn University, Bangkok, 10330, Thailand. Piyanan.T@chula.ac.th.
  • Biomarkers in Animals Parasitology Research Unit, Chulalongkorn University, Bangkok, 10330, Thailand. Piyanan.T@chula.ac.th.

MeSH Terms

  • Animals
  • Female
  • Male
  • Biodiversity
  • DNA Barcoding, Taxonomic
  • DNA, Ribosomal / genetics
  • DNA, Ribosomal Spacer / genetics
  • Feces / parasitology
  • Horse Diseases / parasitology
  • Horse Diseases / epidemiology
  • Horses / parasitology
  • Parasite Egg Count / veterinary
  • Prevalence
  • Risk Factors
  • Strongylida Infections / veterinary
  • Strongylida Infections / parasitology
  • Strongylida Infections / epidemiology
  • Strongyloidea / genetics
  • Strongyloidea / classification
  • Strongyloidea / isolation & purification
  • Thailand / epidemiology

Grant Funding

  • FOODF68310009 / This research project was funded by the Thailand Science Research and Innovation Fund, Chulalongkorn University

Conflict of Interest Statement

Declarations. Ethics approval and informed consent: This study has been approved by the Institutional Animal Care and Use Committee, and the Institutional Biosafety Committee of the Faculty of Veterinary Science, Chulalongkorn University (IACUC No. 2331052; IBC No. 2231037). The study procedures were conducted following university guidelines, regulations, and biosafety policies. The owners of the horse farms willingly participated in the study, providing essential details about their horses, animal welfare, and the timing of the deworming protocol. Competing interests: The authors declare no competing interests.

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Citations

This article has been cited 3 times.
  1. Abbas G, Nielsen MK, E-Hage C, Ghafar A, Beveridge I, Bauquier J, Beasley A, Wilkes EJA, Carrigan P, Cudmore L, Jacobson C, Hughes KJ, Jabbar A. Recent advances in intestinal helminth parasites of horses in the Asia-Pacific region: Current trends, challenges and future directions.. Int J Parasitol Drugs Drug Resist 2025 Dec;29:100622.
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  2. Lu Y, Ru P, Qin S, Zhang Y, Fu E, Cai M, Tuohuti N, Wu H, Zhang Y, Zhang Y. Epidemiological Patterns of Gastrointestinal Parasitic Infections in Equine Populations from Urumqi and Ili, Xinjiang, China.. Vet Sci 2025 Jul 6;12(7).
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  3. Ochigbo GO, Ahn S, Belhumeur KA, Poissant J, Rosa BV. Nemabiome sequencing reveals seasonal and age associated patterns of strongyle infection and high prevalence of Strongylus vulgaris in Alberta feral horses.. Int J Parasitol Parasites Wildl 2025 Aug;27:101091.
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