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Pathogens (Basel, Switzerland)2026; 15(3); 309; doi: 10.3390/pathogens15030309

Theileria haneyi: An Emerging Equids Hemoparasite with Milder Virulence but Major Diagnostic and Therapeutic Implications.

Abstract: , a recently discovered tick-borne hemoparasite infecting equids globally, has significant implications for equine health. Although it is closely related to (sharing 23% genomic divergence), it establishes an asymptomatic carrier state in persistently infected horses, creating a silent transmission reservoir. Its discovery and unique genetics justify its classification as a new taxon. A critical diagnostic challenge is that the lack of the gene in prevents its detection by the standard cELISA, emphasizing the need for species-specific tools. Although species-specific PCR assays, including PCR and qPCR targeting genes like or , respectively, and an indirect ELISA targeting the EMA-11 recombinant protein, have been developed, global genetic variations may limit their serological utility. Therapeutically, exhibits resistance to the key antiparasitic drug, imidocarb dipropionate (ID), and interferes with the clearance of co-infecting . Major knowledge gaps persist, particularly regarding the identification of its competent vector. The current work presents an overview of virulence, transmission, diagnostics, and therapeutic gaps while pinpointing the deficits in current information necessary for advancing our understanding of the parasite's biology. Finally, the review discusses and recommends further studies to develop effective control and surveillance strategies for infection.
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Publication Date: 2026-03-12 PubMed ID: 41901762PubMed Central: PMC13029178DOI: 10.3390/pathogens15030309Google 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.

Theileria haneyi is a newly identified parasite infecting horses worldwide, causing less severe illness but posing significant challenges for diagnosis and treatment. This research review highlights its unique characteristics, diagnostic difficulties, resistance to conventional therapy, and gaps in knowledge, emphasizing the need for improved detection and control methods.

Overview of Theileria haneyi

  • Recently discovered tick-borne hemoparasite infecting equine species globally.
  • Closely related to Theileria equi but diverges by 23% at the genomic level.
  • Causes an asymptomatic carrier state in horses, resulting in silent, ongoing transmission.
  • Considered a distinct taxon due to its unique genetics and biological behavior.

Virulence and Clinical Impact

  • Exhibits milder virulence compared to T. equi, often resulting in asymptomatic infections.
  • Persistent infections enable horses to act as reservoirs without obvious disease signs.
  • Potential to complicate equine health surveillance and management due to subtle clinical presentation.

Diagnostic Challenges

  • Standard diagnostic tool, the competitive ELISA (cELISA) targeting the equi-specific gene, fails to detect T. haneyi due to absence of this gene.
  • Development of species-specific molecular diagnostics, such as PCR assays targeting particular genes, including conventional PCR and quantitative PCR (qPCR).
  • Indirect ELISA using recombinant EMA-11 protein developed to detect T. haneyi antibodies.
  • Global genetic variability within T. haneyi strains may affect the sensitivity and specificity of serological tests.
  • Current lack of universally applicable diagnostic methods impedes effective detection and surveillance worldwide.

Therapeutic Implications and Drug Resistance

  • T. haneyi demonstrates resistance to imidocarb dipropionate (ID), the primary antiparasitic drug used against equine theileriosis.
  • Resistance complicates treatment efforts, potentially leading to persistent infections or treatment failures.
  • Inhibits clearance of T. equi when co-infections occur, posing challenges in managing mixed infections.

Transmission and Vector Knowledge Gaps

  • The competent tick vector responsible for transmitting T. haneyi remains unidentified.
  • Lack of vector knowledge limits understanding of epidemiology and hinders control measures.
  • Understanding vector biology is critical for developing targeted interventions.

Recommendations and Future Research Directions

  • Further investigations needed to identify tick vectors and transmission dynamics of T. haneyi.
  • Development and validation of improved, species-specific diagnostic tests that account for genetic diversity.
  • Research into alternative therapeutics or combination therapies to overcome drug resistance issues.
  • Comprehensive epidemiological studies to assess the global prevalence and impact of T. haneyi infection.
  • Implementation of surveillance strategies tailored to detect and monitor T. haneyi in equine populations worldwide.
  • Integration of findings into control programs to mitigate the impact of this emerging hemoparasite on equine health.

Cite This Article

APA
Elsawy BSM, Alzan HF. (2026). Theileria haneyi: An Emerging Equids Hemoparasite with Milder Virulence but Major Diagnostic and Therapeutic Implications. Pathogens, 15(3), 309. https://doi.org/10.3390/pathogens15030309

Publication

Pathogens (Basel, Switzerland)
ISSN: 2076-0817
NlmUniqueID: 101596317
Country: Switzerland
Language: English
Volume: 15
Issue: 3
PII: 309

Researcher Affiliations

Elsawy, Bassma S M
  • Parasitology and Animal Diseases Department, Veterinary Research Institute, National Research Centre, Dokki, Giza 12622, Egypt.
  • Tick and Tick-Borne Diseases Research Unit, Veterinary Research Institute, National Research Centre, Dokki, Giza 12622, Egypt.
Alzan, Heba F
  • Parasitology and Animal Diseases Department, Veterinary Research Institute, National Research Centre, Dokki, Giza 12622, Egypt.
  • Tick and Tick-Borne Diseases Research Unit, Veterinary Research Institute, National Research Centre, Dokki, Giza 12622, Egypt.
  • Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164, USA.

MeSH Terms

  • Animals
  • Theileria / pathogenicity
  • Theileria / genetics
  • Theileria / drug effects
  • Theileria / classification
  • Horses
  • Theileriasis / diagnosis
  • Theileriasis / drug therapy
  • Theileriasis / parasitology
  • Theileriasis / transmission
  • Virulence
  • Horse Diseases / diagnosis
  • Horse Diseases / parasitology
  • Horse Diseases / drug therapy
  • Imidocarb / analogs & derivatives
  • Imidocarb / therapeutic use
  • Imidocarb / pharmacology
  • Equidae / parasitology

Grant Funding

  • 13050515 / National Research Centre

Conflict of Interest Statement

The authors declare no conflicts of interest.

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