Analyze Diet
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.
Publication Date: 2026-03-12 PubMed ID: 41901762PubMed Central: PMC13029178DOI: 10.3390/pathogens15030309Google Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
  • Journal Article
  • Review

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

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.

References

This article includes 26 references
  1. Knowles DP, Kappmeyer LS, Haney D, Herndon DR, Fry LM, Munro JB, Sears K, Ueti MW, Wise LN, Silva M. Discovery of a Novel Species, Theileria haneyi n. Sp., Infective to Equids, Highlights Exceptional Genomic Diversity within the Genus Theileria: Implications for Apicomplexan Parasite Surveillance.. Int. J. Parasitol. 2018;48:679–690.
    doi: 10.1016/j.ijpara.2018.03.010pubmed: 29885436google scholar: lookup
  2. Elsawy BSM, Nassar AM, Alzan HF, Bhoora RV, Ozubek S, Mahmoud MS, Kandil OM, Mahdy OA. Rapid Detection of Equine Piroplasms Using Multiplex PCR and First Genetic Characterization of Theileria haneyi in Egypt.. Pathogens 2021;10:1414.
    doi: 10.3390/pathogens10111414pmc: PMC8620363pubmed: 34832570google scholar: lookup
  3. Sears KP, Kappmeyer LS, Wise LN, Silva M, Ueti MW, White S, Reif KE, Knowles DP. Infection Dynamics of Theileria equi and Theileria haneyi, a Newly Discovered Apicomplexan of the Horse.. Vet. Parasitol. 2019;271:68–75.
    doi: 10.1016/j.vetpar.2019.06.009pubmed: 31303207google scholar: lookup
  4. Bishop RP, Kappmeyer LS, Onzere CK, Odongo DO, Githaka N, Sears KP, Knowles DP, Fry LM. Equid Infective Theileria Cluster in Distinct 18S RRNA Gene Clades Comprising Multiple Taxa with Unusually Broad Mammalian Host Ranges.. Parasites Vectors 2020;13:261.
    doi: 10.1186/s13071-020-04131-0pmc: PMC7236219pubmed: 32430015google scholar: lookup
  5. Mshelia PW, Kappmeyer L, Johnson WC, Kudi CA, Oluyinka OO, Balogun EO, Richard EE, Onoja E, Sears KP, Ueti MW. Molecular Detection of Theileria Species and Babesia Caballi from Horses in Nigeria.. Parasitol. Res. 2020;119:2955–2963.
    doi: 10.1007/s00436-020-06797-ypmc: PMC7431391pubmed: 32647992google scholar: lookup
  6. Zhou B, Yang G, Hu Z, Chen K, Guo W, Wang X, Du C. Development of a Real-Time Quantitative PCR Based on a Taqman-MGB Probe for the Rapid Detection of Theileria haneyi.. Microorganisms 2023;11:2633.
  7. Yang G, Chen Y, Chen K, Hu Z, Li J, Wang J, Guo W, Wang X, Du C. Prevalence and Molecular Epidemiology of the Novel Equine Parasite Theileria haneyi in China.. Equine Vet. J. 2025;58:638–649.
    doi: 10.1111/evj.14505pubmed: 40257377google scholar: lookup
  8. Matjila PT, Leisewitz AL, Oosthuizen MC, Jongejan F, Penzhorn BL. Detection of a Theileria Species in Dogs in South Africa.. Vet. Parasitol. 2008;157:34–40.
    doi: 10.1016/j.vetpar.2008.06.025pubmed: 18687528google scholar: lookup
  9. Beck R, Vojta L, Mrljak V, Marinculić A, Beck A, Živičnjak T, Cacciò SM. Diversity of Babesia and Theileria Species in Symptomatic and Asymptomatic Dogs in Croatia.. Int. J. Parasitol. 2009;39:843–848.
    doi: 10.1016/j.ijpara.2008.12.005pubmed: 19367832google scholar: lookup
  10. Salim B, Alanazi AD, Omori R, Alyousif MS, Alanazi IO, Katakura K, Nakao R. Potential Role of Dogs as Sentinels and Reservoirs for Piroplasms Infecting Equine and Cattle in Riyadh City, Saudi Arabia.. Acta Trop. 2019;193:78–83.
  11. Mahdy OA, Nassar AM, Elsawy BSM, Alzan HF, Kandil OM, Mahmoud MS, Suarez CE. Cross-Sectional Analysis of Piroplasma Species-Infecting Camel (Camelus Dromedaries) in Egypt Using a Multipronged Molecular Diagnostic Approach.. Front. Vet. Sci. 2023;10:1178511.
    doi: 10.3389/fvets.2023.1178511pmc: PMC10175621pubmed: 37187929google scholar: lookup
  12. Zhang J, Kelly P, Li J, Xu C, Wang C. Molecular Detection of Theileria Spp. in Livestock on Five Caribbean Islands.. Biomed. Res. Int. 2015;2015:624728.
    doi: 10.1155/2015/624728pmc: PMC4689888pubmed: 26783522google scholar: lookup
  13. Azmi K, Al-Jawabreh A, Abdeen Z. Molecular Detection of Theileria ovis and Theleiria equi in Livestock from Palestine.. Sci. Rep. 2019;9:11557.
    doi: 10.1038/s41598-019-47965-0pmc: PMC6688999pubmed: 31399617google scholar: lookup
  14. Sears KP, Knowles DP, Fry LM. Clinical Progression of Theileria haneyi in Splenectomized Horses Reveals Decreased Virulence Compared to Theileria equi.. Pathogens 2022;11:254.
    doi: 10.3390/pathogens11020254pmc: PMC8879895pubmed: 35215197google scholar: lookup
  15. Wise LN, Kappmeyer LS, Knowles DP, White SN. Evolution and Diversity of the EMA Families of the Divergent Equid Parasites, Theileria equi and T. haneyi.. Infect. Genet. Evol. 2019;68:153–160.
    doi: 10.1016/j.meegid.2018.12.020pubmed: 30576837google scholar: lookup
  16. Kappmeyer LS, Grimsley M, Hicks J, Bastos RG. A High-Quality Genome Sequence of the Equine Apicomplexan Hemoparasite Theileria haneyi Eagle Pass Isolate.. Microbiol. Resour. Announc. 2025;15:e00563-25.
    doi: 10.1128/mra.00563-25pmc: PMC12797955pubmed: 41384744google scholar: lookup
  17. Poh KC, Oyen K, Onzere CK, Kappmeyer LS, Bastos RG. Haemaphysalis longicornis Ticks Are Unable to Transstadially Transmit Theileria Haneyi to Horses.. Front. Vet. Sci. 2025;12:1572944.
    doi: 10.3389/fvets.2025.1572944pmc: PMC11999960pubmed: 40241805google scholar: lookup
  18. Bhoora RV, Collins NE, Schnittger L, Troskie C, Marumo R, Labuschagne K, Smith RM, Dalton DL, Mbizeni S. Molecular Genotyping and Epidemiology of Equine Piroplasmids in South Africa.. Ticks Tick Borne Dis. 2020;11:101358.
    doi: 10.1016/j.ttbdis.2019.101358pubmed: 31870636google scholar: lookup
  19. Bhoora RV, Mbaba TV, Troskie M, Ackermann RE, Collins NE. Quantitative Detection of Theileria haneyi in South African Horses.. Ticks Tick Borne Dis. 2025;16:102487.
    doi: 10.1016/j.ttbdis.2025.102487pubmed: 40354693google scholar: lookup
  20. Machado RZ, André MR, Pereira JG, do Socorro Costa Oliveira M, dos Santos Ribeiro LS, de Toledo CZP, Gonçalves LR. Newly Designed PCR Assays Based on the Ema-10 and Ema-11 Genes Confirm the Circulation of Theileria haneyi in Horses in Brazil.. Rev. Bras. De Parasitol. Veterinária. 2025;34:e005225.
    doi: 10.1590/s1984-29612025049pmc: PMC12643233pubmed: 41124531google scholar: lookup
  21. Benitez-Ibalo AP, Debárbora VN, Mangold AJ, Nava S, Sebastian PS. Molecular Genotyping of Theileria Spp. Detected in Horses from Corrientes City, Argentina.. Vet. Res. Commun. 2025;49:54.
    doi: 10.1007/s11259-024-10618-3pubmed: 39718660google scholar: lookup
  22. Bastos RG, Sears KP, Dinkel KD, Kappmeyer L, Ueti MW, Knowles DP, Fry LM. Development of an Indirect ELISA to Detect Equine Antibodies to Theileria haneyi.. Pathogens 2021;10:270.
    doi: 10.3390/pathogens10030270pmc: PMC7997436pubmed: 33673478google scholar: lookup
  23. Coultous RM, McDonald M, Raftery AG, Shiels BR, Sutton DGM, Weir W. Analysis of Theileria equi Diversity in The Gambia Using a Novel Genotyping Method.. Transbound. Emerg. Dis. 2020;67:1213–1221.
    doi: 10.1111/tbed.13454pubmed: 31845493google scholar: lookup
  24. Facile V, Magliocca M, Dini FM, Imposimato I, Mariella J, Freccero F, Urbani L, Rinnovati R, Sel E, Gallina L. Molecular Diagnosis and Identification of Equine Piroplasms: Challenges and Insights from a Study in Northern.. Animals 2025;15:437.
    doi: 10.3390/ani15030437pmc: PMC11815923pubmed: 39943207google scholar: lookup
  25. Onzere CK, Hassan A, Sears K, Kappmeyer LS, Villarino NF, Fry LM, Bastos RG. Transient Efficacy of Buparvaquone against Theileria haneyi in Chronically Infected Horses.. Parasites Vectors 2024;17:337.
    doi: 10.1186/s13071-024-06397-0pmc: PMC11318256pubmed: 39129000google scholar: lookup
  26. Cardillo NN, Villarino NF, Kappmeyer LS, Chung CJ, Suarez CE, Bastos RG. Tafenoquine Succinate Inhibits the Growth of the Equine Piroplasmosis Hemoparasites Theileria equi and Babesia caballi.. Parasites Vectors 2026;19:61.
    doi: 10.1186/s13071-026-07262-ypmc: PMC12862906pubmed: 41593688google scholar: lookup

Citations

This article has been cited 0 times.