Equine Piroplasmosis: What the Research Says
Evidence from 21 peer-reviewed studies
What Professionals Should Know
- •Current antiparasitic drugs have significant limitations—imidocarb causes toxicity and failures, buparvaquone is unreliable for T. equi—so expect treatment challenges and plan accordingly
- •Pre-export diagnostic testing is unreliable with current methods; use combined PCR and serology rather than single tests to reduce risk of unknowingly trading infected horses
- •Tick control alone is unsustainable due to environmental concerns and resistance development; integrated control strategies and novel therapeutics are needed and under development
- •T. equi is present in Kyrgyzstan grazing populations at ~7% prevalence; practitioners should consider serological/molecular screening protocols for horses in endemic regions, particularly older males
- •Knowledge of specific T. equi genotypes (A and E) circulating locally may inform vaccine selection and control strategies as they become available
- •Absence of B. caballi and Anaplasma species in this survey does not rule out transmission risk; continued surveillance and tick control remain important
- •Clinically healthy racehorses may harbour T. equi or B. caballi infections that cause subclinical inflammatory changes and impact performance; consider PCR testing in underperforming horses
- •Blood work abnormalities and reduced muscle mass in apparent clinically sound horses warrants investigation for piroplasmosis as a potential underlying cause
- •T. equi and B. caballi infections should be considered in the differential diagnosis for standardbred racehorses with unexplained poor racing performance or training difficulties
- •Implement rigorous tick control and monitoring programs on farms, as tick presence on horses or shared cattle increases infection risk 3-4 fold
- •Establish quarantine and testing protocols for horses entering tick-free zones to prevent introduction of T. equi, given the dramatic difference in seroprevalence between areas (6% vs 70%)
- •Consider geographic location and local tick burden when assessing disease risk and implementing herd health strategies for equine piroplasmosis prevention
- •EP remains rare in Dutch horses but is significantly more prevalent in imported horses—screening imported animals is essential before introducing them to your facilities
- •Although tick vectors are established in the Netherlands, the disease has not become endemic; continued surveillance is warranted but panic is not justified
- •If sourcing horses internationally, particularly from Southern Europe (Spain 6.0% prevalence), request EP serology results and consider quarantine protocols
- •If you work with horses in Mexican tropical/subtropical regions, expect high exposure rates to both parasites; serological testing alone underestimates active infections compared to molecular methods
- •Theileria equi appears more prevalent and persistent than B. caballi in this region—PCR testing is more reliable than serology for detecting current infections
- •Tick control and vector management are critical in endemic areas; consider screening horses before movement to non-endemic regions
- •Military and working horses in Portugal carry a significant burden of T. equi infection (>1 in 3 horses); implement tick control and biosecurity protocols appropriate to your region
- •Theileria equi can have two different genotypes, which may affect treatment responses and international movement restrictions—know the genotype status of horses being exported or moved between countries
- •Apparently healthy horses can be infected; use serological or molecular screening before moving horses between regions or internationally to prevent disease spread
- •In Italian Standardbreds with poor racing performance, include chronic piroplasmosis in your differential diagnosis list—9% prevalence justifies testing in endemic areas
- •Don't rely solely on hematological and biochemical parameters to diagnose piroplasmosis; request blood smear cytology and molecular tests (PCR/ELISA) for definitive diagnosis since results overlap significantly with normal horses
- •Know that piroplasmosis-positive horses may appear only mildly anemic and have subtle blood abnormalities, so clinical suspicion based on performance and geographic history is important
- •Donkeys in Southern Italy represent a significant reservoir for equine piroplasmosis; practitioners should consider serological screening before introducing donkeys to horse populations
- •Co-grazing with horses increases transmission risk for B. caballi; separate management of donkeys and horses may reduce infection spread
- •Although most infected donkeys are asymptomatic, clinical disease can occur; monitor donkeys with poor body condition or high antibody titres for acute piroplasmosis signs
- •Implement rigorous tick control programs in Indigenous equine communities, particularly targeting Dermacentor nitens, which carries both major equine piroplasmosis agents
- •Screen horses showing clinical signs of piroplasmosis and test tick vectors to assess local disease burden; consider tick surveillance as part of routine herd health monitoring
- •Work with community stakeholders to establish integrated vector management and disease surveillance systems as part of One-Health initiatives in endemic regions
- •H. longicornis tick presence in the US does not represent an additional risk pathway for T. haneyi transmission through transstadial tick-borne spread, simplifying epidemiological risk assessment
- •Other tick vectors or direct transmission routes remain the primary concern for T. haneyi exposure and should be the focus of biosecurity and surveillance protocols
- •Clinical diagnosis of T. haneyi infection should not be attributed to H. longicornis parasitism alone; investigation of other potential vector species and transmission sources is warranted
- •Nested PCR offers superior sensitivity for detecting both T. equi and B. caballi but requires gel electrophoresis for differentiation; duplex qPCR is faster and directly distinguishes parasites but may miss low-level infections
- •Choice of diagnostic method should depend on laboratory capability and clinical priority: prioritize sensitivity (nPCR) for screening or specificity/speed (duplex qPCR) when infection type must be identified quickly
- •Mixed infections with both parasites occur in field populations (5.56% prevalence here), so diagnostic methods capable of detecting both organisms are essential for comprehensive screening programs
- •Donkeys in West Africa carry significantly higher piroplasm infection rates than horses and may serve as disease reservoirs—implement targeted screening and tick control for donkey populations
- •The presence of multiple T. equi genotypes suggests diverse parasite strains circulating in the region; consider this genetic diversity when selecting diagnostic tests and treatment protocols
- •Nigeria's role as an animal transport hub increases risk of EP dissemination across West Africa—veterinarians should maintain high clinical suspicion and implement biosecurity measures for imported equids
- •Theileria equi establishes infection through innate immune mechanisms independent of adaptive immunity, meaning vaccination strategies must focus on non-lymphocyte-dependent pathways or early parasite stages
- •The intraleukocyte schizont stage can persist in multiple white blood cell types, complicating diagnostic and therapeutic targeting strategies
- •Understanding T. equi tropism to macrophages may inform treatment approaches targeting the intracellular parasitic stage
- •Veterinarians in China should be aware that equine piroplasmosis may now include T. haneyi as a causative agent, requiring updated diagnostic protocols beyond traditional T. equi and B. caballi screening
- •Tick control and disease surveillance programs should be adapted to account for this newly identified pathogen affecting the equine industry in China
- •Consider T. haneyi in differential diagnosis for horses presenting with clinical signs consistent with piroplasmosis in Chinese populations
- •This novel lateral flow assay could enable rapid point-of-care diagnosis of equine piroplasmosis without requiring specialized laboratory equipment, improving early detection on farms and in field settings
- •The simplified testing protocol may reduce diagnostic delays and support faster treatment initiation, potentially improving outcomes in Theileria equi-infected horses
- •Field-deployable diagnostics of this type could improve disease surveillance and control in equine populations, particularly in resource-limited settings
- •Maintain awareness of equine piroplasmosis as an emerging disease threat; familiarize yourself with clinical signs and transmission routes to enable early detection
- •Implement biosecurity protocols for imported horses and those with travel history, particularly from endemic regions, to prevent disease establishment
- •Advocate for formal surveillance systems and practitioner education to improve UK preparedness for potential EP incursion
- •Equine practitioners in Spain should be aware that piroplasmosis remains a significant tick-borne disease threat affecting horse health and industry economics
- •Regional variation in EP prevalence suggests risk assessment and prevention strategies should be tailored to local epidemiological patterns
- •Serological and molecular screening may be warranted for horses with clinical signs consistent with piroplasmosis or in endemic regions
- •Carrier horses pose an underestimated biosecurity risk to the UK horse population; practitioners should be alert to clinical signs and request appropriate testing for horses with compatible symptoms or recent import history
- •Current EP screening requirements are inadequate for importation purposes—clinicians should consider recommending EP testing for imported horses and those in contact with recently imported animals as a precautionary measure
- •PCR testing may underestimate true infection prevalence compared to serology; practitioners should interpret negative PCR results cautiously and consider serological testing as a complementary diagnostic approach
- •This research identifies novel vaccine targets that could eventually reduce transmission of economically important parasitic diseases in cattle and horses
- •The species-specific and stage-specific expression patterns of CCp proteins suggest that any future vaccine approach would need to be tailored to the target parasite and life stage
- •Understanding parasite biology at the molecular level may lead to new control strategies beyond current tick management and treatment approaches
- •Clinicians should recognize tick-borne piroplasmosis as a cause of anemia in horses, particularly with T. equi re-emergence in the US, requiring appropriate diagnostic testing
- •Tick control is critical for disease prevention since both parasites are tick-transmitted; however, B. caballi's transovarial transmission makes eradication more challenging
- •Long-term carrier status in recovered horses necessitates screening protocols before movement or breeding to prevent disease transmission
Key Research Findings
Equine piroplasmosis is caused by three intraerythrocytic apicomplexan parasites (T. equi, B. caballi, T. haneyi) transmitted by multiple tick species and through iatrogenic/vertical routes
Imidocarb dipropionate (ID) has significant side effects and recurrent treatment failures, while buparvaquone (BPQ) is less effective against T. equi and unavailable in some countries
Current diagnostic limitations include lack of standardized PCR tests and serological assay limitations, creating risk of exporting infected animals
Combination of standardized PCR-based techniques and improved serological tests are proposed to enhance diagnostic accuracy and trade safety
T. equi detected in 7.4% (23/311) of grazing horses in Kyrgyzstan; B. caballi, hemotropic mycoplasmas, and Anaplasma species not detected
T. equi infection rate higher in males (8.11%) versus females (6.35%) and in horses >5 years (9.02%) versus 1-4 years (6.35%), though differences not statistically significant
Phylogenetic analysis identified A and E genotypes of T. equi circulating in Kyrgyzstan horse populations
First molecular investigation of A. capra in horses in Kyrgyzstan; pathogen not detected despite wide host spectrum in region
Theileria equi and/or Babesia caballi PCR positivity was detected in Italian Standardbred racehorses presented as clinically healthy
Haematological and blood chemistry parameters differed between PCR-positive and PCR-negative horses
Chronic equine piroplasmosis infection was associated with altered muscle mass scores in positive horses
Performance metrics showed differences between infected and non-infected standardbred racehorses
Seroprevalence of T. equi was 6% in R. microplus-free zone compared to 70% in tick-infested zone
Observation of ticks on horses increased odds of T. equi seropositivity by 4-fold
Observation of ticks on cattle sharing paddocks with horses increased odds of T. equi seropositivity by 3-fold
Evidence Base
New insights in the diagnosis and treatment of equine piroplasmosis: pitfalls, idiosyncrasies, and myths.
Mendoza Francisco J, Pérez-Écija Alejandro, Kappmeyer Lowell S et al. (2024) — Frontiers in veterinary science
Altay Kursat, Erol Ufuk, Sahin Omer Faruk et al. (2024) — Frontiers in veterinary science
A cross-sectional study on performance evaluation in Italian standardbred horses' real-time PCR-positive for Theileria equi.
Coluccia Pierpaolo, Gizzarelli Manuela, Scicluna Maria Teresa et al. (2024) — BMC veterinary research
Comparison of Seroprevalence and Identification of Risk Factors for Theileria equi in Horses From Vector-Free and Infested Areas in Southern Brazil.
Pereira Marco Rocha, Trein Cristina Rodrigues, Webster Anelise et al. (2023) — Journal of equine veterinary science
Low seroprevalence of equine piroplasmosis in horses exported from the Netherlands between 2015 and 2021.
Graham Heather, van Kalsbeek Paul, van der Goot Jeanet et al. (2022) — Frontiers in veterinary science
Serological and molecular detection of Babesia caballi and Theileria equi in Mexico: A prospective study.
Salinas-Estrella Elizabeth, Ueti Massaro W, Lobanov Vladislav A et al. (2022) — PloS one
Survey of Zoonotic and Non-zoonotic Vector-Borne Pathogens in Military Horses in Lisbon, Portugal.
Fuehrer Hans-Peter, Alho Ana Margarida, Kayikci Feodora Natalie et al. (2020) — Frontiers in veterinary science
Piroplasmosis in Italian Standardbred Horses: 15 Years of Surveillance Data.
Padalino Barbara, Rosanowski Sarah M, Di Bella Caterina et al. (2019) — Journal of equine veterinary science
Seroprevalence and risk factors associated with Babesia caballi and Theileria equi infections in donkeys from Southern Italy.
Piantedosi D, D'Alessio N, Di Loria A et al. (2014) — Veterinary journal (London, England : 1997)
Babesia caballi and Theileria equi in ticks from horses in four Indigenous communities of Costa Rica.
Posada-Guzmán M F, Jiménez-Rocha A E, Sánchez-Bermúdez J F et al. (2026) — Journal of equine veterinary science
Poh Karen C, Oyen Kennan, Onzere Cynthia K et al. (2025) — Frontiers in veterinary science
Lv Kunying, Zhang Yiwei, Yang Yixin et al. (2022) — Frontiers in veterinary science
Genetic Characterization of Piroplasms in Donkeys and Horses from Nigeria.
Sunday Idoko Idoko, Tirosh-Levy Sharon, Leszkowicz Mazuz Monica et al. (2020) — Animals : an open access journal from MDPI
Lymphocytes and macrophages are infected by Theileria equi, but T cells and B cells are not required to establish infection in vivo.
Ramsay Joshua D, Ueti Massaro W, Johnson Wendell C et al. (2013) — PloS one
Prevalence and molecular epidemiology of the novel equine parasite Theileria haneyi in China.
Yang Guangpu, Chen Yongyan, Chen Kewei et al. (2026) — Equine veterinary journal
Rapid and sensitive detection of Theileria equi using a novel integrated RPACRISPR/Cas13a lateral flow assay.
Alsultan Amjed, Karim Salah Mahdi, Al-Saadi Mohammed et al. (2025) — Journal of equine veterinary science
A risk assessment of equine piroplasmosis entry, exposure and consequences in the UK.
Coultous Robert M, Sutton David G M, Boden Lisa A (2023) — Equine veterinary journal
Sero-molecular survey and risk factors of equine piroplasmosis in horses in Spain.
Camino Eliazar, Buendia Aranzazu, Dorrego Abel et al. (2021) — Equine veterinary journal
Equine piroplasmosis status in the UK: an assessment of laboratory diagnostic submissions and techniques.
Coultous Robert M, Phipps Paul, Dalley Charlie et al. (2019) — The Veterinary record
Differential expression of three members of the multidomain adhesion CCp family in Babesia bigemina, Babesia bovis and Theileria equi.
Bastos Reginaldo G, Suarez Carlos E, Laughery Jacob M et al. (2013) — PloS one