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Home / Equine Research Bank / Vet Sci / Equine Granulocytic Anaplasmosis: A Systematic Review and Me...
Veterinary sciences2024; 11(6); 269; doi: 10.3390/vetsci11060269

Equine Granulocytic Anaplasmosis: A Systematic Review and Meta-Analysis on Clinico-Pathological Findings, Diagnosis, and Therapeutic Management.

Abstract: Equine granulocytic anaplasmosis (EGA) is a tick-borne disease affecting horses worldwide, caused by . The disease ranges from non-specific clinical signs to fatal outcomes. This paper aimed to analyze EGA cases reported in peer-reviewed journals, particularly on clinico-pathological findings, diagnosis, and therapeutic management. Overall, 189 clinical cases from 31 publications were included in the study. Extensive symptomatology for the EGA cases was reported, of which mostly was fever (90.30%), followed by limb edema (48.51%), anorexia (41.79%), depression (32.84%), icterus (22.39%), ataxia (17.91), tachycardia (16.42%), and lethargy (15.67%). Laboratory tests revealed thrombocytopenia (90.32%), anemia (75%), decreased hematocrit (70.59%), leukopenia (55.88%), lymphopenia (58.14%), and neutropenia (41.67%) as the most common hematological abnormalities. For a subset of tested animals, hyperbilirubinemia (20/29), hyperfibrinogenemia (13/15), and hyponatremia (10/10) were also reported. The diagnosis was established by microscopic identification of morulae (in 153 cases), and/or PCR (120 cases), isolation (1 case), or serology (56 cases). For treatment, oxytetracycline was used in the majority (52.24%) of EGA cases, but recovery without antibiotherapy (10.34%) was also noted. In conclusion, the variety of clinical and pathological findings and the challenging therapeutic approaches reported suggest that EGA should be included in the differential diagnosis when fever occurs.
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Publication Date: 2024-06-13 PubMed ID: 38922016PubMed Central: PMC11209296DOI: 10.3390/vetsci11060269Google 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.

Equine granulocytic anaplasmosis (EGA) is a tick-borne disease in horses that presents with a wide range of clinical signs and laboratory abnormalities, and this systematic review and meta-analysis summarizes current findings on its diagnosis and treatment strategies.

Overview of Equine Granulocytic Anaplasmosis

  • EGA is caused by the bacterium Anaplasma phagocytophilum, transmitted by ticks.
  • The disease affects horses globally and can range from mild symptoms to fatal outcomes.
  • The study synthesized clinical cases reported in peer-reviewed literature to better understand symptom patterns, diagnostic methods, and treatments.

Clinical Signs Observed in EGA Cases

  • The review included 189 horses from 31 published studies.
  • The most common symptom was fever, present in over 90% of cases.
  • Other frequently observed clinical signs included:
    • Limb edema (swelling) in almost half of cases (approx. 48%).
    • Anorexia (loss of appetite) in around 42% of horses.
    • Depression (32.8%) and lethargy (15.7%), reflecting systemic illness.
    • Icterus (jaundice) in about 22% of cases, indicating possible liver involvement.
    • Neurological signs such as ataxia (loss of coordination) were seen in nearly 18%.
    • Tachycardia (increased heart rate) in around 16% of horses.
  • This broad range of symptoms highlights the variable clinical presentation of EGA and its potential severity.

Laboratory and Hematological Findings

  • Common blood abnormalities in infected horses included:
    • Thrombocytopenia (low platelet count) seen in over 90% of cases, which may contribute to bleeding tendencies.
    • Anemia (reduction in red blood cells) in 75% of horses, confirmed by decreased hematocrit in about 71%.
    • Leukopenia (low white blood cell count) in over half the cases (56%), which includes:
      • Lymphopenia (decreased lymphocytes) in 58%.
      • Neutropenia (low neutrophils) in 42%.
  • Additional biochemical abnormalities included:
    • Hyperbilirubinemia (elevated bilirubin) found in 20 of 29 tested cases, often correlating with icterus.
    • Hyperfibrinogenemia (elevated fibrinogen) in 13 of 15 tested animals, indicating systemic inflammation.
    • Hyponatremia (low sodium levels) in all ten tested cases, which can affect neurological function.

Diagnostic Methods

  • The diagnosis was primarily confirmed by identification of morulae (intracellular bacterial clusters) within granulocytes under the microscope:
    • This was reported in 153 cases, making it the most common diagnostic method.
  • Molecular detection by PCR (polymerase chain reaction) was used in 120 cases, providing a sensitive and specific confirmation.
  • Serological testing to detect antibodies against the bacterium was performed in 56 cases.
  • Isolation of the bacterium in culture was rare, reported in only one case, reflecting the difficulty of this approach.
  • These diagnostic tools together help to accurately identify EGA, especially in cases with ambiguous clinical signs.

Treatment and Therapeutic Management

  • The antibiotic oxytetracycline was the main treatment in over half of the reported cases (52.24%), being effective against the intracellular bacterium.
  • A noteworthy proportion of horses (10.34%) recovered without any antibiotic therapy, suggesting that mild cases may self-resolve.
  • Other therapeutic interventions were not detailed but would typically focus on supportive care for affected horses.
  • The variability in response and management indicates challenges in therapeutic decision-making and the importance of early diagnosis.

Conclusions and Clinical Implications

  • EGA presents with diverse and sometimes non-specific clinical and laboratory signs, making it a diagnostic challenge.
  • The high prevalence of thrombocytopenia, anemia, and fever should alert clinicians to consider EGA in the differential diagnosis of febrile horses.
  • Early identification using microscopy and PCR can guide timely treatment to improve outcomes.
  • Because some horses can recover without antibiotics, the severity of disease may vary, underscoring the need for further research into prognostic factors.
  • The study emphasizes incorporating EGA in the list of possible causes when horses exhibit fever and related symptoms, especially in tick-endemic areas.

Cite This Article

APA
Bogdan AM, Mitrea IL, Ionita M. (2024). Equine Granulocytic Anaplasmosis: A Systematic Review and Meta-Analysis on Clinico-Pathological Findings, Diagnosis, and Therapeutic Management. Vet Sci, 11(6), 269. https://doi.org/10.3390/vetsci11060269

Publication

Veterinary sciences
ISSN: 2306-7381
NlmUniqueID: 101680127
Country: Switzerland
Language: English
Volume: 11
Issue: 6
PII: 269

Researcher Affiliations

Bogdan, Andreea Monica
  • Department of Parasitology and Parasitic Diseases & Animal Biology, Faculty of Veterinary Medicine, University of Agronomic Sciences and Veterinary Medicine of Bucharest, 011464 Bucharest, Romania.
Mitrea, Ioan Liviu
  • Department of Parasitology and Parasitic Diseases & Animal Biology, Faculty of Veterinary Medicine, University of Agronomic Sciences and Veterinary Medicine of Bucharest, 011464 Bucharest, Romania.
Ionita, Mariana
  • Department of Parasitology and Parasitic Diseases & Animal Biology, Faculty of Veterinary Medicine, University of Agronomic Sciences and Veterinary Medicine of Bucharest, 011464 Bucharest, Romania.

Conflict of Interest Statement

The authors declare no conflicts of interest.

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Citations

This article has been cited 3 times.
  1. Dorrego A, Olvera-Maneu S, Jose-Cunilleras E, Gago P, Raez A, Rivera B, Oporto A, Gonzalez S, Cruz-Lopez F. Molecular Detection of Theileria equi, Babesia caballi, and Borrelia burgdorferi Sensu Lato in Hippobosca equina from Horses in Spain.. Pathogens 2026 Jan 15;15(1).
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  2. Ullah A, Geng M, Chen W, Zhu Q, Shi L, Zhang X, Akhtar MF, Wang C, Khan MZ. Effect of Parasitic Infections on Hematological Profile, Reproductive and Productive Performance in Equines.. Animals (Basel) 2025 Nov 14;15(22).
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  3. Arshad A, Reif AH, Cavalleri JV, Desvars-Larrive A. Zoonotic pathogens in equids in Central Europe: a systematic review.. BMC Vet Res 2025 Jul 8;21(1):451.
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