[Equine anaplasmosis and equine piroplasmosis in Germany, Austria and Switzerland – previously anecdotal, now relevant?].

Horses in Germany, Austria, and Switzerland are increasingly at risk from two tick-borne diseases: equine granulocytic anaplasmosis (EGA) and equine piroplasmosis (EP). EGA is already endemic, while EP is still considered sporadic but likely underdiagnosed, especially due to persistently infected carriers of Theileria equi.

Scope and significance of the article

• Explains two major tick-borne infections of horses—EGA (Anaplasma phagocytophilum) and EP (Babesia caballi, Theileria equi)—that cause overlapping clinical and laboratory abnormalities.
• Highlights changing risk in Central Europe (Germany, Austria, Switzerland) due to expanding tick ranges and increased horse travel/imports.
• Underscores diagnostic strategies (PCR vs. serology), treatment goals, and the need to detect subclinical carriers to prevent spread.

Pathogens and transmission biology

• EGA: Caused by the intracellular bacterium Anaplasma phagocytophilum, which invades neutrophils and other granulocytes.
• EP: Caused by intraerythrocytic protozoa Babesia caballi and Theileria equi that parasitize red blood cells.
• Vectors:
  • Ixodes ricinus (very common in Central Europe) efficiently transmits A. phagocytophilum.
  • Dermacentor spp., Rhipicephalus spp., and Hyalomma spp. can transmit EP agents; Dermacentor spp. are expanding in parts of Germany and neighboring countries.
• Other routes: Iatrogenic transmission (shared needles, blood transfusion) can spread EP; EGA is primarily tick-borne.
• Carrier states:
  • T. equi commonly establishes long-term, sometimes lifelong, low-level parasitemia; animals can remain apparently healthy but infectious to ticks.
  • B. caballi can persist for months to years; spontaneous clearance is more likely than with T. equi but not guaranteed.

Clinical presentation and key laboratory abnormalities

• Shared signs:
  • Fever, lethargy, inappetence, reduced performance.
  • Tachycardia/tachypnea during fever, variable limb edema.
• EGA tends to show:
  • Acute high fever, stiffness, ataxia-like weakness, distal limb edema, reluctance to move.
  • Thrombocytopenia and leukopenia (often neutropenia), mild anemia; elevated inflammatory proteins (e.g., SAA), mild liver enzyme increases possible.
  • Morulae may be seen within neutrophils on blood smear during acute phase (low sensitivity).
• EP tends to show:
  • Fever with hemolysis: icterus, pale mucous membranes, dark urine (hemoglobinuria) in severe cases, colic-like signs may occur.
  • Regenerative anemia, hyperbilirubinemia, variable thrombocytopenia; hemoconcentration may be present early, then anemia predominates.
  • Piroplasms may be visible within erythrocytes on blood smear during higher parasitemia (sensitivity variable).
  • Chronic or subclinical carriers may show nonspecific poor performance or no signs.

Diagnostic strategy: pairing direct and indirect tests

• Direct detection (best for acute disease):
  • PCR on EDTA blood: Highly sensitive during active parasitemia; preferred for both EGA and EP in acutely ill horses.
  • Blood smear cytology: Quick but insensitive; A. phagocytophilum morulae in neutrophils (EGA), piroplasms in RBCs (EP). Positive smears are confirmatory, but negative smears do not rule out infection.
• Indirect detection (best for exposure, chronic infection, and carrier screening):
  • Serology (ELISA/IFA); competitive ELISAs (cELISA) are highly sensitive and, for EP, very specific and widely used for international movement testing.
  • Acute infections may be seronegative early; paired serology (acute and 2–3 weeks later) improves sensitivity for EGA and EP.
• Test selection by scenario:
  • Febrile horse with compatible signs: PCR (EGA ± EP) plus smear; add acute/paired serology.
  • Chronic poor performance or import/travel history: cELISA for EP (T. equi and B. caballi) plus PCR to identify carriers.
  • Post-treatment monitoring: Serial PCR combined with declining antibody titers to document parasite clearance or low-level persistence.
• Interpretation cautions:
  • Negative PCR does not exclude infection if parasitemia is intermittent/low; repeat testing can be necessary.
  • Antibodies can persist after parasite clearance, especially for T. equi; trends over time are more informative than a single titer.

Distinguishing EGA from EP in practice

• More suggestive of EGA:
  • Acute fever with marked limb edema, stiffness, neutropenia/thrombocytopenia, minimal icterus.
  • Seasonal spike aligned with Ixodes activity; multiple herd-mates may develop febrile illness without hemolysis.
• More suggestive of EP:
  • Evidence of hemolysis (icterus, hemoglobinuria), anemia out of proportion to leukocyte changes.
  • History of travel/import from endemic areas or previous blood transfusion; chronicity or relapses under stress.
• Definitive differentiation requires PCR and serology directed at each pathogen.

Treatment principles and follow-up

• EGA (Anaplasma phagocytophilum):
  • Antibiotics: Doxycycline (commonly used) or oxytetracycline; rapid clinical response is typical.
  • Supportive care: NSAIDs for fever/pain, rest, fluids if needed.
  • Prognosis: Generally excellent with timely therapy.
• EP (Babesia caballi, Theileria equi):
  • Antiprotozoals: Imidocarb dipropionate is standard; dosing protocols vary by species and region to balance efficacy and adverse effects.
  • Adverse effect management: Cholinergic signs are common; anticholinergic premedication and monitoring are recommended.
  • Supportive care: IV fluids, NSAIDs, anti-oxidative support; blood transfusion in severe anemia.
  • Clearance goals: T. equi is harder to clear than B. caballi; repeated treatment and prolonged monitoring may be required.
  • Monitoring: Combine serial PCR (e.g., spaced weeks apart) with antibody titer trends to document parasite elimination or persistent carriage.

Epidemiology in Germany, Austria, and Switzerland (DACH)

• EGA:
  • Endemic across Central Europe, paralleling Ixodes ricinus distribution.
  • Seasonality typically spring through autumn, with regional variation.
• EP:
  • Classically sporadic in DACH, often associated with imported animals or travel to endemic regions.
  • Underdiagnosis is likely due to subclinical carriers, especially of T. equi, and limited routine screening.
  • Vector expansion (e.g., Dermacentor spp.) and warmer seasons may increase local transmission risk; occasional autochthonous detections have been reported in parts of Central Europe.
• Drivers of changing risk:
  • Climate change and land-use patterns favoring tick survival and activity.
  • Movement of horses for sports, trade, and leisure increasing introduction of pathogens.
• Regulatory note: EP is notifiable in some jurisdictions and subject to movement restrictions; veterinarians should check current national and regional rules.

Prevention and control: from the horse to the herd and beyond

• Tick exposure reduction (challenging but beneficial):
  • Topical repellents/acaricides labeled for equine use (e.g., permethrin-based products), applied per manufacturer guidance.
  • Physical barriers: Fly/tick rugs, leg protection, stabling during peak tick hours, daily tick checks and prompt removal.
  • Pasture management: Regular mowing, brush/leaf litter removal, fencing to limit wildlife access where feasible.
• Biosecurity to prevent iatrogenic spread (especially EP):
  • Do not share needles/syringes; use sterile, single-use equipment.
  • Screen donor horses for EP before blood transfusion; maintain transfusion records.
• Surveillance and movement control:
  • Screen at-risk horses (imports, return from endemic travel) with cELISA and PCR before mixing with resident herds.
  • Identify and manage T. equi carriers to reduce transmission to ticks and other horses.
  • Monitor regional tick activity; adjust turnout and preventive measures seasonally.
• One Health consideration:
  • A. phagocytophilum is zoonotic via tick bites; equine cases signal local tick-borne risk to humans and other animals (not via direct horse-to-human spread).

Key takeaways for clinicians

• Include EGA and EP in the differential for febrile horses with cytopenias or anemia, especially with tick exposure or travel/import history.
• Use PCR for acute cases and cELISA for carrier detection; pair modalities when possible and repeat testing if suspicion remains high.
• Treat promptly and monitor for clearance—particularly crucial for T. equi to prevent long-term carriage and transmission.
• Given imperfect tick-bite prevention, emphasize surveillance, biosecurity, and management of carriers to protect individual horses and the regional population.