Abstract
Background:
Canine monocytic ehrlichiosis (CME) and canine granulocytic anaplasmosis (CGA), caused by Ehrlichia canis and Anaplasma phagocytophilum, are prevalent tick-borne diseases in dogs. Both trigger systemic inflammation, with C-reactive protein (CRP) and tumor necrosis factor-alpha (TNF-α) as potential biomarkers of severity.

Aim:
To compare serum CRP and TNF-α in CME, CGA, and co-infected dogs, and to assess their relationships with hematological, biochemical, and liver enzyme changes.

Methods:
In 134 dogs showing clinical signs of CME/CGA, infections were confirmed using SNAP® 4Dx® Plus, indirect immunofluorescence assay, and PCR. CRP and TNF-α were quantified using canine-specific ELISA kits.

Results:
Of the dogs tested, 112 (83.6%) were seropositive and 77 (68.8%) PCR positive (E. canis: 27; A. phagocytophilum: 29; co-infection: 21). Co-infected group had the highest CRP (135.2–154.8 mg/L) and TNF-α (161.5–174.0 pg/mL), significantly exceeding in CME (104.6–120.9 mg/L; 148.7–162.2 pg/mL), CGA (88.5–104.4 mg/L; 140.1–156.5 pg/mL), PCR-negative (33.1–45.8 mg/L; 12.3–18.9 pg/mL) and control groups (0.9–4.0 mg/L;0.2–2.3 pg/mL) with p < 0.001. Thrombocytopenia was common in all infected groups, with the lowest platelet counts in co-infected dogs (median 106.0 ×10⁹/L, p < 0.001). ALT and AST were significantly elevated only in co-infections (ALT: 89.25 U/L; AST: 69.38 U/L; p < 0.001). CRP correlated moderately with ALT/AST; TNF-α showed weaker positive associations.

Conclusion:
CRP and TNF-α are valuable indicators of systemic inflammation in CME and CGA, with maximal increases and stronger links to liver injury in co-infections, supporting their use in diagnosis and prognosis.

Key words: Ehrlichia canis; Anaplasma phagocytophilum; CRP; TNF-α; Co-infection; Dogs.