Acute Phase Proteins in Cats Naturally Infected or Seropositive for Leishmania infantum

Feline leishmaniosis (FeL) caused by Leishmania infantum is increasingly recognized in endemic areas, but the inflammatory profile during infection remains poorly defined. This case–control study evaluated the acute phase proteins (APPs) serum amyloid A (SAA), haptoglobin (Hp), and ceruloplasmin (Cp) in cats with anti-L. infantum antibodies and/or DNA and compared them with healthy negative controls. A total of 125 cats were enrolled, including 62 cats positive by IFAT and/or qPCR and 63 healthy controls. Total protein, albumin, albumin-to-globulin ratio (A/G), and serum protein electrophoresis were also assessed, and correlations with APPs were investigated in positive cats. Compared with controls, L. infantum-positive cats had significantly higher Hp and Cp concentrations, whereas SAA did not differ significantly. They also showed higher total protein, beta2- and gamma-globulin concentrations and lower albumin and A/G ratio. SAA and Hp were negatively correlated with albumin, whereas Cp was positively correlated with total protein and beta-globulin fractions. No significant correlations were found between APPs and IFAT antibody titer. In exploratory analyses, IFAT seropositivity (cut-off ≥ 1:80) was associated with higher Hp, whereas qPCR positivity was associated with higher SAA and Cp concentrations; however, these results should be interpreted cautiously because qPCR-positive cats were few. These findings indicate a measurable inflammatory and dysproteinemic profile in cats with laboratory evidence of L. infantum exposure and/or infection, but do not establish APPs as disease-specific diagnostic markers. However, diagnostic heterogeneity, limited qPCR testing, lack of standardized clinical staging, and possible confounding diseases limit causal and clinical interpretation.