Seroprevalence of Dirofilaria Immitis and assessment of systemic inflammatory indexes in apparently healthy dogs from coastal northeastern Brazil

Abstract

Dirofilaria immitis is a vector-borne zoonotic parasite of considerable veterinary and public health significance. This study aimed to determine the seroprevalence of D. immitis and investigate associated hematological and inflammatory changes in clinically healthy dogs from the coastal municipalities of Beberibe and Cascavel, Ceará, Brazil. Between November 2024 and March 2025, blood samples were collected from 100 clinically healthy dogs (72 from Beberibe and 28 from Cascavel). Diagnostic testing included immunochromatographic assays for D. immitis antigens and microscopic evaluation for circulating microfilariae. Seropositivity for D. immitis was detected in 17 % of dogs, while microfilariae were identified in 7 %, including one discordant case (microfilaremic but antigen-negative). Hematological analysis revealed significantly reduced lymphocyte counts (p < 0.01) and elevated total plasma protein concentrations (p < 0.05) in D. immitis-positive animals. Furthermore, the platelet-to-lymphocyte ratio (PLR) was significantly increased in infected dogs (p < 0.05), whereas neutrophil counts and other systemic inflammatory indices (NLR, SII, SIRI) exhibited non-significant upward trends. These findings indicate the silent circulation of D. immitis among clinically healthy dogs and point to early hematological and immune system alterations. Notably, the elevation of PLR may serve as a potential biomarker for subclinical immune-vascular involvement in heartworm disease. The study underscores the importance of continued regional surveillance and vector control measures to reduce the risk of zoonotic transmission.