Bartonella spp. are Gram-negative bacteria that cause granulomatous inflammation and non-neoplastic vasoproliferative diseases in dogs. These bacteria are transmitted through arthropod vectors or animal bites and scratches.
Bartonella DNA has been detected in canine cancers, particularly perivascular wall tumors, and hemangiosarcoma, which tends to affect middle-aged and neutered dogs. Previous research in North Carolina found that Bartonella spp. DNA was more frequently amplified in dogs with HSA than those with nodular lymphoid hyperplasia or histologically normal spleens from specific pathogen-free dogs. The current study sought to determine the proportion of dogs with Bartonella spp. DNA in splenic HSA versus non-neoplastic splenic specimens from three institutional pathology repositories, while also evaluating how sample preservation methods influence Bartonella detection in dogs with HSA.
Diagnosing bartonellosis in dogs with histologically confirmed HSA remains challenging due to the bacteria’s fastidious growth, low and intermittent bacteremia, and the limited sensitivity of existing serological tests. As a result, molecular testing of surgical or postmortem tissues is often necessary. However, a common limitation in clinical and diagnostic workflows is the routine use of formalin fixation for histologic evaluation, which may impair microbial pathogen detection.
In this study, the proportion of Bartonella-positive qPCR results from dogs with splenic HSA or NLH was significantly lower than reported in prior research using FFPE tissues from North Carolina dogs with HSA. This discrepancy likely stems from methodological differences, particularly the use of paraffin scrolls (150 μm thick) rather than histologically selected core punches (25 mg), which may have reduced the tissue quantity per extraction and led to an underestimation of Bartonella prevalence.
Additionally, the study compared matched FFPE and fresh tissue samples from 48 dogs with HSA to assess the impact of storage conditions on Bartonella detection. Results showed that the molecular prevalence of Bartonella spp. was significantly lower in formalin-fixed tissues when tested with qPCR but did not differ significantly when analyzed via ddPCR. This suggests that ddPCR offers superior sensitivity and inhibitor tolerance, particularly in cases with low bacterial loads.
The findings indicate that FFPE scrolls are not ideal for detecting Bartonella infection in splenic samples from dogs with HSA. Instead, PCR testing of fresh frozen tissues substantially improves detection sensitivity. When fresh tissues are unavailable, droplet digital PCR (ddPCR) applied to core formalin-fixed tissues provides a more reliable alternative to conventional FFPE testing.
