The authors of a new study say their findings further support the connection between persistent infection and some types of cancer.

Researchers from North Carolina State University (NCSU) have found a very high prevalence of Bartonella bacteria in tumors and tissue samples taken from dogs with hemangiosarcoma (HSA), a cancer of the blood vessels. Oddly enough, the bacteria weren’t found in blood samples.

Hemangiosarcoma is an aggressive and deadly cancer that develops from endothelial cells, the cells that create blood vessels. It’s responsible for two-thirds of all heart or spleen tumors in dogs. Since HSA usually can’t be diagnosed without major abdominal surgery, most cases remain undetected until they’ve reached an advanced stage, resulting in a one-year survival rate of only 12 to 20%.

Given the established links between chronic inflammation and cancer, the authors wanted to determine whether chronic infection of blood vessels due to bacteria could be a contributing cause of HSA. They looked at tumor tissue, nontumor tissue, and blood samples from 110 dogs with HSA from across the US.

Bartonella was present in 74% of the dogs with HSA; it was present in 34% of tumor tissue and 63% of nontumor tissue, but appeared in none of the blood samples.

The researchers note that Bartonella is a “stealth” pathogen that can hide in the cells that line blood vessel walls, which is part of what makes it so difficult to detect, and say that their findings add more evidence to the connection between infection and cancer risk.

NEWStat reached out to corresponding author Ed Breitschwerdt, DVM, professor of medicine and infectious diseases at NCSU’s College of Veterinary Medicine, to find out more.

NEWStat: What makes the discovery of Bartonella bacteria in the tissue of dogs with HSA so significant?

Ed Breitschwerdt: Currently, 20%–50% of all human cancers are caused by or associated with an infectious agent, [but] in most instances research emphasis has focused on viruses. To a substantial degree, the potential role of bacteria as a cause of cancer has been ignored. [Documentation of Bartonella in 74% of dogs with splenic or cardiac HSA] supports an association of this genus of bacteria with this serious canine cancer.

NEWStat: Given that HAS is a cancer of the blood vessels, why doesn’t Bartonella show up in blood samples from these dogs?

EB: Good question. Based upon our research involving dogs, horses, and humans, infected individuals have very low levels of bacteria in the blood stream, unless severely immunosuppressed. In addition experimental infection of rodents and cats with various Bartonella species has documented a relapsing bacteremia. Presumably the bacteria preferentially infects endothelial cells (cells that line the interior surface of blood vessels) and pericytes (cells that surround endothelial cells) and only enters systemic circulation on a periodic and at potentially unpredictable time points. 

NEWStat: Given the difficulty of diagnosing HSA, can the presence of Bartonella help in diagnosing or predicting it?

EB: We have and continue to work on the enhanced diagnostic detection of these bacteria in blood and serum samples. Although slower and more challenging than one would hope, we continue to make progress in a forward direction in the context of more sensitive yet specific diagnostic testing modalities. Although yet to be proven, prevention of Bartonella infection via vaccination or early diagnosis of the infection with therapeutic intervention could potentially prevent the ultimate development of HSA.

NEWStat: What do these findings say about the relation between infection and cancer risk?

EB: Due to the fact that Bartonella species induce antibiotic-reversible vasoproliferative lesions in immunosuppressed dogs and humans, it is perhaps logical to speculate that long-term, undetected infection could induce [HAS]. In addition, we have previously isolated Bartonella species or documented infection with these bacteria by polymerase chain reaction amplification and DNA sequencing in dogs with HSAs and in humans with epitheliod hemangioendothelioma, providing additional indirect evidence that this genus of bacteria could be involved in carcinogenesis.

NEWStat: What’s your next step?

EB: We have another study of HSA and Bartonella prevalence in progress. We continue to work on enhanced serological, bacteriological, and molecular diagnostic modalities. As Bartonella causes endocarditis, myocarditis, and other serious [diseases] in dogs and humans, we’re also focusing on the identification and characterization of immunogenic peptides that could be used to vaccinate dogs and prevent this infection.

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