by 
An enlarged spleen can present a diagnostic mystery. The spleen is an organ that is like a large lymph node (see our previous blog post on bartonellosis and lymph nodes). It cleans old red blood cells from the bloodstream and as part of that process is exposed to everything in the body.
The spleen can become enlarged (splenomegaly) due to a pathogen, a metastasized cancer, or other reasons such as autoimmune disease. Rarely, the spleen can rupture. A person with an enlarged spleen may be advised to avoid contact activities in order to prevent rupture.
Sometimes the changes to the spleen can be hard to interpret or hard to treat, leading to splenectomy (spleen removal surgery) that may not be necessary. For example, a case report from 2009 warns that changes caused by Bartonella species infection (bartonellosis) may be mistaken for splenic lymphoma.
One question is just what role the spleen plays in controlling bartonellosis. This has been tested in both cats and mice. In the mice, spleens were removed from some mice and how they responded to bartonellosis was compared to mice with intact spleens. The mice without spleens had 10 times higher bacteremia (the total bacteria load in the blood), and their infections lasted an average of two weeks longer. A similar experiment done in cats had the same result. Clearly, the spleen plays an important role in managing bartonellosis.
Research in dogs suggests there may be a link between Bartonella species and cancer of the spleen as well. Splenic disease is a cause of mortality in older dogs, especially Golden Retrievers, which have the highest prevalence of hemangiosarcomas (cancer of the blood/blood vessels) among breeds. The highly vascular splenic tissue makes a suitable home for these cancers. Once the mass grows large enough, it can cause the spleen to rupture and/or cells can metastasize to other places such as the heart.
In one study, Galaxy Diagnostics co-founder Dr. Breitschwerdt and his team at the North Carolina State College of Veterinary Medicine used PCR on tissue biopsies to discover that Bartonella species DNA was more prevalent in splenic hemangiosarcomas compared to Babesia and Mycoplasma species. In 2018, the American Kennel Club’s Canine Health Foundation awarded a $220,000 grant to the Bartonella Research Project at the college to further examine the link between bartonellosis and splenic hemangiosarcomas in dogs.
In humans, Bartonella species infections of the spleen have been reported with other symptoms including fever and other infected organs. Bartonellosis has been associated with abscesses or nodules in the spleen. Bacillary peliosis can also occur in the spleen (see our previous blog post on bacillary peliosis and bacillary angiomatosis).
In one reported case, a spleen rupture occurred spontaneously with no prior signs of infection such as fever. A lymph node from the splenic hilum was found to have necrotizing granulomas and microabscesses. The individual was tested for a variety of pathogens and found to be infected with Bartonella henselae.
Bartonellosis is notoriously hard to detect, which can make spleen symptoms caused by Bartonella species particularly mysterious. A patient in the United States had an enlarged spleen, skin lesions, and anemia. Blood testing did not reveal bartonellosis, but the spleen was eventually removed and tissue tests revealed the presence of Bartonella bacilliformis. This is a species of Bartonella that is primarily transmitted by sand flies in South America. The patient, it turns out, had visited South America three years earlier.
Conclusion
An enlarged spleen can be caused by a variety of things, making it difficult for physicians to determine why it is happening and therefore an effective treatment. For many patients, it can be safer to remove the spleen immediately and perform further diagnostics later. Bartonellosis is one cause which can be difficult to detect, but it is treatable.
References
Rising, T. et al. (2016). Splenorenal manifestations of Bartonella henselae infection in a pediatric patient. Case Reports in Radiology, 2016, 7803732. doi:10.1155/2016/7803832 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4835656/
Liberto, M. C. et al. (2013). Diagnosis and follow-up of Bartonella henselae infection in the spleen of an immunocompetent patient by real-time quantitative PCR. Journal of Medical Microbiology, 62(7). doi:10.1099/jmm.0.050617-0 Available at: https://www.microbiologyresearch.org/docserver/fulltext/jmm/62/7/1081_jmm050617.pdf?expires=1573610642&id=id&accname=guest&checksum=CCB170A5F5F432F02D4BC09F1D47E638
Bieraugel, K. et al. (2015). Cat got your spleen? Hepatosplenic Bartonella infection. The American Journal of Medicine, 128(3), 246-249. doi:10.1016/j.amjmed.2014.11.003 https://www.amjmed.com/article/S0002-9343(14)01022-5/abstract
Daybell, D. et al. (2004). Disseminated infection with Bartonella henselae as a cause of spontaneous splenic rupture. Clinical Infectious Diseases, 39(3), e21-e24. doi:10.1086/422001 https://academic.oup.com/cid/article/39/3/e21/354202
Lydy, S. L. et al. (2008). Isolation and characterization of Bartonella bacilliformis from and expatriate Ecuadorian. Journal of Clinical Microbiology, 42(2), 627-637. doi:10.1128/JCM.01207-07 https://jcm.asm.org/content/46/2/627
Ghez, D. et al. (2001). Bartonella henselae infection mimicking a splenic lymphoma. Scandinavian Journal of Infectious Diseases, 33(12), 935-936. doi:10.1080/00365540110076705 https://www.tandfonline.com/doi/abs/10.1080/00365540110076705?journalCode=infd19
Sykes, J. E. et al. (2007). Bartonella henselae infection in splenectomized domestic cats previously infected with hemotropic Mycoplasma species. Veterinary Immunology and Immunopathology, 116(1-2): 104-8. doi:10.1016/j.vetimm.2006.12.004 https://www.ncbi.nlm.nih.gov/pubmed/17254639
Varanat, M. et al. (2011). Molecular prevalence of Bartonella, Babesia, and Hemotropic Mycoplasma sp. in dogs with splenic disease. Journal of Veterinary Internal Medicine, 25(6), 1284-1291. doi:10.1111/j.1939-1676.2011.00811.x https://onlinelibrary.wiley.com/doi/full/10.1111/j.1939-1676.2011.00811.x
North Carolina State University. (2018). AKC-CHF grant funds new CVM Bartonella research project. Available at: https://cvm.ncsu.edu/akc-chf-grant-funds-new-cvm-bartonella-research-project/