Laboratory tests are important tools that physicians use to diagnose patients. When it comes to stealth pathogens, however, testing is often only a piece of the puzzle. Physicians must understand the pathogens and the symptoms they may cause as well as assess the likelihood that the patient is infected to arrive at an accurate diagnosis.   

Bartonellosis is the umbrella term used to describe diseases caused by Bartonella species infection in people. Current medical literature focuses mostly on acute infections of the following species:

• B. henselae (cat scratch disease of cat scratch fever)
• B. quintana (trench fever)
• B. bacilliformis (Carrion’s disease)

“Atypical” bartonellosis in the form of acute and chronic infections has been explored in emerging research and case reports, but not to the extent needed to fully understand the pathogenesis of Bartonella species infection and the susceptibility of certain patient populations to chronic bartonellosis. Because of this, many physicians may not have bartonellosis on their radar when seeing a patient who has complex, non-specific symptoms that are seemingly unexplainable.

Start with these 5 questions/topics to have a productive conversation about bartonellosis with your physician(s):

1. Do you live and/or work with dogs, cats, or other animals?

Research indicates that sharing an environment with animals can lead to a higher risk of bartonellosis for people and their families. This may be because animals are brought into the home as companions or because vermin cannot be kept out of the living area, including when an individual is underhoused or unhoused. There are about 40 named Bartonella species, 17 of which are implicated in human illnesses, meaning that exposure to at least one could occur depending on your and your family’s lifestyle.

Bartonella species are adapted to living in small mammals, where they may or may not cause clinical symptoms, like Bartonella washoensis in squirrels, B. henselae in cats or B. vinsonii berkhoffii in dogs. However, zoonotic species, like B. henselae, are considered opportunistic pathogens and can lead to disease in humans if the conditions are right. Transmission to humans is much more likely when flea or other arthropod infestations occur, but there are reported cases of patients becoming directly infected from animals. For example, a woman in Ohio became blind in one eye from B. henselaeinfection after her cat licked her eyeball.

Veterinarians and other animal health workers who are prone to animal-related injuries seem to be at the highest risk for bartonellosis. A study from 2014 showed that 28% of symptomatic veterinarians had at least one Bartonella species in their bloodstream. There are also numerous case reports of veterinarians with chronic symptoms due to bartonellosis. One example of this is a veterinarian who developed severe symptoms and was found to have B. henselae in her hip joint despite receiving treatment for cat scratch disease years prior.

2. Have you had any animal-related injuries or known exposure to Bartonella vectors?

Bartonella species are typically found in the bloodstream of mammalian reservoir hosts and are transmitted by arthropod vectors such as fleas, lice, and biting flies. The bacteria may gain entry to humans directly by a vector, such as sandflies and B. bacilliformis, or with help from the reservoir host.

Trench fever (B. quintana infection), often referred to as urban fever, is transmitted by human body lice. It is historically known for causing fever and shin bone pain in WWI soldiers, but nowadays may be found among homeless populations.

Cat scratch disease (CSD) is the most common Bartonella species infection resulting from animal injury that is reported globally. A recent study from the CDC estimates that 80-95% of reported CSD cases follow the typical presentation of the disease (fever, swollen lymph nodes near site of inoculation), but the remainder manifest as atypical with more severe symptoms. Infection commonly occurs when flea dirt (feces) containing viable B. henselae is trapped under the cat’s claws and forced into an open wound following a scratch.

Case reports of infection following animal bites indicates that saliva may also be a route of transmission for these bacteria.

3. Are you immunocompromised or do you have a naturally weaker immune system?

Bartonella species were essentially re-discovered as a human pathogen in the 1990s during research on HIV/AIDS patients experiencing moderate to severe symptoms that were not typical. Researchers found that B. henselae and B. quintana were the culprits of serious health conditions including bacillary angiomatosis and bacillary pelosis. These findings showed that bartonellosis was not always a self-limiting infection as had previously been thought and that individuals with compromised immune systems were at a higher risk of developing severe disease.

Since the 1990s, research has proven this to be true in a variety of cases, such as organ transplant recipients and patients receiving cancer treatment. These conditions result in a weaker immune system that makes clearing infections difficult.

Individuals with developing or naturally weaker immune systems, like children or older adults, may be more likely to develop atypical symptoms. In a recent study, the CDC estimated that children younger than 14 accounted for 36% of atypical cases, with ocular conditions such as neuroretinitis accounting for about 60% of bartonellosis-related hospitalizations between 2005 and 2014.

4. Have you traveled recently?

The risk of tick and flea exposure varies in different areas of large countries like the United States and in the world in general. In addition, transportation depots may facilitate exposure to vermin as well as to other people’s companion animals or stray animals.

Certain species of Bartonella may be endemic to certain regions, such as Bartonella bacilliformis in South America.

Your physician may not be familiar with tick and flea exposure risks from other regions. If you are aware of published research or case reports, bring them with you.

5. Why do you think bartonellosis could be causing your symptoms?

If you have read research or case reports linking your symptoms to bartonellosis, bring them with you. Many of these cases are new, and physicians may not be aware of unusual presentations of bartonellosis.

Conclusion

Prepare for a conversation with your physician about bartonellosis by being prepared to talk about your risk factors for having encountered Bartonella  species in your environment. Bring any materials you may have that link your specific symptoms to bartonellosis, and be prepared to listen to your physician discuss other possible causes of your symptoms. Diagnosing bartonellosis is a clinical process of evaluating signs and symptoms against their possible causes. An accurate diagnosis, whatever it is, is the first step in managing or treating your condition.

 

References

Nawrocki, C. C. et al. (2020). Atypical manifestations of cat-scratch disease, United States, 2005-2014. Emerging Infectious Diseases, 26(7). doi:10.3201/eid2607.200034 https://wwwnc.cdc.gov/eid/article/26/7/20-0034_article?deliveryName=USCDC_331-DM31124

Breitschwerdt, E. B. (2014). Bartonellosis: One health perspectives for an emerging infectious disease. ILAR Journal, 55(1), 46-58. doi:10.1093/ilar/ilu015 https://academic.oup.com/ilarjournal/article/55/1/46/846503

Cheslock, M. A., & Embers, M. E. (2019). Human Bartonellosis: An underappreciated public health problem? Tropical Medicine and Infectious Disease, 4(2), 69. doi:10.3390/tropicalmed4020069 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6630881/

Lantos, P. M. et al. (2014). Detection of Bartonella species in the blood of veterinarians and veterinary technicians: A newly recognized occupational hazard? Vector-Borne and Zoonotic Diseases, 14(8), 563-570. doi:10.1089/vbz.2013.1512 https://www.liebertpub.com/doi/abs/10.1089/vbz.2013.1512

Ericson, M. et al. (2016). Culture, PCR, DNA sequencing, and second harmonic generation (SHG) visualization of Bartonella henselae from a surgically excised human femoral head. Clinical Rheumatology, 36(7), 1669-1675. doi:10.1007/s10067-016-3524-2 https://pubmed.ncbi.nlm.nih.gov/28028681/

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