Bartonella & Brucella: Cousins in the Bacteria Kingdom

written on October 30, 2020

Bartonella and Brucella: Cousins in the Bacteria Kingdom

Bartonella and Brucella species are cousins in the taxonomy that describes the relationships between all life, and developed out of a common ancestor. The extent of similar DNA sequences in their genomes suggests their division occurred relatively recently. They are both intracellular pathogens (live inside certain kinds of cells in their hosts) that manipulate the host cell and immune response in similar ways. Consequently, they both have a wide variety of possible presentations, from mild to severe illness to chronic infections that may exist with or without symptoms.

These overlapping characteristics, along with their similar-sounding names, often make it difficult to keep them separate when patients and providers are researching zoonotic pathogens.

Zoonotic Pathogens

Both bacteria are considered zoonotic, or transmissible between animals and people. Although there are preferred host species that they likely evolved with, Bartonella and Brucella species can be found in a variety of animals. Only one species out of both genera seems to prefer humans, Bartonella bacilliformis, and even that preference is an assumption because an animal reservoir has not been determined.

This ability to survive in hosts that are not preferred means that these bacteria are able maintain their populations in animals (known as a “reservoir”) and cause illness in people when transmission occurs. A major distinction between these relatives is that Bartonella species typically require a vector to gain access to a new host, whereas Brucella species do not.

Bartonella henselae, the causative agent of cat scratch disease, is primarily associated with cats. Although there is case report evidence of direct transmission from cat bites, current research suggests that transmission is more likely where fleas and ticks are prevalent. Viable bacteria can be found in flea feces for up to 8 days following excretion.

Brucella canis is primarily associated with dogs. These bacteria can be transmitted to humans through direct mucosal contact with infected bodily fluids. The highest concentration of viable bacteria is found in vaginal discharge, semen, and placenta, but studies show that urine, feces, saliva, and blood are all potentially infective as well. Brucella canis, along with other Brucella species, can also become airborne and infect people via inhalation of live bacteria.

Scientific History

Both bacteria genera have been rediscovered several times in history, identified by their symptoms. Between the early 1900s and the 1980s, scientists gradually realized that the same bacterial families were causing various diseases. It wasn’t until 2006 that scientists finally settled on the division of species in Brucella, and new species of Bartonella are still being identified today.

Find out more about the history of human Bartonella identification.

The disease caused by infection with Brucella species is called brucellosis and infection with Bartonella species is called bartonellosis. Both species can cause cyclic fever, arthritis and neurological symptoms as well as endocarditis (swelling around the heart).

Surveys of fever around the world turn up Brucella along with the other usual suspects, including Bartonella. Even when the expectation is that most fever comes from a similar outbreak of disease such as Dengue virus, these additional pathogens are found.

Brucellosis and bartonellosis are both occupational risks for animal care workers. Before milk pasteurization was common, brucellosis was a household risk from milk products. In the United States, brucellosis is the most common infection acquired by laboratory workers. In China, there have been recent large infections among animal researchers, as well as a large community exposure when a production facility without adequate sanitary procedures spewed the bacteria into the air.

Source: Shutterstock

The fact that Brucella can be acquired by breathing it in makes it more of a target as a bioweapon than Bartonella. Consequently, there has been more funding available for a vaccine.


Comparing these pathogens can help identify genetic differences that lead to significant differences in the host response. For example, Bartonella shares a change to its flagella (whip tail) with H. pylori (a pathogen discovered in 1982 that causes certain gastric diseases) but not with Brucella. This change helps it evade identification by the host immune system. By studying these differences, it is possible both to learn more about how these species function and also to identify potential diagnostics or treatments.

Because of its impact on agriculture and agricultural products and its potential as a bioweapon, Brucella has received some research funding that isn’t available to Bartonella researchers. Nonetheless, Bartonella researchers can benefit from Brucella research findings.

Consequently, scientific developments around Brucella are important to anyone with an interest in Bartonella.


Ben-Tekaya, H. et al. (2013). Bartonella and Brucella – Weapons and strategies for stealth attack. Cold Spring Harbor Perspectives in Medicine, 3(8), a010231. 10.1101/cshperspect.a010231

Saenz, H. L. et al. (2007). Genomic analysis of Bartonella identifies type IV secretion systems as host adaptability factors. Nature Genetics, 39(12), 1469-1476. 10.1038/ng.2007.38

Ali, M. A. et al. (2020). Etiologic agents of fever of unknown origin among patients attending Mnazi Mmoja Hospital, Zanzibar. Journal of Community Health, 45(5), 1073-1080. 10.1007/s10900-020-00832

Cyranoski, D. (2019, 17 December). Chinese institutes investigate pathogen outbreaks in lab workers. Nature. Available at:

Yeung, J., & Cheung, E. (2020, September 17). Bacterial outbreak infects thousands after factory leak in China. Available at:

Moreno, E. (2020). The one hundred year journey of the genus Brucella (Mayer and Shaw 1920) [online ahead of print]. FEMS Microbiology Review, fuaa04510.1093/femsre/fuaa045

Kazmierczak, J. (2012). Public health implications of Brucella canis infections in humans.Available at:

Centers for Disease Control and Prevention. (2012). Brucellosis. Available at:


For more:  An retrospective review of a specific type of joint infections in the pediatric population that showed Brucella and Bartonella.  I also show in the comment section that transmission occurs through animal contact (birth) or animal products, inhalation of infected particles, STD, breastfeeding, bone marrow transplants, blood products, and yes, ticks.  Pathogens are found in macrophages which are transported to lymph nodes, then spread throughout the body.  Treatment consists of doxycycline, rifampicin, & gentamicin.  The One Hundred Year Journey of the Genus Brucella

Outbreak in China:

November 1, 2020

Madison Area Lyme Support Group

Author: uwe.roland.gross

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