Bartonellae are small facultative intracellular, gram-negative bacteria, belonging to the alpha-2 subdivision Proteobacteria (Birtles, Raoult 1996). To date, more than 33 species were included in the Bartonella genus. In general, bartonellae are considered to be transmitted by bloodsucking arthropod vectors (Kosoy et al. 2012; Morick et al. 2013), spreading the bacteria from one animal to another. Bartonella spp. infect mammalian endothelial cells and erythrocytes, causing persistent infections, which can last for months and probably for years. A great variety of mammals including rodents were documented to harbor Bartonella spp. Rodents were found to have a high prevalence of Bartonella infection worldwide, ranging from 6% in greater Jakarta to 82% in Western Colorado, USA, with a high diversity of Bartonella species and strains (Buffet et al. 2013). Moreover, simultaneous infection with several Bartonella species is common (Morick et al. 2010; Gutiérrez et al. 2014).

The composition of Bartonella infection was explored in wild Gerbillus andersoni rodents and their Synosternus cleopatrae fleas by a 454-pyrosequencing analysis targeting a specific Bartonella citrate synthase gene (gltA) fragment. Out of the 91 bartonellae-positive samples, 89% were found to be co-infected with more than two phylogenetically distant Bartonella genotypes and additional closely related (but distinguishable) variants. These bartonellae lineages were distributed in a non-random manner, and a negative interaction between lineages was discovered. Interestingly, the overall composition of those infections greatly varied among samples. This variability was partially explained by factors, such as type of sample (blood versus fleas), flea sex and period of collection (Gutiérrez et al. 2014). It is acceptable that the diversification is caused mainly by recombination processes, and arthropods have a major impact by promoting these recombinations (Buffet et al. 2013).

At least 20 Bartonella species were detected in rodents, and several Bartonella spp. of rodent origin were suspected as a cause of human diseases: Bartonella elizabethae, Bartonella rochalimae and Bartonella washoensis were associated with endocarditis or myocarditis, Bartonella vinsonii subsp. arupensis and Bartonella grahamii were associated with a neurologic disease, and Bartonella tamiae as well as Bartonella tribocorum were associated with a febrile disease (Kosoy et al. 2010; Buffet et al. 2013).

Evolutionary processes have resulted in a close contact between rodents and cats. It is therefore important to acknowledge that five Bartonella species have been detected in cats including Bartonella henselae, Bartonella clarridgeiae, Bartonella koehlerae, Bartonella quintana and Bartonella bovis. Beside B. bovis, the other four Bartonella species have been detected in rodents or rodent-fleas. Of these, Bartonella henselae is the most known species, causing cat scratch disease (CSD), which may manifest in several clinical syndromes in humans. Immunocompetent human individuals present usually more local signs while immunocompromised individuals may present systemic signs which may be fatal. Veterinarians and veterinary staff are at greater risk for CSD. Transmission of B. henselae from cats to humans probably occurs through contamination of cat scratches with flea excrement. Transmission may also occur through cat bites (blood, saliva, flea-excrement).

Although the impact of rodent associated bartonellae on public health is not fully understood, the close contact between human and rodent populations creates excellent condition for transmission of Bartonella spp. from rodents to humans. The increasing numbers of reports associating Bartonella of rodent origin with animal and human diseases should alert physicians, veterinarians and public health workers to their veterinary and zoonotic potential hazard.

References

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2.  Birtles RJ, Raoult D. Comparison of partial citrate synthase gene (gltA) sequences for phylogenetic analysis of Bartonella species. Int J Syst Bacteriol. 1996;46:891–897.

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4.  Gutiérrez R, Morick D, Cohen C, Hawlena H, Harrus S. The effect of ecological and temporal factors on the composition of Bartonella infection in rodents and their fleas. ISME J. 2014. doi 10.1038/ismej.2014.22.

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