Bartonella - Epidemiology of an Emerging Pathogen
This study was initiated to determine the source of infection in a human case of endocarditis (inflammation of the heart) with an unknown cause that occurred in Washoe County. The causative organism was later identified as a previously unknown bacterium and was named Bartonella washoensis. Several other members in the genus Bartonella are known to cause human disease. Among them are Oroya fever (South America), trench fever and cat scratch disease.
The Vector-Borne Disease Prevention Program staff collaborated with researchers from the Centers for Disease Control and Prevention (CDC) in Fort Collins to identify the most likely animal source of the Bartonella infection in the human case. As rodents are often hosts for Bartonella species, blood samples were collected from a variety of rodents throughout the Truckee Meadows area. The samples were cultured to isolate Bartonella organisms. Using genetic sequencing techniques, it was then possible to compare the relatedness of the rodent bacterial isolates with those from the patient. Two of the isolates were found to be 100% genetic matches.*
The rodent species identified is the California ground squirrel (Spermophilus beecheyi), which is common in Washoe County. This squirrel also happens to be the primary host species for the plague bacterium (Yersinia pestis) in Nevada that is transmitted primarily through the bite of infected fleas found on the squirrel. The next step in the Bartonella investigation will be to attempt to identify the possible mode of transmission between squirrels and humans and will focus on the flea common to the squirrels (Oropsylla montana).
* Kosoy, M., Murray, M., Gilmore Jr., R.D, Bai, Y., and Gage, K.L. 2003. Bartonella Strains from Ground Squirrels Are Identical to Bartonella washoensis Isolated from a Human Patient. Journal of Clinical Microbiology. 41:645-650.