Bartonella


 * This article is about the bacteria. For the disease, see Bartonellosis.

Overview
Bartonella (formerly known as Rochalimaea) is a genus of  Gram-negative bacteria. Facultative intracellular parasites, Bartonella species can infect healthy people but are considered especially important as opportunistic pathogens. Bartonella are transmitted by insect vectors such as ticks, fleas, sand flies and mosquitoes. At least eight Bartonella species or subspecies are known to infect humans. In June 2007, a new species under the genus, called Bartonella rochalimae, was discovered. This is the sixth species known to infect humans, and the ninth species and subspecies, overall, known to infect humans.

History
Bartonella species have been infecting humans for thousands of years, as demonstrated by Bartonella quintana DNA in a 4000 year old tooth. The genus is named after Alberto Leonardo Barton Thompson, a Peruvian scientist born in Argentina.

Bartonella was found to be a tick borne pathogen in 1999.

In 2001 doctors treating Lyme disease first reported that their patients were co-infected with Bartonella. Multiple reports of this finding seem to indicate that Bartonella is not only a tick borne but a tick-transmitted pathogen; however, actual transmission via this route has not yet been proven.

Infection cycle
The currently accepted model explaining the infection cycle holds that the transmitting vectors are blood-sucking arthropods and the reservoir hosts are mammals. Immediately after infection, the bacteria colonize a primary niche, the endothelial cells. Every five days, a part of the Bartonella in the endothelial cells are released in the blood stream where they infect erythrocytes. The bacteria then invade and replicate within a phagosomal membrane inside the erythrocytes. Inside the erythrocytes, bacteria multiply until they reach a critical population density. At this point, the Bartonella has simply to wait until it is taken with the erythrocytes by a blood-sucking arthropod.

Pathophysiology
Bartonella infections are remarkable in the wide range of symptoms an infection can produce: the time course (acute or chronic) as well as the underlying pathology are highly variable.

Treatment
Treatment is dependent on which strain of Bartonella is found in a given patient. While Bartonella species are susceptible to a number of standard antibiotics in vitro&mdash;macrolides and tetracycline, for example&mdash;the efficacy of antibiotic treatment in immunocompetent individuals is uncertain. Immunocompromised patients should be treated with antibiotics because they are particularly susceptible to systemic disease and bacteremia. Drugs of particular effectiveness include trimethoprim-sulfamethoxazole, gentamicin, ciprofloxacin, and rifampin; B. henselae is generally resistant to penicillin, amoxicillin, and nafcillin.

Epidemiology
Whether because rodent associated, IV transmitted or because tick borne disease is higher risk for the homeless, homeless IV drug users are at high risk for Bartonella infections, particularly B. elizabethae. B. elizabethae seropositivity rates in this population range from 12.5% in Los Angeles, to 33% in Baltimore, Maryland, 46% in New York, and in Sweden 39%.