Bartonella

Bartonella is a genus of Gram-negative bacteria. It is the only genus in the family Bartonellaceae. Bartonella species cause bartonellosis, which is a group of zoonotic infectious diseases that affects both humans and animals. Common forms include cat-scratch disease (Bartonella henselae) and trench fever (Bartonella quintana). As Facultative intracellular parasites, Bartonella species can infect healthy people, but are considered especially important as opportunistic pathogens. Bartonella species are transmitted by vectors such as fleas, sand flies, ticks and mosquitoes. Currently, 12 Bartonella species are known to infect humans. As research continues, more species transmissible to humans from vectors can be discovered. 37 different species and 3 subspecies of Bartonella exist. While 12 species can infect humans, 3 Bartonella pathogens are largely associated with human transmission and infection: B. henselae, B. quintana, and Bartonella bacilliformis.

Bartonella is a genus of Gram-negative bacteria. It is the only genus in the family Bartonellaceae. Bartonella species cause bartonellosis, which is a group of zoonotic infectious diseases that affects both humans and animals. Common forms include cat-scratch disease (Bartonella henselae) and trench fever (Bartonella quintana). As Facultative intracellular parasites, Bartonella species can infect healthy people, but are considered especially important as opportunistic pathogens. Bartonella species are transmitted by vectors such as fleas, sand flies, ticks and mosquitoes. Currently, 12 Bartonella species are known to infect humans. As research continues, more species transmissible to humans from vectors can be discovered. 37 different species and 3 subspecies of Bartonella exist. While 12 species can infect humans, 3 Bartonella pathogens are largely associated with human transmission and infection: B. henselae, B. quintana, and Bartonella bacilliformis.

History

Bartonella species have been infecting humans for thousands of years, as demonstrated by Bartonella quintana DNA being found in a 4000-year-old tooth. The genus is named for Alberto Leonardo Barton Thompson (1871 – October 26, 1950), an Argentine-born Peruvian scientist. The numerous Bartonella species have different origins. For many Bartonella species discoveries, dental pulp was the body source where the bacteria was found. Bartonella henselae, B. quintana, and Bartonella tribocorum are just some of the species discovered through dental pulp. While the discoveries of the various bacteria are different, B. henselae, B. quintana, and Bartonella bacilliformis have the most researched origins.

Infection cycle

Bartonella species are well-known to be transmissible to both animals and humans through various other vectors, such as fleas, lice, and sand flies. Bartonella bacteria are associated with cat-scratch disease, but a study in 2010 concluded, "Clinicians should be aware that ... a history of an animal scratch or bite is not necessary for disease transmission." All current Bartonella species identified in canines are human pathogens. Mammal hosts, cat bites, and cat saliva have also been shown to spread the bacteria. The arthropod Bartonella infection cycle starts through the bite of an insect, typically a flea, lice, or other common blood-sucking arthropods. The infected arthropod's bite causes the Bartonella bacteria to enter the host–human or animal. In the early stages of the bite, Bartonella cannot infect red blood cells immediately, causing the host to show no symptoms or signs of infection. Instead, the bacteria must find a "primary niche", or a temporary place of existence in the body to prepare for the next stage of infection. From the primary niche, the Bartonella bacteria is able to move into the bloodstream. Once inside the bloodstream, the bacteria attaches to red blood cells, invades them, and either survives or dies inside of the cells. During the infection process, a lack of immune response from the host is beneficial to the bacteria. Living inside the red blood cells helps the bacteria survive without being detected by the immune system. This overall process allows for the bacteria to stay in the blood. If another insect were to bite an infected host, the insect could then transmit the infection from one host to another due to the live bacteria in the original host's blood.

Pathophysiology

Bartonella infections can produce a wide range of symptoms. The course of the diseases (acute or chronic) and the underlying pathologies are variable.

Treatment

Treatment is dependent on which species of Bartonella is found in an individual. While Bartonella species are susceptible to a number of standard antibiotics in vitro—macrolides and tetracycline, for example—the efficacy of antibiotic treatment in immunocompetent individuals is currently not known. 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; Bartonella henselae is generally resistant to penicillin, amoxicillin, and nafcillin. Currently, the research on whether Bartonella infections can be shortened by treatments such as antibiotics is mixed. Additionally, Bartonella infections can become more complicated in some individuals, making the remedies different from standard treatment practices. Antibiotic treatments are agreed upon to aid the infection. Individuals with HIV should be treated with antibiotics. If exposure to a Bartonella bacterium turns into an infection that impacts the central nervous system, antibiotics are also needed. However, some Bartonella species can be treated on their own without the use of standard medications.

Epidemiology

Homeless intravenous drug users are at high risk for Bartonella infections, particularly Bartonella elizabethae. Bartonella elizabethae seropositivity rates in this population range from 12.5% in Los Angeles, to 33% in Baltimore, Maryland, 46% in New York City, and 39% in Sweden.

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN). The phylogeny is based on whole-genome analysis. Bartonella genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID New Bartonella Species That Infects Humans Discovered

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