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 and trench fever. 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, 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.
''B. henselae''
B. henselae is the most common Bartonella bacterium that causes infection and is commonly referred to as “cat-scratch disease.” Historically, the B. henselae bacterial infection was thought to have been transmitted through an infected cat’s scratch or bite. However, recent research suggests that vectors such as ticks, chiggers, and mosquitoes can also infect humans with B. henselae. Fleas from infected cats can also transmit the bacteria to humans.''B. quintana''
B. quintana is also a common Bartonella pathogen that infects humans, often referred to as “trench fever.” B. quintana primarily spreads through body louse. This bacterium is known to only infect humans. While B. henselae is the most common Bartonella bacteria, B. quintana still sees new cases of the infection every year globally.''B. bacilliformis''
B. bacilliformis is a bacteria that humans can contract various Bartonella infections from. Specific parts of South America have vectors that can transmit this infection, such as Peru and the Andes Mountains. This bacterium is spread through the bite of sandflies that have B. bacilliformis. However, research about the cycle of this disease is unknown. This bacterium is responsible for acute and chronic Bartonella, also referred to as Carrion's disease, and can cause serious health complications.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, 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.
''B. henselae''
The B. henselae pathogen was discovered in 1990 by researchers through biological experiments involving skin lesions. It was initially named Rochalimaea henselae after its discovery, but was then classified as a Bartonella species in 1993 and then renamed B. henselae.Years later in 2004, researchers found B. henselae in dental pulp in remains of cats spanning from the 13th, 14th, and 16th centuries in European burial sites. Researchers then tested the remains using gene analyses, discovering that animals could be a reservoir for the pathogen.
''B. quintana''
B. quintana has been found in individuals dating back to 2230 and 1950 BC through radiocarbon testing.During a search for lice-transmitted bacteria, remains of soldiers from Napoleon's Grand Army were tested using gene testing, and other methods discovered B. quintana in body lice fragments and soldiers' teeth. In 1981, a grave from the 18th century in France had young male corpses that were thought to be soldiers. Out of the 23 individuals, 55 teeth tested positive for B. quintana.
In 2001, soldiers' remains–from Napoleon’s Grand Army–in a Lithuanian grave were discovered and used for lice-transmitted pathogen testing. The testing discovered B. quintana in body lice fragments and in tooth pulp. In 2004, the earliest presence of B. quintana was found in a buried individual’s dental pulp from approximately 4000 years ago. This discovery also marked the oldest evidence of infection from a zoonotic pathogen.
Over the span of 4,000 years, other discoveries of B. quintana were found in multiple different human remains. In 2007, burial sites from the Middle Ages in France had human skeletons that contained B. quintana in their dental pulp. Additionally, through analyses like gene assessments, a plague outbreak was explained to have been linked to body lice infected with B. quintana.
''B. bacilliformis''
Documentation of verruga peruana–a Bartonella disease caused by B. bacilliformis–was first shown on Ecuadorian fiigurines in the 14th century.Oroya fever–also caused by B. bacilliformis–is thought to have been recognized by South American Pre-Columbian Indians due to their use of the word, “sirki” or anemia that comes from the Quechua language. Verruga peruana and Oroya fever’s cause was discovered in the 20th century when it was observed by Alberto Barton in red blood cells. The red blood cells came from sick individuals who were infected with Oroya fever.
Currently, past evidence of B. bacilliformis was documented in 1974. This evidence came from the 1960s where bacterial clusters had biological similarities to the Bartonella bacteria on a male corpse infected with verruga peruana. This corpse was dated back to the 10th century.
Carrion’s Disease
Carrion’s disease is also known as Oroya fever. In 1885 Daniel Alcides Carrión–a Peruvian medical student–injected himself with verruga pathogens. After becoming ill from Oroya fever, he died, leading to Oroya fever also being referred to as “Carrion disease.”B. bacilliformis is the bacteria responsible for Carrion disease. Carrion's disease has two distinct phases, Oroya fever and verruga peruana. Oroya fever occurs after one’s initial exposure to the B. bacilliformis bacteria and is considered the acute phase of the illness. Then, verruga peruana can occur after one’s recovery from the bacteria and is considered the chronic phase of the disease.
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.
Bartonella transmission through ticks
There is mixed information on whether ticks can be a vector for Bartonella in humans. Ticks, such as Ixodes ricinus ticks, have been found to contract and transmit Bartonella bacteria from animals. However, there is no specific research that indicates that Ixodes ricinus ticks, or other tick species, have transmitted their Bartonella infection to humans, making it an area of ongoing research.As of 2025, the Centers for Disease Control and Prevention states that there is no evidence of ticks being able to transmit Bartonella to humans.
One study in Austria found Bartonella DNA present in Ixodes ricinus ticks, but the study concluded that ticks are not a risk factor for humans in developing Bartonella species such as Bartonella henselae or Bartonella quintana. Since there are various ticks and Bartonella species, more research is needed to make causal links between tick species and Bartonella in animals.
Acute Bartonella and Chronic Bartonella
Acute and chronic Bartonella are two different infections that individuals can develop after contracting the Bartonella ''bacilliformis bacteria.''Acute Bartonella
Acute Bartonella, also referred to as Oroya fever or Carrion's disease, is an infection caused by the Bartonella bacteria species, B. bacilliformis. Symptoms of acute Bartonella in humans include discomfort, headaches, fever, muscle aches, joint pain, increased sweating, skin growths, and swollen lymph nodes.Relapses with Oroya Fever are rare. If acute Bartonella is left untreated, chronic Bartonella can develop. Animals that have acute Bartonella may also experience the same symptoms as humans; however, it varies based on the animal species. Bartonella’s various bacterial species can also have different symptoms with varying degrees of severity.