Potential for Tick-borne Bartonelloses | CDC EID

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Volume 16, Number 3–March 2010
Perspective
Potential for Tick-borne Bartonelloses
Emmanouil Angelakis, Sarah A. Billeter, Edward B. Breitschwerdt, Bruno B. Chomel, and Didier Raoult
Author affiliations: Université de la Méditerranée, Marseille, France (E. Angelakis, D. Raoult); North Carolina State University College of Veterinary Medicine, Raleigh, North Carolina, USA (S.A. Billeter, E.B. Breitschwerdt); and University of California School of Veterinary Medicine, Davis, California, USA (B.B. Chomel)

Suggested citation for this article

Abstract
As worldwide vectors of human infectious diseases, ticks are considered to be second only to mosquitoes. Each tick species has preferred environmental conditions and biotopes that determine its geographic distribution, the pathogens it vectors, and the areas that pose risk for tick-borne diseases. Researchers have identified an increasing number of bacterial pathogens that are transmitted by ticks, including Anaplasma, Borrelia, Ehrlichia, and Rickettsia spp. Recent reports involving humans and canines suggest that ticks should be considered as potential vectors of Bartonella spp. To strengthen this suggestion, numerous molecular surveys to detect Bartonella DNA in ticks have been conducted. However, there is little evidence that Bartonella spp. can replicate within ticks and no definitive evidence of transmission by a tick to a vertebrate host.
Bartonella spp. are gram-negative bacilli or coccobacilli that belong to the α-2 subgroup of Proteobacteria. According to 16S rDNA gene comparisons, they are closely related to the genera Brucella and Agrobacterium (1). A remarkable feature of the genus Bartonella is the ability of a single species to cause either acute or chronic infection that can cause either vascular proliferative lesions or suppurative and granulomatous inflammation. The pathologic response to infection with Bartonella spp. varies substantially with the status of the host's immune system; vasoproliferative lesions are most frequently reported for immunocompromised patients. To date, 13 Bartonella species and subspecies have been associated with an increasing spectrum of clinical syndromes in humans, including cat-scratch disease and chronic bacteremia (B. henselae), bacillary angiomatosis (B. henselae, B. quintana), peliosis hepatitis (B. henselae), bacteremia and/or endocarditis (B. henselae, B. quintana, B. elizabethae, B. vinsonii subsp. arupensis, B. vinsonii subsp. berkhoffii, B. koehlerae, and B. alsatica), Carrión disease (B. bacilliformis), trench fever (B. quintana), retinitis and uveitis (B. henselae, B. grahamii), myocarditis (B. vinsonii subsp. berkhoffii, B. washoensis), splenomegaly (B. bacilliformis, B. henselae, B. rochalimae), and fever and fatigue (B. henselae, B. vinsonii subsp. berkhoffii, B. tamiae) (1–3).

Ticks
Ticks were first identified as potential vectors of Babesia bigemina, the agent of Texas cattle fever, in 1893 (4). There are 2 major tick families (≈865 tick species worldwide): the Ixodidae, or hard ticks, characterized by a sclerotized dorsal plate, and the Argasidae, or soft ticks, characterized by their flexible cuticle. A third family, the Nuttalliellidae, is represented by a single species that is confined to southern Africa. The genus Ixodes, family Ixodidae, contains >200 species, of which 14 make up the I. ricinus complex (4). Among these 14 species, I. scapularis, I. pacificus, I. ricinus, and I. persulcatus ticks are involved in the transmission of the Borrelia burgdorferi complex, which is a prevalent cause of Lyme disease in persons in the Northern Hemisphere.

Ticks in various regions of the world are vectors for bacterial, viral, and protozoal pathogens (5). Ticks may act not only as vectors but also as reservoirs of tick-transmitted bacteria that are transmitted transstadially and transovarially in a tick species (e.g., certain Rickettsia spp. and Borrelia spp.) (5). When feeding on an infected small-mammal host, larvae and nymphs can ingest >1 pathogens while obtaining a blood meal. Some organisms are then passaged to the next stage in the tick life cycle and can be transmissible during the subsequent blood meal (5). For each tick species, the optimal environmental conditions determine the geographic distribution; the spectrum of tick-borne pathogens; and as a result, the geographic areas of risk for tick-borne diseases, particularly when ticks are both vectors and reservoirs of specific pathogens.

Hard ticks are the primary vectors of a variety of bacterial pathogens, including Anaplasma spp., Borrelia spp., Ehrlichia spp., Coxiella burnetii, and Rickettsia spp (5–7). Anaplasma phagocytophilum is transmitted by I. persulcatus–complex ticks, including I. scapularis, I. pacificus, and I. ricinus, whereas Ehrlichia chaffeensis and Ehrlichia ewingii are transmitted by Amblyomma americanum ticks (5,6). Although some pathogens are carried by a single or limited number of tick species, other organisms such as Coxiella burnetii have been identified in >40 tick species (7). Lyme disease, caused by B. burgdorferi, is transmitted by I. scapularis and I. pacificus ticks within the United States, by I. ricinus ticks in Europe, and by other Ixodes spp. ticks in the Northern Hemisphere (5,8). Although specific Bartonella spp. are transmitted by blood-sucking arthropods, including fleas, lice, or sandflies, the only evidence to support the possibility of tick-borne transmission is indirect.

We present an overview of the various Bartonella spp. that have been detected in ticks and discuss human cases of Bartonella infection that are suggestive of tick transmission. Because of the rapidly expanding number of reservoir host–adapted Bartonella spp. that have been discovered in recent years, efforts to clarify modes of transmission are relevant to public health in terms of interrupting the transmission process. As evolving evidence supports the ability of this genus to induce chronic intravascular infections in humans, improved understanding of vector competence could facilitate efforts to block pathogen transmission, which would help improve human health (9).

Host Associations and Specificity
Bartonella spp. have a natural cycle of chronic intravascular infection in a reservoir host and a sustained pattern of bacterial transmission by a defined and evolutionarily well-adapted vector from the reservoir hosts to new susceptible hosts. Current information leads to the presumption of a long-standing and highly adapted species-specific association between a given Bartonella sp. and the preferred animal host and vector (10). Inadvertent infection of persons with at least 13 Bartonella spp. has resulted in a wide spectrum of disease manifestations. After primary infection of the natural mammalian host, a chronic, relapsing, nonclinical bacteremia occurs. At times, in wild and stray animal populations, including cats, cows, and various rodent species, the prevalence of infection within the population can approach 100% (1). Although the geographic distribution of a specific Bartonella sp. may reflect the geographic distribution of its hosts or vectors, knowledge related to vector transmission of Bartonella organisms remains inadequate.


Figure. Worldwide locations of ticks (blue boxes) identified with Bartonella spp. (pink boxes). I., ixodes; C., Carios; R., Rhipicephalus; B., Bartonella; H., Haemaphysalis; A., Amblyomma; D., Dermacentor.

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Potential for Tick-borne Bartonelloses | CDC EID

Suggested Citation for this Article
Angelakis E, Billeter SA, Breitschwerdt EB, Chomel BB, Raoult D. Potential for tick-borne bartonelloses. Emerg Infect Dis [serial on the Internet]. 2010 Mar [date cited]. http://www.cdc.gov/EID/content/16/3/385.htm

DOI: 10.3201/eid1603.091685