Bartonella spp. as emerging human pathogens

Members of the genus Bartonella (formerly Rochalimaea) were virtually unknown to modern-day clinicians and microbiologists until they were associated with opportunistic infections in AIDS patients about 6 years ago. Since that time, Bartonella species have been associated with cat scratch disease, bacillary angiomatosis, and a variety of other disease syndromes. Clinical presentation of infection with Bartonella ranges from a relatively mild lymphadenopathy with few other symptoms, seen in cat scratch disease, to life-threatening systemic disease in the immunocompromised patient. In some individuals, infection manifests as lesions that exhibit proliferation of endothelial cells and neovascularization, a pathogenic process unique to this genus of bacteria. As the spectrum of disease attributed to Bartonella is further defined, the need for reliable laboratory methods to diagnose infections caused by these unique organisms also increases. A brief summary of the clinical presentations associated with Bartonella infections is presented, and the current status of laboratory diagnosis and identification of these organisms is reviewed.

Bartonella spp. in pets and effect on human health

Pets represent a large reservoir for human infection.

Among the many mammals infected with Bartonella spp., pets represent a large reservoir for human infection because most Bartonella spp. infecting them are zoonotic. Cats are the main reservoir for Bartonella henselae, B. clarridgeiae, and B. koehlerae. Dogs can be infected with B. vinsonii subsp. berkhoffii, B. henselae, B. clarridgeiae, B. washoensis, B. elizabethae, and B. quintana. The role of dogs as an important reservoir of Bartonella spp. is less clear than for cats because domestic dogs are more likely to be accidental hosts, at least in nontropical regions. Nevertheless, dogs are excellent sentinels for human infections because a similar disease spectrum develops in dogs. Transmission of B. henselae by cat fleas is better understood, although new potential vectors (ticks and biting flies) have been identified. We review current knowledge on the etiologic agents, clinical features, and epidemiologic characteristics of these emerging zoonoses.

Factors associated with the rapid emergence of zoonotic Bartonella infections

Within the last 15 years, several bacteria of the genus Bartonella were recognized as zoonotic agents in humans and isolated from various mammalian reservoirs. Based on either isolation of the bacterium or PCR testing, eight Bartonella species or subspecies have been recognized as zoonotic agents, including B. henselae, B. elizabethae, B. grahamii, B. vinsonii subsp. arupensis, B. vinsonii subsp. berkhoffii, B. grahamii, B. washoensis and more recently B. koehlerae. The present manuscript reviews the factors associated with the emergence of these zoonotic pathogens, including better diagnostic tools and methods to identify these fastidious bacteria, host immunosuppression (caused by infectious agents, cancer, aging or induced by immunosuppressive drugs), the interaction of co-infection by several infectious agents that may enhanced the pathogenecity of these bacteria, increased outdoor activity leading to exposure to wildlife reservoirs or vectors, poverty and low income associated with infestation by various ectoparasites, such as body lice and finally the dispersal of Bartonellae around the world. Furthermore, a description of the main epidemiological and clinical features of zoonotic Bartonellae is given. Finally, the main means for diagnosis, treatment and prevention of these diseases are presented.

Bartonella infection in animals: carriership, reservoir potential, pathogenicity, and zoonotic potential for human infection

Recent observations have begun to support a role for Bartonella spp. as animal as well as human pathogens. Bartonella spp. are vector-transmitted, blood-borne, intracellular, gram-negative bacteria that can induce prolonged infection in the host. Persistent infections in domestic and wild animals result in a substantial reservoir of Bartonella organisms in nature that can serve as a source for inadvertent human infection. The prevalence of bacteremia can range from 50 to 95% in selected rodent, cat, deer, and cattle populations. Dogs infected with Bartonella spp. can develop lameness, endocarditis, granulomatous lymphadenitis, and peliosis hepatis, lesions that have also been reported in association with human infection. Understanding the role of Bartonella spp. as pathogens in cats and other wild or domestic animals awaits the results of additional studies. Considering the extensive animal reservoirs and the large number of insects that have been implicated in the transmission of Bartonella spp., both animal and human exposure to these organisms may be more substantial than is currently believed.

Intruders below the radar: molecular pathogenesis of Bartonella spp

Bartonella spp. are facultative intracellular pathogens that employ a unique stealth infection strategy comprising immune evasion and modulation, intimate interaction with nucleated cells, and intraerythrocytic persistence. Infections with Bartonella are ubiquitous among mammals, and many species can infect humans either as their natural host or incidentally as zoonotic pathogens. Upon inoculation into a naive host, the bartonellae first colonize a primary niche that is widely accepted to involve the manipulation of nucleated host cells, e.g., in the microvasculature. Consistently, in vitro research showed that Bartonella harbors an ample arsenal of virulence factors to modulate the response of such cells, gain entrance, and establish an intracellular niche. Subsequently, the bacteria are seeded into the bloodstream where they invade erythrocytes and give rise to a typically asymptomatic intraerythrocytic bacteremia. While this course of infection is characteristic for natural hosts, zoonotic infections or the infection of immunocompromised patients may alter the path of Bartonella and result in considerable morbidity. In this review we compile current knowledge on the molecular processes underlying both the infection strategy and pathogenesis of Bartonella and discuss their connection to the clinical presentation of human patients, which ranges from minor complaints to life-threatening disease.

Prevalence of Bartonella henselae antibodies in pet cats throughout regions of North America

Cat exposure has been directly associated with the development of human Bartonella henselae infections, resulting in cat-scratch disease, bacillary angiomatosis, or bacteremia. The prevalence of serum antibody titers to B. henselae was determined for selected pet cats from 33 geographic locations throughout the United States and several areas in western Canada. Seroprevalences paralleled increasing climatic warmth (P < .02) and annual precipitation (P < .03). These warm, humid areas with the highest seroprevalence would also have the highest number of potential arthropod vectors. The southeastern United States, Hawaii, coastal California, the Pacific Northwest, and the south central plains had the highest average prevalences (54.6%, 47.4%, 40.0%, 34.3%, and 36.7%, respectively). Alaska, the Rocky Mountain-Great Plains region, and the Midwest had low average prevalences (5.0%, 3.7%, and 6.7%, respectively). Overall, 27.9% (175/628) of the cats tested were seropositive. The seroprevalence of B. henselae in cats varies throughout the United States and appears to be influenced by climate.

Rats of the genus Rattus are reservoir hosts for pathogenic Bartonella species: an Old World origin for a New World disease?

Bartonella species were isolated from the blood of 63 of 325 Rattus norvegicus and 11 of 92 Rattus rattus from 13 sites in the United States and Portugal. Infection in both Rattus species ranged from 0% (e.g., 0/87) to approximately 60% (e.g., 35/62). A 337-bp fragment of the citrate synthase (gltA) gene amplified by polymerase chain reaction was sequenced from all 74 isolates. Isolates from R. norvegicus were most similar to Bartonella elizabethae, isolated previously from a patient with endocarditis (93%-100% sequence similarity), followed by Bartonella grahamii and other Bartonella species isolated from Old World rodents (Clethrionomys species, Mus musculus, and Rattus species). These data suggest that Rattus species are a reservoir host for pathogenic Bartonella species and are consistent with a hypothesized Old World origin for Bartonella species recovered from Rattus species introduced into the Americas.

Molecular and Cellular Basis ofBartonellaPathogenesis

The genus Bartonella comprises several important human pathogens that cause a wide range of clinical manifestations: cat-scratch disease, trench fever, Carrion's disease, bacteremia with fever, bacillary angiomatosis and peliosis, endocarditis, and neuroretinitis. Common features of bartonellae include transmission by blood-sucking arthropods and the specific interaction with endothelial cells and erythrocytes of their mammalian hosts. For each Bartonella species, the invasion and persistent intracellular colonization of erythrocytes are limited to a specific human or animal reservoir host. In contrast, endothelial cells are target host cells in probably all mammals, including humans. Bartonellae subvert multiple cellular functions of human endothelial cells, resulting in cell invasion, proinflammatory activation, suppression of apoptosis, and stimulation of proliferation, which may cumulate in vasoproliferative tumor growth. This review summarizes our understanding of Bartonella-host cell interactions and the molecular mechanisms of bacterial virulence and persistence. In addition, current controversies and unanswered questions in this area are highlighted.

Current knowledge of Bartonella species

Bartonella species are now considered emerging pathogens. Of the 11 currently recognized species, four have been implicated in human disease, although only two have been encountered in Europe. Bartonella quintana infections are now being diagnosed among the urban homeless and deprived, manifesting as trench fever, and Bartonella henselae has been shown to be the causative agent of cat scratch disease. Both species also cause a variety of HIV-associated infections, including bacillary anglomatosis. However, perhaps the most significant presentation of bartonellae infection is culture-negative endocarditis. The epidemiologies of Bartonella infections are poorly understood; most Bartonella henselae infections are probably acquired from infected cats, either directly by contact with a cat or indirectly via fleas. No animal reservoir has been implicated for Bartonella quintana; however, infection can be transmitted via the human body louse. Diagnosis of Bartonella infections can be made using histological or microbiological methods. The demonstration of specific antibodies may be useful in some instances, although certainly not in all. Cultivation of Bartonella is difficult, as the bacteria are extremely fastidious. Polymerase chain reaction-based or immunological methods for the detection of bartonella in infected tissues have proven useful. Clinical relapse is often associated with Bartonella infections despite a wide range of prescribed regimens. Only aminoglycosides display in vitro bactericidal activity against intracellular Bartonella species; therefore, they are recommended for treatment of Bartonella infections.

Canine bartonellosis: serological and molecular prevalence in Brazil and evidence of co-infection with Bartonella henselae and Bartonella vinsonii subsp. berkhoffii

The purpose of this study was to determine the serological and molecular prevalence of Bartonella spp. infection in a sick dog population from Brazil. At the São Paulo State University Veterinary Teaching Hospital in Botucatu, 198 consecutive dogs with clinicopathological abnormalities consistent with tick-borne infections were sampled. Antibodies to Bartonella henselae and Bartonella vinsonii subsp. berkhoffii were detected in 2.0% (4/197) and 1.5% (3/197) of the dogs, respectively. Using 16S-23S rRNA intergenic transcribed spacer (ITS) primers, Bartonella DNA was amplified from only 1/198 blood samples. Bartonella seroreactive and/or PCR positive blood samples (n=8) were inoculated into a liquid pre-enrichment growth medium (BAPGM) and subsequently sub-inoculated onto BAPGM/blood-agar plates. PCR targeting the ITS region, pap31 and rpoB genes amplified B. henselae from the blood and/or isolates of the PCR positive dog (ITS: DQ346666; pap31 gene: DQ351240; rpoB: EF196806). B. henselae and B. vinsonii subsp. berkhoffii (pap31: DQ906160; rpoB: EF196805) co-infection was found in one of the B. vinsonii subsp. berkhoffii seroreactive dogs. We conclude that dogs in this study population were infrequently exposed to or infected with a Bartonella species. The B. henselae and B. vinsonii subsp. berkhoffii strains identified in this study are genetically similar to strains isolated from septicemic cats, dogs, coyotes and human beings from other parts of the world. To our knowledge, these isolates provide the first Brazilian DNA sequences from these Bartonella species and the first evidence of Bartonella co-infection in dogs.

Bats as reservoir hosts of human bacterial pathogen, Bartonella mayotimonensis

A plethora of pathogenic viruses colonize bats. However, bat bacterial flora and its zoonotic threat remain ill defined. In a study initially conducted as a quantitative metagenomic analysis of the fecal bacterial flora of the Daubenton's bat in Finland, we unexpectedly detected DNA of several hemotrophic and ectoparasite-transmitted bacterial genera, including Bartonella. Bartonella spp. also were either detected or isolated from the peripheral blood of Daubenton's, northern, and whiskered bats and were detected in the ectoparasites of Daubenton's, northern, and Brandt's bats. The blood isolates belong to the Candidatus-status species B. mayotimonensis, a recently identified etiologic agent of endocarditis in humans, and a new Bartonella species (B. naantaliensis sp. nov.). Phylogenetic analysis of bat-colonizing Bartonella spp. throughout the world demonstrates a distinct B. mayotimonensis cluster in the Northern Hemisphere. The findings of this field study highlight bats as potent reservoirs of human bacterial pathogens.

Prevalence of Bartonella henselae and Bartonella clarridgeiae in stray cats

The aim of the present work was to determine by blood culture the prevalence of blood infection with Bartonella species in a well-defined, European, urban stray cat population. Therefore, 94 stray cats were trapped from 10 cat colonies. Blood samples of these cats were cultured on both blood agar and liquid medium in order to raise the likelihood of bacterial detection. Fifty blood samples (53%) gave a positive culture result for Bartonella species. Isolate identification was performed by sequencing the first 430 bases of the 16S ribosomal DNA. Three types of sequences were thus obtained. The first type (17 isolates; 34%) was identical to that of B. henselae Houston-1 and the corresponding strains were referred as B. henselae type I. The second sequence type (18 isolates; 36%) was identical to that initially described as "BA-TF," and the corresponding strains were referred to as B. henselae type II. The third sequence type (15 isolates; 30%) was identical to that of the Bartonella clarridgeiae type strain (ATCC 51734). Our study points out the major role of stray cats as a reservoir of Bartonella spp. which can be transmitted to pet cats and, consequently, to humans. The study also highlights the high prevalence of B. clarridgeiae (16%) in the blood of stray cats.

Disruption of a host-parasite system following the introduction of an exotic host species

The potential of biological invasions to threaten native ecosystems is well recognized. Here we describe how an introduced species impacts on native host-parasite dynamics by acting as an alternative host. By sampling sites across an invasion front in Ireland, we quantified the influence of the introduced bank vole (Clethrionomys glareolus) on the epidemiology of infections caused by flea-transmitted haemoparasites of the genus Bartonella in native wood mice (Apodemus sylvaticus). Bartonella infections were detected on either side of the front but occurred exclusively in wood mice, despite being highly prevalent in both rodent species elsewhere in Europe. Bank vole introduction has, however, affected the wood mouse-Bartonella interaction, with the infection prevalence of both Bartonella birtlesii and Bartonella taylorii declining significantly with increasing bank vole density. Whilst flea prevalence in wood mice increases with wood mouse density in areas without bank voles, no such relationship is detected in invaded areas. The results are consistent with the dilution effect hypothesis. This predicts that for vector-transmitted parasites, the presence of less competent host species may reduce infection prevalence in the principal host. In addition we found a negative relationship between B. birtlesii and B. taylorii prevalences, indicating that these two microparasites may compete within hosts.

Bartonella species in blood of immunocompetent persons with animal and arthropod contact

Using PCR in conjunction with pre-enrichment culture, we detected Bartonella henselae and B. vinsonii subspecies berkhoffii in the blood of 14 immunocompetent persons who had frequent animal contact and arthropod exposure.

Infections by Leptospira interrogans, Seoul virus, and Bartonella spp. among Norway rats (Rattus norvegicus) from the urban slum environment in Brazil

Norway rats (Rattus norvegicus) are reservoir hosts for zoonotic pathogens that cause significant morbidity and mortality in humans. Studies evaluating the prevalence of zoonotic pathogens in tropical Norway rat populations are rare, and data on co-infection with multiple pathogens are nonexistent. Herein, we describe the prevalence of leptospiral carriage, Seoul virus (SEOV), and Bartonella spp. infection independently, in addition to the rates of co-infection among urban, slum-dwelling Norway rats in Salvador, Brazil, trapped during the rainy season from June to August of 2010. These data were complemented with previously unpublished Leptospira and SEOV prevalence information collected in 1998. Immunofluorescence staining of kidney impressions was used to identify Leptospira interrogans in 2010, whereas isolation was used in 1998, and western blotting was used to detect SEOV antibodies in 2010, whereas enzyme-linked immunosorbent assay (ELISA) was used in 1998: in 2010, Bartonella spp. were isolated from a subsample of rats. The most common pathogen in both years was Leptospira spp. (83%, n=142 in 1998, 63%, n=84 in 2010). SEOV was detected in 18% of individuals in both 1998 and 2010 (n=78 in 1998; n=73 in 2010), and two species of Bartonella were isolated from 5 of 26 rats (19%) tested in 2010. The prevalence of all agents increased significantly with rat mass/age. Acquisition of Leptospira spp. occurred at a younger mass/age than SEOV and Bartonella spp. infection, suggesting differences in the transmission dynamics of these pathogens. These data indicate that Norway rats in Salvador serve as reservoir hosts for all three of these zoonotic pathogens and that the high prevalence of leptospiral carriage in Salvador rats poses a high degree of risk to human health.

Survey of tickborne infections in Denmark

We conducted a study of the distribution and prevalence of tickborne infections in Denmark by using roe deer as sentinels. Blood samples from 237 roe deer were collected during the 2002-2003 hunting season. Overall, 36.6% of deer were Borrelia seropositive, while 95.6% were Anaplasma phagocytophilum positive; all animals were negative for Bartonella quintana and B. henselae by indirect immunofluorescence assay. When a hemagglutination-inhibition test was used, 8.7% of deer were found positive for tickborne encephalitis (TBE)-complex virus. A total of 42.6% were found positive by polymerase chain reaction (PCR) for A. phagocytophilum with significant seasonal variation. All were PCR negative for Rickettsia helvetica. PCR and sequencing also showed a novel bacterium in roe deer previously only found in ticks. The study showed that the emerging pathogen A. phagocytophilum is widely distributed and that a marked shift has occurred in the distribution of TBE-complex virus in Denmark. This finding supports studies that predict alterations in distribution due to climatic changes.

Identification of Bartonella infections in febrile human patients from Thailand and their potential animal reservoirs

To determine the role of Bartonella species as causes of acute febrile illness in humans from Thailand, we used a novel strategy of co-cultivation of blood with eukaryotic cells and subsequent phylogenetic analysis of Bartonella-specific DNA products. Bartonella species were identified in 14 blood clots from febrile patients. Sequence analysis showed that more than one-half of the genotypes identified in human patients were similar or identical to homologous sequences identified in rodents from Asia and were closely related to B. elizabethae, B. rattimassiliensis, and B. tribocorum. The remaining genotypes belonged to B. henselae, B. vinsonii, and B. tamiae. Among the positive febrile patients, animal exposure was common: 36% reported owning either dogs or cats and 71% reported rat exposure during the 2 weeks before illness onset. The findings suggest that rodents are likely reservoirs for a substantial portion of cases of human Bartonella infections in Thailand.

Bartonella infections in cats and dogs including zoonotic aspects

Bartonellosis is a vector-borne zoonotic disease with worldwide distribution that can infect humans and a large number of mammals including small companion animals (cats and dogs). In recent years, an increasing number of studies from around the world have reported Bartonella infections, although publications have predominantly focused on the North American perspective. Currently, clinico-pathological data from Europe are more limited, suggesting that bartonellosis may be an infrequent or underdiagnosed infectious disease in cats and dogs. Research is needed to confirm or exclude Bartonella infection as a cause of a spectrum of feline and canine diseases. Bartonella spp. can cause acute or chronic infections in cats, dogs and humans. On a comparative medical basis, different clinical manifestations, such as periods of intermittent fever, granulomatous inflammation involving the heart, liver, lymph nodes and other tissues, endocarditis, bacillary angiomatosis, peliosis hepatis, uveitis and vasoproliferative tumors have been reported in cats, dogs and humans. The purpose of this review is to provide an update and European perspective on Bartonella infections in cats and dogs, including clinical, diagnostic, epidemiological, pathological, treatment and zoonotic aspects.

Bartonellosis. New and old

The number of species that comprise the family of Bartonellaceae, genus Bartonella, has recently increased from one to 11 species, five of which have been associated with different diseases and syndromes in humans. The rapidly growing number of human pathogens has led several investigators to regard bartonellosis and other associated syndromes as important emerging infectious diseases. This article presents the history and epidemiology, clinical features, diagnosis, and treatment of bartonellosis and associated diseases, including Carrión's disease, trench fever, endocarditis and bacteremia, bacillary angiomatosis, and cat-scratch disease.

Pathogen carriage by the cat flea Ctenocephalides felis (Bouché) in the United Kingdom

The carriage of Bartonella, Rickettsia felis and haemoplasma species was investigated in cat fleas (Ctenocephalides felis) collected from 121 cats and dogs in the United Kingdom. DNA extracted from fleas was analysed using genus and species-specific PCR and amplicons were characterised using DNA sequencing. Fifty percent of flea samples were PCR positive for at least one pathogen. Twenty one percent were positive for R. felis, 17% for Bartonella henselae, 40% for haemoplasma species and 20% were infected with more than one of the pathogen species studied. It is clear from the results in this study that companion cats and dogs are commonly infested with Ct. felis carrying bacterial pathogens of significance to human and animal health. These findings raise the possibility that Ct. felis found on dogs and cats are a potential source of infection with such pathogens for humans.

Genetic and ecologic characteristics of Bartonella communities in rodents in southern China

Ecologic and bacteriologic observations of small mammals captured in Yunnan Province in the People's Republic of China indicated that Bartonella infections occurred at a high prevalence among some rodent species. Sequence analyses of the citrate synthase genes of these Bartonella demonstrated that rodents in this region harbored a diverse assemblage of strains. The Bartonella isolates obtained from Apodemus, Eothenomys, and Rattus typically clustered separately by genus of rodent host. Cultures obtained from Rattus rats were genetically related to Bartonella elizabethae, a recognized human pathogen. The finding of Bartonella species in a high proportion of the rodent samples from Yunnan suggests the need to investigate whether these agents might be responsible for cases of febrile illnesses of unknown etiology in southern China and elsewhere in southeastern Asia.

Bartonella-associated infections

Bartonella-associated infections occur in immunocompetent and immunocompromised patients. The spectrum of diseases caused by Bartonella species has expanded and now includes cat-scratch disease, bacillary angiomatosis, bacillary peliosis, bacteremia, endocarditis, and trench fever. Most Bartonella-associated infections that occur in North America and Europe are caused by B. henselae or B. quintana. The domestic cat serves as the major reservoir for B. henselae; the reservoir for the modern day B. quintana infection remains unknown. Methods used to diagnose Bartonella-associated infections include histopathologic analysis of biopsy specimens, culture of tissue samples, blood culture, and serology. Available data on treatment of Bartonella-associated infections remain relatively sparse but would suggest that erythromycin or doxycycline provide the best responses.

Bartonellosis (Carrión's disease) in the modern era

Bartonellosis remains a major problem in Peru, but many contemporary aspects of this disease have not been adequately described. We examined the cases of 145 symptomatic patients in Lima, Peru, in whom bartonellosis was diagnosed from 1969 through 1992, including 68 patients in the acute (hematic) phase and 77 patients in the eruptive (verruga) phase. In modern Peru, symptomatic patients who have acute-phase bartonellosis typically present with a febrile illness and systemic symptoms caused by profound anemia; most patients respond successfully to treatment with chloramphenicol. Patients who have eruptive-phase bartonellosis most often present with cutaneous verrugas but may have less specific symptoms, such as fever and arthralgias; diagnosis can be confirmed in such patients by Western immunoblotting, and most patients appear to respond to treatment with rifampin.