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Journal of Clinical Microbiology, September 2008, p. 2856-2861, Vol. 46, No. 9
0095-1137/08/$08.00+0 doi:10.1128/JCM.00832-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Intracellular Pathogens Research Laboratory, Center for Comparative Medicine and Translational Research, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina,1 Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, Georgia,2 Duke University Medical Center, Durham, North Carolina3
Received 1 May 2008/ Returned for modification 16 June 2008/ Accepted 10 July 2008
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Although CSD is considered to be self-limiting, persistent intravascular infection of a child with B. henselae for 4 months after a cat scratch has been reported previously (2). Furthermore, we recently described chronic intravascular infection with both B. henselae and B. vinsonii subsp. berkhoffii in immunocompetent people with occupational animal contact and arthropod exposure (5). Cats are the primary reservoir hosts for B. henselae, whereas to date, B. vinsonii subsp. berkhoffii has been isolated only from dogs, coyotes, foxes, or people (9, 27). Domestic and wild canines serve as the primary environmental reservoir for B. vinsonii subsp. berkhoffii, and dogs can be involved in the transmission of B. vinsonii subsp. berkhoffii and B. henselae to people (7, 9, 10, 27, 36).
In this study, we report the isolation of B. henselae or B. vinsonii subsp. berkhoffii from, or the molecular detection of these pathogens in, blood samples from six people who exhibited a spectrum of neurological and neurocognitive abnormalities.
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A standardized questionnaire, approved by the North Carolina State University Institutional Review Board (IRB no. 4925-03), was completed by each individual and included questions on age, gender, animal and arthropod exposure, outdoor activity, travel, clinical symptoms, and comorbid conditions.
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TABLE 1. Ages, genders, and neurological abnormalities of immunocompetent patients in this study and Bartonella species detected in the blood samples
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Patient 2, a golf coach, traveled extensively throughout the United States and other countries, had frequent arthropod exposure, and had lived on a farm as a teenager, during which time she had been bitten by a pig and pecked frequently by roosters, turkeys, and pheasants. Her illness was characterized by severe bouts of fatigue, accompanied by subtle neurological abnormalities (Table 1).
Patient 3 owned a horse farm, had frequent arthropod exposure, and reported at least yearly cat scratches. At the time of her initial blood sample, she had been ill approximately 4 years. She had been diagnosed previously with Lyme disease and babesiosis and had been treated with long courses of oral and intravenous antibiotics.
Patients 4 and 5 were veterinarians who reported weekly bites or scratches from cats, dogs, rodent pocket pets, and an assortment of wild and zoo animals. In association with a period of work-related stress, patient 4 developed debilitating depression, insomnia, fatigue, loss of coordination, memory loss, disorientation, and headaches of fluctuating severity that continued for over a year. Patient 4 maintained cats, chickens, cattle, dogs, and horses as pets.
One year prior to testing in our laboratory, patient 5 developed an acute febrile illness and malaise, which abated over the next week. In the subsequent months, neurological symptoms consisted of stumbling during jogging, muscle weakness, and fatigue, which was thought to be associated with viral neuropathy. During the next year, symptoms worsened to the extent that running was no longer possible and he could not walk unaided any distance; leg myoclonus worsened, hand numbness became problematic, and resting three to four times a day was a necessity. Multiple sclerosis was diagnosed, and treatment with intravenous interferon, intravenous immunoglobulin G, and glucocorticoids was initiated.
Patient 6 was the 14-year-old son of a veterinarian, and although exposed to both cats and dogs, the boy did not report previous scratches or bites. Ten days after an attached tick was removed from his left ankle, the boy developed severe debilitating migraine headaches, which required him to be hospitalized. Because of the more rapid turnaround time of PCR than of serological testing, PCR testing was used initially to screen an extracted blood sample for Anaplasma, Bartonella, Ehrlichia, and Rickettsia DNA. Only Bartonella DNA was detected in the child's blood sample, and subsequently, sequential serological testing demonstrated seroreactivity to B. henselae and B. quintana and seroconversion to B. vinsonii subsp. berkhoffii. Despite multiple attempts, cloning and sequencing of the initial Bartonella amplicon were not successful; however, B. henselae DNA from an agar plate isolate obtained after BAPGM preenrichment culture was sequenced. Based upon seroconversion, infection with B. vinsonii subsp. berkhoffii was implicated; however, based upon culture results, the boy was infected with B. henselae.
Fatigue, insomnia, memory loss and/or disorientation, blurred vision and loss of coordination, headaches, and depression were the most commonly reported symptoms (Table 1). Seizures, severe paresis, and debilitating migraines were the predominant neurological abnormalities in patients 1, 5, and 6, respectively. Patients 2 to 4 each reported fatigue with accompanying neurological abnormalities that persisted for 3 to 5 years (Table 1).
Medical care, diagnostic evaluations, the timing of sample collection for Bartonella testing, and treatment interventions, including plasmapheresis, antibiotics, corticosteroids, intravenous immunoglobulin, anticonvulsants, and other drugs, were extensive and varied among patients. In all instances, there was an evaluation by one or more neurologists. In addition to receiving other symptomatic treatments, patients 1, 5, and 6 were treated specifically for their Bartonella infections and experienced progressive improvement (patients 1 and 5) or the resolution of disease manifestations (patient 6). Patient 1 was treated with doxycycline for 6 weeks, remains healthy, and has experienced no seizures during a 36-month follow-up period while receiving an anticonvulsant medication. Patient 5 was initially treated with doxycycline for 5 weeks, followed by azithromycin for 6 weeks and then by levofloxacin for 9 weeks. There was a progressive improvement in neurological status (improved muscle strength and coordination accompanied by a return to work as a veterinary surgeon). During the past year, this individual received doxycycline and rifampin, in conjunction with other treatments, which resulted in continued improvement in muscle strength, improved coordination when walking, less myoclonus, and no relapses, which typically occurred prior to the addition of antibiotics to the treatment regimen. Patient 6 was treated with azithromycin for 6 weeks, with a rapid and progressive decrease in the severity of migraines following the initiation of antibiotics. The boy gradually returned to all preillness activities with no residual neurological abnormalities. Patients 2 and 3 were treated with doxycycline without obvious long-term benefits. Patient 4 has received continuous doxycycline treatment for the past 2 years for rosacea and has experienced a decrease in headaches, back pain, and joint pain, although there are still occasional flare-ups of pain in the joints.
Serological testing at the Centers for Disease Control and Prevention identified antibodies to Bartonella spp. (IFA reciprocal titers of 64 or greater) in samples from three of six patients (patients 1, 2, and 6). Antibodies were not detected in samples from patients 3 (six serum samples spanning July 2005 to 14 September 2006), 4 (three serum samples spanning June to November 2006), and 5 (one serum sample). For patient 1, IFA titers of antibodies to B. henselae, B. quintana, and B. vinsonii subsp. berkhoffii in samples spanning a 4-month period remained stable and were decreased but still detectable 1 year later, following antibiotic treatment (Table 2). Patient 2 had reciprocal titers of antibodies to B. henselae, B. quintana, and B. vinsonii subsp. berkhoffii of 256, 128, and 128, respectively, when initially tested on 4 January 2005, after which a significant drop in antibodies occurred following antibiotic treatment, with reciprocal titers of less than 64 for all three test antigens in samples collected on 12 May 2005 and 11 September 2006. Patient 6 seroconverted to B. vinsonii subsp. berkhoffii antigens, developed the highest IFA titers of antibodies to this organism, and had a decremental decrease in titers following treatment with azithromycin (Table 3).
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TABLE 2. Serological, PCR, and culture results for a 23-year-old woman with progressive neurological dysfunction, seizures, and persistent B. henselae infection
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TABLE 3. Serological, PCR, and culture results for a 14-year-old boy with migraine headaches following recent tick exposure
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The neuropathogenesis of B. henselae infection remains incompletely understood. B. henselae can invade and colonize human dendritic cells, CD34 progenitor cells, erythrocytes, and vascular endothelial cells (14, 28). In vitro intracellular infection of feline microglial cells has also been demonstrated previously (31). In a previous study involving a patient with classical CSD accompanied by encephalopathy, B. henselae DNA was amplified from an epitrochlear mass and from the cerebrospinal fluid (18). The involvement of the central nervous system in patients with CSD is infrequent, and the spontaneous resolution of neurological abnormalities, without residual neurological dysfunction, is the most frequently reported outcome (18). However, there may be exceptions, as illustrated by the case of a 17-year-old girl who developed epilepsia partialis continua 6 weeks after being scratched by a cat, followed by residual partial epilepsy (34). We hypothesize that patient 1 in this study developed persistent intravascular B. henselae infection and progressive neurological involvement following a cat scratch. Despite reporting other neurological problems, this patient denied having a history of muscle pain, loss of sensation, numbness, and joint pain, which were frequently reported abnormalities in two previous studies (5, 22). Identical B. henselae 16S-23S ITS sequences were amplified from samples obtained from patient 1 on three independent occasions. These DNA sequences were obtained by five different approaches, including direct extraction from blood (two samples), BAPGM enrichment blood culture, BAPGM enrichment cerebrospinal fluid culture, and isolation from an agar plate subculture. These results were also obtained at three different sample collection and processing times spanning 9 months, during which time the patient maintained stable B. henselae antibody titers. Based upon ITS sequences, all isolates obtained from this individual were most similar to the H1 type strain of B. henselae (ATCC 49882), which was originally isolated from the blood of a human immunodeficiency virus-infected person.
Patient 5 had the most severely debilitating neurological abnormalities. This previously healthy 49-year-old veterinarian developed progressive muscle weakness, myoclonus, paresis, and severe fatigue, which followed an acute febrile illness. Initially, a viral infection was diagnosed, and subsequently, multiple sclerosis was diagnosed. Neurological dysfunction resulted in a curtailment of prior athletic activities, such as jogging, and ultimately this individual required assistance during extended walks. Previously, a chronic inflammatory demyelinating polyradiculoneuropathy was reported as a complication of CSD in a 3-year-old boy (29). Six weeks after the onset of classical CSD, the boy developed difficulty in walking, an inability to run or climb stairs, and susceptibility to frequent falling, which became progressively worse during the subsequent 8 weeks (29). Potentially, B. henselae infection in patient 5 in this study induced an immune-mediated demyelinating central nervous system disease that mimicked multiple sclerosis.
Blood from the 14-year-old boy described in this study was provided by the attending neurologist when the boy's mother, a companion animal veterinarian, contacted our laboratory, to which she routinely submitted diagnostic samples for testing for tick-borne organisms in the blood of cats and dogs. Although vector competence has not been established for tick transmission of Bartonella species, there is both case-based and seroepidemiological evidence supporting transmission by Rhipicephalus sanguineus and Ixodes scapularis (4, 8, 9). Several recent studies have found Bartonella DNA in questing ticks, ticks attached to animals, or ticks attached to human beings (1, 23, 35). In addition, there are previously described case studies in which tick attachment preceded the onset of illness and the documentation of B. henselae infection in children or adults (24, 26). Unfortunately, concurrent or prior exposure to cats or kittens and the potential for persistent B. henselae infection in children or adults with a history of tick attachment limit the utility of case-based evidence of B. henselae transmission by ticks. More recently, investigators from the United States and Poland have documented concurrent infection of the central nervous system with Borrelia burgdorferi and B. henselae, supporting the possibility of the cotransmission of these pathogens by Ixodes spp. (20, 33). Similar to patients 2, 3, 4, and 6 in this study, four individuals residing in a region where B. burgdorferi was endemic reported frontal headaches, cognitive dysfunction, and fatigue in a study by Eskow and colleagues, and B. henselae DNA was amplified from the blood and/or cerebrospinal fluid samples (20). Also, similar to the 14-year-old boy in this study, one individual in the study by Eskow et al. became ill within a week after the removal of two attached ticks, whereas a second individual became ill 3 months after the removal of a tick from the scalp and, for the other two chronically ill patients, the timing of tick attachment was unknown. Evolving evidence appears to support the potential for the transmission of B. henselae to people following tick attachment.
Most recently, our research group has amplified and sequenced DNA of four Bartonella species from saliva samples obtained from healthy or sick dogs (17). Although the finding of Bartonella DNA does not confirm the presence of viable Bartonella organisms in an animal's mouth, it does indicate that bites or contact with saliva from cats or dogs may be an incompletely defined risk factor for the transmission of these organisms to people (17). Prospective studies are needed to determine the variability in the duration of infection and the prevalence of Bartonella bacteremia among healthy humans and various patient populations and to evaluate bite wounds as a mode of Bartonella transmission to people and the clinical relevance of long-term intravascular infection with these bacteria. Other authors have proposed that Bartonella spp. represent an exceptional example of a "stealth pathogen," suggesting that chronic vascular infection can ultimately predispose to complex disease expression, including but perhaps not limited to angiogenesis (30). Comparative medical data obtained from Bartonella-infected dogs and people would strongly support this contention (8, 9). As cats and dogs serve as reservoir hosts for B. henselae and B. vinsonii subsp. berkhoffii, respectively, pet contact may represent an incompletely defined risk for disease transmission to people, particularly individuals such as veterinarians, animal handlers, and farmers with extensive animal contact (3, 7, 10, 17, 36). The additional use of a combined approach of enrichment culture and PCR should assist in the microbiological detection of B. henselae and B. vinsonii subsp. berkhoffii. Clearly, joint efforts by physicians and veterinarians are required to further address the role of Bartonella species as contemporary pathogens in sick animals and in human patients (8, 9, 19).
This study was approved by the North Carolina State University Institutional Review Board. None of the funding sources had any role in study design, data collection, the analysis and interpretation of data, the writing of the report, or the decision to submit the manuscript for publication consideration. In conjunction with Sushama Sontakke and North Carolina State University, E. B. Breitschwerdt holds U.S. patent no. 7,115,385, "Media and Methods for Cultivation of Microorganisms," which was issued 3 October 2006. He is the chief scientific officer for Galaxy Diagnostics, a newly formed company that will provide advanced diagnostic testing for the detection of Bartonella species infection in animals. R. G. Maggi's salary is funded in part by IDEXX Laboratories. All other authors have no potential conflicts.
Published ahead of print on 16 July 2008. ![]()
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