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Journal of Clinical Microbiology, December 2002, p. 4670-4674, Vol. 40, No. 12
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.12.4670-4674.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina
Received 27 March 2002/ Returned for modification 23 July 2002/ Accepted 30 August 2002
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In 1993, blood cultures from a human with valvular endocarditis grew a fastidious gram-negative bacterium. DNA from the isolate showed 98.9% similarity to Bartonella (previously Rochalimaea) species (7). The new strain was designated Rochalimaea elizabethae (now Bartonella elizabethae), and the DNA sequence was recorded in GenBank under accession no. L35103 (7). To our knowledge, B. elizabethae has only been isolated from this patient and from rats (Rattus norvegicus) (10). In contrast, B. henselae has been isolated from cats throughout the world and occasionally from people with fever of unknown origin (12, 26) or endocarditis (24) or from homeless patients (5). Data on the prevalence of B. henselae in dogs are limited. Two studies (1, 8) reported B. henselae seroprevalences of 6.5 and 3%, respectively, in their dog populations. However, bacteria were not isolated and PCR was not performed. A study from Japan reported a B. henselae seroprevalence of 7.7% (4 of 52 dogs) and positive B. henselae PCR results from peripheral blood, nail clippings, and oral swabs; however, these amplicons were never sequenced (M. Tsukahara, H. Tsuneoka, H. Iino, I. Murano, H. Takahashi, and M. Uchida, Letter, Lancet 352:1682, 1998).
During the last decade, studies with dogs have provided evidence that B. vinsonii subsp. berkhoffii can cause endocarditis (2, 3), granulomatous lymphadenitis, and granulomatous rhinitis (21). In contrast, B. henselae DNA has been amplified and sequenced from only one dog that died of peliosis hepatis (16). To date, B. henselae is the only Bartonella sp. that has been implicated as a cause of peliosis hepatis in dogs (16) and in humans (17). In 1993, Breitschwerdt et al. isolated a novel Bartonella species, eventually named B. vinsonii subspecies berkoffii, from the blood of a dog with vegetative valvular endocarditis (3, 18). Subsequently, B. vinsonii subsp. berkoffii DNA was amplified and sequenced from blood and/or heart valves of three additional dogs with endocarditis (2). Epidemiologic evidence suggested tick exposure as a risk factor for Bartonella infection in dogs (22). Recently, 5 of 18 dogs (28%) with endocarditis, including three dogs infected with B. vinsonii subsp. berkoffii, examined at the Veterinary Medicine Teaching Hospital, University of California, Davis, were seroreactive to Bartonella spp. antigens and PCR positive for Bartonella spp. (B. Chomel, Abstr. Second Workshop on Comparative Medicine, Lyon, France, p. 61, 2001). These results prompted a study of archived cardiac valves from U.S. Army working dogs, which led to the addition of six more PCR-positive cases of B. vinsonii subsp. berkoffii to the literature (B. Chomel, Abstr. Second Workshop on Comparative Medicine, Lyon, France). Most recently, B. clarridgeiae, which was first described after its isolation from a cat in 1995, was amplified and sequenced from the heart valve of a young Boxer dog with vegetative endocarditis at the University of California, Davis (6).
Thus, although B. vinsonii subsp. berkhoffii was the first Bartonella sp. to be identified as a pathogen in dogs, it is increasingly evident that B. henselae, B. clarridgeiae, and potentially other Bartonella spp. may also cause illness in dogs. Furthermore, infection with these bacteria appears to induce disease manifestations, such as endocarditis, peliosis hepatis, and granulomatous disease, that are similar to those observed in both dogs and humans. The purpose of this report is to describe cases involving three dogs infected with B. henselae and one dog infected with B. elizabethae for which there were no compatible signs or diagnostic evidence of endocarditis or liver disease, manifestations previously associated with Bartonella spp. infection in dogs. We are not aware of other reports describing the molecular detection of B. henselae or B. elizabethae DNA from the blood of sick dogs. Future studies should be aimed at elucidating the pathogenic significance of infection of dogs with various Bartonella spp.
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Hematologic abnormalities included thrombocytosis (platelet count, 453,000/µl; reference range, 181,000 to 350,000/µl), mild lymphopenia (lymphocyte count, 987/µl; reference range, 1,000 to 5,000/µl), and eosinophilia (eosinophil count, 846/µl; reference range, 100 to 750/µl). Thoracic radiographs were unremarkable, and abdominal radiographs were potentially consistent with partial intestinal obstruction. Exploratory surgery revealed a toothpick penetrating the wall of the small intestine. Resection and anastomosis were completed with no complications. Aspiration cytology from several enlarged peripheral lymph nodes identified reactive lymphoid hyperplasia with high numbers of mast cells and eosinophils. Serum from the dog was reactive to B. vinsonii subsp. berkhoffii antigens at a reciprocal titer of 256. B. henselae DNA was amplified and sequenced from a peripheral blood sample. Enrofloxacin treatment (5 mg/kg of body weight; administered orally [p.o.] twice a day [BID]) and ampicillin (22 mg/kg; p.o., BID) was dispensed for six weeks for a presumptive diagnosis of bartonellosis. Ten weeks later, the dog was alert, active, and eating normally. The chorioretinitis had also resolved. Thrombocytosis (platelet count, 418,000/µl; reference range, 181,000 to 350,000/µl) persisted, but the lymphopenia and eosinophilia had resolved. The lymph node cytopathology was again consistent with lymphoid hyperplasia, without accompanying mast cells or eosinophils. Convalescent-phase serum antibodies to B. vinsonii subsp. berkhoffii or B. henselae antigens were no longer detected.
Case 2. A 5-year-old, female, spayed Great Dane (dog 2) from Fayetteville, N.C., was referred to the NCSU-VTH with a history of refractory thrombocytopenia (platelet counts ranging from 37,000 to 91,000/µl; reference range, 175,000 to 300,000/µl) and a previous serologic diagnosis of ehrlichiosis, which was treated with a protracted course of doxycycline. During the 19-month period of illness, the dog had lost approximately 16 kg. Physical examination was unremarkable. Hematologic abnormalities included mild lymphopenia (lymphocyte count, 930/µl; reference range, 1,000 to 5,000/µl), eosinophilia (eosinophil count, 930/µl; reference range, 100 to 750/µl), and marked thrombocytopenia (platelet count, 9,000/µl; reference range, 181,000 to 350,000/µl). Urine abnormalities included hematuria and proteinuria, with a urine protein-to-creatinine ratio of 1.5 and a specific gravity of 1.016. Antibodies to B. vinsonii subsp. berkoffii or B. henselae antigens were not detected. A blood culture maintained for 6 weeks failed to grow bartonella or other fastidious bacteria, and Bartonella DNA was not detected by PCR. Due to the persistently low platelet counts, the dog was treated with prednisone at immunosuppressive doses (1 mg/kg; p.o., BID) for a presumptive diagnosis of immune-mediated thrombocytopenia and concurrently with enrofloxacin (5 mg/kg; p.o., every 24 h), ampicillin (22 mg/kg; p.o., BID), and doxycycline (5 mg/kg; p.o., BID) for 2 weeks while awaiting blood culture results. During the next 4 weeks, the platelet count normalized (190,000/µl) and the dog's appetite began to increase while the animal received antibiotics and corticosteroids. Following the course of antibiotics, the corticosteroids were tapered and another EDTA blood sample was submitted for PCR testing. B. henselae DNA was amplified and sequenced from this sample, which was obtained 3 months after the initial presentation to our hospital. Six months later, the dog remained healthy without taking any medications; however, the most recent platelet count was only 92,000/µl.
Case 3. An 8-year-old, male, castrated Labrador retriever (dog 3) from Shelby, N.C., was examined at an emergency clinic because of acute onset of ataxia. The dog was hypermetric, with conscious proprioception deficits in the hind limbs. Hematologic abnormalities included mild leukocytosis (leukocyte count, 16,700/µl; reference range, 4,000 to 15,500/µl) with mature neutrophilia (neutrophil count, 14,028/µl; reference range, 2,060 to 10,600/µl), lymphopenia (lymphocyte count, 668/µl; reference range, 690 to 4,500/µl), and monocytosis (monocyte count, 1,837/µl; reference range, 0 to 840/µl). The reciprocal titer to B. vinsonii antigens was 128. Antibodies against B. burgdorferi, Babesia canis, Rickettsia rickettsii, or Ehrlichia canis antigens were not detected. Azithromycin (10 mg/kg; once a day for 5 days, then every other day for 40 days) was used for treatment of Bartonella infection. Three months later, the dog continued to have difficulty ambulating and was referred to a neurologist for evaluation of possible cauda equina syndrome. A myelogram and epidurogram revealed no compressive lesions in the cervical, thoracic, or lumbar spine; however, there was attenuation of the contrast column around the level of L5-L6, suggestive of an inflammatory lesion. There was a mild increase in cerebrospinal fluid protein content (59 mg/dl; normal range, 0 to 48 mg/dl), with no white blood cells. Prior to initiation of antibiotics, a serum sample was negative for antibodies to B. vinsonii and B. henselae antigens; however, B. henselae DNA was amplified by PCR. Treatment consisted of a 6-week course of amoxicillin-clavulanic acid (13 mg/kg; p.o., BID) and azithromycin (10 mg/kg; p.o., every 24 h).
Case 4. An 8-year-old male Shetland Sheepdog (dog 4) from Annapolis, Md., was examined by a veterinarian after a 2-month history of lethargy, decreased appetite, weight loss, and occasional vomiting of undigested food. On physical examination, mucous membranes were pale, the dog was very thin, and breathing was labored. Hematologic abnormalities included anemia (red blood cells, 3.97 M/liter [reference range, 5.20 to 8.33 M/liter]; hematocrit, 25.8% [reference range, 36 to 60%]; hemoglobin, 8.4 g/dl [reference range, 12.4 to 19.2 g/dl]), leukocytosis (leukocyte count, 26,900/µl; reference range, 5,100 to 17,600/µl), mature neutrophilia (neutrophil count, 21,800/µl; reference range, 1,900 to 14,200/µl), monocytosis (monocyte count, 1,900/µl; reference range, 0.0 to 1.4/µl), and eosinophilia (eosinophil count, 1,900/µl; reference range, 0.0 to 1,300/µl). Biochemical abnormalities included azotemia (blood urea nitrogen, 71 mg/dl; [reference range, 3 to 28 mg/dl]; creatinine, 2.8 mg/dl [reference range, 0 to 1.5 mg/dl]) and elevated amylase activity (3,702 IU/liter; reference range, 26 to 2,150 IU/liter). The urine specific gravity was 1.017, with 3+ protein, 2+ blood, 1+ bilirubin, 3 to 5 white blood cells per high-power field, 3 to 5 red blood cells per high-power field, and 2+ cocci, with amorphous crystals and granular casts. Serum and EDTA blood samples were submitted to the Vector Borne Disease Diagnostic Laboratory at North Carolina State University for diagnostic testing. During the next 2 days, the dog's condition deteriorated rapidly, and he died before results were obtained. The EDTA blood sample was later found to contain B. elizabethae DNA by PCR amplification and sequencing. Antibodies to B. burgdorferi, E. canis, or B. canis antigens were not detected, whereas the reciprocal titers to B. vinsonii subsp. berkhoffii and to R. rickettsii were 64 and 512, respectively.
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Serology. All dogs were tested at least once for antibodies against B. vinsonii subsp. berkoffii and B. henselae by using previously described methods (22). Antigens used in testing for B. elizabethae antibodies were not available in our laboratory.
PCR. Blood obtained aseptically from the jugular vein was placed in tubes containing EDTA. DNA was extracted with a commercially available QIAamp blood kit (QIAGEN, Chatsworth, Calif.). Sample processing, DNA extraction, and PCR amplification were performed in separate rooms to avoid PCR contamination. Positive (tissue culture-grown B. henselae) and negative (reagent and uninfected EDTA blood) controls were processed with each patient sample. DNA was extracted from 200 µl of blood. The PCR methods used for sample analysis amplified a fragment of the 16S-23S rRNA intergenic region with primers complementary to conserved sequences among Bartonella species that are known to infect mammals (13). The advantages of this test are that it can be performed as a one-step process and that it facilitates speciation according to band size after fractionization by gel electrophoresis (12). The primers used, 5'-CTCTTTCTTCAGATGATGATCC-3' and 5'-AACCAACTGAGCTACAAGCCCT-3', resulted in amplified products of the expected size, 163 bp (B. henselae) and 232 bp (B. elizabethae), as previously described (13). In each case, the amplicon was then sequenced using a SequiTherm EXCEL II DNA sequencing kit-LC as recommended by the supplier (Epicentre Technologies, Madison, Wis.). The sequencing reactions were performed as follows: 2 min at 92°C, followed by 30 amplification cycles (30 s at 92°C, 15 s at 55°C, and 30 s at 72°C) (Hybaid PCR Express). The sequencing reactions were analyzed by polyacrylamide gel electrophoresis (3.75%) on a LI-COR 4200 automated DNA sequencer.
Culture. At the time of the first evaluation at NCSU-VTH, blood samples from dogs 1 and 2 were submitted for Bartonella culture and were processed using previously described techniques (17).
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PCR amplification of DNA from EDTA-anticoagulated blood samples, followed by DNA sequencing as described above, resulted in the identification of B. henselae 16S-23S rDNA in dogs 1 to 3, with amplicons that had complete homology to the B. henselae sequence (GenBank accession no. L35101). When sequenced, the amplicon from dog 4 contained 16S-23S ribosomal DNA with complete homology to the sequence for B. elizabethae (GenBank accession no. L35103) (12).
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The clinical relevance derived from the microbiologic evaluation of these dogs is difficult to infer due to the small number of cases and the wide variation in historical, clinical, hematologic, and biochemical abnormalities. Interpretation is further complicated by the concurrent presence of other diseases (e.g., an intestinal foreign body in dog 1, potential immune-mediated thrombocytopenia in dog 2, and renal failure in dog 4). However, it is important to note several features shared among these dogs which may support a primary or opportunistic pathogenic role for B. henselae and B. elizabethae. Nonspecific clinical abnormalities, such as severe weight loss, protracted lethargy, and anorexia, in addition to a chronic disease course were common to all four cases. Evidence suggesting that B. vinsonii subsp. berkhoffii is a cause of chronic infections in dogs is well documented in experimentally infected beagles (20) and is further supported by the chronic disease course observed in naturally infected dogs (2, 3). Experimental infection of dogs with B. vinsonii subsp. berkoffii causes immune suppression that is characterized by decreased numbers of CD8+ T lymphocytes, defects in monocytic phagocytosis, and impaired antigen presentation within lymph nodes (20), which could potentially predispose infected dogs to the development of autoimmune or immune-mediated disease manifestations. Although these nonspecific clinical findings are common in other occult infections, as well as noninfectious diseases, these changes are also commonly associated with the terminal stages of conditions of unknown or poorly defined etiology, such as glomerulonephritis, idiopathic immune-mediated disorders, and neoplasia. It is possible that advanced diagnostic techniques, such as PCR, may help to implicate occult infections with Bartonella spp. as a cause of or a cofactor in chronic diseases of poorly defined causation.
The most obvious hematologic and biochemical abnormalities observed in these four dogs included eosinophilia, monocytosis, alterations in platelet numbers, and elevations in serum amylase values. During the course of illness, three dogs had monocytosis, which is most commonly associated with acute or chronic tissue inflammation. Monocytosis was a common finding in a previous report that implicated B. vinsonii subsp. berkhoffii and related alpha Proteobacteria as a cause of cardiac arrhythmias, endocarditis, or myocarditis in dogs (2). Thrombocytosis was documented in dogs 1, 3, and 4, while dog 2 had persistent and presumably immune-mediated thrombocytopenia. This persistent thrombocytopenia in dog 2 was attributed to immune-mediated platelet destruction, and the dog responded to immunosuppressive corticosteroid therapy. Thrombocytopenia, generally mild in degree, is the most consistent hematologic abnormality in humans chronically infected with B. quintana (5, 23); however, thrombocytosis has also been reported in humans infected with B. henselae (19).
Three dogs had increased amylase values within 1 year of diagnosis of Bartonella infection, while only one dog had an increased amylase value at the time Bartonella DNA was detected by PCR. However, the increased serum amylase value in this dog may have been secondary to early renal insufficiency. The role of Bartonella infections in causing an increase in serum amylase values cannot be elucidated from these cases. Future studies can focus on attempts to isolate Bartonella DNA from healthy and diseased pancreatic tissues in an attempt to confirm or disprove a possible association.
Ocular manifestations of Bartonella infections have been described previously in humans infected with B. henselae (9) and B. grahamii (15) and in cats infected with B. henselae. Chorioretinitis was noted only in dog 1; however, ocular lesions may not have been detected because a thorough ophthalmic examination was not performed in the other cases.
Bartonella spp. are capable of causing patent infections in several mammalian species, namely, human beings, cats, dogs and coyotes, cows, deer, rabbits, and rodents (4). The disease conditions associated with these organisms in nonreservoir hosts, such as humans and dogs, appear to be relatively similar, as evidenced by reports of endocarditis, peliosis hepatis, and granulomatous disease in canines and humans. This study adds another species (B. elizabethae) to the list of Bartonella organisms that can be detected in canine tissues and describes other potential disease manifestations that may be associated with B. henselae infection in dogs. As has been suggested previously (11), it may be necessary to apply molecular Koch's postulates to establish the pathogenicity of these highly adapted organisms that can persist within the vasculature for long periods of time.
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