Bartonellosis

Overview of Bartonellosis in Dogs and Cats.

First Described: Peru, 1905 (Alberto Barton Thompson) (Bartonella bacilliformis).¹ Identification of Bartonella as the cause of cat scratch disease in humans did not occur until 1983.²

Causes: The most common species in cats are Bartonella henselae and Bartonella clarridgeiae; in dogs, they are Bartonella vinsonii subsp. berkhoffii and B. henselae.

Geographic Distribution: Worldwide, with highest prevalence in subtropical and tropical regions

Major Mode of Transmission: Fleas (Ctenocephalides felis); possibly other flea species (such as Pulex spp.) and vectors such as ticks, lice, biting flies

Major Clinical Signs: Signs that relate to infective endocarditis (lethargy, fever, cardiac murmur, cough, tachypnea, lameness, neurologic signs) are the most frequent and well understood manifestations of bartonellosis in dogs. Bartonella can also cause endocarditis and myocarditis in cats and is suspected to cause (or contribute to) caudal stomatitis and possibly other systemic inflammatory disorders such as uveitis.

Differential Diagnoses: Cats: major differential diagnoses are other bacterial causes of endocarditis and feline infectious peritonitis. Dogs: other bacterial causes of endocarditis, other vector-borne diseases such as ehrlichiosis, anaplasmosis, borreliosis and babesiosis, and immune-mediated inflammatory diseases.

Human Health Significance: Bartonella causes cat scratch disease in immunocompetent humans as well as vasculoproliferative disorders in immunocompromised humans.

Etiology and Epidemiology

Bartonella spp. are fastidious, intraerythrocytic gram-negative bacteria that infect a wide range of domestic and wild mammalian host species. Different Bartonella species have adapted to specific mammalian reservoir hosts and can infect and occasionally cause disease in alternative, incidental hosts. More than 10 species of Bartonella infect cats or dogs worldwide (TABLE 52-1, TABLE 52-2 ). Bartonella infections are important because cats are the principal reservoir host for Bartonella henselae, the main cause of cat scratch disease (CSD) in humans, and subclinical bacteremia in cats is widespread (8% to 56% of healthy cats worldwide).³

TABLE 52-1.

Species of Bartonella Known to Infect Cats

Bartonella Species	Primary Reservoir	Primary Vector
B. henselae	Cats	Cat flea (Ctenocephalides felis)
B. clarridgeiae	Cats	Cat flea?
B. koehlerae	Probably cats	Cat flea
B. quintana	Humans	Human body louse (Pediculus humanus)
B. bovis	Ruminants (cattle, deer)	Biting flies?
B. vinsonii subspecies berkhoffii	Coyotes, domestic dogs	Unknown (fleas, ticks?)

TABLE 52-2.

Species of Bartonella Known to Infect Dogs

Bartonella Species	Primary Reservoir	Primary Vector
B. henselae	Domestic cats	Cat flea (Ctenocephalides felis)
B. vinsonii subsp. berkhoffii	Coyotes, domestic dogs, foxes	Unknown (fleas, ticks?)
B. rochalimae	Wild carnivores, domestic dogs	Fleas (Pulex irritans)
B. clarridgeiae	Domestic cats	Cat flea
B. koehlerae	Domestic cats	Unknown
B. quintana	Human	Body louse (Pediculus humanus) (in humans)
B. washoensis	California ground squirrel	Unknown
B. bovis	Ruminants (cattle, deer)	Unknown
B. elizabethae	Rats	Oriental rat flea (Xenopsylla cheopis)
B. grahamii	Wild mice	Rodent fleas (Ctenophthalmus nobilis)
B. taylorii	Wild mice	Rodent fleas (Ctenophthalmus nobilis)
B. vinsonii subsp. arupensis	White-footed mouse	Unknown
B. volans-like	Southern flying squirrel	Unknown
"Candidatus B. merieuxii" (strain HMD)	Dogs, jackals	Unknown

Cat fleas (Ctenocephalides felis) play a major role in the transmission of feline Bartonella infections. The presence of cat fleas is essential for maintenance of the infection within the cat population.⁴ B. henselae can multiply in the digestive system of the flea and survive several days in flea feces.⁵ The main source of infection appears to be flea feces that are inoculated by contaminated cat claws.⁶ There is some evidence that Bartonella is present in the saliva of cats, but shedding of B. henselae in cat saliva has not been clearly documented. Other potential vectors, such as Pulex flea species, ticks, lice, and biting flies, also harbor Bartonella DNA, and experimental transmission of Bartonella birtlesii has been accomplished with Ixodes ricinus ticks.⁷ There is epidemiologic evidence that ticks may transmit Bartonella to dogs.

Because Bartonella infections are often subclinical in dogs and cats, the full extent to which Bartonella spp. cause disease in naturally infected dogs and cats remains unclear. Bartonella spp. have been widely studied for their role in a number of idiopathic inflammatory disorders of cats, including uveitis, lymphadenopathy, caudal stomatitis, and rhinitis, without definitive evidence of disease causation. Without doubt, they are important causes of endocarditis in dogs and occasionally cause endocarditis and myocarditis in cats (Table 52-3 and Box 52-1 ).

TABLE 52-3.

Examples of Clinical Manifestations That May, in Some Circumstances, Be Associated with Bartonella Infection in Naturally Infected Cats

Strength of Association	Clinical Manifestation	Bartonella Species
Definite	Endocarditis26	B. henselae
	Myocarditis and diaphragmatic myositis27
Probable	Osteomyelitis28	B. v. berkhoffii
	Systemic reactive angioendotheliomatosis29
Possible∗	Caudal stomatitis32., 33., 34., 35., 36., 37.	Unknown
	Lower urinary tract disease32., 36.
	Uveitis30., 31.
	Lymphadenopathy37
	Fever38

^∗Results of experimental studies are conflicting or there is insufficient evidence to prove an association with disease.

BOX 52-1. Descriptive Case Reports or Small Case Series Where Bartonella Has Been Detected within Lesions in Dogs using Culture or PCR.

Endocarditis

• B. v. berkhoffii 45., 46., 47.

• B. henselae 45., 48.

• B. clarridgeiae ⁴⁶

• B. koehlerae ⁴⁸

• B. quintana ⁴⁹

• B. rochalimae ⁵⁰

Chronic lymphocytic hepatitis with copper accumulation (Doberman)

• B. clarridgeiae ⁵¹

Systemic pyogranulomatous disease, hyperviscosity syndrome

• Bartonella spp.⁵²

Pyogranulomatous lymphadenitis

• B. henselae ⁵³

Granulomatous hepatitis

• B. henselae ⁵¹

Peliosis hepatis

• B. henselae ⁵⁴

Systemic granulomatous disease and sialometaplasia

• B. henselae

• B. v. berkhoffii ⁵⁵

Chronic erosive polyarthritis

• B. henselae

• B. v. berkhoffii ⁵⁶

Massive post-traumatic seroma

• B. henselae

• B. v. berkhoffii ⁵⁷

Hemangiopericytoma

• B. v. berkhoffii or B. henselae ²⁹

Epistaxis

• B. v. berkhoffii or B. henselae ⁵⁸

Meningoradiculoneuritis and pyogranulomatous dermatitis or panniculitis

• B. v. berkhoffii ⁵⁹

Bacillary angiomatosis

• B. v. berkhoffii ⁶⁰

Epidemiology of Bartonella in Cats

The most common Bartonella species isolated from cats is B. henselae. Less commonly, cats are infected with Bartonella clarridgeiae or Bartonella koehlerae, which also have been linked to human disease.5., 8. Young cats (≤1 year) are more likely than older cats to be bacteremic, and stray or feral cats are more likely to be bacteremic than pet cats.5., 9., 10. Older cats are more likely to be seropositive than young cats, which likely reflects the increased chance of exposure over time. The prevalence of Bartonella bacteremia in cats is also highest in warm, humid climates (e.g., 68% in the Philippines), whereas it is low in colder climates (e.g., 0% in Norway).⁵ At least two genotypes of B. henselae infect cats, type Houston-1 (type I) and type Marseille (type II). B. henselae type Marseille predominates among cats in the western United States, western continental Europe, the United Kingdom, and Australia; type Houston-1 is dominant in Asia (Japan and the Philippines).⁵ However, within a given country, the prevalence of these types varies among cat populations, and type Houston-1 is more often isolated from humans with bartonellosis, even when type Marseille is more prevalent in the cat population. Some molecular typing methods reveal an even broader genetic diversity among feline strains, and most of the strains that infect humans cluster in a limited number of groups.

Epidemiology of Bartonella in Dogs

Dogs are most commonly infected with Bartonella vinsonii subsp. berkhoffii or B. henselae. Domestic and wild dogs are thought to be the natural reservoir for B. v. berkhoffii, because B. v. berkhoffii establishes prolonged bacteremia in dogs. In California, 35% of coyotes (Canis latrans) tested were seropositive, and 28% of coyotes from a highly endemic region were bacteremic.⁵ Other Bartonella species have also been detected in dogs (see Table 52-2). Novel species also have been identified in dogs from Thailand, Sri Lanka, and the Mediterranean.11., 12., 13.

Because it is often difficult to culture Bartonella from domestic dog blood, prevalence studies in dogs are usually based on antibody detection. Unfortunately, this correlates poorly with bacteremia. In addition, serologic cross-reactivity occurs among Bartonella species so seroprevalence studies cannot be Bartonella species-specific. The prevalence of antibodies to B. v. berkhoffii in dogs is highest in tropical or subtropical regions. For example, seroprevalences as high as 47% were detected in stray dogs from Morocco.¹⁴ In the southeastern United States, the prevalence of B. henselae antibodies in healthy dogs was 10%; a higher prevalence (27%) was found in sick dogs.¹⁵ Risk factors identified in dogs in the southeastern United States were tick exposure, residence in a rural environment, roaming, and outdoor exposure.¹⁶ The prevalence of B. henselae antibodies in sick dogs from the western United States is less than 2%.¹⁷

Clinical Features

Signs and Their Pathogenesis

After infection, Bartonella replicates in erythrocytes and can also infect endothelial cells and bone marrow progenitor cells.¹⁸ It then establishes chronic, often subclinical bacteremia, which can last for weeks, months, or even more than a year and may be a specific adaptation to a mode of transmission by blood-sucking arthropods.¹⁹ Infection of endothelial cells may be more likely to occur in incidental hosts and appears to be necessary for the development of disorders such as vasculoproliferative disease and endocarditis. Bartonella is thought to cause vasculoproliferative disease via cytokine-induced stimulation of endothelial cell proliferation and inhibition of endothelial cell apoptosis. Virulence factors characterized in Bartonella species include adhesins, heme acquisition mechanisms, type IV secretion systems, and a low-potency lipopolysaccharide, among others.²⁰ Host immunocompromise, such as due to genetic susceptibility (e.g., breed-related immunodeficiency syndromes), poor nutrition, overcrowding, co-infections with other pathogens, immunosuppressive drug treatment, or defects in normal host barriers (such as congenital valvular disease in dogs with endocarditis), may also influence whether disease ultimately develops in infected dogs and cats.

The vast majority of infected dogs and cats show no overt clinical signs of illness when bacteremic. In some situations, disease manifestations that occur in Bartonella spp.-infected dogs and cats are otherwise uncommon to rare and/or known to be associated with Bartonella infection in human patients; organisms may also have been visualized with silver stains using light microscopy in affected tissues (e.g., endocarditis or myocarditis lesions). In other situations, nonspecific clinical signs are present (e.g., uveitis, gingivostomatitis, chylothorax, polyarthritis, chronic rhinitis, idiopathic lower urinary tract disease, lymphadenopathy, reproductive disease, or neurologic disorders), and it has been impossible to clearly assign a role to Bartonella in disease causation. A clear understanding of the role of Bartonella in disease causation has also been thwarted by limitations of diagnostic tests available for detection of infection.

Clinical Manifestations in Cats

Experimental infections of specific pathogen free cats with Bartonella have shed light on disease processes that can follow infection of cats with Bartonella. Cats infected with B. henselae develop a small papule at the site of inoculation, and transient fever and lymphadenopathy.21., 22., 23., 24. Transient neurologic signs (such as staring and behavioral abnormalities) and reproductive disorders can also occur. Some cats infected with B. henselae and/or B. clarridgeiae show no clinical signs, and gross lesions are lacking at necropsy. However, histopathology reveals peripheral lymph node hyperplasia, splenic follicular hyperplasia, lymphocytic cholangitis/pericholangitis, lymphocytic hepatitis, lymphoplasmacytic myocarditis, and/or interstitial lymphocytic nephritis.21., 23.

In naturally infected cats, Bartonella can rarely cause endocarditis and myocarditis. Generally speaking, infective endocarditis is rare in cats, but a few of the reported cases have been associated with Bartonella infection. B. henselae DNA has been amplified from aortic valvular vegetative lesions of cats, with visualization of the organism in lesions using silver stains.25., 26. Dramatic pyogranulomatous myocarditis and diaphragmatic myositis were associated with B. henselae infection in two cats that died in a North Carolina shelter, and organisms were detected in lesions with silver stains and immunohistochemistry (IHC) (Figure 52-1 ).²⁷ Carpal and metacarpal osteomyelitis was also associated with a B. v. berkhoffii infection in a cat; Bartonella DNA was detected in bone lesions as well as in the blood.²⁸ The DNA of B. v. berkhoffii and B. henselae was also detected in cardiac tissues of several cats with systemic reactive angioendotheliomatosis.²⁹

FIGURE 52-1.

A, Granulomatous myocarditis associated with Bartonella henselae infection in an 8-week-old female domestic shorthair introduced to a shelter that was ridden with fleas. B, Histopathology of the heart of the affected cat showing intralesional agyrophilic bacteria (arrows). Warthin-Starry stain. C, Short bacilli (arrows) in an inflammatory focus are immunoreactive (brown) for Bartonella henselae-specific monoclonal antibody. Immunohistochemistry with diaminobenzidine chromogen, hematoxylin counterstain.

(A, Courtesy Drs. Jack Broadhurst and Edward Breitschwerdt. From Varanat M, Broadhurst J, Linder KE, et al. Identification of Bartonella henselae in 2 cats with pyogranulomatous myocarditis and diaphragmatic myositis. Vet Pathol 2012;49:608-611.)

Bartonella has been investigated for its role in a large number of idiopathic conditions in cats (see Table 52-3).26., 27., 28., 29., 30., 31., 32., 33., 34., 35., 36., 37., 38. These include uveitis,30., 31., 32. caudal gingivostomatitis,32., 33., 34., 35., 36., 37. fever of unknown origin,³⁸ lower urinary tract disease,32., 36., 39. chronic kidney disease,32., 36. pancreatitis,⁴⁰ lymphadenopathy (Figure 52-2 ),³⁷ neurologic disease,32., 41., 42. pododermatitis,⁴³ and chronic idiopathic rhinosinusitis.⁴⁴ There is currently no convincing and repeatable scientific evidence that Bartonella infection causes any of these conditions. Studies have varied in the methodology used to detect infection (serology, culture, and/or PCR assays), and many of the conditions investigated likely have multifactorial etiologies. An understanding of the significance of Bartonella in these conditions will probably require prospective study of large numbers of cats with clearly defined clinical illness using Bartonella culture and/or PCR assays.

FIGURE 52-2.

Lymph node of a 1-year-old, retrovirus-negative, flea-ridden cat with a 3-month history of fever, mild lethargy, and generalized peripheral lymphadenopathy but a normal appetite. The right axillary and both mandibular lymph nodes measured 3 cm in diameter; the remaining peripheral lymph nodes were 2 cm in diameter. A serum chemistry profile revealed hyperglobulinemia (6.5 g/dL). Serum protein electrophoresis revealed a polyclonal gammopathy. Histopathology of the right axillary, right mandibular and right popliteal lymph node showed lymphofollicular hyperplasia and marked neutrophilic, lymphocytic, and histiocytic capsulitis and perilymphadenitis. Note the florid capsulitis to the right of the arrows, which indicate the outer extent of the lymph node parenchyma. Silver stains (Warthin-Starry and Steiner stains) showed a small amount of granular staining within cells, which possibly represented intracellular agyrophilic bacteria. The DNA of Bartonella henselae and Bartonella clarridgeiae was detected in the lymph node using PCR, and blood cultures were positive for B. henselae. Interestingly, the cat was seronegative to B. henselae and B. clarridgeiae.

Clinical Manifestations in Dogs

Bartonella spp. are important causes of blood-culture-negative endocarditis in dogs (see Box 52-1).25., 29., 45., 46., 47., 48., 49., 50., 51., 52., 53., 54., 55., 56., 57., 58., 59., 60. Infection with Bartonella was identified in 6 (19%) of 31 dogs with culture-negative endocarditis in California.⁶¹ Worldwide, the DNA of several Bartonella species has been detected in the heart valves of dogs with endocarditis. The most common species identified has been B. v. berkhoffii. In dogs, Bartonella endocarditis usually involves the aortic valve, although the mitral valve is occasionally affected, so the possibility of bartonellosis should not be ruled out in dogs with mitral valve endocarditis. Dogs with Bartonella endocarditis are more likely to be afebrile and more likely to have congestive heart failure than dogs with other causes of endocarditis, and their median survival time is shorter (Figure 52-3 ).⁶¹ Complications of Bartonella endocarditis include thromboembolic disease and neutrophilic polyarthritis.

FIGURE 52-3.

Kaplan-Meier survival curve comparing survival of dogs with Bartonella infectious endocarditis (IE) with that of dogs with IE caused by other pathogens.

(From Sykes JE, Kittleson MD, Pesavento PA, et al. Evaluation of the relationship between causative organisms and clinical characteristics of infective endocarditis in dogs: 71 cases (1992-2005). J Am Vet Med Assoc 2006;228:1723-1734.)

Bartonella, or Bartonella DNA, has been detected in lesions from dogs with a variety of chronic pyogranulomatous or granulomatous inflammatory and vasculoproliferative diseases (see Box 52-1). Bartonella was detected in a dog with peliosis hepatis and a dog with bacillary angiomatosis, rare conditions that are strongly associated with Bartonella infection in humans.54., 60. Peliosis hepatis and bacillary angiomatosis are vasculoproliferative diseases characterized by the presence of blood-filled proliferations of vascular tissue in the liver and skin, respectively. Based on case reports and seroprevalence studies, Bartonella is suspected to cause polyarthritis, epistaxis, thrombocytopenia, and/or splenomegaly in dogs.¹⁷ However, these associations could also reflect the presence of other detected or undetected, co-transmitted vector-borne pathogens that cause these disorders. Bartonella has been investigated for its role in canine lymphoma⁶²; neurologic disease⁶³; splenic disorders including lymphoid nodular hyperplasia, hemangiosarcoma, and fibrohistiocytic nodules⁶⁴; idiopathic cavitary effusion⁶⁵; and idiopathic rhinitis.⁶⁶ As for cats, the role that Bartonella plays in these conditions, if any, is unclear and requires further study.

Physical Examination Findings

In dogs with Bartonella endocarditis, physical examination findings include lethargy, inappetence and thin body condition; lameness or recumbency due to thromboembolic complications, weakness, or polyarthritis; joint effusion; and, uncommonly, fever (as high as 104.9°F [41°C]). Evidence of cardiac disease and congestive heart failure is often present, including respiratory distress, cough, increased lung sounds, and systolic and/or diastolic heart murmurs, cardiac arrhythmias, and pulse deficits. Neurologic signs such as anisocoria and obtundation can occur in dogs with thromboembolism that involves the central nervous system. There may also be evidence of flea or tick infestations in some dogs. Other physical examination findings that might be present in dogs with other manifestations of bartonellosis are mass lesions that involve the nasal cavity, lymph nodes, or salivary glands; splenomegaly or hepatomegaly; cavitary effusions; peripheral edema; epistaxis; or nodular skin lesions.

Physical examination findings in cats with Bartonella endocarditis or myocarditis have included fever, lethargy, respiratory distress, cardiac murmurs, and arrhythmias.26., 27.

Diagnosis

Diagnosis of bartonellosis is based on the presence of consistent clinical abnormalities (especially endocarditis or myocarditis, but also other systemic inflammatory or vasculoproliferative diseases), histopathologic findings, and positive culture or PCR assay results on blood and affected tissues (Table 52-4 ). It may be impossible to identify Bartonella as the cause of disease if the organism is detected only in the blood and if affected tissues (e.g., valvular vegetations) cannot be obtained for analysis, because healthy dogs and especially cats can be bacteremic. Other possible causes of disease must also be investigated, and a response to antibiotic treatment could be evaluated (see Case Example).⁶⁷ It is even more difficult to establish a definitive diagnosis based on serology, but when culture and PCR assay results are negative, positive serologic test results in dogs may be of some value in the presence of consistent clinical abnormalities. More specifically (and as occurs in humans), dogs with Bartonella endocarditis usually have high antibody titers to Bartonella spp. Organism detection tests are insensitive in dogs because dogs tend to have very low levels of bacteremia when compared with cats.

TABLE 52-4.

Diagnostic Assays Available for Bartonella Infection in Dogs and Cats

Assay	Specimen Type	Target	Performance
Culture	Whole blood, tissue specimens obtained at necropsy (e.g., heart valve, myocardium) or by biopsy (e.g., liver biopsy, skin biopsy)	Bartonella spp.	Confirms infection and allows species identification. Specialized culture conditions required; best performed in laboratories with special expertise. Requires several weeks' incubation. Sensitivity is especially low in dogs because of low-level or intermittent bacteremia. Use of BAPGM enrichment media followed by PCR may increase sensitivity but may increase the chance of false-positive results due to PCR-related contamination. Positive culture results alone do not apply disease causation, because healthy dogs and cats can have Bartonella in their blood.
Histopathology with organism detecting using silver stains or IHC	Tissue specimens obtained by biopsy or necropsy	Bartonella spp. organisms	Low sensitivity, but supports disease causation when positive and properly performed and interpreted.
Serology	Serum	Antibodies to Bartonella spp.	Variable cross-reactivity between Bartonella species; species-specific assays are required. Immunofluorescent antibody, ELISA, and Western immunoblot assays are available. Results correlate poorly with bacteremia. Positive results do not imply disease causation, because a significant proportion of healthy dogs and cats are seropositive. Positive titers are usually present in dogs and cats with endocarditis.
PCR	Whole blood, splenic or lymph node aspirates, tissue specimens obtained at necropsy or biopsy	Bartonella spp. DNA	Confirms active infection more rapidly than culture. Sensitivity and specificity may vary depending on assay design and specimen type; may not necessarily be more sensitive than culture. Because healthy animals may be PCR positive, positive PCR results must be interpreted in light of the clinical signs. False positive results may occur as a result of PCR-related contamination.

CASE EXAMPLE.

Signalment

"Pesto," a 16-month-old female spayed domestic medium hair cat from Rio Vista in northern California

History

Pesto was evaluated at the University of California, Davis, Veterinary Medical Teaching Hospital for progressive lethargy over the previous month. Since obtained as a kitten, she had shown intermittent signs of upper respiratory tract disease, characterized by sneezing, serous to mucopurulent nasal and ocular discharges, inappetence, blepharospasm, tachypnea, and a cough, for which she had been treated with amoxicillin or doxycycline on at least three separate occasions. Between episodes she appeared healthy, but she had always been thin. There had been no vomiting, diarrhea, or changes in thirst or urination. Pesto was obtained as a stray kitten, tested negative for FeLV and FIV, and had been housed indoors ever since. She was neutered at 8 months of age without complication. Five months earlier, she traveled briefly to Oregon with the owner. She lived with a dog and a retrovirus-negative kitten that was introduced 5 months ago. One other sibling had died of FIP, which was confirmed on necropsy. Pesto was up to date on vaccinations for respiratory viruses, panleukopenia virus, and rabies. She was not receiving any medications.

Physical Examination

Body Weight

2.9 kg.

General

Quiet, alert, responsive, and hydrated. T = 103°F (39.5°C), HR = 240 beats/min, RR = 40 breaths/minute, moist and pink mucous membranes, CRT <2 s.

Integument

No ectoparasites were noted. The haircoat was full and lustrous.

Eyes, Ears, Nose, and Throat

In the left eye, mild conjunctivitis with moderate serous ocular discharge was present. Mild corneal opacity was present in the right eye. No abnormalities detected on examination of the oral cavity. There was no evidence of nasal discharge or abnormal nasal airflow.

Musculoskeletal

Body condition score 4.5/9, ambulatory, adequate muscle mass.

All Other Systems

No clinically significant abnormalities were detected. A full neurologic examination was not performed.

Ophthalmologic Examination

Pesto behaved as if visual and was relatively comfortable with mild blepharospasm. The menace response, palpebral reflexes, and pupillary light reflexes were normal. There was no evidence of eyelid abnormalities or episcleral or conjunctival injection. Mild chemosis was present bilaterally. There was no aqueous flare, the lenses were normal, and a fundic examination was normal. The dorsal third of the right cornea had superficial vessels that extended from the limbus and a 2- to 3-mm central area where ghost vessels were present, which may have represented a previous dendritic ulcer. A rose Bengal stain was negative for ulceration.

Laboratory Findings

CBC

HCT 31% (30%-50%)

MCV 37.8 fL (42-53 fL)

MCHC 34.2 g/dL (30-33.5 g/dL)

Reticulocytes 29,000 cells/µL (7000-60,000 cells/µL)

WBC 7030 cells/µL (4500-14,000 cells/µL)

Neutrophils 4570 cells/µL (2000-9000 cells/µL)

Lymphocytes 2179 cells/µL (1000-7000 cells/µL)

Monocytes 141 cells/µL (50-600 cells/µL)

Eosinophils 70 cells/µL (150-1100 cells/µL)

Basophils 70 cells/µL (0-50 cells/µL)

Platelets clumped but adequate. A few Dohle bodies were seen within neutrophils.

Serum Chemistry Profile

Sodium 146 mmol/L (151-158 mmol/L)

Potassium 4.5 mmol/L (3.6-4.9 mmol/L)

Chloride 110 mmol/L (117-126 mmol/L)

Bicarbonate 18 mmol/L (15-21 mmol/L)

Phosphorus 5.1 mg/dL (3.2-6.3 mg/dL)

Calcium 9.8 mg/dL (9.0-10.9 mg/dl)

BUN 20 mg/dL (18-33 mg/dL)

Creatinine 1.0 mg/dL (1.1-2.2 mg/dL)

Glucose 119 mg/dL (63-118 mg/dL)

Total protein 12.0 g/dL (6.6-8.4 g/dL)

Albumin 2.4 g/dL (2.2-4.6 g/dL)

Globulin 9.6 g/dL (2.8-5.4 g/dL)

ALT 42 U/L (27-101 U/L)

AST 25 U/L (17-58 U/L)

ALP 8 U/L (14-71 U/L)

GGT 9 U/L (0-4 U/L)

Cholesterol 134 mg/dL (89-258 mg/dL)

Total bilirubin 0.2 mg/dL (0-0.2 mg/dL).

Serum Protein Electrophoresis

Results were consistent with a polyclonal gammopathy.

Imaging Findings

Thoracic Radiographs

No clinically significant abnormalities were noted.

Abdominal Ultrasound

Lymph nodes were moderately enlarged throughout the abdomen, including the gastric, splenic, and jejunal nodes. Hepatic and sublumbar nodes were enlarged to a lesser degree. The echotexture of the enlarged nodes was homogeneous. The left adrenal gland was moderately enlarged, measuring 0.66 cm in thickness. The right adrenal gland could not be differentiated from multiple enlarged nodes. No free fluid was identified.

Microbiologic Testing

In-clinic FeLV antigen and FIV antibody ELISA assay: Negative.

Feline coronavirus serum antibody IFA assay: Positive at 1:25,600.

Treatment

Pesto was treated with l-lysine (500 mg PO q12h), for possible FHV-1 infection, and doxycycline (10 mg/kg PO q24h, immediately followed by a bolus of water), for possible chlamydiosis or mycoplasmosis. The owner could not administer the l-lysine, only the doxycycline, and reported improvement in Pesto's activity level and appetite several days after starting the doxycycline.

Additional Diagnostics and Outcome

Pesto was evaluated again 2 weeks later for possible lymph node aspiration or biopsy under sedation. Abdominal ultrasound showed persistent abdominal lymphadenomegaly. Cytologic examination of an ultrasound-guided aspirate of a mesenteric lymph node revealed mild to moderate lymphoid reactivity. Plasma cells were increased in number and were admixed throughout the specimen with rare mast cells and eosinophils. Low numbers of vacuolated macrophages and nondegenerate neutrophils were also observed. RT-PCR for feline coronavirus RNA on the lymph node aspirate was negative. IFA serology for antibodies to B. clarridgeiae was negative, whereas serology for antibodies to B. henselae was positive at 1:64. B. henselae was cultured from the blood. Treatment was changed from doxycycline to azithromycin, and again there was mild improvement in Pesto's attitude. However, several days later the cat became lethargic again, and her appetite decreased further. After 3 weeks of treatment with azithromycin, Pesto was reexamined. Because of the cat's fractious temperament, sedation was required. No abnormalities were detected on physical examination. A CBC showed a hematocrit of 23%, MCV of 39.2 fL, MCHC of 32.6 g/dL, reticulocyte count of 23,200 cells/µL, 8220 slightly toxic neutrophils/µL, 788 band neutrophils/µL, 1239 lymphocytes/µL, 788 eosinophils/µL, and 298,000 platelets/µL. A biochemistry panel showed similar abnormalities to those previously present (mild hyponatremia, hypochloremia, and hyperglycemia and low creatinine), and the globulin had increased to 12.4 mg/dL, with a total protein of 14.4 mg/dL. IFA serology and culture for Bartonella were repeated and showed a titer of 1:1024 to B. clarridgeiae and 1:4096 to B. henselae; Bartonella spp. culture was negative. An ultrasound-guided biopsy of an enlarged mesenteric lymph node was obtained. Histopathology showed a mixed, dense inflammatory infiltrate composed of neutrophils, lymphocytes, and plasma cells. Some of the macrophages present stained positive using immunohistochemistry for feline coronavirus antigen. Treatment with prednisone (1 mg/kg PO q12h for 5 days, then 1 mg/kg PO q24h thereafter) was initiated. Four days later, the cat became anorectic and tachypneic and was euthanized. A necropsy was not performed.

Diagnosis

Feline infectious peritonitis and concurrent B. henselae bacteremia

Comments

Bartonella infection in this cat was initially suspected because of fever and lymphadenopathy, and infection with B. henselae was confirmed with Bartonella culture. Ultimately, an alternate diagnosis (FIP) was made based on the presence of the combination of marked hyperglobulinemia, a very high feline coronavirus titer, and histopathology of a mesenteric lymph node and IHC for coronavirus antigen. There was also minimal response to antimicrobial drugs with activity against Bartonella. Thus, the Bartonella bacteremia was an incidental finding. Bartonella bacteremia was detected in the face of doxycycline treatment, which highlights the fact that antimicrobial drug treatment does not always clear bacteremia. The cat was fractious and the owner could not effectively administer the l-lysine twice daily, but assured the veterinarian that Pesto had received the doxycycline. The owner may have been exposed to Bartonella during treatment. Treatment with azithromycin was followed by a single negative culture, but antibody titers increased, so the Bartonella infection may have been relatively recent.

Laboratory Abnormalities

Hematologic and biochemistry abnormalities in dogs and cats with Bartonella endocarditis are nonspecific and often mild. The CBC may show a mild nonregenerative anemia (31% to 39%), variable leukocytosis primarily due to neutrophilia (up to 43,000 neutrophils/µL), and mild thrombocytopenia (usually above 100,000 platelets/µL). In a few dogs, low to moderate numbers of circulating band neutrophils, lymphocytosis, and/or monocytosis are present.49., 68., 69. The biochemistry panel may reveal mild azotemia (creatinine <3 mg/dL), mild hypoalbuminemia, and, less often, hyperglobulinemia. Isosthenuria, proteinuria, cylindruria, and slightly increased urine protein-to-creatinine ratios have been present in the urine of some affected dogs. Dogs with hepatic disorders associated with Bartonella infection have had moderately increased activities of serum ALT and/or ALP.51., 54.

Diagnostic Imaging

Plain Radiography

Thoracic radiographs in dogs with Bartonella endocarditis often show evidence of congestive heart failure, with venous engorgement and pulmonary edema (Figure 52-4 ). Lung lobe consolidation and hilar lymphadenopathy were described in a dog with systemic granulomatous disease and sialometaplasia.⁵⁵

FIGURE 52-4.

Lateral thoracic radiograph from a 3-year-old female spayed Doberman pinscher with early congestive heart failure due to endocarditis, before (A) and after (B) treatment with furosemide. The dog was seroreactive to Bartonella vinsonii subsp. berkhoffii with a titer of 1:256 and Bartonella henselae with a titer of 1:64. A, There is mild cardiomegaly with left atrial enlargement. There is increased pulmonary interstitial opacity that is most pronounced in the accessory lung lobe, as well as cranial to the heart. B, Pulmonary infiltrates have significantly resolved.

Abdominal Ultrasound

Ultrasound of dogs with systemic granulomatous or pyogranulomatous disease may reveal lymphadenomegaly and organomegaly,⁵² and mixed echogenic patterns within the liver.⁵¹ The dog with peliosis hepatis had ascites and multiple, small nodular masses and hypoechoic cystic lesions within the liver.⁵⁴

Echocardiography

Echocardiography in dogs and cats with Bartonella endocarditis reveals oscillating valvular vegetations or thickened and hyperechoic valve leaflets, which usually involve the aortic valve (Figure 52-5 ). There may be evidence of aortic regurgitation or insufficiency and eccentric hypertrophy of the left ventricle in some dogs.

FIGURE 52-5.

Echocardiogram images from a 13-year old German shepherd dog with blood culture-negative endocarditis. The dog also had biopsy-confirmed glomerulonephritis. IFA serology for Bartonella vinsonii subsp. berkhoffii, Bartonella clarridgeiae, and Bartonella henselae were positive at titers of 1:512, 1:1024, and 1:128, respectively. On the long-axis view (A) there is an irregular hyperechoic lesion attached to the aortic valve cusps (arrow), and the cusps appear thickened. On the short-axis view (B), the normal "Mercedes Benz" sign has been destroyed by the aortic valvular thickenings.

Microbiologic Tests

Culture

Culture of blood or other tissues for Bartonella allows definitive diagnosis of infection. However, blood culture requires special techniques and can be insensitive because of the relapsing nature of bacteremia. In contrast to the situation in cats, culture has especially low sensitivity in dogs because of the low level of bacteremia in dogs (especially when they act as incidental hosts and develop disease). Blood for culture should be obtained using sterile technique and the blood placed in EDTA-containing tubes, and then chilled or frozen during shipment. Collection of blood into plastic EDTA tubes allows the tubes to be frozen directly, which releases organisms from erythrocytes after which they are plated onto special media. Blood should be sent to laboratories familiar with the culture of these fastidious organisms, and the laboratories should be contacted for specific instructions regarding specimen collection and submission. Special media (such as fresh chocolate agar, or brain-heart infusion agar enriched with 5% to 10% blood) and culture conditions (5% CO₂, temperatures of 35°C to 37°C) are used to enhance the likelihood of isolation of Bartonella.⁶² Extended incubation times of up to 6 to 8 weeks are often required. Serial Bartonella blood cultures may enhance the chance of a positive result. The use of an insect growth medium (Bartonella Alpha Proteobacteria Growth Medium, or BAPGM) that is enriched with multiple micronutrients and defibrinated sheep blood for pre-enrichment culture of blood and potentially other tissues, followed by PCR assay of the liquid culture and subinoculation of the liquid culture onto agar plates, may enhance the sensitivity of culture for diagnosis of Bartonella infections of dogs. It also has the potential to yield other fastidious organisms not cultured under routine conditions that may play a role in endocarditis.⁷⁰

Molecular Diagnosis Using the Polymerase Chain Reaction

A variety of PCR-based assays have been developed for rapid detection of Bartonella DNA in blood or other tissues. Some veterinary diagnostic laboratories offer real-time PCR assays for detection of Bartonella species as a component of vector-borne PCR panels. Some assays detect all species of Bartonella, whereas others are species-specific. Genetic analysis of the resultant PCR products can also be performed to identify the infecting species. The clinical performance of many of these assays when compared with culture has not been well studied. When used directly on blood specimens, PCR assays may be no more sensitive than culture for detection of Bartonella, and detection of DNA does not always equate to detection of living organisms. False-positive PCR assay results due to laboratory contamination have the potential to occur.

Serologic Diagnosis

Immunofluorescent antibody (IFA), ELISA, and Western immunoblot assays are available for detection of antibodies to Bartonella species. Some degree of cross-reactivity occurs among Bartonella species, but multiple species-specific assays still should be performed to increase the chance of antibody detection. Paired titers are not valuable because disease typically results from chronic and persistent infection. If serologic testing is performed in dogs, at a minimum it should include testing for B. henselae, B. v. berkhoffii, B. rochalimae, and B. clarridgeiae. Measurement of serum antibodies to Bartonella has a limited ability to help determine whether a sick animal has an active Bartonella infection. In both cats and dogs, bacteremia can occur in the absence of detectable antibodies (see Figure 52-2), and seropositive cats and dogs are not always bacteremic. Fewer than half of antibody-positive cats are bacteremic, and 3% to 15% of antibody-negative cats are bacteremic.⁶⁷ Because of this, serology is not recommended for routine diagnosis of Bartonella infection in cats. Because of the low sensitivity of PCR and culture in dogs, serology could be considered when these assays and routine blood cultures are negative (or in conjunction with PCR and culture) to support a diagnosis of Bartonella endocarditis (which is usually associated with high antibody titers).

Pathologic Findings

Gross necropsy of dogs and cats with Bartonella endocarditis may reveal evidence of congestive heart failure, with lung congestion and edema. Single or multiple, variably sized nodules are typically present on the periphery of valvular leaflets, which may be small and firm or large, granular, and friable (Figure 52-6 ). White plaques may be found adherent to the adjacent endocardial surfaces. Histopathology reveals chronic inflammation, with fibrous tissue and extensive mineral deposits. The presence of valvular mineralization should raise suspicion for Bartonella endocarditis, because mineralization is uncommonly associated with endocarditis caused by other bacteria.⁶¹ Small bacilli may be seen within lesions with silver stains or immunohistochemical stains for B. henselae.26., 27., 60. Silver stains must be interpreted with caution, because necrotic debris and nuclear material can mimic positive staining. Gross lesions in the dog with peliosis hepatis consisted of multiple, 0.1- to 0.3-cm cysts in the liver that were filled with cloudy, serosanguineous fluid.⁵⁴ The cysts were lined with endothelial cells, and there was evidence of telangiectasia scattered through other parts of the liver. Nodular granulomatous or pyogranulomatous lesions in lymphoid or other tissues (such as the liver, lymph nodes, and nasal cavity) have also been described in dogs with bartonellosis,47., 51., 71. and nodular pyogranulomatous inflammatory lesions with intralesional bacteria were described in the myocardium and diaphragm of cats with Bartonella myocarditis and diaphragmatic myositis.²⁷

FIGURE 52-6.

Gross pathologic findings (A) and histopathology (B) of the aortic valve from a dog with Bartonella endocarditis. A, The periphery of the valve is eroded. Variably sized, mineralized nodules expand the valve leaflet. There are multifocal, slightly raised, dull white plaques on the surface of the adjacent aorta and ventricular endocardium. B, Aortic valve, aorta, and ventricular septum. The distal leaflet is fragmented and contains mineral deposits (arrow) and hemorrhage. At the base of the valve, the endothelial surface is lifted and there are broad bands of loose connective tissue, small vessels, and endothelial-lined clefts (arrowheads). H&E stain. Bar = 180 µm.

(Reprinted from Pesavento PA, Chomel BB, Kasten RW, et al. Pathology of Bartonella endocarditis in six dogs. Vet Pathol 2005;3:370-373.)

Treatment and Prognosis

Efficacy has not been established for any antimicrobial that could be used to eliminate Bartonella bacteremia in cats or dogs. In humans, doxycycline, erythromycin, and rifampin are the most frequently recommended antimicrobials for treatment of Bartonella infection, but clinical improvement has been reported after the use of penicillin, gentamicin, ceftriaxone, ciprofloxacin, or azithromycin. Treatment for 2 weeks is recommended for immunocompetent patients (e.g., for CSD), and for a minimum of 6 weeks in immunocompromised humans. Relapses in bacteremia, fever, or other disease manifestations have been reported in immunocompromised humans, despite a 6-week treatment regimen.

The prognosis for Bartonella endocarditis in dogs and cats is generally poor. Supportive care and medications such as furosemide to manage congestive heart failure are often required. A combination of a β-lactam and an aminoglycoside or doxycycline is recommended for treatment of Bartonella endocarditis in human patients, and valve replacement is usually indicated (see Chapter 86).⁷² Oral antimicrobial alternatives for dogs that are stable include high-dose doxycycline, alone or in combination with rifampin; azithromycin; or fluoroquinolones, alone or in combination with amoxicillin (Table 52-5 ). Resistance of B. henselae to azithromycin and fluoroquinolones has been documented.⁷³ Data from experimentally or naturally infected cats indicate that a high dose of doxycycline may be necessary to eliminate Bartonella infection in cats. Amoxicillin-clavulanic acid may also be an appropriate choice for treatment of infected cats when a definitive diagnosis is not known. If there is no response after 7 days, a change to a fluoroquinolone or azithromycin could be considered.⁶⁷ Extreme care should be taken to avoid scratches or bites when administering drugs to bacteremic cats.

TABLE 52-5.

Medications That Could Be Used to treat Bartonella spp. Infections in Sick Dogs and Cats Suspected to have Bartonellosis

Drug	Dose (mg/kg)	Route	Interval (hours)
Ampicillin sodium	10-20	IV	6-8
Gentamicin sulfate∗	9-14 (dogs), 5-8 (cats)	IV, IM, SC	24
Amoxicillin-clavulanate	12.5-25	PO	8
Doxycycline	10	PO	12
Rifampin†	5	PO	12
Azithromycin	5-10	PO	24
Marbofloxacin	2.75-5.5	PO	24
Enrofloxacin‡	5 (cats), 5-20 (dogs)	PO	24

^∗Use in combination with ampicillin for initial treatment of endocarditis; other aminoglycosides could be substituted for gentamicin (such as amikacin). Monitor renal values during treatment.

^†Use in combination with doxycycline; avoid monotherapy with rifampin because of the potential for rapid selection for resistant bacteria. May cause gastrointestinal adverse effects.

^‡Other fluoroquinolones are preferred in cats due to the higher risk of retinal toxicity with enrofloxacin. Doses of 5 mg/kg q24h should never be exceeded in cats.

Immunity and Vaccination

There are no vaccines for prevention of bartonellosis in cats or dogs. Bartonella evades the host immune system and establishes a persistent intracellular infection. Dogs and cats can be co-infected with multiple different Bartonella species and genotypes. Vaccination and challenge with the same or different Bartonella species results in variable protection, and protection is generally species specific.74., 75., 76.

Prevention

Prevention of Bartonella infections in cats and dogs is best accomplished by avoiding exposure to arthropod vectors. Flea control measures, such as use of ectoparasiticides, can interrupt transmission of B. henselae among cats and should be maintained year-round.67., 77. Housing cats indoors may also reduce exposure to fleas. B. henselae and B. clarridgeiae have been transmitted through inoculation of infected cat blood; therefore, cats of unknown Bartonella status or cats that are positive by culture, serology, and/or PCR for Bartonella should be excluded as blood donor cats.

Public Health Aspects

Cats are the major reservoirs for B. henselae, the principal cause of CSD in immunocompetent humans. CSD is characterized by formation of a pustule at the site of inoculation (a cat scratch) within 14 days, followed by development of local lymphadenopathy and malaise 1 to 3 weeks after the scratch (or bite), which can persist for weeks to months. Most cases of CSD are self-limiting after several months and respond minimally to antimicrobial drug treatment. Occasionally CSD is complicated by other disorders such as encephalopathy, relapsing bacteremia, osteomyelitis, neuroretinitis, or endocarditis, which require antimicrobial drug treatment. Vasculoproliferative diseases such as bacillary peliosis (e.g., peliosis hepatis) and bacillary angiomatosis (Figure 52-7 ) are among the most common complications in immunocompromised humans.²⁰ Young cats are most often implicated in transmission to humans, because young cats are more likely to be bacteremic than older cats. Dogs are less likely to act as reservoirs for human disease when compared with cats, because the prevalence of Bartonella infection and the magnitude of bacteremia in dogs are lower than that in cats. Nevertheless, dogs have occasionally been implicated in transmission of Bartonella to humans through bite wounds or scratches, and to date, all Bartonella species identified in sick dogs are also pathogenic or potentially pathogenic in humans. Immunocompromised humans should preferably choose adult, well-socialized cats over kittens as pets and should be properly educated in regard to the need for flea prevention. Cats' claws should be trimmed regularly, but there is no evidence that declawing prevents transmission. Animal scratches or bites should be avoided, and if they occur, they should be washed thoroughly with soap and water, after which prompt medical attention should be sought. The Guidelines for Preventing Opportunistic Infections among HIV-Infected Persons (United States Public Health Service and Infectious Diseases Society of America) state "No evidence indicates any benefits to cats or their owners from routine culture or serologic testing of the pet for Bartonella infection."⁷⁸ There is also no antimicrobial drug treatment that reliably eliminates bacteremia from cats, and administration of antimicrobial drugs to cats may result in unnecessary bites, scratches, and contact with cat saliva. Pros and cons for the testing of healthy cats for Bartonella infection are shown in Box 52-2 .⁶⁷

FIGURE 52-7.

A crop of cutaneous bacillary angiomatosis lesions on the elbow of an AIDS patient. All lesions involuted with doxycycline treatment.

(From Slater LN, Welch DF. Bartonella, including cat-scratch disease. In: Mandell GL, Bennett JE, Dolin R, eds. Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases, 7 ed. Philadelphia, PA: Churchill Livingstone Elsevier; 2010:2995-3009.)

BOX 52-2. Advantages and Disadvantages of Routine Testing of Healthy Cats for Bartonella spp. Infection.

Advantages

• Cats with positive Bartonella test results can be eliminated as blood donors or breeding animals

• Cats with negative Bartonella test results (serology and culture or PCR) may be safer pets than cats that test positive

• Testing cats for Bartonella spp. may allow veterinarians to avoid claims or litigation

Disadvantages

• Bartonella serology and PCR can be falsely positive

• Some cats with positive serologic test results may have eliminated infection and be immune to reinfection

• Cats with negative test results may still be bacteremic, or become bacteremic within the near future

• Detection of positive Bartonella spp. test results in some situations may lead to needless euthanasia

• A focus on testing may lead to underappreciation of the need for other relevant health care such as flea control

• There is no treatment that reliably eliminates bacteremia in healthy cats, and antimicrobial drug treatment of cats has not been shown to prevent human infection

• Treatment of positive cats may increase the risk of human infection due to an increased risk of bites and scratches

• Treatment of positive cats may lead to unnecessary life-threatening adverse drug reactions such as esophageal strictures (doxycycline) or blindness (fluoroquinolones); it also selects for antimicrobial-resistant bacteria

Bartonella has the potential to be transmitted to veterinarians as a result of scratches or bite wounds as well as needle-stick injuries.79., 80. Because of the high prevalence of Bartonella bacteremia in stray and young cats, veterinarians should take care to avoid these injuries (consider use of sedation whenever possible if necessary), thoroughly wash wounds that occur, and seek medical attention early if necessary. Gloves should be worn if skin contact with animal blood or saliva is anticipated.

Although cats and dogs are important reservoirs of Bartonella, humans can also develop bartonellosis through other routes of transmission, such as via other arthropods and possibly through blood transfusions.⁸¹ Human body lice primarily transmit B. quintana among humans (especially the homeless), which causes relapsing fever (trench fever) and endocarditis.