JOURNAL OF CLINICAL MICROBIOLOGY, Nov. 2003, p. 5327–5332
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Vol. 41, No. 11
Isolation of Bartonella washoensis from a Dog with Mitral
Bruno B. Chomel,1* Aaron C. Wey,2and Rickie W. Kasten1
Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, California
95616,1and Veterinary Centers of America, Emergency Animal Hospital & Referral Center, San Diego, California 921082
Received 7 March 2003/Returned for modification 22 June 2003/Accepted 11 August 2003
We report the first documented case of Bartonella washoensis bacteremia in a dog with mitral valve endo-
carditis. B. washoensis was isolated in 1995 from a human patient with cardiac disease. The main reservoir
species appears to be ground squirrels (Spermophilus beecheyi) in the western United States. Based on
echocardiographic findings, a diagnosis of infective vegetative valvular mitral endocarditis was made in a
spayed 12-year-old female Doberman pinscher. A year prior to presentation, the referring veterinarian had
detected a heart murmur, which led to progressive dyspnea and a diagnosis of congestive heart failure the week
before examination. One month after initial presentation, symptoms worsened. An emergency therapy for
congestive heart failure was unsuccessfully implemented, and necropsy evaluation of the dog was not permit-
ted. Indirect immunofluorescence tests showed that the dog was strongly seropositive (titer of 1:4,096) for
several Bartonella antigens (B. vinsonii subsp. berkhoffii, B. clarridgeiae, and B. henselae), highly suggestive of
Bartonella endocarditis. Standard aerobic and aerobic-anaerobic cultures were negative. However, a specific
blood culture for Bartonella isolation grew a fastidious, gram-negative organism 7 days after being plated.
Phenotypic and genotypic characterizations of the isolate, including partial sequencing of the citrate synthase
(gltA), groEL, and 16S rRNA genes, indicated that this organism was identical to B. washoensis. The dog was
seronegative for all tick-borne pathogens tested (Anaplasma phagocytophilum, Ehrlichia canis, and Rickettsia
rickettsii), but the sample was highly positive for B. washoensis (titer of 1:8,192) and, according to indirect
immunofluorescent-antibody assay, weakly positive for phase II Coxiella burnetii infection.
On 2 August 2001, a spayed 12-year-old female mixed Do-
berman pinscher dog weighing 30 kg presented to the Veteri-
nary Centers of America Emergency Animal Hospital and
Referral Center for evaluation of a murmur by a board-certi-
fied cardiologist. One year prior to presentation, the referring
veterinarian had detected a heart murmur and placed the pa-
tient on a treatment regimen of 0.33 mg of enalapril/kg of body
weight per os (p.o.) twice daily (BID). One week prior to
referral, the patient had been evaluated for progressive dys-
pnea. Thoracic radiographs performed at that time revealed
moderate cardiomegaly and severe enlargement of the left
atrium, as well as a mild perihilar pulmonary interstitial pat-
tern. A solitary pulmonary nodule, approximately 2 cm in di-
ameter, was also visible within the left caudal lung lobe. Based
on thoracic radiographic changes, a presumptive diagnosis of
congestive heart failure was made, and the patient was placed
on a regimen of 1.67 mg of furosemide/kg p.o. BID. Other
diagnostics performed at that time included a serum chemistry
profile, a complete blood count, and a measurement of the
serum thyroxine concentration. The diagnostics were unre-
markable with the exception of mild monocytopenia (990
monocytes/?l; normal range, 1,000 to 4,800/?l) and mild hy-
perchloridemia (116 meq/liter; normal range, 105 to 115 meq/
The history for the patient included intermittent inconti-
nence that was managed with diethylstilbestrol twice weekly
and degenerative joint disease that was treated with intermit-
tent therapy with various nonsteroidal anti-inflammatory
agents. Therapy with levothyroxine (0.02 mg/kg p.o. BID) had
been carried out for 2 years for hypothyroidism. At 3 years of
age, the patient underwent bilateral surgical correction of rup-
tured cranial cruciate ligaments. The patient also had a previ-
ous history of exposure to ticks and fleas.
On presentation to the cardiologist (A. C. Wey), the patient
was tachycardic (160 beats/min) but normothermic (39°C,
102.2°F) with a normal respiratory rate of 28 breaths/min.
Physical examination revealed multiple soft, small (?1-cm)
cutaneous nodules consistent with lipomas. On thoracic aus-
cultation, a grade IV to VI systolic murmur in the left apex was
present, as well as an S3 gallop sound and an occasional ar-
rhythmia with pulse deficits. The patient was slow to rise and
appeared stiff in the hind limbs when ambulatory, but no joint
swellings were noted. Electrocardiography revealed a heart
rate of 120 beats/min, sinus arrhythmia with occasional prema-
ture atrial and ventricular contractions, and a normal mean
electrical axis (60 degrees; normal range, 40 to 100). Echocar-
diography revealed moderate eccentric left-ventricular dilation
(left-ventricular end diastolic diameter, 4.7 cm), severe left
atrial enlargement (left atrium, 4.5 cm; left atrium/aorta, 2.0
cm), and severe mitral regurgitation (velocity decreased at 4.2
m/s). A large, hyperechoic mass lesion was noted adherent to
the anterior mitral valve leaflet that prolapsed into the left
atrium during systole. The anatomy of all other cardiac valves
appeared normal, and no other valvular insufficiencies were
noted. Based on the echocardiographic findings, a presumptive
* Corresponding author. Mailing address: Department of Popula-
tion Health and Reproduction, School of Veterinary Medicine, Uni-
versity of California, Davis, CA 95616. Phone: (530) 752-8112. Fax:
(530) 752-2377. E-mail:email@example.com.
diagnosis of vegetative endocarditis of the mitral valve was
made. Further possible diagnostics discussed with the owner
included spinal radiographs, abdominal ultrasound, urine and
blood cultures, various serological tests, and joint taps. Only
serology for the presence of Bartonella sp. antibodies and a
blood culture to attempt Bartonella isolation were performed
at that time. However, because the dog had a history of tick
and flea exposure, we later performed various serological tests.
Therapy initiated at that time included amoxicillin-clavulanic
acid (16.7 mg/kg p.o. BID), enrofloxacin (4.5 mg/kg p.o. BID),
and an increase in the dosage of furosemide (3.3 mg/kg p.o.
After 3 days, urine cultures were negative. Serial blood cul-
tures obtained 30 min apart by a sterile technique from three
different sites were negative for bacterial pathogens after 1
week. However, the dog was reported to have a high titer of
antibodies to various Bartonella species, and the Bartonella-
specific blood culture yielded a positive culture after 1 week
(see below). At this time, therapy with amoxicillin-clavulanic
acid was discontinued, and therapy with doxycycline (10 mg/kg
p.o. BID) was initiated.
One month after initial presentation to the referred cardi-
ologist, the patient was presented to another emergency ani-
mal hospital for treatment of progressive lethargy, anorexia,
and dyspnea. Thoracic radiographs at that time revealed a
severe perihilar pulmonary interstitial-to-alveolar pattern and
persistent cardiomegaly (left-atrial enlargement). Emergency
therapy for congestive heart failure, including intravenous di-
uresis, oxygen supplementation, and a topical venodilator,
were unsuccessful, and the patient experienced cardiopulmo-
nary arrest. Cardiopulmonary resuscitation was not attempted.
Unfortunately, necropsy evaluation of the patient was not
Bartonella species are emerging pathogens in humans, caus-
ing severe diseases in immunocompromised individuals (10).
At least eight Bartonella species or subspecies are known to be
pathogenic for humans, including B. bacilliformis, B. quintana,
B. henselae, B. elizabethae, B. grahamii, B. vinsonii subsp. aru-
pensis (1, 18, 27, 47), B. vinsonii subsp. berkhoffii (44), and B.
washoensis (10, 32). Furthermore, based on serological evi-
dence, B. clarridgeiae has been associated with cat scratch dis-
ease in humans (29, 35, 45). Among these Bartonella species or
subspecies, mainly B. quintana and B. henselae (1, 7, 10, 19, 41,
42, 46) but also B. elizabethae and B. vinsonii subsp. berkhoffii
have been identified as causative agents of human endocarditis
(18, 44), and B. washoensis has been identified as a cause of
myocarditis (10, 32). The main reservoir species for B.
washoensis appears to be ground squirrels (Spermophilus
beecheyi) in Nevada (32) and California (B. B. Chomel, C. C.
Chang, A. C. Ziedins, R. W. Kasten, and C. M. Hew, Abstr.
55th Int. Northwest. Conf. Dis. Nat. Commun. Man, 30 July to
2 August, 2000).
The number of Bartonella species or subspecies causing clin-
ical diseases in dogs has been increasing in recent years. B.
vinsonii subsp. berkhoffii has been shown to cause endocarditis,
arrhythmia, and myocarditis (8, 11, 30), as well as granuloma-
tous lymphadenitis and granulomatous rhinitis (39). B. clar-
ridgeiae was isolated from the blood of a dog suffering from
aortic endocarditis (17). B. clarridgeiae DNA was also detected
by PCR in a dog with lymphocytic hepatitis (22). B. henselae
DNA was initially detected in a dog with peliosis hepatis (28)
and more recently in a dog with hepatopathy (22) and in three
dogs with various clinical entities (37). These three B. henselae-
PCR-positive dogs presented nonspecific clinical abnormali-
ties, such as severe weight loss, protracted lethargy, and an-
orexia. A fourth dog was diagnosed as being infected with B.
elizabethae by PCR amplification and sequencing, increasing
the number of Bartonella species identified in infected dogs
(37). We report the first isolation of another Bartonella species,
B. washoensis, from the blood of a dog suffering from mitral
valve vegetative endocarditis.
Strain sources. The type strains of B. vinsonii subsp. berk-
hoffii (ATCC 51672) and B. clarridgeiae (ATCC 51734) were
obtained from the American Type Culture Collection (Manas-
sas, Va.). Isolate B. henselae strain U4 was obtained from our
culture collection at the University of California, Davis. Isolate
UCD-dog2 was cultured from the blood of the dog described in
Clinical samples. Blood (6 ml) was collected aseptically
from the dog’s external jugular vein at the time of clinical
examination by A. C. Wey. Blood samples were subjected to
aerobic and aerobic-anaerobic cultures. A blood sample, col-
lected in a plastic EDTA tube (Becton Dickinson, Franklin
Lakes, N.J.), was also submitted for specific Bartonella isola-
tion, and the blood was plated on fresh blood agar (5% defi-
brinated rabbit blood) (15). Serum was submitted for Bar-
tonella antibody titers and was later tested for several tick-
borne pathogens (Ehrlichia canis, Anaplasma phagocytophilum,
and Rickettsia rickettsii), including Coxiella burnetii, a known
agent of endocarditis in humans and animals.
Isolation procedure. A blood sample was collected in a plas-
tic 2-ml EDTA tube and frozen at ?70°C until plated. The
blood sample was cultured on heart infusion agar containing
5% rabbit blood and incubated in 5% CO2at 35°C for up to 4
weeks. Identification of the isolates as Bartonella spp. was
initially based on morphological and growth characteristics, as
previously described (17, 24). The isolates were then confirmed
by PCR and restriction fragment length polymorphism (RFLP)
analysis and sequence analysis of the citrate synthase (gltA),
groEL, and 16S rRNA genes, as previously described (23, 36,
Microscopic and biochemical analysis. DNA extraction. A
loopful (10 ?l) of the bacterial isolate grown from the dog’s
blood was heated at 95°C for 10 min in 100 ?l of sterile water.
The supernatant was used as a DNA template, as previously
described (12, 17).
PCR assay. Five microliters of extracted DNA from the
bacterial isolate was added to a 45-?l reaction mixture consist-
ing of 15 mM Tris-HCl (pH 8.0), 50 mM KCl, 1.5 mM MgCl2,
a 200 ?M concentration of each deoxynucleoside triphosphate,
1.25 U of AmpliTaq Gold DNA polymerase (Perkin Elmer,
Foster City, Calif.), and a 0.25 ?M concentration of each
primer. The primers used for the gltA gene were 5?-GGGGA
CCAGCTCATGGTGG-3? and 5?-AATGCAAAAAGAACA
GTAAACA-3? (38). Thermocycling was performed in an MJ
Research PTC-100 (Watertown, Mass.) apparatus under the
following conditions: 94°C for 10 min and 45 cycles of 94°C for
5328 CASE REPORTSJ. CLIN. MICROBIOL.
0.5 min, 57°C for 1 min, and 72°C for 2 min, followed by 72°C
for 5 min. For the 16S rRNA gene, the primers were 5?-AGA
GTTTGATCCTGGCTCAG-3? and 5?-AAGGAGGTGATCC
AGCCGCA-3? (23), and the running cycles were as follows:
95°C for 10 min and 35 cycles of 93°C for 0.5 min, 60°C for 1
min, and 72°C for 1 min, followed by 72°C for 8 min. For the
groEL gene, the primers were 5?-CGTGAAGTTGCCTCAAA
AACC-3? and 5?-AATCCATTCCGCCCATTC-3? (36), and
the running cycles were as follows: 95°C for 10 min and 40
cycles of 95°C for 1 min, 56°C for 1 min, and 72°C for 1 min,
followed by 72°C for 5 min.
RFLP analysis. An approximately 400-bp fragment ampli-
fied from the gltA gene was verified by gel electrophoresis and
then digested with the TaqI (Promega, Madison, Wis.), HhaI,
AciI, and MseI (New England Laboratories, Beverly, Mass.)
restriction endonucleases (5, 43). The digestion conditions
used were the ones recommended by the enzymes’ manufac-
turers. Banding patterns of the digests were compared to those
of digests from B. vinsonii subsp. berkhoffii (ATCC 51672), B.
henselae (strain U-4; University of California, Davis), and B.
clarridgeiae (ATCC 51734).
DNA sequencing. The PCR products from the gltA, 16S
rRNA, and groEL genes used for DNA sequencing were pu-
rified with Microcon centrifugal filter devices (Millipore Corp.,
Bedford, Mass.) and sequenced with a fluorescence-based au-
tomated sequencing system (Davis Sequencing, Davis, Calif.),
as previously described (14, 36). The FastA program of Seq-
Web version 2 (Wisconsin Package; Accelrys Inc., San Diego,
Calif.) was applied first to search the GenBank and EMBL
databases for the closest bacterial species or subspecies. Then,
the GAP and Evolution programs were used for sequence
alignments and determination of the percentage of DNA sim-
IFA tests. (i) Bartonella spp. B. henselae, B. clarridgeiae, B.
vinsonii subsp. berkhoffii, and B. washoensis indirect immun-
ofluorescent-antibody (IFA) tests were performed as previ-
ously described (14–16). The intensity of bacillus-specific flu-
orescence was scored subjectively from 1 to 4, and a
fluorescence score of ?2 at a dilution of 1:64 was reported as
a positive result, as previously described (14–16). Except for B.
washoensis, the same two readers performed a double-blind
reading of each slide. Positive serum control samples were
obtained from dogs that had been confirmed to be infected
with Bartonella. Specific IFA serology for B. washoensis was
performed at the Division of Vector-Borne Infectious Dis-
eases, Centers for Disease Control and Prevention, Fort Col-
(ii) E. canis, A. phagocytophilum, R. rickettsii, and C. burnetii.
An IFA test was used to detect antibodies to E. canis (North
Carolina State University canine strain), A. phagocytophilum
(New York strain, human origin), and R. rickettsii (Domino
canine strain) on 30-well Teflon-coated slides (9, 40). Serial
twofold dilutions of the dog’s serum were reacted with fluo-
rescein isothiocyanate anti-canine immunoglobulin G conju-
gate (Cappel; ICN Pharmaceuticals, Inc., Costa Mesa, Calif.).
Endpoint titers were determined as the last dilution at which
brightly stained organisms could be detected on a fluorescence
microscope with exciter and barrier filters. Antibodies against
phase I and phase II of C. burnetii infection were evaluated
with a commercially available IFA substrate slide (Fuller Lab-
oratories, Fullerton, Calif.) at a 1:64 dilution (17).
Isolation and identification of B. washoensis. Standard blood
cultures for aerobic and anaerobic bacteria failed to grow bac-
teria. However, blood collected from the dog at the same time
and cultured from the frozen and thawed EDTA tube grew a
nonhemolytic gram-negative organism after 7 days, with only a
few (60 CFU per ml) small (0.5- to 1-mm) white colonies.
These colony growth characteristics and morphologies were
suggestive of Bartonella spp., based on size, color, and time for
colonies to appear. Microscopic examination demonstrated
small gram-negative rods. PCR amplification with gltA primers
produced a 400-bp fragment strongly suggestive of Bartonella.
Digestion with TaqI, HhaI, AciI, and MseI endonucleases pro-
duced a unique RFLP profile.
A search (FastA) of the GenBank and EMBL databases
with the gltA fragment (352 bp) resulted in the closest matches
to B. washoensis (accession no. AF050108) and Bartonella sp.
strain Sb944nv (AF470616) isolated from a California ground
squirrel, with z scores of 1,334.8 and 1,330.9, respectively,
where z is an indication of relatedness. A direct comparison of
the dog isolate to B. washoensis (AF050108) with the GAP
program yielded a 100% identity. Comparison of this sequence
with other Bartonella gltA sequences (Evolution/Grow Tree
program) resulted in a cluster containing the dog’s isolate, B.
washoensis, and the California ground squirrel Bartonella sp.
strain Sb944nv (AF470616) isolate with identical sequences.
Numerous other strains isolated from Nevada rodents (ground
squirrels, least chipmunks, and bushytail woodrats) were also
closely related to the dog isolate, with a divergence of 1.94 to
3.59 base substitutions per 100 bases (Table 1). A group of
isolates cultured from deer mice (Peromyscus maniculatus) ap-
pear to be more divergent, with values of 7.01 to 7.68 base
substitutions per 100 bases. Divergences of other standard
Bartonella strains were 6.98 (B. vinsonii subsp. arupensis) to
greater than or equal to 7.68 (B. henselae) base substitutions
per 100 bases. Similarly, a fragment of the groEL gene (306 bp)
of the dog isolate was compared to Bartonella strains listed in
the GenBank and EMBL databases. The dog isolate was iden-
tical to B. washoensis and Bartonella sp. strain Sb944nv
(AF484066) from a ground squirrel and similar to Bartonella
sp. strain Sb1963nv (AF484067) from another California
ground squirrel, with a base substitution rate of 0.33 per 100
bases compared to at least 6.82 per 100 bases for other Bar-
tonella strains (Table 2). Finally, when a fragment of the 16S
rRNA gene (511 bp) was compared, the dog isolate was 100%
identical to B. washoensis (AF070463). A slightly longer frag-
ment (577 bp) indicated a minor divergence, with 0.17 base
substitutions per 100 bases, although the 16S rRNA gene com-
parison indicated a variance of less than 3 base substitutions
per 100 bases for the group analyzed.
Serological analysis. Serum antibodies to B. clarridgeiae, B.
vinsonii subsp. berkhoffii, and B. henselae were detected in the
dog by IFA assay at the reciprocal titer of 4,096. Because of the
dog’s history of being exposed to fleas and ticks, the dog serum
was later tested for potential tick-borne pathogens. The dog
was seronegative for A. phagocytophilum, E. canis, and R. rick-
ettsii but was weakly positive for the C. burnetii phase II anti-
gen. After identification of the isolate as B. washoensis, the dog
VOL. 41, 2003CASE REPORTS5329
serum was tested against this specific antigen and revealed a
reciprocal titer of 8,192.
Conclusions. We report the first isolation of B. washoensis
from a dog and the second isolation of this species outside of
its natural rodent reservoir. It is also the first known case of
endocarditis associated with B. washoensis, as it caused fever
and myocarditis in the human patient (32). In this dog, several
factors are suggestive that B. washoensis was the etiological
agent, including (i) isolation of the organism from the blood,
(ii) failure to isolate other bacteria by conventional blood cul-
ture, and (iii) the presence of high titers of antibody against
various Bartonella species, including B. washoensis, as previ-
ously reported for cases of Bartonella endocarditis in humans
(21, 42) and dogs (K. A. MacDonald, B. B. Chomel, M. D.
Kittleson, R. W. Kasten, W. P. Thomas, and P. A. Pesavento.
Abstr. Am. Coll. Vet. Intern. Med., 21st Annu. Forum, J. Vet.
Intern. Med. 17:399, 2003). Unfortunately, tissues were not
available for microscopic examination or PCR testing of the
The valvular lesion was located on the mitral valve, as pre-
viously reported for other Bartonella endocarditis cases in dogs
(8). However, most Bartonella endocarditis cases in dogs usu-
ally involve the aortic valve or both cardiac valves (8, 11;
MacDonald et al., Abstr. Am. Coll. Vet. Intern. Med.). Simi-
larly, in a series of 33 human patients with Bartonella endocar-
ditis, 29 (88%) had involvement of the aortic valve, including 2
with concurrent aortic and mitral valvular involvement, com-
pared to only 4 patients with only involvement of the mitral
valve (41). In a more recent study of 61 confirmed cases of
Bartonella endocarditis, involvement of only the aortic valve
(36 cases) was four times more frequent than involvement of
only the mitral valve (9 cases) (42).
Genetic analysis of the dog isolate indicates that the organ-
ism isolated is B. washoensis, as the sequence analysis of frag-
ments from three different genes revealed genetic identity with
B. washoensis isolated from a human patient with myocarditis
and a California ground squirrel (32). Furthermore, the dog
isolate was clustered with several other rodent isolates cultured
from animals captured in the vicinity of the human patient. We
also found a complete match between the human and dog
isolates for the groEL gene partial sequence and a minor mis-
match with isolate Sb1963nv, as reported by Kosoy et al. (32).
Analysis of the gltA gene has historically been used to com-
pare Bartonella strains since it provides a good discriminatory
power at the species level (5, 38). While analysis of the 16S
rRNA gene provides usable information at the genus level, the
high degree of similarity among Bartonella strains disallows
strong discriminatory power for many of the new species of
Bartonella (5, 26). Sequences from other genes, such as groEL,
are beginning to be published and provide an opportunity to
compare more fragments from each isolate.
The dog’s source of infection and the mode of transmission
of B. washoensis will most likely remain unexplained. We know
that the dog had a history of tick and flea exposure. However,
this dog was seronegative for associated bacteria, in contrast to
dogs infected with B. vinsonii subsp. berkhoffii, for which a
strong association has been reported between seropositivity to
Bartonella and seropositivity to several tick-borne pathogens,
especially Ehrlichia, Anaplasma, and Babesia spp. (9, 31, 40).
Furthermore, the weak positive reaction to the C. burnetii
TABLE 2. Estimated number of nucleotide substitutions per 100
bases for a 306-base segment of the groEL gene
Strain and/or species GenBank accession no.
Rate of divergent
Bartonella sp. (Sb944nv)
Bartonella sp. (Sb1963nv)
B. vinsonii subsp. arupensis
B. vinsonii subsp. berkhoffii
B. vinsonii subsp. vinsonii
TABLE 1. Estimated number of nucleotide substitutions per 100
bases for a 315-base segment of the gltA gene
Strain and/or speciesGenBank accession no.
Rate of divergent
Bartonella sp. (Sb944nv)
Bartonella sp. (Sb1659nv)
Bartonella sp. (Al7763nv)
Bartonella sp. (Al7760nv)
Bartonella sp. (S1311nv)
Bartonella sp. (Sb1865nv)
Bartonella sp. (Tm1950nv)
Bartonella sp. (Tm918nv)
Bartonella sp. (Tm916nv)
Bartonella sp. (Sb1859nv)
Bartonella sp. (Tm1781nv)
Bartonella sp. (Tm6313nv)
Bartonella sp. (Tm1794nv)
B. vinsonii subsp. arupensis
Bartonella sp. (Pm1785nv)
Bartonella sp. (Pm1780nv)
Bartonella sp. (Pm1783nv)
Bartonella sp. (Pm1857nv)
B. vinsonii subsp. berkhoffii
B. vinsonii subsp. vinsonii
5330CASE REPORTS J. CLIN. MICROBIOL.
phase II antigen is more likely to result from serological cross-
reactivity, as was previously demonstrated for humans (34). B.
washoensis has been reported to have a rodent reservoir (10,
32). In California and Nevada, a high percentage of California
ground squirrels are infected with this species and represent its
main reservoir (32; B. B. Chomel et al. Abstr. 55th Int. North-
west. Conf. Dis. Nat. Commun. Man).
However, the arthropod vector of B. washoensis has not yet
been identified. The ground squirrels from northern Califor-
nia, among which B. washoensis bacteremic animals were iden-
tified, were heavily infested with fleas (Chomel et al., unpub-
lished observations). As indicated by Kosoy et al. (32), S.
beecheyi are commonly and heavily infested with Oropsylla
montana, a flea species that readily feeds on humans and
generally is considered to be the most important vector of
human plague in the United States. These fleas might play a
main role as the vector of infection between rodents and also
might be involved in the transmission of B. washoensis to dogs
and humans. However, the potential role of ticks still cannot be
excluded, as several questing adult Ixodes pacificus ticks have
also been reported to harbor B. washoensis DNA (13).
Rodents constitute a wide reservoir of Bartonella species in
many parts of the world (2, 3, 4, 6, 10, 20, 24, 25, 33, 48). In
North America, several Bartonella species or subspecies have
been identified, including B. vinsonii, B. vinsonii subsp. arupen-
sis, B. elizabethae, B. peromysci, and B. washoensis (6, 10, 20, 25,
33, 47), and many more are still waiting to be fully described (4,
20, 33, 48). Among these rodent-borne Bartonella spp., four
species (B. elizabethae, B. vinsonii subsp. arupensis, B. grahamii,
and B. washoensis) have now been related to human infections,
causing mainly cardiopathy, endocarditis, or neuroretinitis (10,
32). Furthermore, B. elizabethae DNA was recently identified
in a sick dog with a 2-month history of lethargy, decreased
appetite, weight loss, and occasional vomiting of undigested
food (37). With the present report, it is the second rodent-
borne Bartonella species to be found in sick dogs, suggesting
that many other Bartonella species may cause severe infections
in domestic dogs.
This project was supported in part by a grant from the Morris
Animal Foundation and a grant from the Center for Companion An-
imal Health, School of Veterinary Medicine, University of California,
We thank Barbara Hegarty and Edward Breitschwerdt, College of
Veterinary Medicine, North Carolina State University, for testing the
dog serum for the various tick-borne pathogens and Michael Kosoy,
Division of Vector-Borne Infectious Diseases, Centers for Disease
Control and Prevention, for providing assistance for the B. washoensis
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