Page 985 - Clinical Small Animal Internal Medicine

96 Bartonellosis 923

isolation in blood‐based solid media and specific PCR
(a)
(b)
VetBooks.ir testing of samples pre‐ and postenrichment culture,
with DNA sequencing to confirm the species of
Bartonella involved (so‐called “enrichment PCR” plat-
form). This approach is capable of detecting more than
twice the number of infected dogs than the direct PCR
from clinical specimens. In addition, using this plat-
form allows initial results to be obtained as early as two
weeks, with a number of new Bartonella species being
detected in dogs. This assay is available at one com-
mercial laboratory (www.galaxydx.com).
The direct detection of Bartonella DNA by PCR from
blood, other body fluids or tissues is also available through
commercial laboratories. Depending upon the assay
design, this test may have high specificity but sensitivity is
always limited by the magnitude of bacteremia (see
Table 96.2). Therefore, direct PCR is a good diagnostic
tool for feline samples, but it has limited sensitivity for
Figure 96.4 Radiograph images of the right forelimb of a cat with
osteomyelitis due to Bartonella vinsonii subsp. berkhoffii. canine samples. In a recent study, direct PCR from clini-
Dorsopalmar (a) and mediolateral (b) views show cortical bone cal specimens only detected 44.7% of dogs infected with
destruction, irregular osteoproliferation and moderate thickening Bartonella spp. Therefore, negative PCR results should
of the soft tissue (white arrows). Source: Varanat et al. (2009). never be used to rule out Bartonella spp. infection in
Reproduced with permission of John Wiley & Sons. dogs. It is important that clinicians choose a diagnostic
laboratory that offers PCR testing for the entire Bartonella
Table 96.2 Average bacteremia level found in immunocompetent genus, not only for selected species, because a growing
cats, dogs, and humans number of new Bartonella species has been described in
sick and healthy companion animals recently.
Cats Humans Dogs Serology assays are available through veterinary labo-
ratories, but have limited diagnostic use in dogs and cats
Host type Reservoir Accidental Accidental because presence of antibodies does not correlate with
5
Genome 10 –10 6 1–10 1–10 infection. Only one‐third to one‐half of infected dogs
copies/μL and cats have detectable antibodies against Bartonella
5
6
5
6
Bacteria per red 1/10–100 1/10 –1/10 1/10 –1/10 spp. Therefore, negative serologic testing does not rule
blood cell RBC RBC RBC out infection with Bartonella spp. Also, seropositivity
(RBC)
does not indicate infection because only one‐third of
Source: Breitschwerdt et al. (2010). Reproduced with permission of seropositive animals are bacteremic. When seropositive
John Wiley & Sons. dogs are detected, serology may be helpful to monitor
therapy progression, because many dogs that experience
other body fluids (cavitary effusions, synovial fluid, resolution of disease manifestation have decrease in
cerebrospinal fluid, etc.) or tissue specimens by spe- antibody titers within 3–6 months following treatment.
cific polymerase chain reaction (PCR) assays or isola- Serology has better diagnostic use in Bartonella endo-
tion by blood culture. While isolation remains the carditis, which is usually associated with high anti-
microbiologic gold standard, standard blood culture body titers. There is some level of cross‐reactivity among
has limited diagnostic use because Bartonella spp. Bartonella spp. but multiple species‐specific assays
are fastidious bacteria that take months to grow in should be performed, including specific assays for B.
standard culture media. In addition, Bartonella bacte- henselae, B. vinsonii subsp. berkhoffii, B. koehlerae, and
remia levels in dogs are very low (see Table 96.2) when B. clarridgeiae (which cross‐reacts with B. rochalimae).
compared to cats. Therefore, sensitivity of standard
blood culture is very low in dogs. Consequently, preen-
richment techniques are required in dog samples Therapy
to increase the number of organisms to detection lev-
els of PCR assays. Currently, the most sensitive diag- The optimal treatment protocol for Bartonella spp.
nostic technique combines preenrichment culture in infection in dogs and cats is unknown. Similar to other
an insect‐based liquid media (BAPGM) coupled with vector‐borne infections, elimination of Bartonella may