Diagnosis of Bartonella infections can be confirmed by detection of serum antibodies, by immunohistochemical analysis of tissue biopsies (lymph nodes, skin, liver, or other affected organs), by molecular detection of Bartonella DNA by PCR assays or by using a combination of Bartonella alpha Proteobacteria growth medium, followed by PCR. The latter is suggested to be the most sensitive method of detecting Bartonella infection in dogs.
One common method for the laboratory diagnosis of Bartonella infections is serology, using indirect immunofluorescence techniques. Serological tests such as IFAT (indirect fluorescence antibody test) can be used for the diagnosis of infection, present or previous. However, to a certain extent dogs naturally infected with Bartonella may remain seronegative. Cross-reactions between the different species, and also between genera such as Coxiella and Chlamydia have also been observed – and with chronic intracellular infection antibody titers decline to non-diagnostic levels. However, serology can be used as a screening test to detect past exposure in populations. The IFAT (indirect fluorescence antibody test) is considered the gold standard test for serological diagnosis.
Detection of Bartonella spp. by culture on agar plates is also possible, but time-consuming – and during chronic infection the pathogen is hard to isolate from the blood because of the low bacteremia. Further, some species may be difficult to culture like B. vinsoniii subsp. berkhoffii.
Recently, a novel chemically-modified liquid culture medium (Bartonella ⁄ alpha-Proteobacteria growth media, BAPGM), supporting the growth of several Bartonella species, has been developed. The combination of BAPGM culture with PCR assay was developed for diagnostic use, to characterise and quantify Bartonella infection in blood samples.
Microscopic examination of stained blood smears is only effective to visualise B. bacilliformis, a solely human pathogen in South America. Other Bartonella spp. cannot be visualised on blood smears. When isolated on an agar plate, colonies are described as silvery-white shining, with a rough or smooth, mucoid appearance.
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