There are several methods used for diagnosing Bartonella infection including microscopy, serology, and PCR. Microscopy of blood smears is used to diagnose Carrión’s disease (B. bacilliformis), however for other Bartonella species, microscopy and silver staining are insensitive, not highly specific, and cannot differentiate species. The CDC does not recommend lymph node aspiration for diagnostic purposes. Serology and protein-based methods IFA (immunofluorescence antibody assay) testing for the presence of antibodies in serum is used to diagnose B. henselae infection at the acute onset of Cat Scratch Disease symptoms, followed by PCR to confirm infecting species. IFA can generally be used to confirm a diagnosis of Bartonella infection, but is limited by antibody cross-reactivity with other bacteria species which can cause a false positive, and antigen variability which can result in false negatives. Bartonella spp. often evade an immune response, thus antibodies may not be detected even concurrent with an infection, resulting in an IFA false negative rate of up to 83% in chronically infected patients when other test results (e.g. organism isolation or PCR) are positive. IFA sensitivity may range from 14-100%, causing discrepancies between PCR and serology test results. Positive IFA results do not distinguish between current infection and prior exposure. ELISA (enzyme-linked immunosorbent assay) is another method that has been used to detect Bartonella, but it has a low sensitivity (17-35%). Western blot for protein detection of Bartonella-associated proteins has also been reported, but this method does not show clear immunoreactive profiles. PCR The CDC states that PCR testing from a single blood draw is not sufficiently sensitive for B. henselae testing, and can result in high false negative rates due to a small sample volume and levels below the limit of molecular detection. Bartonella spp. are fastidious, slow-growing bacteria that are difficult to grow using traditional solid agar plate culture methods due to complex nutritional requirements and potentially a low number of circulating bacteria. This conventional method of culturing Bartonella spp. from blood inoculates plated directly onto solid agar plates requires an extended incubation period of 21 days due to the slow growth rate. Enrichment Culture Bartonella growth rates improve when cultured in an enrichment inoculation step in a liquid insect-based medium such as Bartonella α-Proteobacteria Growth Medium (BAPGM) or Schneider’s Drosophila-based insect powder medium. Several studies have optimized the growing conditions of Bartonella spp. cultures in these liquid media, with no change in bacterial protein expressions or host interactions in vitro. Insect-based liquid media supports the growth and co-culturing of at least seven Bartonella species, reduces bacterial culturing time and facilitates PCR detection and isolation of Bartonella spp. from animal and patient samples. Research shows that DNA may be detected following direct extraction from blood samples and become negative following enrichment culture, thus PCR is recommended after direct sample extraction and also following incubation in enrichment culture. Several studies have successfully optimized sensitivity and specificity by using PCR amplification (pre-enrichment PCR) and enrichment culturing of blood draw samples, followed by PCR (post-enrichment PCR) and DNA sequence identification. Serial Testing As Bartonella spp. infect at low levels and cycle between blood and tissues, multiple blood draws over time may be necessary to detect infection.
Bartonellosis
Brucellosis
Shigellosis
Salmonellosis
Leptospirosis
Bacillary dysentery
Listeriosis
Rhinosporidiosis