Rank: Species
Lineage: Bacteria;Proteobacteria;Alphaproteobacteria;Rhizobiales;Bartonellaceae;Bartonella;Bartonella henselae
Description: This organism was identified as the causative agent of cat scratch fever, a disease found commonly in children or in immunocompromised adults. Cats, which are infected by fleas carrying the bacteria, in turn infect humans when scratching them, hence the name. A small red bump forms at the site of infection, followed 2-3 weeks later by a painful swelling of the lymph node. In immunocompromized patients, more severe progress may be observed, including encephalitis, swelling of the spleen, and heart valve infection. Approximately 24 000 cases are reported in the US each year. This intracellular pathogen is internalized by an actin-dependent mechanism, and primarily targets endothelial cells, although other cells can be infected. The proliferation of the vascular endothelium (bacillary angiomatosis) is characterisitic of Bartonella infection and results in multiplication of the bacterium's host cells. Infected macrophages are stimulated to release vascular endothelial growth factor (VEGF) and interleukin 1 beta, both of which promote angiogenesis. Endothelial cells are also stimulated to grow and divide by direct contact with bacterial cells. In addition, programmed cell death (apoptosis) of endothelial cells is inhibited, combatting a common mechanism eukaryotic cells use to deal with bacterial infection. Secretion of effector molecules is probably via a type IV secretion system. Other pathogenicity factors include pili and outer membrane adhesins for attachment to host cells.
Reference Material:
https://www.ncbi.nlm.nih.gov/genome/?term=Bartonella%20henselae
