More than a dozen species of Bartonella have been isolated that can infect humans, and is typically spread by insect bites. It is also the primary causative agent of cat scratch disease.

 B. Henselae and B. quintana are the two species that most commonly cause disease in humans. While unlikely, co-infection with Bartonella bacteria species can happen with insect bites. 

Image courtesty of Harms, A.,2012. 

Bartonella infects specialized white blood cells called CD 34+. These blood cells are precursors for cells that line blood vessels and other tissues. The microbe enters the cell and creates a protective cyst around itself. It also turns off the ability of the cell to self-destruct. Chemical messengers stimulated by bartonella microbes cause more CD 34+ cells to congregate. These messengers simultaneously suppress other key parts of the immune response. Bartonella-laden CD 34+ migrate throughout the body and replace damaged endothelial cells. Once established inside blood vessels, bartonella starts scavenging red blood cells as a nutrient source. Symptoms are generally a result of damage to these small blood vessels.​

Signs and Symptoms​

  • Fever (may present as a single bout of fever or bouts of recurrent fever)
  • Headache
  • Rash
  • Bone pain, mainly in the shins, neck, and back