- Rickettsial infections are caused by micro-organisms known as rickettsiae. According to David H. Walker, an author of the University of Texas book "Medical Microbiology," these tiny creatures are intracellular gram-negative bacteria.
- According to Walker, these disease-causing bacteria have four subsections: rickettsiae, ehrlichia, orientia and coxiella. EMedicine.com divides the type of diseases caused by the microbes into three biogroups: the spotted fever biogroup, the typhus biogroup and the scrub typhus biogroup. Each biogroup is caused by a different subset of the rickettsial organisms.
- Rickettsiae are coccobacillary forms, according to eMedicine.com, or a form that is between a bacteria and a virus. They have gram-negative cell walls, which means they turn pink when stained with Gram stain (a lab method of identifying the organisms), though eMedicine.com notes that they do not stain well with typical Gram stain. They do not have flagella and they have a small genome base.
- Rickettsiae are parasites, meaning they live off a live host. Walker notes that they are present in several types of carriers, including ticks, lice, fleas, mites, chiggers, and mammals.
- Generally, Walker reports, rickettsiae are transmitted when a human is bit by an infected host, such as a tick or flea. If a mammal, such as a dog or cat, is bitten by an infected host, it can become a host as well and transmit to other mammals or people.
- Once in a mammal or human, rickettsiae travel via the blood stream from one part of the body to another. They enter cells and multiply.
- Rckettsiae respond to treatments such as antibiotics, according to Walker. A typhus vaccine also exists, but is not common.
