What Is Rickettsiosis?

Rickettsiosis (Rickettsial diseases) are caused by organisms within the genus of rickettsiae. They are divided into the following 3 biogroups: Spotted fever, Typhus, and Scrub Typhus biogroup. [See table below for more details.] 


Rickettsia is a genus of nonmotile, gram-negative, nonspore-forming, highly pleomorphic bacteria that can present as cocci (0.1 μm in diameter), rods (1–4 μm long), or thread-like (10 μm long). A characteristic feature of the rickettsiae is that they all multiply in an arthropod (lice, ticks, fleas, or mites) as part of their life cycle. Rickettiae are also infectious for a wide variety of mammals including humans, which either serve as reservoirs for the organisms or ensure the survival of the parasitic vectors that feed on them.

Rickettsia rickettsii

Rickettsia rickettsii

How Is Rickettsiosis Transmitted?

It is transmitted to humans by the bite of infected tick species. In the United States, these include the following ticks:

  • American Dog Tick (Dermacentor Variabilis)
  • Rocky Mountain Wood Tick (Dermacentor Andersoni)
  • Brown Dog Tick (Rhipicephalus Sanguineus)

What Are the Infected Regions?

The disease is spread worldwide. In the US, most cases occur in the southern Atlantic states (Delaware, Maryland, Washington D.C., Virginia, West Virginia, North Carolina, South Carolina, Georgia, and Florida) and the south central states (Arkansas, Oklahoma, Louisiana, Texas). North Carolina and Oklahoma account for approximately 35% of the total reported human cases each year. Infections also occur in the Pacific Northwest (Oregon, Washington, California). Although the first cases of RMSF were described from the Rocky Mountain region, fewer than 5% of human cases are currently reported from that region.

What Are the Symptoms?

Rickettsial diseases are very difficult to diagnose clinically, even for experts because: (1) of their nonspecific symptoms and (2) the disease presentation varies from patient to patient. Some common symptoms that may appear in the first 2 weeks of infection include headaches, general malaise, fever, and in some cases nausea and vomiting.  Other symptoms vary from disease to disease therefore laboratory testing can be useful in identifying Rickettsia.

How Is Rickettsia Diagnosed?

The diagnosis should be considered in patients bitten by a tick or have been in a tick-infested area and have any of the symptoms typical of Rickettsial infections, even mild ones. Patients should be examined by their healthcare professional. The healthcare professional will use clinical symptoms along with laboratory tests to find out whether a patient has Rickettsiosis or perhaps some other tick-borne infection.

Click here on how to order a test kit from IGeneX. Test kits can be ordered by both patients and physicians. 

FOR HEALTHCARE PROFESSIONAL:  Click here for more information on the type of diagnostic tests to detect Rickettsia.  In addition, physicians may want to consider having blood tested for other possible causes of their patient’s symptoms, including other tick-borne infections, such as Lyme disease. 

Can A Tick Be Tested?

At IGeneX, ticks can be tested for presence of Rickettsia by a PCR test. Any tick including one that has been removed from a patient or collected in the yard, can be sent to IGeneX for testing. 

Click here for more information on how to test a tick.