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Rickettsia species cause moderate to severe symptoms ranging from fever to internal hemorrhaging.
The symptoms and their severity depend on which species is present and how long the patient has been infected. Like Bartonella and Ehrlichia, Rickettsia species are intracellular bacteria, which means that they can live inside cells in the host.
Rocky Mountain spotted fever (RMSF) is perhaps the most notorious of the rickettsioses (Rickettsia-related illnesses) reported in the United States. The CDC started tracking cases back in the early 20th century because of patients’ high fatality rate. Researchers soon found that the causative agent was R. rickettsii, which was transmitted primarily by Dermacentor ticks like the American dog tick.
The fatality rate for RMSF has decreased tremendously since the invention of doxycycline in the 1940s. However, reported cases have risen since CDC criteria for reporting expanded in 2010 to include Rickettsia species that cause similar yet milder symptoms. Our new Rickettsia species webpage is designed to give you an overview of rickettsioses found around the world and how Galaxy Diagnostics tests can detect the spectrum of species that cause them.
Figure 1: Reported cases and case fatality rates of spotted fever rickettsioses
The rise in reported cases of rickettsiosis and newly discovered species has created a need for diagnostics with increased specificity. R. parkeri, R. philipii, and R. akari cause similar symptoms, but conventional tests that are available often cannot discern which species is present.
Serology is the most common method used for laboratory evidence of a Rickettsia species infection. Labs will use antigens from a certain species to test for an immune response in a blood sample, but the chances of cross-reactivity are high because the bacteria are closely related. This means that the test for a certain species could be positive, but it actually may be a different species that is present. Furthermore, serology results can be hard to interpret because antibodies could indicate current or past infection.
Galaxy Diagnostics offers highly sensitive and specific PCR testing for pathogenic Rickettsia species. If DNA from Rickettsia is detected, the sample is DNA sequenced and the exact species is determined.
References
Centers for Disease Control and Prevention. (2019). Rocky Mountain spotted fever (RMSF). Retrieved from https://www.cdc.gov/rmsf/index.html