Rickettsia - Classification

Classification

The classification of Rickettsia into three groups (spotted fever, typhus and scrub typhus) was based on serology. This grouping has since been confirmed by DNA sequencing. All three of these contain human pathogens. The scrub typhus group has been reclassified as a new genus – Orientia – but many medical textbooks still list this group under the rickettsial diseases.

However more recently it has become apparent that rickettsia are more widespread than previously believed and are known to be associated with arthropods, leeches and protists. Divisions have also been identified in the spotted fever group and it has been suggested that this should be divided into two clades. Arthropod-inhabiting rickettsiae are generally associated with reproductive manipulation (such as parthenogenesis) to persist in host lineage

In March 2010 Swedish researchers reported a case of bacterial meningitis in woman caused by Rickettsia helvetica previously thought to be harmless.