Rickettsiae and Tick-borne Diseases

Tick-borne diseases (TBDs) are increasing in prevalence and represent a growing occurrence of arthropod-borne infectious diseases. This chapter discusses the most common agents associated with TBD and details the testing methodologies currently available for laboratory diagnosis. It describes rickettsial diseases transmitted by ticks. Ticks are excellent vectors for disease transmission, with more than 800 recognized species. The genus Rickettsia is divided by their phylogenetic clustering into the spotted fever group (SFG) and typhus group (TG). The SFG contains bacteria that are generally recognized as human pathogens, including R. rickettsii, R. conoriiand R. africae, which are respectively the causative agents of Rocky Mountain spotted fever (RMSF), Mediterranean spotted fever and African tick-borne fever. The diagnoses of RMSF, boutonneuse fever, and African tick-bite fever, have been established by immunohistochemical detection of rickettsiae in formalin-fixed, paraffin- embedded sections of biopsy specimens of rash and eschar lesions.