Update on tick-borne rickettsioses around the world: a geographic approach

Abstract

Tick-borne rickettsioses are caused by obligate intracellular bacteria belonging to the spotted fever group of the genus Rickettsia. These zoonoses are among the oldest known vector-borne diseases. However, in the past 25 years, the scope and importance of the recognized tick-associated rickettsial pathogens have increased dramatically, making this complex of diseases an ideal paradigm for the understanding of emerging and reemerging infections. Several species of tick-borne rickettsiae that were considered nonpathogenic for decades are now associated with human infections, and novel Rickettsia species of undetermined pathogenicity continue to be detected in or isolated from ticks around the world. This remarkable expansion of information has been driven largely by the use of molecular techniques that have facilitated the identification of novel and previously recognized rickettsiae in ticks. New approaches, such as swabbing of eschars to obtain material to be tested by PCR, have emerged in recent years and have played a role in describing emerging tick-borne rickettsioses. Here, we present the current knowledge on tick-borne rickettsiae and rickettsioses using a geographic approach toward the epidemiology of these diseases.

Fig 1

Genome sequence-based phylogenetic tree of Rickettsia species. This tree was constructed by aligning the 597 orthologous genes of all studied genomes. Phylogenetic relationships were inferred by using the parsimony method.

Fig 2

Three tick vectors of spotted fever group rickettsioses. From top to bottom are Rhipicephalus sanguineus, the primary vector of R. conorii subsp. conorii, the agent of Mediterranean spotted fever; Dermacentor marginatus, vector of R. slovaca and R. raoultii; and Amblyomma variegatum, vector of R. africae, the agent of ATBF. Males are on the left side, and females are on the right. Bar scale, 1 mm.

Fig 3

Tick-borne rickettsiae in North America (except Mexico). Colored symbols indicate pathogenic rickettsiae. White symbols indicate rickettsiae of possible pathogenicity and rickettsiae of unknown pathogenicity. (Adapted from reference .)

Fig 4

Tick-borne rickettsiae in Mexico and Central America. Colored symbols indicate pathogenic rickettsiae. White symbols indicate rickettsiae of possible pathogenicity and rickettsiae of unknown pathogenicity. (Adapted from reference .)

Fig 5

Petechial rash on a patient with Rocky Mountain spotted fever caused by Rickettsia rickettsii.

Fig 6

Tick-borne rickettsiae in South America. Colored symbols indicate pathogenic rickettsiae. White symbols indicate rickettsiae of possible pathogenicity and rickettsiae of unknown pathogenicity. (Adapted from reference .)

Fig 7

Tick-borne rickettsiae in Europe. Colored symbols indicate pathogenic rickettsiae. White symbols indicate rickettsiae of possible pathogenicity and rickettsiae of unknown pathogenicity. (Adapted from reference .)

Fig 8

Generalized maculopapular rash including face, palms, and soles on a patient with Mediterranean spotted fever caused by R. conorii subsp. conorii.

Fig 9

Enlarged cervical lymph nodes (left) and inoculation eschar of the scalp (right) in a patient with Rickettsia slovaca infection.

Fig 10

Tick-borne rickettsiae in North Africa. Colored symbols indicate pathogenic rickettsiae. White symbols indicate rickettsiae of possible pathogenicity and rickettsiae of unknown pathogenicity. (Adapted from reference .)

Fig 11

Tick-borne rickettsiae in sub-Saharan Africa. Colored symbols indicate pathogenic rickettsiae. White symbols indicate rickettsiae of possible pathogenicity and rickettsiae of unknown pathogenicity. (Adapted from reference .)

Fig 12

Eschar in a patient with African tick bite fever caused by R. africae.

Fig 13

Tick-borne rickettsiae in Asia. Colored symbols indicate pathogenic rickettsiae. White symbols indicate rickettsiae of possible pathogenicity and rickettsiae of unknown pathogenicity. (Adapted from reference .)

Fig 14

Tick-borne rickettsiae in Australia. Colored symbols indicate pathogenic rickettsiae. White symbols indicate rickettsiae of possible pathogenicity and rickettsiae of unknown pathogenicity. (Adapted from reference .)

Fig 15

Maculopapular rash on the legs of a patient with Queensland tick typhus caused by Rickettsia australis.

Fig 16

Use of swabs of skin eschar in the diagnosis of a case of Rickettsia sibirica mongolitimonae by qPCR.