Spotted Fever Group Rickettsiae in Ticks Feeding on Humans in Northwestern Spain

Abstract

During a 7-year study, we identified and analyzed by PCR 4,049 ticks removed from 3,685 asymptomatic patients in Castilla y León (northwestern Spain). A total of 320 ticks (belonging to 10 species) were PCR-positive for rickettsiae. Comparison of amplicon sequences in databases enabled us to identify eight different spotted fever group (SFG) rickettsiae: Rickettsia slovaca, Rickettsia sp. IRS3/IRS4, R. massiliae/Bar29, R. aeschlimannii, Rickettsia sp. RpA4/DnS14, R. helvetica, Rickettsia sp. DmS1, and R. conorii. Although Mediterranean spotted fever (MSF) is an endemic disease in Castilla y León, R. conorii was found in only one Rhipicephalus sanguineus tick, whereas other pathogenic SFG rickettsiae were much more prevalent in the same area. Our data suggest that in Castilla y León, many MSF or MSF-like cases attributed to R. conorii could have been actually caused by other SFG rickettsiae present in ticks biting people in this region of Spain.

Update on Tick-Borne Rickettsioses around the World: a Geographic Approach

“…2 and 7) (206). However, the excellent fitness of an R. conorii-infected tick laboratory colony contrasts with the low prevalence of infected Rhipicephalus sanguineus ticks collected in the wild (Ͻ1%), even in regions of endemicity such as Southern Europe, with the exception of small foci (25,177,207,208). The influence of extrinsic factors on infections in diapaused Rhipicephalus sanguineus ticks has been suggested, and infected quiescent ticks may not survive the winter (25).…”

“…Rickettsia sp. strain DmS1 was detected in D. marginatus ticks in France and Spain, and 80% of ticks of this species were positive at the fifth generation of a laboratory-maintained infected colony, attesting to the tick reservoir in the wild (208,325). "Candidatus Rickettsia rioja" was detected in D. marginatus ticks collected from patients with SENLAT syndrome in Spain and France (326,327).…”

“…Rickettsia monacensis was detected in I. ricinus ticks in Spain, Portugal, Italy (including Sardinia), Turkey, Switzerland, Luxembourg, Germany (including Greifswalder Oie Island), Sweden, Slovakia, Albania, Hungary, Bulgaria, Moldova, Ukraine, Serbia, northwestern Russia (Kaliningrad), Belarus, and Poland (208,280,283,289,(297)(298)(299)(300)(301). The prevalence of R. monacensis in ticks varied between 1% in Germany, 15% in Serbia, 35% Turkey, and 57% in Italy (299,302).…”

“…9). These bacteria have been found in Dermacentor marginatus and Dermacentor reticulatus ticks in a great majority of European countries, with a high percentage of ticks infected with these bacteria (208,(280)(281)(282)(283)(284)(285)(286)(287)(288)(289)(290). Dermacentor ticks usually bite hairy domestic and wild animals (291).…”

Questions on Mediterranean Spotted Fever a Century after Its Discovery

“…In this study, R. conorii conorii was isolated from only 1 Rh. sanguineus (22). In this context, we can hypothesize that cases of spotted fever acquired in southern Europe and associated with the presence of several eschars can be caused by R. aeschlimannii.…”