Rickettsia felis Infection Acquired in Europe and Documented by Polymerase Chain Reaction

We report the first case of Rickettsia felis infection in Europe to be documented by polymerase chain reaction (PCR) and serologic testing.

tein (12.8 mg/L for the woman and 11.4 mg/L for the man [normal <5]) and thrombocytopenia (93.000 x 10 9 /L) for the man. Other clinical laboratory investigations were normal. An abdominal ultrasonography showed splenomegaly in both patients.
Serologic testing for leptospirosis, as well as for other infections endemic in Germany, such as cat-scratch disease, Lyme borreliosis, ehrlichiosis, and Q fever, was negative.
The patients received doxycycline (200 mg/day) for 7 days, recovered within 3 days, and have remained well. Because symptoms resembled those of Mediterranean spotted fever, serum samples were tested for antibodies to R. conorii; when titers were found to be elevated, further clinical history was obtained. The patients had traveled to Costa Rica 7 months before the onset of symptoms but had not left Germany since that date. They owned two dogs, one of which had recently been adopted from an animal shelter. Neither of the dogs nor their littermates had traveled outside Germany. Both dogs, which were asymptomatic, had repeatedly had ticks and fleas, but the patients did not recall any recent arthropod bite.
Results of serologic tests were negative for C. burnetii, B. henselae, and F. tularensis. The woman had antibody titers to R. felis of 0/0 (immunoglobulin [Ig] G/IgM), 128/64, 128/64, and 128/64 for serum samples #1, 2, 3, and 4, respectively. The man had titers of 0/0, 32/16, 32/0, and 0/0 for serum samples #1, 2, 3, and 4, respectively. Cross-reactions were observed between the rickettsiae tested except for R. typhi, preventing the identification of the species infecting the man. A twofold difference in immunoglobulin (Ig) M titer in favor of R. felis compared with other antigens was noted for the woman. Both dogs had an IgG titer to R. felis of 128, but antibody crossreactions did not allow the specific etiologic agent to be identified. A Western blot with the same antigens was performed on patient specimen #2 and the dog samples (6). Antibodies specifically directed at R. felis were observed for the woman and one of the dogs. Additionally, R. felis infection was confirmed by nested polymerase chain reaction (PCR) (7). DNA was extracted from serum #1 from both patients, taken before antibiotic therapy, and from both dog specimens with QIAGEN columns (QIAamp Tissue Kit, QIAGEN, Hilden, Germany). To avoid contamination, no positive control was used. The assay amplified from the woman's serum a fragment of the gene encoding the PS120 protein ( Figure), an intracytoplasmic protein with sequence signatures specific for most rickettsiae, including R. felis (8)

Conclusions
Because our patients were in contact with dog ticks, a tickborne rickettsiosis was suspected. However, no endemic tickborne rickettsiosis has been identified in Germany to date. The most frequent rickettsiosis in Europe, Mediterranean spotted fever due to R. conorii, is contracted in the Mediterranean area; clustered cases, as observed for our patients, are exceptional. In contrast, African tick-bite fever, a rickettsiosis due to R. africae, is frequently encountered in travelers to southern Africa (7). Murine typhus, caused by R. typhi, which has long been considered the only flea-transmitted rickettsiosis, has not been reported in Germany but is present in southern Europe, including Spain, Portugal, Cyprus, and Greece (9)(10)(11)(12). Until 1997, R. felis had only been detected in the United States. Since then, it has been detected by PCR in humans in Mexico (4) and Brazil (5) and in cat fleas from Ethiopia (5) and Spain (Marquez FJ, pers. comm.), thus demonstrating its presence in various areas, including the Old World, and supporting our preliminary serologic findings in French patients (5). In this study, serologic techniques discriminated among several rickettsiae for the woman but not her husband. Neither patient had antibodies to R. typhi, which suggests that antibodies to R. felis should be evaluated systematically in patients with typhuslike illnesses. Although no direct or indirect evidence of R. felis infection was obtained for the man, the simultaneous occurrence of symptoms similar to those observed in his wife strongly suggests infection with the same microorganism. Contact with fleas carried by their dogs would account for the simultaneous infection, as R. felis has been identified in C. felis fleas collected from a dog (13). However, neither fleas nor ticks from of the two dogs were available at the time of examination.
Our report describes the first PCR-confirmed case of human R. felis infection in Europe and supports the concept that R. felis may be widely distributed in the Old World and should be considered in the diagnosis of typhuslike illnesses, especially following a flea bite. Further studies should be conducted to identify the vectors of this rickettsia in Europe.