Genetic sequencing should be used to confirm cases because purpura fulminans is a rare finding.
The clinical features of spotted fever group (SFG) Rickettsia induced disease range from a mild to severe illness. The clinical complexity is even greater due to the fact that the disease can be caused by different species with varying degrees of virulence. Current knowledge asserts that the Israeli SFG (ISF) strain Rickettsia conorii israelensis is the only human pathogenic SFG member in Israel. Current diagnostic procedures distinguish between SFG and the typhus group rickettsiosis, assuming all SFG-positive clinical samples positive for ISF. Molecular studies on questing ticks over the past decade have uncovered the existence of other SFG strains besides ISF in Israel and the region. This study describes the first documented analysis of SFG-positive samples from Israeli patients with the goal of distinguishing between ISF and non-ISF SFG strains. We managed to identify a new Rickettsia isolate from three independent clinical samples in Israel which was shown to be an as-yet unknown SFG member, showing no absolute identity with any known Rickettsia species present in the NCBI database.
S potted fever group rickettsioses (SFGRs) are arthropodborne diseases caused by obligate intracellular, gram-negative bacteria of the genus Rickettsia.SFGRs are associated with ≈20 species of Rickettsia, of which 16 are considered human pathogens (1,2). Recent introduction of molecular methods provided more information about SFGR agents causing human disease and enabled their identifi cation, for which the clinical signifi cance of some remains lacking (3). R. conorii complex, the etiologic agent of Mediterranean spotted fever, includes 4 strains: R. conorii Malish (cause of Mediterranean spotted fever), R. conorii Astrakhan (cause of Astrakhan fever), R. conorii Indian tick typhus (cause of Indian tick typhus), and R. conorii Israeli tick typhus strain (ITTS, cause of Israeli spotted fever [ISF]) (4-7).ISF begins as fever followed by a maculopapular rash, usually involving the palms and soles and frequently accompanied by systemic symptoms. Most cases are self-limiting, but some may lead to organ failure and death. Clinical and epidemiologic presentations caused by other strains of rickettsiae may vary (5,(8)(9)(10)(11). Studies from Portugal indicate that compared with Mediterranean spotted fever, ISF is characterized by lower rates of eschar and tick-exposure history, higher frequency of gastrointestinal symptoms, and greater severity of illness with a high case-fatality rate (10,12,13). Case-fatality rates in Israel before 1998 were reportedly 0.7%, but incidence in some years (e.g., 1997) was higher (3.5%) ( 14). Since 1998, several case reports of fatal SFGR in Israel have been published (9,15-17), along with reports of 22 other patients with sepsis requiring hospitalization (9,(17)(18)(19)(20)(21)(22). Of these, isolates from only 3 patients were sequenced and identifi ed as R. conorii ITTS; 2 of these patients exhibited purpura fulminans and all 3 died (9,15). Few studies of ISF have been conducted in Israel; most were conducted during the 1990s and relied on serologic diagnostic methods that cannot differentiate between the SFGRs (23). In Israel, SFGR is a notifi able disease, and in recent years, incidence has increased; 51 cases (including 7 deaths) were reported to the Israeli Ministry of Health in 2017, compared
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