Genetic analysis of isolates of the spotted fever group of rickettsiae belonging to the R. conorii complex

Boutonneuse Fever in Southeastern Romania

Boutonneuse fever (BF) is an eruptive disease and is classified as a spotted fever, which is endemic in the Mediterranean basin (i.e., Marseille fever or Mediterranean spotted fever) and the Black Sea, caused by Rickettsia conorii, with dog ticks being a vector (i.e., Rhipicephalus sanguineus). In Romania, although the first reported outbreak of BF occurred during the summer of 1931 in Constanta, the disease was discovered in 1910. Although the disease has occurred most frequently in the two counties of the Dobruja region (Constanta and Tulcea), a region of the Balkan Peninsula, during the last few years, other counties in southeastern Romania have started to report BF cases. In a period of 9 years, 533 cases were registered in Constanta county, while in a period of 11 years, 339 cases were registered in Bucharest county. In this review, we describe the bacterial tick-borne disease caused by R. conorii in southeastern Romania, focusing on its history and epidemiology, pathophysiology, clinical aspects, diagnosis, treatment and preventive measures in the context of climate changes. Although R. conorii is the principal etiologic agent of BF in southeastern Romania, we should take into consideration that other Rickettsia spp. could be present and involved in disease transmission.

Naming of Rickettsiae and Rickettsial Diseases

Over the last 20 years, advances in molecular techniques have greatly facilitated the identification of the members of the Rickettsiales, and numerous new species and diseases have been described. In this paper, we review taxonomic rules and appropriate approaches to valid naming of rickettsial species and the diseases they cause.

Tick-borne rickettsioses around the world: emerging diseases challenging old concepts

During most of the 20th century, the epidemiology of tick-borne rickettsioses could be summarized as the occurrence of a single pathogenic rickettsia on each continent. An element of this paradigm suggested that the many other characterized and noncharacterized rickettsiae isolated from ticks were not pathogenic to humans. In this context, it was considered that relatively few tick-borne rickettsiae caused human disease. This concept was modified extensively from 1984 through 2005 by the identification of at least 11 additional rickettsial species or subspecies that cause tick-borne rickettsioses around the world. Of these agents, seven were initially isolated from ticks, often years or decades before a definitive association with human disease was established. We present here the tick-borne rickettsioses described through 2005 and focus on the epidemiological circumstances that have played a role in the emergence of the newly recognized diseases.

Proposal to create subspecies of Rickettsia conorii based on multi-locus sequence typing and an emended description of Rickettsia conorii

BACKGROUND

Rickettsiae closely related to the Malish strain, the reference Rickettsia conorii strain, include Indian tick typhus rickettsia (ITTR), Israeli spotted fever rickettsia (ISFR), and Astrakhan fever rickettsia (AFR). Although closely related genotypically, they are distinct serotypically. Using multilocus sequence typing (MLST), we have recently found that distinct serotypes may not always represent distinct species within the Rickettsia genus. We investigated the possibility of classifying rickettsiae closely related to R. conorii as R. conorii subspecies as proposed by the ad hoc committee on reconciliation of approaches to bacterial systematics. For this, we first estimated their genotypic variability by using MLST including the sequencing of 5 genes, of 31 rickettsial isolates closely related to R. conorii strain Malish, 1 ITTR isolate, 2 isolates and 3 tick amplicons of AFR, and 2 ISFR isolates. Then, we selected a representative of each MLST genotype and used multi-spacer typing (MST) and mouse serotyping to estimate their degree of taxonomic relatedness.

RESULTS

Among the 39 isolates or tick amplicons studied, four MLST genotypes were identified: i) the Malish type; ii) the ITTR type; iii) the AFR type; and iv) the ISFR type. Among these four MLST genotypes, the pairwise similarity in nucleotide sequence varied from 99.8 to 100%, 99.4 to 100%, 98.2 to 99.8%, 98.4 to 99.8%, and 99.2 to 99.9% for 16S rDNA, gltA, ompA, ompB, and sca4 genes, respectively. Representatives of the 4 MLST types were also classified within four types using MST genotyping as well as mouse serotyping.

CONCLUSION

Although homogeneous genotypically, strains within the R. conorii species show MST genotypic, serotypic, and epidemio-clinical dissimilarities. We, therefore, propose to modify the nomenclature of the R. conorii species through the creation of subspecies. We propose the names R. conorii subsp. conorii subsp. nov. (type strain = Malish, ATCC VR-613), R. conorii subspecies indica subsp. nov. (type strain = ATCC VR-597), R. conorii subspecies caspia subsp. nov. (type strain = A-167), and R. conorii subspecies israelensis subsp. nov. (type strain = ISTT CDC1). The description of R. conorii is emended to accomodate the four subspecies.

Isolation of a rickettsia related to Astrakhan fever rickettsia from a patient in Chad

We isolated a novel spotted fever group rickettsia from a patient coming back from Chad with fever and a maculopapulous rash. In Africa, only six pathogenic spotted fever group rickettsiae have been identified, R. conorii, R. africae, R. akari, R. aeschlimannii, "R. mongolotimonae," and R. felis. Our isolate was identified by PCR amplification and sequencing of the 16S rRNA (16S rDNA), citrate synthase (gltA), and rOmpA (ompA) encoding genes. The 16S rDNA, gltA, and ompA sequences of the isolate were found to be 99.7, 99.6, and 99.5% identical with that of Astrakhan fever rickettsia, respectively. This rickettsia is endemic in the Caspian sea area and has also recently been identified in Kosovo. Using mouse serotyping, the currently accepted method for the identification of spotted fever group rickettsiae, the Chad isolate exhibited a specificity difference of 2 when compared to Astrakhan fever rickettsia and at least 4 when compared with other members of the R. conorii complex. The Chad isolate should be considered a variant of Astrakhan fever rickettsia. This is the first description of Astrakhan fever rickettsia outside Europe and the bacterium may be responsible for cases of spotted fever in Chad. Although Astrakhan fever rickettsia is transmitted by Rhipicephalus ticks in Europe, further studies are indicated to identify its vector in Africa where these ticks are also prevalent.