Molecular Detection and Characterization of Rickettsia asembonensis in Human Blood, Zambia.

Rickettsia asembonensis is a flea-related Rickettsia with unknown pathogenicity to humans. We detected R. asembonensis DNA in 2 of 1,153 human blood samples in Zambia. Our findings suggest the possibility of R. asembonensis infection in humans despite its unknown pathogenicity.

Novel evidence suggests that a 'Rickettsia felis-like' organism is an endosymbiont of the desert flea, Xenopsylla ramesis.

Fleas are acknowledged vectors and reservoirs of various bacteria that present a wide range of pathogenicity. In this study, fleas collected from wild rodents from the Negev desert in southern Israel were tested for RickettsiaDNA by targeting the 16S rRNA (rrs) gene. Thirty-eight Xenopsylla ramesis, 91 Synosternus cleopatrae and 15 Leptopsylla flea pools (a total of 568 fleas) were screened. RickettsiaDNA was detected in 100% of the X. ramesis and in one S. cleopatrae flea pools. None of L. algira flea pools was found positive. All positive flea pools were further characterized by sequencing of five additional genetic loci (gltA, ompB, ompA, htrA and fusA). The molecular identification of the positive samples showed all sequences to be closely related to the 'Rickettsia felis-like' organisms (99-100% similarities in the six loci). To further investigate the association between 'R. felis-like' and X. ramesis fleas, ten additional single X. ramesis adult fleas collected from the wild and five laboratory-maintained X. ramesis imago, five larva pools (2-18 larvae per pool) and two egg pools (18 eggs per pool) were tested for the presence of 'R. felis-like' DNA. All samples were found positive by a specific ompAPCR assay, confirming the close association of this Rickettsia species with X. ramesis in all its life stages. These results suggest a symbiotic association between 'Rickettsia felis-like' and X. ramesis fleas.

Identification of Rickettsial Infections (Rickettsia sp. TH2014) in Ctenocephalides orientis Fleas (Siphonaptera: Pulicidae).

Rickettsia felis (Rickettsiales: Rickettsiaceae) is an emergent human pathogen that causes febrile illnesses in various parts of the world. This study describes the identification and growth characteristics of a R. felis-like organism (designated as Rickettsia sp. TH2014) cultured from Ctenocephalides orientis fleas in rural Malaysia. In this study, culturing of rickettsiae from filtered triturated flea lysates was performed in Aedes albopictus C6/36 cells. Cytopathic effects were observed from one of the samples 4 d post-inoculation. Electron microscopy revealed actively replicating intracytosolic coccobacillary organisms in the rickettsia-infected cells. Sequence analysis of amplified citrate synthase (gltA) gene fragment shows complete match of the rickettsia with Rickettsia sp. Rf31 in Southeast Asia, and 'Candidatus Rickettsia senegalensis' strain PU01-02 in Africa. The whole-genome sequence of Rickettsia sp. TH2014 was determined and assembled. The estimated genome size and guanine + cytosine content of the rickettsia are 1.37 Mb and 32.9%, respectively. The high values of average nucleotide identity and tetra-nucleotide signature correlation index obtained from pairwise genome comparison study suggest the identification of the rickettsia as R. felis. The whole-genome single-nucleotide polymorphism analysis demonstrates close genetic relatedness of the rickettsia with R. felis and Rickettsia asemboensis. However, based on sequence analyses of rickettsial genes (16S rDNA, gltA, ompB, and sca4), Rickettsia sp. TH2014 is found to be distinct from R. felis and R. asemboensis. The sequence analyses reveal that Rickettsia sp. TH2014 is highly similar to 'Ca. Rickettsia senegalensis' detected in fleas from Africa, Asia, and North America. Further investigation to provide insights on pathogenic potential and transmission dynamics of the rickettsia is warranted.

Worldwide Presence and Features of Flea-Borne Rickettsia asembonensis.

Rickettsia asembonensis, the most well-characterized rickettsia of the Rickettsia felis-like organisms (RFLO), is relatively unknown within the vector-borne diseases research community. The agent was initially identified in peri-domestic fleas from Asembo, Kenya in an area in which R. felis was associated with fever patients. Local fleas collected from domestic animals and within homes were predominately infected with R. asembonensis with < 10% infected with R. felis. Since the identification of R. asembonensis in Kenya, it has been reported in other locations within Africa, Asia, the Middle East, Europe, North America, and South America. With the description of R. asembonensis-like genotypes across the globe, a need exists to isolate these R. asembonensis genotypes in cell culture, conduct microscopic, and biological analysis, as well as whole genome sequencing to ascertain whether they are the same species. Additionally, interest has been building on the potential of R. asembonensis in infecting vertebrate hosts including humans, non-human primates, dogs, and other animals. The current knowledge of the presence, prevalence, and distribution of R. asembonensis worldwide, as well as its arthropod hosts and potential as a pathogen are discussed in this manuscript.

"Candidatus Rickettsia asemboensis" in Rhipicephalus sanguineus ticks, Brazil.

"Candidatus Rickettsia asemboensis" is an obligate intracellular bacterium of the Rickettsiales order, genetically related to species belonging to the Rickettsia felis group, agents of flea-borne spotted fever. Here we report for the first time the detection of "Ca. R. asemboensis", a flea-associated organism, in Rhipicephalus sanguineus ticks. It is the first occurrence of this emerging bacterium in Brazil, which increases the geographical distribution of this R. felis-like agent.