Abstract
Crucial factors influencing the epidemiology of Rickettsia felis rickettsiosis include pathogenesis and transmission. Detection of R. felis DNA in a number of arthropod species has been reported, with characterized isolates, R. felis strain LSU and strain LSU-Lb, generated from the cat flea, Ctenocephalides felis, and the non-hematophagous booklouse, Liposcelis bostrychophila, respectively. While it is realized that strain influence on host biology varies, the rickettsial response to these distinct host environments remained undefined. To identify a panel of potential rickettsial transmission determinants in the cat flea, the transcriptional profile for these two strains of R. felis were compared in their arthropod hosts using RNAseq. Rickettsial genes with increased transcription in the flea as compared to the booklouse were identified. Genes previously associated with bacterial virulence including LPS biosynthesis, Type IV secretion system, ABC transporters, and a toxin-antitoxin system were selected for further study. Transcription of putative virulence-associated genes was determined in a flea infection bioassay for both strains of R. felis. A host-dependent transcriptional profile during bloodfeeding, specifically, an increased expression of selected transcripts in newly infected cat fleas and flea feces was detected when compared to arthropod cell culture and incubation in vertebrate blood. Together, these studies have identified novel, host-dependent rickettsial factors that likely contribute to successful horizontal transmission by bloodfeeding arthropods.
Highlights
In the last three decades, several species of Rickettsia have emerged as human pathogens, including Rickettsia felis, a Gram-negative bacterium predominately described in the cat flea, Ctenocephalides felis
Among the 115 differentially expressed genes, 63 genes had higher transcriptional levels in R. felis within fleas in comparison to the booklice. These differentially expressed genes in fleas were blasted against the R. felis genome URRWXCal2 and putative assignments were given to 80.9% (51/63) of the genes with the remainder consisting of hypothetical proteins (S1 Table)
The combination of pathogenicity of bacterial isolates and transmission modalities in the maintenance of pathogens in arthropod vectors are crucial factors which influence the epidemiology of the emerging R. felis rickettsiosis [8,9,10]
Summary
In the last three decades, several species of Rickettsia have emerged as human pathogens, including Rickettsia felis, a Gram-negative bacterium predominately described in the cat flea, Ctenocephalides felis. Since its discovery in cat fleas and the first human case reported from Texas, R. felis has been recognized as a cosmopolitan pathogen [3,4,5,6,7]. Highlighting its emergent nature in sub-Saharan Africa, R. felis was detected in a number of flea species [8,9,10] and recently identified as a common (3– 15%) cause of fever among febrile patients [3, 11, 12]. In the Americas, R. felis rickettsiosis is associated primarily with suburban foci corresponding with the detection of rickettsial DNA in a variety of peri-domestic vertebrate hosts and their fleas [13,14,15,16]
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