Cutaneous Immunoprofiles of Three Spotted Fever Group Rickettsia Cases

Stomach as the target organ of Rickettsia heilongjiangensis infection in C57BL/6 mice identified by click chemistry

Spotted fever group rickettsiae (SFGR) are obligate intracellular bacteria that cause spotted fever. The limitations of gene manipulation pose great challenges to studying the infection mechanisms of Rickettsia. By combining bioorthogonal metabolism and click chemistry, we developed a method to label R. heilongjiangensis via azide moieties and achieved rapid pathogen localization without complex procedures. Moreover, we constructed a C57BL/6 mice infection model by simulating tick bites and discovered that the stomach is the target organ of R. heilongjiangensis infection through in vivo imaging systems, which explained the occurrence of gastrointestinal symptoms following R. heilongjiangensis infection in some cases. This study offers a unique perspective for subsequent investigations into the pathogenic mechanisms of SFGR and identifies a potential target organ for R. heilongjiangensis.

Molecular detection of Rickettsia, Anaplasma, and Bartonella in ticks from free-ranging sheep in Gansu Province, China

Ticks pose a serious threat to public health as carriers and often vectors of zoonotic pathogens. There are few systematic studies on the prevalence and genetic diversity of tick-borne bacterial pathogens in Western China. In this study, 465 ticks were collected from free-ranging sheep in Gansu Province in China. Ticks were divided into 113 pools and tick DNA was extracted from these ticks. PCR assays were performed using specific primers to screen for tick-borne pathogens as well as sequence analysis based on the 16S rRNA (rrs), ompB, gltA, ompA genes for Rickettsia, rrs, groEL genes for Anaplasma, and ssrA and rpoB genes for Bartonella. The PCR results showed that the minimum infection rates with Rickettsia, Anaplasma, and Bartonella were 16.8% (78/465), 18.9% (88/465), and 0.9% (4/465), respectively. Sequence analysis based on the concatenated sequences of rrs-ompB-gltA-ompA indicated that the Rickettsia species identified in the ticks belonged to Rickettsia raoultii, Rickettsia slovaca, and Rickettsia sibirica, respectively; phylogenetic analysis based on the groEL gene showed that all Anaplasma strains identified were Anaplasma ovis; and phylogenetic analysis based on the ssrA and rpoB genes indicated that all Bartonella strains in the ticks belonged to Bartonella melophagi. The results of this study showed that ticks in Gansu Province harbored multiple pathogens that may cause rickettsial diseases and bartonellosis. These diseases were neglected in the area and physicians and public health workers need to pay attention to their diagnoses to prevent human infection.

Update on Accepted Novel Bacterial Isolates Derived from Human Clinical Specimens and Taxonomic Revisions Published in 2020 and 2021

A number of factors, including microbiome analyses and the increased utilization of whole-genome sequencing in the clinical microbiology laboratory, has contributed to the explosion of novel prokaryotic species discovery, as well as bacterial taxonomy revision. This review attempts to summarize such changes relative to human clinical specimens that occurred in 2020 and 2021, per primary publication in the International Journal of Systematic and Evolutionary Microbiology or acceptance on Validation Lists published by the International Journal of Systematic and Evolutionary Microbiology. Of particular significance among valid and effectively published taxa within the past 2 years were novel Corynebacterium spp., coagulase-positive staphylococci, Pandoraea spp., and members of family Yersiniaceae. Noteworthy taxonomic revisions include those within the Bacillus and Lactobacillus genera, family Staphylococcaceae (including unifications of subspecies designations to species level taxa), Elizabethkingia spp., and former members of Clostridium spp. and Bacteroides spp. Revisions within the Brucella genus have the potential to cause deleterious effects unless the relevance of such changes is properly communicated by microbiologists to stakeholders in clinical practice, infection prevention, and public health.

Skin infectome of patients with a tick bite history

Introduction

Ticks are the most important obligate blood-feeding vectors of human pathogens. With the advance of high-throughput sequencing, more and more bacterial community and virome in tick has been reported, which seems to pose a great threat to people.

Methods

A total of 14 skin specimens collected from tick-bite patients with mild to severe symptoms were analyzed through meta-transcriptomic sequencings.

Results

Four bacteria genera were both detected in the skins and ticks, including Pseudomonas, Acinetobacter, Corynebacterium and Propionibacterium, and three tick-associated viruses, Jingmen tick virus (JMTV), Bole tick virus 4 (BLTV4) and Deer tick mononegavirales-like virus (DTMV) were identified in the skin samples. Except of known pathogens such as pathogenic rickettsia, Coxiella burnetii and JMTV, we suggest Roseomonas cervicalis and BLTV4 as potential new agents amplified in the skins and then disseminated into the blood. As early as 1 day after a tick-bite, these pathogens can transmit to skins and at most four ones can co-infect in skins.

Discussion

Advances in sequencing technologies have revealed that the diversity of tick microbiome and virome goes far beyond our previous understanding. This report not only identifies three new potential pathogens in humans but also shows that the skin barrier is vital in preventing horizontal transmissions of tick-associated bacteria or virus communities to the host. It is the first research on patients' skin infectome after a tick bite and demonstrates that more attention should be paid to the cutaneous response to prevent tick-borne illness.

Rickettsia-Host-Tick Interactions: Knowledge Advances and Gaps

Ticks are hematophagous ectoparasites capable of transmitting multiple human pathogens. Environmental changes have supported the expansion of ticks into new geographical areas that have become the epicenters of tick-borne diseases (TBDs). The spotted fever group (SFG) of Rickettsia frequently infects ticks and causes tick-transmitted rickettsioses in areas of endemicity where ixodid ticks support host transmission during blood feeding. Ticks also serve as a reservoir for SFG Rickettsia. Among the members of SFG Rickettsia, R. rickettsii causes Rocky Mountain spotted fever (RMSF), the most lethal TBD in the United States. Cases of RMSF have been reported for over a century in association with several species of ticks in the United States. However, the isolation of R. rickettsii from ticks has decreased, and recent serological and epidemiological studies suggest that novel species of SFG Rickettsia are responsible for the increased number of cases of RMSF-like rickettsioses in the United States. Recent analyses of rickettsial genomes and advances in genetic and molecular studies of Rickettsia provided insights into the biology of Rickettsia with the identification of conserved and unique putative virulence genes involved in the rickettsial life cycle. Thus, understanding Rickettsia-host-tick interactions mediating successful disease transmission and pathogenesis for SFG rickettsiae remains an active area of research. This review summarizes recent advances in understanding how SFG Rickettsia species coopt and manipulate ticks and mammalian hosts to cause rickettsioses, with a particular emphasis on newly described or emerging SFG Rickettsia species.

Interferon receptor-deficient mice are susceptible to eschar-associated rickettsiosis

Arthropod-borne rickettsial pathogens cause mild and severe human disease worldwide. The tick-borne pathogen Rickettsia parkeri elicits skin lesions (eschars) and disseminated disease in humans; however, inbred mice are generally resistant to infection. We report that intradermal infection of mice lacking both interferon receptors (Ifnar1-/-;Ifngr1-/-) with as few as 10 R. parkeri elicits eschar formation and disseminated, lethal disease. Similar to human infection, eschars exhibited necrosis and inflammation, with bacteria primarily found in leukocytes. Using this model, we find that the actin-based motility factor Sca2 is required for dissemination from the skin to internal organs, and the outer membrane protein OmpB contributes to eschar formation. Immunizing Ifnar1-/-;Ifngr1-/- mice with sca2 and ompB mutant R. parkeri protects against rechallenge, revealing live-attenuated vaccine candidates. Thus, Ifnar1-/-;Ifngr1-/- mice are a tractable model to investigate rickettsiosis, virulence factors, and immunity. Our results further suggest that discrepancies between mouse and human susceptibility may be due to differences in interferon signaling.