Orientia tsutsugamushi is an obligately intracellular bacterium and the etiological agent of scrub typhus. Human studies and animal models of scrub typhus have shown robust type 1-skewed proinflammatory responses during severe infection. Macrophages (Mφ) play a critical role in initiating such responses, yet mechanisms of innate recognition for O. tsutsugamushi remain unclear. In this study, we investigated whether Syk-dependent C-type lectin receptors (CLRs) contribute to innate immune recognition and the generation of proinflammatory responses. To validate a role of CLRs in scrub typhus, we infected murine bone marrow-derived (Mφ) with O. tsutsugamushi in the presence of selective Syk inhibitors and analysed a panel of CLRs and proinflammatory markers via qRT-PCR. We found that Mincle/Clec4a and Clec5a transcription was significantly abrogated upon Syk inhibition at 6 hours of infection. The effect of Syk inhibition on Mincle protein expression was validated via western blot. Syk-inhibited Mφ had diminished expression of type 1 cytokines/chemokines (Il12p40, Tnf, Il27p28, Cxcl1) during infection. Additionally, expression of innate immune cytosolic sensors (Mx1 and Oas1-3) was highly induced in the brain of lethally infected mice. We established that Mx1 and Oas1 expression was reduced in Syk-inhibited M, while Oas2, Oas3, and MerTK were not sensitive to Syk inhibition. This study reveals that Syk-dependent CLRs contribute to inflammatory responses to O. tsutsugamushi. It also provides the first evidence for Syk-dependent activation of intracellular defenses during infection, suggesting a role of pattern recognition receptor crosstalk in orchestrating macrophage-mediated responses to this poorly studied bacterium.

Scrub typhus threatens one billion people in the Asia-Pacific area and cases have emerged outside this region. It is caused by infection with any of the multitude of strains of the bacterium, Orientia tsutsugamushi. A vaccine that affords heterologous protection and a commercially available molecular diagnostic assay are lacking. Herein, we determined that the nucleotide and translated amino acid sequences of outer membrane protein A (OmpA) are highly conserved among 51 O. tsutsugamushi isolates. Molecular modeling revealed the predicted tertiary structure of O. tsutsugamushi OmpA to be very similar to that of the phylogenetically related pathogen, Anaplasma phagocytophilum, including the location of a helix that contains residues functionally essential for A. phagocytophilum infection. PCR primers were developed that amplified ompA DNA from all O. tsutsugamushi strains, but not from negative control bacteria. Using these primers in quantitative real-time PCR enabled sensitive detection and quantitation of O. tsutsugamushi ompA DNA from organs of mice that had been experimentally infected with the Karp or Gilliam strains. The high degree of OmpA conservation among O. tsutsugamushi strains evidences its potential to serve as a molecular diagnostic target and justifies its consideration as a candidate for developing a broadly protective scrub typhus vaccine.

Scrub typhus is a neglected tropical disease predominantly occurring in Asia. The causative agent is a bacterium transmitted by the larval stage of mites found in rural vegetation in endemic regions. Cases of scrub typhus frequently present as acute undifferentiated febrile illness, and without early diagnosis and treatment, the disease can develop fatal complications. We retrospectively reviewed de-identified data from a 23-year-old woman who presented to an emergency department with complaints of worsening abdominal pain. On presentation, she appeared jaundiced and toxic-looking. Other positive findings on abdominal examination were a positive Murphey’s sign, abdominal guarding and hepatosplenomegaly. Magnetic resonance cholangiopancreatography demonstrated acalculous cholecystitis. Additional findings included eschar on the medial aspect of the left thigh with inguinal regional lymphadenopathy. Further, positive results were obtained for immunoglobulins M and G, confirming scrub typhus. Workups for other infectious causes of acute acalculous cholecystitis detected human herpesvirus 4 (Epstein-Barr virus). Whether that represented acute infection or re-activation of the Epstein-Barr virus could not be determined. As other reports have described acute acalculous cholecystitis in adult scrub typhus patients, we recommend doxycycline to treat acute acalculous cholecystitis in endemic regions while awaiting serological confirmation.

Scrub typhus (ST) is one of the most neglected tropical diseases, a leading cause of acute undifferentiated febrile illness in areas of the ‘tsutsugamushi triangle’, diagnosed frequently in South Asian countries. The bacteria Orientia tsutsugamushi is the causative agent of the disease, which enters to human body through the bite of trombiculid mite (Chigger) of the genus Leptotrombidium deliense.The diagnosis of the disease becomes challenging as its early symptoms mimic other febrile illnesses like dengue, influenza, and corona viruses. Lack of rapid, reliable, and cost-effective diagnostic methods further complicates the identification process. Northeast India, a mountainous region with a predominantly rural tribal population, has witnessed a resurgence of scrub typhus cases in recent years. Various ecological factors, including rodent population, habitat characteristics, and climatic conditions, influence its prevalence. Entomological investigations have confirmed the abundance of vector mites, highlighting the importance of understanding their distribution and the probability of transmission of scrub typhus in the region. Proper diagnosis, awareness campaigns, and behavioral interventions are essential for controlling scrub typhus outbreaks and reducing its impact on public health in Northeast India. Further research and community-based studies are necessary to accurately assess the disease burden and implement effective prevention strategies.

The existence of multiple copies of genes is a well-known phenomenon. A gene family is a set of sufficiently similar genes, formed by gene duplication. In earlier works conducted on limited number of completely sequenced and annotated genomes it was found that size of gene family and size of genome are positively correlated. Additionally, it was found that several atypical microbes deviated from the observed general trend. In this study, we reexamined these associations on a larger dataset consisting of 1484 prokaryotic genomes and using several ranking approaches. We applied ranking methods in such a way that genomes with lower number of paralogs would have lower rank. Until now only simple ranking methods were used; we applied the Kemeny optimal aggregation approach as well. Regression and correlation analysis were utilized in order to accurately quantify and characterize the relationships between measures of paralog indices and genome size. In addition, boxplot analysis was employed as a method for outlier detection. We found that, in general, all paralog indexes positively correlate with an increase of genome size. As expected, different groups of atypical prokaryotic genomes were found for different types of paralog quantities.