A retrospective cohort study comparing outcomes following hip fractures in Australian indigenous patients with non-Australian indigenous patients.

BACKGROUND: Australian Indigenous (AI) populations face significant socioeconomic disadvantage and have poorer health outcomes when compared to their non-AI counterparts. There is a paucity of published literature on outcomes following hip fracture in the AI population. METHODS: We performed a retrospective cohort study comparing outcomes following hip fracture in AI and non- AI patients presenting to a single regional trauma centre. The primary outcome of interest was all-cause mortality. Secondary outcomes of interest were the odds of postoperative delirium and length of stay in hospital. All outcomes were adjusted against collected baseline covariates. RESULTS: One hundred and twenty-seven hip fractures were identified across 125 patients. There were 62 hip fractures in the AI group and 65 in the non-AI group. The adjusted hazard ratio (HR) for all-cause mortality was not statistically significant when comparing Indigenous versus non-Indigenous patients (HR = 2.37, P = 0.055). Adjusted odds of postoperative delirium was lower in Indigenous patients (OR = 0.12; P = 0.018). The AI cohort had a 4 day longer median length of stay, which was not statistically significant when adjusted for covariates. CONCLUSION: AI patients with hip fractures were younger, had a higher Charlson Comorbidity Index Score and American Society of Anaesthesiologists grade, as well as a higher incidence of diabetes and associated end-organ sequalae. There was no difference in all-cause mortality. Odds of postoperative delirium was lower in the AI group. We did not find any difference in the length of hospital stay.

Evaluation of the EQ-5D-5L, EQ-VAS stand-alone component and Oxford knee score in the Australian knee arthroplasty population utilising minimally important difference, concurrent validity, predictive validity and responsiveness.

PURPOSE: To evaluate the Oxford Knee Score (OKS), EQ-5D-5L utility index and EQ-5D visual analogue scale (EQ-VAS) for health-related quality of life outcome measurement in patients undergoing elective total knee arthroplasty (TKA) surgery. METHODS: In this prospective multi-centre study, the OKS and EQ-5D-5L index scores were collected preoperatively, six weeks (6w) and six months (6 m) following TKA. The OKS, EQ-VAS and EQ-5D-5L index were evaluated for minimally important difference (MID), concurrent validity, predictive validity (Spearman's Rho of predicted and observed values from a generalised linear regression model (GLM)), responsiveness (effect size (ES) and standard response mean (SRM)). The MID for the individual patient was determined utilising two approaches; distribution-based and anchor-based. RESULTS: 533 patients were analysed. The EQ-5D-5L utility index showed good concurrent validity with the OKS (r = 0.72 preoperatively, 0.65 at 6w and 0.69 at 6 m). Predictive validity for the EQ-5D-5L index was lower than OKS when regressed. Responsiveness was large for all fields at 6w for the EQ-5D-5L and OKS (EQ-5D-5L ES 0.87, SRM 0.84; OKS ES 1.35, SRM 1.05) and 6 m (EQ-5D-5L index ES 1.31, SRM 0.95; OKS ES 1.69, SRM 1.59). The EQ-VAS returned poorer results, at 6w an ES of 0.37 (small) and SRM of 0.36 (small). At 6 m, the EQ-VAS had an ES of 0.59 (moderate) and SRM of 0.47 (small). It, however, had similar predictive validity to the OKS, and better than the EQ-5D-5L index. MID determined using anchor approach, was shown that for OKS at 6 weeks it was 8.84 ± 9.28 and at 6 months 13.37 ± 9.89. For the EQ-5D-5L index at 6 weeks MID was 0.23 ± 0.39, and at 6 months 0.26 ± 0.36. CONCLUSIONS: The EQ-5D-5L index score and the OKS demonstrate good concurrent validity. The EQ-5D-5L index demonstrated lower predictive validity at 6w, and 6 m than the OKS, and both PROMs had adequate responsiveness. The EQ-VAS had poorer responsiveness but better predictive validity than the EQ-5D-5L index. This article includes MID estimates for the Australian knee arthroplasty population.

Comparison of Lethal and Nonlethal Mouse Models of Orientia tsutsugamushi Infection Reveals T-Cell Population-Associated Cytokine Signatures Correlated with Lethality and Protection.

The antigenic diversity of Orientia tsutsugamushi as well as the interstrain difference(s) associated with virulence in mice impose the necessity to dissect the host immune response. In this study we compared the host response in lethal and non-lethal murine models of O. tsutsugamushi infection using the two strains, Karp (New Guinea) and Woods (Australia). The models included the lethal model: Karp intraperitoneal (IP) challenge; and the nonlethal models: Karp intradermal (ID), Woods IP, and Woods ID challenges. We monitored bacterial trafficking to the liver, lung, spleen, kidney, heart, and blood, and seroconversion during the 21-day challenge. Bacterial trafficking to all organs was observed in both the lethal and nonlethal models of infection, with significant increases in average bacterial loads observed in the livers and hearts of the lethal model. Multicolor flow cytometry was utilized to analyze the CD4+ and CD8+ T cell populations and their intracellular production of the cytokines IFNγ, TNF, and IL2 (single, double, and triple combinations) associated with both the lethal and nonlethal murine models of infection. The lethal model was defined by a cytokine signature of double- (IFNγ-IL2) and triple-producing (IL2-TNF-IFNγ) CD4+ T-cell populations; no multifunctional signature was identified in the CD8+ T-cell populations associated with the lethal model. In the nonlethal model, the cytokine signature was predominated by CD4+ and CD8+ T-cell populations associated with single (IL2) and/or double (IL2-TNF) populations of producers. The cytokine signatures associated with our lethal model will become depletion targets in future experiments; those signatures associated with our nonlethal model are hypothesized to be related to the protective nature of the nonlethal challenges.

Neuropathic Pain after Adolescent Idiopathic Scoliosis Correction Surgery.

STUDY DESIGN: Prospective study. PURPOSE: To investigate the prevalence and the associated risk factors of chronic neuropathic pain symptoms using painDETECT questionnaire in adolescent idiopathic scoliosis (AIS) patients who underwent posterior spinal fusion (PSF) surgery. OVERVIEW OF LITERATURE: Post-lumbar surgery syndrome is a disease entity that describes neuropathic pain following spinal surgery. However, few studies have investigated the prevalence and risk factors for neuropathic pain in pediatric population undergoing corrective spinal surgery. METHODS: Forty AIS patients were recruited. Demographic, preoperative, and postoperative data were recorded. The magnitude and characteristics of postoperative pain were assessed using the painDETECT questionnaire through telephone enquiries at intervals of 2, 6, 12, and 24 weeks. Statistical analyses were followed by Pearson correlation test to determine the relationship between pain scores at 6, 12, and 24 weeks with the risk factors. RESULTS: Based on the painDETECT questionnaire, 90% of the patients had nociceptive pain, and 10% had a possible neuropathic pain component at 2 weeks postoperatively as per a mean painDETECT score of 7.1±4.5. Assessments at 6, 12, and 24 weeks showed that no patients had neuropathic pain with painDETECT scores of 4.4±3.2, 2.9±2.9, and 1.5±2.0, respectively. There was a significant correlation between total postoperative morphine use during 48 hours after the surgery and a tendency to develop neuropathic pain (p=0.022). CONCLUSIONS: Chronic neuropathic pain was uncommon in AIS patients who had undergone PSF surgery. Higher opioid consumption will increase the possibility of developing chronic neuropathic pain.

Regulation of Serum Exosomal MicroRNAs in Mice Infected with Orientia tsutsugamushi.

Exosomes are small extracellular vesicles that carry proteins, lipids, and nucleic acids. They are circulated in many body fluids and play an important role in intercellular communications. MicroRNAs (miRNAs), as major components of exosomes, are often regulated in many diseases including bacterial and viral infections. Functionally, exosome-carried miRNAs interact with various immune cells and affect their behavior. Little is known whether exosomal miRNAs are regulated during scrub typhus, a potentially lethal infection caused by intracellular bacteria, Orientiatsutsugamushi. In the present study, we utilized a scrub typhus mouse model and collected serum at various time points post infection. A custom quantitative PCR array covering 92 murine miRNAs was used to profile serum exosomal miRNAs. A total of 12 miRNAs were found to be significantly up- or down-regulated at least at one time point post infection when compared to uninfected animals. Further analysis identified multiple miRNAs in the let-7 family that were consistently down-regulated at early and late phase of infection. Functionally, serum exosomes isolated from infected mice displayed strong proinflammatory effect when incubated with bone marrow-derived macrophages. Our data revealed dynamic regulations of serum exosomal miRNA during scrub typhus infection, which could significantly influence host immune responses and disease outcome.

Comparative pan-genomic analyses of Orientia tsutsugamushi reveal an exceptional model of bacterial evolution driving genomic diversity.

Orientia tsutsugamushi, formerly Rickettsia tsutsugamushi, is an obligate intracellular pathogen that causes scrub typhus, an underdiagnosed acute febrile disease with high morbidity. Scrub typhus is transmitted by the larval stage (chigger) of Leptotrombidium mites and is irregularly distributed across endemic regions of Asia, Australia and islands of the western Pacific Ocean. Previous work to understand population genetics in O. tsutsugamushi has been based on sub-genomic sampling methods and whole-genome characterization of two genomes. In this study, we compared 40 genomes from geographically dispersed areas and confirmed patterns of extensive homologous recombination likely driven by transposons, conjugative elements and repetitive sequences. High rates of lateral gene transfer (LGT) among O. tsutsugamushi genomes appear to have effectively eliminated a detectable clonal frame, but not our ability to infer evolutionary relationships and phylogeographical clustering. Pan-genomic comparisons using 31 082 high-quality bacterial genomes from 253 species suggests that genomic duplication in O. tsutsugamushi is almost unparalleled. Unlike other highly recombinant species where the uptake of exogenous DNA largely drives genomic diversity, the pan-genome of O. tsutsugamushi is driven by duplication and divergence. Extensive gene innovation by duplication is most commonly attributed to plants and animals and, in contrast with LGT, is thought to be only a minor evolutionary mechanism for bacteria. The near unprecedented evolutionary characteristics of O. tsutsugamushi, coupled with extensive intra-specific LGT, expand our present understanding of rapid bacterial evolutionary adaptive mechanisms.

Dissemination of Orientia tsutsugamushi, a Causative Agent of Scrub Typhus, and Immunological Responses in the Humanized DRAGA Mouse.

Scrub typhus is caused by Orientia tsutsugamushi, an obligated intracellular bacterium that affects over one million people per year. Several mouse models have been used to study its pathogenesis, disease immunology, and for testing vaccine candidates. However, due to the intrinsic differences between the immune systems in mouse and human, these mouse models could not faithfully mimic the pathology and immunological responses developed by human patients, limiting their value in both basic and translational studies. In this study, we have tested for the first time, a new humanized mouse model through footpad inoculation of O. tsutsugamushi in DRAGA (HLA-A2.HLA-DR4.Rag1KO.IL2RγcKO.NOD) mice with their human immune system reconstituted by infusion of HLA-matched human hematopoietic stem cells from umbilical cord blood. Upon infection, Orientia disseminated into various organs of DRAGA mice resulted in lethality in a dose-dependent manner, while all C3H/HeJ mice infected by the same route survived. Tissue-specific lesions associated with inflammation and/or necroses were observed in multiple organs of infected DRAGA mice. Consistent with the intracellular nature of Orientia, strong Th1, but subdued Th2 responses were elicited as reflected by the human cytokine profiles in sera from infected mice. Interestingly, the percentage of both activated and regulatory (CD4+FOXP3+) human T cells were elevated in spleen tissues of infected mice. After immunization with irradiated whole cell Orientia, humanized DRAGA mice showed a significant activation of human T cells as evidenced by increased number of human CD4+ and CD8+ T cells. Specific human IgM and IgG antibodies were developed after repetitive immunization. The humanized DRAGA mouse model represents a new pre-clinical model for studying Orientia-human interactions and also for testing vaccines and novel therapeutics for scrub typhus.

Flexibility assessment of the unfused thoracic segments above the "potential upper instrumented vertebrae" using the supine side bending radiographs in Lenke 5 and 6 curves for adolescent idiopathic scoliosis patients.

BACKGROUND CONTEXT: Selection of upper instrumented vertebra for Lenke 5 and 6 curves remains debatable, and several authors have described different selection strategies. OBJECTIVE: This study analyzed the flexibility of the unfused thoracic segments above the "potential upper instrumented vertebrae (UIV)" (T1-T12) and its compensatory ability in Lenke 5 and 6 curves using supine side bending (SSB) radiographs. STUDY DESIGN: A retrospective study was used. PATIENT SAMPLE: This study comprised 100 patients. OUTCOME MEASURES: The ability of the unfused thoracic segments above the potential UIV, that is, T1-T12, to compensate in Lenke 5 and 6 curves was determined. We also analyzed postoperative radiological outcome of this cohort of patients with a minimum follow-up of 12 months. METHODS: Right and left SSB were obtained. Right side bending (RSB) and left side bending (LSB) angles were measured from T1 to T12. Compensatory ability of thoracic segments was defined as the ability to return to neutral (center sacral vertical line [CSVL]) with the assumption of maximal correction of lumbar curve with a horizontal UIV. The Lenke 5 curves were classified as follows: (1) Lenke 5-ve (mobile): main thoracic Cobb angle <15° and (2) Lenke 5+ve (stiff): main thoracic Cobb angle 15.0°-24.9°. This study was self-funded with no conflict of interest. RESULTS: There were 43 Lenke 5-ve, 31 Lenke 5+ve, and 26 Lenke 6 curves analyzed. For Lenke 5-ve, >70% of thoracic segments were able to compensate when UIV were at T1-T8 and T12 and >50% at T9-T11. For Lenke 5+ve, >70% at T1-T6 and T12, 61.3% at T7, 38.7% at T8, 3.2% at T9, 6.5% at T10, and 22.6% at T11 were able to compensate. For Lenke 6 curve, >70% at T1-T6, 69.2% at T7, 19.2% at T8, 7.7% at T9, 0% at T10, 3.8% at T11, and 34.6% at T12 were able to compensate. There was a significant difference between Lenke 5-ve versus Lenke 5+ve and Lenke 5-ve versus Lenke 6 from T8 to T11. There were no significance differences between Lenke 5+ve and Lenke 6 curves from T1 to T11. CONCLUSIONS: The compensatory ability of the unfused thoracic segment of Lenke 5+ve curves was different from the Lenke 5-ve curves, and it demonstrated characteristics similar to the Lenke 6 curves.

Trajectory of Postoperative Wound Pain Within the First 2 Weeks Following Posterior Spinal Fusion Surgery in Adolescent Idiopathic Scoliosis Patients.

STUDY DESIGN: A prospective cohort study. OBJECTIVE: The aim of this study was to determine and evaluate the trajectory of surgical wound pain from day 1 to day 14 after posterior spinal fusion (PSF) surgery in patients with adolescent idiopathic scoliosis (AIS). SUMMARY OF BACKGROUND DATA: Information regarding how the postoperative pain improves with time offers invaluable information not only to the patients and parents but also to assist the clinician in managing postoperative pain. METHODS: AIS patients who were planned for elective PSF surgery from September 2015 to December 2015 were prospectively recruited into this study. All patients underwent a similar pain management regimen with patient-controlled anesthesia (PCA) morphine, acetaminophen, celecoxib, and oxycodone hydrochloride. RESULTS: A total of 40 patients (36 F:4 M) were recruited. The visual analogue score (VAS) pain score was highest at 12 hours postoperation (6.0 ±â€Š2.3). It reduced to 3.9 ±â€Š2.2 (day 4), 1.9 ±â€Š1.6 (day 7), and 0.7 ±â€Š1.1 (day 14). The total PCA usage in all patients was 12.4 ±â€Š9.9 mg (first 12 hours), 7.1 ±â€Š8.0 mg (12 to 24 hours), 5.6 ±â€Š6.9 (24-36 hours), and 2.1 ±â€Š6.1 mg (36-48 hours). The celecoxib capsules usage was reducing from 215.0 ±â€Š152.8 mg at 24 hours to 55.0 ±â€Š90.4 mg on day 14. The acetaminophen usage was reducing from 2275 ±â€Š1198 mg at 24 hours to 150 ±â€Š483 mg at day 14. Oxycodone hydrochloride capsules consumption rose to the peak of 1.4 ±â€Š2.8 mg on day 4 before gradually reducing to none by day 13. CONCLUSION: With an adequate postoperation pain regimen, significant pain should subside to a tolerable level by postoperative day 4 and negligible by postoperative day 7. Patient usually can be discharged on postoperative day 4 when the usage of PCA morphine was not required. LEVEL OF EVIDENCE: 2.

Risk factors and clinical outcome of profound thrombocytopenia in adult patients with DENV infections.

Severe thrombocytopenia is common in dengue virus (DENV) infections. However, studies focusing on the role of profound thrombocytopenia (PT) (nadir platelet counts ≤ 20 000/mm3) in DENV infections are scarce. This study aims to identify the associated features and outcome of DENV patients with PT. It involves 237 adult hospitalized patients who were DENV PCR positive. The presence of comorbidity (AOR = 4.625; 95% CI = 1.113-19.230), higher admission hematocrit (AOR = 1.213; 95% CI = 1.067-1.379), lower admission albumin (AOR = 0.870; 95% CI = 0.766-0.988) and lower admission platelets (AOR = 0.980; 95% CI = 0.969-0.991) was associated with platelets ≤ 20 000/mm3 in multivariate logistic regression. PT was not affected by DENV serotypes, coinfections and secondary DENV infections. Patients with PT had significantly higher risk of experiencing warning signs (AOR = 3.709, 95% CI = 1.089-12.634) and longer hospital stay (AOR = 1.943, 95% CI = 1.010-3.774). However, severe dengue disease, hemorrhagic manifestations and need for intensive care were not significantly associated with PT.

Comparison Between Minimally Invasive Surgery and Conventional Open Surgery for Patients With Spinal Metastasis: A Prospective Propensity Score-Matched Study.

STUDY DESIGN: Prospective propensity score-matched study. OBJECTIVE: To compare the outcomes of minimal invasive surgery (MIS) and conventional open surgery for spinal metastasis patients. SUMMARY OF BACKGROUND DATA: There is lack of knowledge on whether MIS is comparable to conventional open surgery in treating spinal metastasis. METHODS: Patients with spinal metastasis requiring surgery from January 2008 to December 2010 in two spine centers were recruited. The demographic, preoperative, operative, perioperative and postoperative data were collected and analyzed. Thirty MIS patients were matched with 30 open surgery patients using propensity score matching technique with a match tolerance of 0.02 based on the covariate age, tumor type, Tokuhashi score, and Tomita score. RESULTS: Both groups had significant improvements in Eastern Cooperative Oncology Group (ECOG), Karnofsky scores, visual analogue scale (VAS) for pain and neurological status postoperatively. However, the difference comparing the MIS and open surgery group was not statistically significant. MIS group had significantly longer instrumented segments (5.5 ±â€Š3.1) compared with open group (3.8 ±â€Š1.7). Open group had significantly longer decompressed segment (1.8 ±â€Š0.8) than MIS group (1.0 ±â€Š1.0). Open group had significantly more blood loss (2062.1 ±â€Š1148.0 mL) compared with MIS group (1156.0 ±â€Š572.3 mL). More patients in the open group (76.7%) needed blood transfusions (with higher average units of blood transfused) compared with MIS group (40.0%). Fluoroscopy time was significantly longer in MIS group (116.1 ±â€Š63.3 s) compared with open group (69.9 ±â€Š42.6 s). Open group required longer hospitalization (21.1 ±â€Š10.8 days) compared with MIS group (11.0 ±â€Š5.0 days). CONCLUSION: This study demonstrated that MIS resulted in comparable outcome to open surgery for patients with spinal metastasis but has the advantage of less blood loss, blood transfusions, and shorter hospital stay. LEVEL OF EVIDENCE: 3.

Impact of dengue virus (DENV) co-infection on clinical manifestations, disease severity and laboratory parameters.

BACKGROUND: The co-circulation of 4 DENV serotypes in geographically expanding area, has resulted in increasing occurrence of DENV co-infections. However, studies assessing the clinical impact of DENV co-infections have been scarce and have involved small number of patients. This study explores the impact of DENV co-infection on clinical manifestations and laboratory parameters. METHODS: This retrospective study involved consecutive hospitalized patients with non-structural protein 1 (NS1) antigen positivity during an outbreak (Jan to April 2014). Multiplex RT-PCR was performed directly on NS1 positive serum samples to detect and determine the DENV serotypes. All PCR-positive serum samples were inoculated onto C6/36 cells. Multiplex PCR was repeated on the supernatant of the first blind passage of the serum-infected cells. Random samples of supernatant from the first passage of C6/36 infected cells were subjected to whole genome sequencing. Clinical and laboratory variables were compared between patients with and without DENV co-infections. RESULTS: Of the 290 NS1 positive serum samples, 280 were PCR positive for DENV. Medical notes of 262 patients were available for analysis. All 4 DENV serotypes were identified. Of the 262 patients, forty patients (15.3 %) had DENV co-infections: DENV-1/DENV-2(85 %), DENV-1/DENV-3 (12.5 %) and DENV-2/DENV-3 (2.5 %). Another 222 patients (84.7 %) were infected with single DENV serotype (mono-infection), with DENV- 1 (76.6 %) and DENV- 2 (19.8 %) predominating. Secondary dengue infections occurred in 31.3 % patients. Whole genome sequences of random samples representing DENV-1 and DENV-2 showed heterogeneity amongst the DENVs. Multivariate analysis revealed that pleural effusion and the presence of warning signs were significantly higher in the co-infected group, both in the overall and subgroup analysis. Diarrhoea was negatively associated with co-infection. Additionally, DENV-2 co-infected patients had higher frequency of patients with severe thrombocytopenia (platelet count < 50,000/mm(3)), whereas DENV-2 mono-infections presented more commonly with myalgia. Elevated creatinine levels were more frequent amongst the co-infected patients in univariate analysis. Haemoconcentration and haemorrhagic manifestations were not higher amongst the co-infected patients. Serotypes associated with severe dengue were: DENV-1 (n = 9), DENV-2 (n = 1), DENV-3 (n = 1) in mono-infected patients and DENV-1/DENV-2 (n = 5) and DENV-1/DENV-3 (n = 1) amongst the co-infected patients. CONCLUSION: DENV co-infections are not uncommon in a hyperendemic region and co-infected patients are skewed towards more severe clinical manifestations compared to mono-infected patients.

Isolation and characterization of a novel Rickettsia species (Rickettsia asembonensis sp. nov.) obtained from cat fleas (Ctenocephalides felis).

A novel rickettsial agent, 'Candidatus Rickettsia asembonensis' strain NMRCiiT, was isolated from cat fleas, Ctenocephalides felis, from Kenya. Genotypic characterization of the new isolate based on sequence analysis of five rickettsial genes, rrs, gltA, ompA, ompB and sca4, indicated that this isolate clustered with Rickettsia felis URRWXCal2. The degree of nucleotide similarity demonstrated that isolate NMRCiiT belongs within the genus Rickettsia and fulfils the criteria for classification as a representative of a novel species. The name Rickettsia asembonensis sp. nov. is proposed, with NMRCiiT (=DSM 100172T=CDC CRIRC RAS001T=ATCC VR-1827T) as the type strain.

Development of an Orientia tsutsugamushi Lc-1 Murine Intraperitoneal Challenge Model for Scrub Typhus: Determination of Murine Lethal Dose (MuLD50), Tissue Bacterial Loads, and Clinical Outcomes.

Currently, no vaccine has been developed to protect humans from naturally acquired heterologous Orientia tsutsugamushi infections. To enhance the validity of vaccine candidates, we are developing a murine chigger challenge model with the O. tsutsugamushi Lc-1-infected Leptotrombidium chiangraiensis Line-1. To this end, an intraperitoneal (i.p.) murine challenge model using an O. tsutsugamushi Lc-1 isolate was developed for eventual validation of the chigger challenge model. We have determined that the murine lethal dose that kills 50% of the challenged mice (MuLD50) of a liver/spleen homogenate developed from O. tsutsugamushi Lc-1-infected ICR Swiss mice to be 10(-6.9). Employing different inoculum doses of this homogenate, the bacterial load using quantitative real-time PCR (qPCR) was determined to range from 60 to 1.6 × 10(5) genome equivalent copies (GEC)/µL of liver and 33.4 to 2.2 × 10(5) GEC/µL of spleen tissue. The clinical outcomes relative to homogenate dose levels followed a dose-dependent pattern. The successful development and characterization of the O. tsutsugamushi Lc-1 i.p. challenge model will assist in the development and validation of a mouse chigger challenge scrub typhus model.

Establishment of Orientia tsutsugamushi Lc-1 (Rickettsiales: Rickettsiaceae) infection in ICR outbred mice (Rodentia: Muridae) by needle challenge.

Orientia tsutsugamushi is a pathogen transmitted by Leptotrombidium that causes scrub typhus. To develop an infection mouse model, a mite-derived isolate of O. tsutsugamushi was established from a laboratory-maintained colony of Leptotrombidium chiangraiensis (O. tsutsugamushi Lc-1). This Lc-1 isolate was initially presented to ICR (CD-1) mice by feeding an infected Lc chigger on the ear of a mouse. Once the Lc-1 was adapted to the ICR mice, quantitative real-time polymerase chain reaction was used to investigate O. tsutsugamushi genomic equivalent copies in tissues and sera. Furthermore, times to onset of the signs of infection are reported in this study. This study provides information useful for future research on this host-pathogen interaction and the associated vaccine efficacy trials.

An intradermal inoculation model of scrub typhus in Swiss CD-1 mice demonstrates more rapid dissemination of virulent strains of Orientia tsutsugamushi.

Scrub typhus is an important endemic disease of the Asia-Pacific region caused by Orientia tsutsugamushi. To develop an effective vaccine to prevent scrub typhus infection, a better understanding of the initial host-pathogen interaction is needed. The objective of this study was to investigate early bacterial dissemination in a CD-1 Swiss outbred mouse model after intradermal injection of O. tsutsugamushi. Three human pathogenic strains of O. tsutsugamushi (Karp, Gilliam, and Woods) were chosen to investigate the early infection characteristics associated with bacterial virulence. Tissue biopsies of the intradermal injection site and draining lymph nodes were examined using histology and immunohistochemistry to characterize bacterial dissemination, and correlated with quantitative real-time PCR for O. tsutsugamushi in blood and tissue from major organs. Soluble adhesion molecules were measured to examine cellular activation in response to infection. No eschar formation was seen at the inoculation site and no clinical disease developed within the 7 day period of observation. However, O. tsutsugamushi was localized at the injection site and in the draining lymph nodes by day 7 post inoculation. Evidence of leukocyte and endothelial activation was present by day 7 with significantly raised levels of sL-selectin, sICAM-1 and sVCAM-1. Infection with the Karp strain was associated with earlier and higher bacterial loads and more extensive dissemination in various tissues than the less pathogenic Gilliam and Woods strains. The bacterial loads of O. tsutsugamushi were highest in the lungs and spleens of mice inoculated with Karp and Gilliam, but not Woods strains. Strains of higher virulence resulted in more rapid systemic infection and dissemination in this model. The CD-1 mouse intradermal inoculation model demonstrates features relevant to early scrub typhus infection in humans, including the development of regional lymphadenopathy, leukocyte activation and distant organ dissemination after low-dose intradermal injection with O. tsutsugamushi.

Protection against scrub typhus by a plasmid vaccine encoding the 56-KD outer membrane protein antigen gene.

The 56-kD outer membrane protein of Orientia tsutsugamushi has previously been shown to be the immunodominant antigen in scrub typhus infections. Its gene was cloned into the DNA vaccine vector pVR1012 as a vaccine candidate (pKarp56). The in vitro expression of this 56-kD antigen by pKarp56 was confirmed in tissue culture by an indirect fluorescence assay and Western blot analysis. The initial antibody responses of mice immunized with varied doses of the pKarp56 were barely detected, but increases were observed after each of three subsequent booster immunizations. Although no protection was observed with a single immunization of pKarp56, after four immunizations, 60% of the mice survived a 1,000 x 50% lethal dose (LD(50)) challenge. These results specifically confirm the importance of the 56-kD protein antigen in protective immunity against O. tsutsugamushi and demonstrate the feasibility of DNA vaccines for the prevention of scrub typhus.

Scrub typhus vaccine candidate Kp r56 induces humoral and cellular immune responses in cynomolgus monkeys.

A truncated recombinant 56-kDa outer membrane protein of the Karp strain of Orientia tsutsugamushi (Kp r56) was evaluated in cynomolgus monkeys (Macaca fascicularis) for immunogenicity and safety as a vaccine candidate for the prevention of scrub typhus. This recombinant antigen induced strong humoral and cellular immune responses in two monkeys and was found to be well tolerated. Antigen-specific immunoglobulin M (IgM) and IgG were produced to almost maximal levels within 1 week of a single immunization. Peripheral blood mononuclear cells from vaccinated animals showed an induction of antigen-specific proliferation and gamma interferon production. The Kp r56 was not as efficient as infection with live organisms in preventing reinfection but was able to reduce the inflammation produced at the site of challenge. This report describes the results of the first systematic study of the immunogenicity of a recombinant scrub typhus vaccine candidate in a nonhuman primate model.

Short- and long-term immune responses of CD-1 outbred mice to the scrub typhus DNA vaccine candidate: p47Kp.

Orientia tsutsugamushi is an obligate intracellular bacterium that is the causative agent of scrub typhus. To develop an effective vaccine to prevent or ameliorate scrub typhus, knowledge of the protective immune response to O. tsutsugamushi needs to be ascertained. Our laboratory has demonstrated that the DNA vaccine vector pVR1012 carrying the O. tsutsugamushi Karp strain 47-kDa protein gene (p47Kp) consistently provides outbred mice protection against homologous challenge.