Risk factors of acute respiratory distress syndrome in Scrub typhus

Background: Scrub typhus is a common tropical infection presenting as acute febrile illness. Acute Respiratory Distress Syndrome (ARDS) is a serious complication of scrub typhus and is often associated with high mortality. This study was aimed to analyse risk factors of ARDS in Scrub typhus patients.Methods: This study was a prospective observational case control study conducted from June 2012 to June 2015 in Kasturba Hospital, Manipal, Karnataka, India. ARDS was diagnosed as per Berlin criteria.Results: During the study period, a total of 320 patients were diagnosed to have scrub typhus as per our criteria. All the patients were from state of Karnataka except for 1 patient, who was from state of Kerala. A total of 20 (6.25%) patients (cases) were diagnosed to have ARDS and 300 (93.75%) patients (controls) did not have ARDS. After multivariate analysis of the risk factors only two risk factors had significant association with development of ARDS: sepsis (OR 4.34,95% CI 0.51,36.76) and septic shock (OR 16.57 95% CI 1.64,166.76).Conclusions: ARDS is a common and serious complication of scrub typhus. It often occurs along with other complications. Presence of dyspnoea, sepsis, septic shock, hypoalbuminemia should alert clinicians about ARDS. ARDS due to scrub typhus is associated with high mortality. Early recognition and prompt therapy can reduce mortality

Detection and distribution of Sca autotransporter protein antigens in diverse isolates of Orientia tsutsugamushi.

Orientia tsutsugamushi (Ots) frequently causes severe scrub typhus infections in the Asia-Pacific region. Korean investigators have demonstrated that Ots encodes five different autotransporter domain (ATD) proteins (ScaA-ScaE). ScaA functions as an adhesin and confers protective immunity in a lethal mouse model of Ots infection. Specific antibodies are detected against ScaA and ScaC in Korean scrub typhus patients. However, there is limited data on the distribution of the Sca protein genes in diverse isolates of Ots. By BLAST analysis with the conserved beta barrel autotransporter domain (ATD) regions of the sca proteins, we discovered a sixth gene scaF among 3 of 10 new partial Ots genome sequences available at NCBI GenBank (Sido, Karp, AFSC7). We designed two to seven specific TaqMan assays to detect the ATD for each of the six sca genes. The TaqMan assays among those for each sca gene which gave the greatest sensitivity and linearity with DNA log dilutions were then used for screening DNAs from Ots isolates grown in L929 mouse cells for sca genes. The sca prevalence survey was performed for all six sca genes with 178 DNAs from isolates from 12 countries. The survey results were confirmed by conventional PCR with primers from conserved regions of the passenger domains (PD) and ATD of the sca proteins. The ATD was highly conserved between the DNAs of different genotypes compared to the sca PD but each TaqMan assay was sca specific. The percentage positivity for 56 kDa and scaA genes in the 178 DNAs using Ha primers was 59.6% and 62.4%, respectively. Our scaA conventional ATD PCR assay was positive in 98.3% but scaA was present in all 178 DNAs (100%) by ATD TaqMan. scaB, scaC, scaD, scaE and scaF were detected in 33.7%, 97.8%, 93.8%, 97.2% and 43.3% isolates by ATD TaqMan, respectively. The ATDs of Ots sca genes are thus sufficiently conserved between different genotypes for molecular assay design. Four sca genes are widely distributed among diverse Ots isolates from diverse geographical areas. scaB and scaF were detected in fewer Ots isolates and absent from some available genome sequences. Whether the utility of the ScaA, ScaC, ScaD, and ScaE antigenic passenger protein domains exceeds that of the mixed 56 kDa type surface antigens of Ots now used in combination diagnostic assays needs to be determined before they can be considered as suitable alternative serological antigens for diagnosis of scrub typhus

Phylogenetic relationships of Ots TSA spacer domains.

<p>All the ATs from each of three spacer domains S-VDI, S-VDII/III and S-VDIII of Indian and South Korean TSA were used for constructing individual Neighbor-Joining phylogenetic trees using their amino acid sequences. The TSA country of origin, the AT type and number of samples with that AT domain type are indicated for each unique AT type for each data set (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0196240#pone.0196240.s006" target="_blank">S3 Table</a>) (e.g., India-24-18). The pairs of identical 12 AT present in both India and South Korea TSAs are highlighted with red circles. Only the nodes with ≥70 bootstrap values are shown (1000 bootstraps). The bracket values show the scale for amino acid differences for each domain.</p

Complexity of type-specific 56 kDa antigen CD4 T-cell epitopes of <i>Orientia tsutsugamushi</i> strains causing scrub typhus in India

<div><p><i>Orientia tsutsugamushi</i> (Ots) is an obligate, intracellular, mite-transmitted human pathogen which causes scrub typhus. Understanding the diversity of Ots antigens is essential for designing specific diagnostic assays and efficient vaccines. The protective immunodominant type-specific 56 kDa antigen (TSA) of Ots varies locally and across its geographic distribution. TSA contains four hypervariable domains. We bioinformatically analyzed 345 partial sequences of TSA available from India, most of which contain only the three variable domains (VDI-III) and three spacer conserved domains (SVDI, SVDII/III, SVDIII). The total number (152) of antigenic types (amino acid variants) varied from 14–36 in the six domains of TSA that we studied. Notably, 55% (787/1435) of the predicted CD4 T-cell epitopes (TCEs) from all the six domains had high binding affinities (HBA) to at least one of the prevalent Indian human leukocyte antigen (HLA) alleles. A surprisingly high proportion (61%) of such TCEs were from spacer domains; indeed 100% of the CD4 TCEs in the SVDI were HBA. TSA sequences from India had more antigenic types (AT) than TSA from Korea. Overall, >90% of predicted CD4 TCEs from spacer domains were predicted to have HBA against one or more prevalent HLA types from Indian, Korean, Asia-Pacific region or global population data sets, while only <50% of CD4 TCEs in variable domains exhibited such HBA. The phylogenetically and immunologically important amino acids in the conserved spacer domains were identified. Our results suggest that the conserved spacer domains are predicted to be functionally more important than previously appreciated in immune responses to Ots infections. Changes occurring at the TCE level of TSA may contribute to the wide range of pathogenicity of Ots in humans and mouse models. CD4 T-cell functional experiments are needed to assess the immunological significance of these HBA spacer domains and their role in clearance of Ots from Indian patients.</p></div

Prevalent HLA-DRB1 alleles in different geographical regions and domain prevalence of Indian 15-amino acid TSA peptides with predicted high binding affinities.

<p>A) Top six most prevalent HLA-DRB1 alleles identified in populations in India, South Korea, Asia-Pacific region and global (<a href="http://allelefrequencies.net/" target="_blank">http://allelefrequencies.net/</a>), which were used to predict the binding affinity of all predicted 15 aa peptides from each AT from six domains of Indian TSA. B) The distribution of HBA T-cell epitopes predicted from Indian TSA antigenic types in each TSA domain. For each domain, the first set of bars shows the total number of predicted unique peptides and the number of these peptides identified with HBA to at-least one prevalent Indian HLA allele. Both the total number of predicted peptides and the peptides with HBA were further classified based on their presence in AT detected in single (SS) or multiple strains (MS) (bar pairs 2 and 3, respectively). C) Distribution (percentages) of peptides (15 aa) with HBAs from ATs identified in single (SS-uniquely present) and multiple (MS-shared sequences ≥2) Ots strains.The peptides present in both single and multiple strain sequences are highlighted in orange, the HBA peptides in SS and MS types are highlighted in purple and green, respectively.</p

Proportion of peptides with HBA (CD4 TCEs) from the six domains of TSA from India and South Korea.

<p>The bar diagrams show that the proportion of predicted HBA peptides from all ATs from each of six domains from A) India TSA and B) South Korea TSA. Six prevalent HLA-DRB1 alleles from four different population sets (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0196240#pone.0196240.g002" target="_blank">Fig 2A</a>) were used to identify the CD4 TSA TCEs with HBA.</p

Properties of peptides exhibiting HBA from Indian and South Korean TSAs.

<p>A) The mean binding affinity score was calculated from the binding affinity (score) of each predicted 15 aa peptides (sliding window approach) from ATs present in multiple strains with six prevalent HLA types studied from each country. A total of 7 and 5 ATs in S-VDI, 11 and 8 ATs in S-VDII/III and 13 and 8 ATs in S-VDIII were present in multiple Ots TSA sample sequences from India (blue) and South Korea (red), respectively. The overlapping 7 identical ATs present in multiple Ots strains from both India (blue dash lines) and Korea (red dash lines) TSA spacer domains are also shown. B) The range and the median average binding affinities of the peptides predicted from three spacer domains. C) Comparison of unique HBA TCEs from Indian and South Korean TSAs.</p