Search Results (34)

Introduction: Scrub typhus is a mite-borne infectious disease caused by “Orientia tsutsugamushi”, a bacterium that was formerly classified under the genus Rickettsia. It is transmitted to humans through the bites of infected chigger mites (larval trombiculid mites). However, clinical data on the cardiac manifestations of scrub typhus and their outcomes remain limited. Methods: This research was retrospectively conducted at a tertiary care hospital in South India. The study included all patients admitted from January 2016 to September 2021 who fulfilled the clinical criteria for a diagnosis of scrub typhus. Data were collected for 426 patients. Patients with previously diagnosed heart disease and mixed infections (leptospirosis, dengue fever, blood culture positivity, and COVID-19 positivity) were excluded. Comprehensive assessments of clinical presentation, electrocardiography (ECG), 2D echocardiography, and outcomes, including all-cause mortality and probable myocarditis, were performed. Multivariate regression analysis was performed to identify independent predictors of all-cause mortality and probable myocarditis. Results: Out of 426 patients, 200 (46.9%) were male and 226 (53.1%) were female. The mean age at presentation was 49.29 ± 14.43 years. A total of 108 (25.4%) patients had diabetes and 82 (19.25%) had hypertension. Sinus tachycardia (29.3%) was the most frequent ECG finding. Echocardiographic evidence of probable myocarditis was observed in 20 (4.7%) patients, while 6 (1.4%) patients had isolated RV dysfunction, 4 (0.9%) had biventricular dysfunction, 7 (1.6%) had significant pulmonary hypertension, and 40 (9.4%) had trivial pericardial effusion. A total of 78 (18.3%) patients had acute respiratory distress syndrome. All-cause mortality was observed in 12 (2.8%) patients. A total of 56 (13.1%) patients developed multiorgan dysfunction syndrome (MODS) during their hospitalization. A total of 78 (18.3%) patients were documented to have acute kidney injury (AKI), and 22 (5.2%) patients underwent hemodialysis. Multivariable binary logistic regression analysis revealed that probable myocarditis and MODS were independent predictors of mortality among patients with scrub typhus, and age, female gender, and LV systolic dysfunction were identified as predictors of overall complications, including mortality, probable myocarditis, congestive heart failure, MODS, AKI, and the need for hemodialysis. Conclusions: Probable myocarditis was the most frequent cardiac manifestation noted in patients with scrub typhus, and in addition to MODS, probable myocarditis was an independent predictor of mortality in this cohort. Thus, it is crucial to maintain clinical vigilance regarding the cardiac status of such patients. Full article

Background: Scrub typhus (ST) is caused by Orientia tsutsugamushi (OT) infection, which is transmitted to humans through the bites of infected chiggers. The clinical presentations range from mild to life-threatening multi-organ dysfunction. This report describes a cluster of ST cases involving five oil palm estate workers in Pekan district, Pahang, Malaysia. Methods: The clinical history, laboratory, and entomological investigation were conducted on the patients, including the index case and four suspected cases in the cluster. Polymerase chain reaction (PCR) tests for OT and genotyping were performed on the patients’ blood and urine samples. Serological testing by indirect immunoperoxidase (IIP) test against Rickettsial diseases was also conducted. Principal Findings: Patients presented with fever, myalgia, headache, rash, cough, and eschar. The index case developed severe ST complicated by acute kidney injury (AKI) and respiratory distress, requiring intubation and ventilation at the intensive care unit of a tertiary hospital. ST was confirmed through PCR analysis of a urine sample, showcasing a novel diagnostic approach. The other four cases were confirmed by a four-fold rise in immunoglobulin G (IgG) antibody titers. Conclusions: Oil palm estate workers are at high risk for chigger exposure in Malaysia. Awareness among clinicians and the public of ST is crucial for effective prevention, accurate diagnosis, and optimal management. Full article

Scrub typhus is an acute febrile vector-borne infectious disease caused by Orientia tsutsugamushi (O. tsutsugamushi) and transmitted through the bite of infected chigger mite larvae. Transmission involves complex ecological interactions among vectors, hosts, and environmental factors. Accumulating evidence indicates complex interactions between the scrub typhus incidence and multilevel environmental determinants, encompassing meteorological factors (e.g., temperature, humidity, precipitation, wind speed, sunshine duration, and atmospheric pressure), geographical conditions (e.g., topography, elevation, and landcover), and socioeconomic factors (e.g., economic level, cultural practices, residential conditions, and human behaviors). However, significant discrepancies persist among studies regarding the effect sizes and temporal associations, and the precise mechanisms remain incompletely elucidated. This review synthesizes the evidence on environment–disease relationships, clarifies the methodological inconsistencies, analyzes the potential sources of heterogeneity, and highlights the critical knowledge gaps to inform targeted prevention and control strategies and guide future research priorities. Full article

Background: Antibodies to galactose-alpha-1,3-galactose (alpha-gal), particularly the IgM and IgG isotypes, are abundant in human sera. These antibodies are known to be an important xenotransplantation barrier, but the full implications of these antibodies to health and disease remain incompletely understood. By contrast, IgE to alpha-gal is uncommon in the population but has been associated with tick bites and causally linked with mammalian meat allergy, often now known as alpha-gal syndrome (AGS). To date, there have been few population-based studies that have investigated alpha-gal IgG levels in relation to demographic factors, diet, tick bites, and mammalian meat allergy. Methods: Adults, predominantly healthcare workers, were recruited for a COVID-19 vaccine study. At least one serum sample was collected, and subjects completed questionnaires to provide demographic, diet, and tick exposure data. Alpha-gal IgG, IgE, and total IgG were measured using the ImmunoCAP platform, and blood group was assessed via reverse typing using stored serum. We also assessed alpha-gal IgG levels among subjects with AGS, recruited from an allergy clinic. Results: The median age of the 267 subjects in the vaccine cohort was 42 years, and median alpha-gal IgG levels were 3.0 μg/mL. Alpha-gal IgG levels were higher among the 43 (16.1%) subjects who had alpha-gal IgE sensitization (≥0.1 IU/mL) and among subjects lacking the B blood group antigen (blood groups A and O). Alpha-gal IgG levels did not differ between the subjects who had asymptomatic alpha-gal IgE sensitization and those who had meat allergy. However, both groups had higher alpha-gal IgG levels than subjects who lacked alpha-gal IgE sensitization. Subjects who reported prior tick or chigger bites had higher alpha-gal IgG levels than those without a bite history, regardless of alpha-gal IgE sensitization status. Conclusions: In a population-based cohort, alpha-gal IgG antibodies were found to be prevalent, and levels were increased in subjects with blood groups A and O, subjects who were alpha-gal IgE sensitized, and those who reported a history of tick bites. Full article

Scrub typhus is an emerging chigger-borne disease caused by the obligate intracellular bacterium Orientia tsutsugamushi. Necroptosis is a form of programmed cell death (PCD) mediated by RIPK3 (serine/threonine kinase receptor interacting protein 3) and its downstream effector MLKL (mixed-lineage kinase domain-like). While O. tsutsugamushi modulates apoptosis, another form of PCD, its interplay with necroptosis is unknown. Much of Orientia pathobiology is linked to its ankyrin repeat (AR)-containing effectors (Anks). Two of these, Ank1 and Ank6, share similarities with the cowpox AR protein, vIRD (viral inducer of RIPK3 degradation) that prevents necroptosis. Here, we show that Ank1 and Ank6 reduce RIPK3 cellular levels although not as robustly as and mechanistically distinct from vIRD. Orientia infection lowers RIPK3 amounts and does not elicit necroptosis in endothelial cells. In HeLa cells ectopically expressing RIPK3, Orientia fails to inhibit RIPK3 and MLKL phosphorylation as well as cell death. MLKL colocalization with Orientia or Listeria monocytogenes, another intracytoplasmic pathogen, was not observed. Thus, O. tsutsugamushi reduces cellular levels of RIPK3 and does not elicit necroptosis but cannot inhibit this PCD pathway once it is induced. This study is a first step toward understanding how the relationship between Orientia and necroptosis contributes to scrub typhus pathogenesis. Full article

Chiggers (chigger mites) and gamasid mites are two groups of ectoparasites on rodents, and they can be the vectors or potential vectors of scrub typhus and hemorrhagic fever with renal syndrome (HFRS), while Bower’s white-toothed rat (Berylmys bowersi) can serve as the reservoir host of the diseases. Based on field investigations at 117 survey sites of southwest China, a total of 2512 mites were collected from 55 B. bowersi rats. Under a microscope, these mites were taxonomically identified as 56 distinct species, comprising 37 chigger mite species and 19 gamasid mite species. The mite infestation burdens on B. bowersi were heavy, with a high prevalence (P_M = 85.45%), mean abundance (MA = 45.67), and intensity (MI = 53.45). Of 56 mite species identified, 7 are vectors of scrub typhus and HFRS. Of the seven vector mite species, Leptotrombidium scutellare was one of dominant chigger species, with a higher infestation index on rats (P_M = 21.82%, MA = 7.76) than the other six vector mite species. The sex ratio of female gamasid mites was higher than that of males. The number and infestation of adult gamasid mites were higher than those of immature mites. The infestation indexes of mites on B. bowersi hosts varied with the host’s sex and age and fluctuated along different environmental gradients. The association coefficient (V) showed a slight positive association between chiggers and gamasid mites, suggesting that these two groups of mites may coexist on B. bowersi rats. Spearman correlation coefficients showed positive correlations among some dominant and vector mite species, indicating that some mite species tend to select the same hosts. A total of 69 mite species (47 chigger mite species and 22 gamasid mite species) on B. bowersi were estimated by species rarefaction and extrapolation curves. In conclusion, Berylmys bowersi has a high susceptibility to mite infestation, and it has the potential to harbor abundant mites, with heavy mite burdens. The occurrence of vector mite species, especially L. scutellare (the dominant species), increases the potential risk of transmission and the focus persistence of scrub typhus and HFRS in southwest China. Full article

Scrub typhus is a mite-borne, re-emerging public health problem in India, particularly in Tamil Nadu, South India. More than 40 serotypes of Orientia tsutsugamushi have been documented worldwide. However, the information on the circulation of its molecular sub-types in India is scanty. A retrospective study was conducted among serologically confirmed cases of scrub typhus. DNA isolated from blood was screened by a nested polymerase chain reaction (nPCR) targeting the GroEL and the 56 kDa type-specific antigen (TSA) genes. Out of 59 samples, 14 partial fragments of GroEL and the twelve 56 kDa genes were PCR-amplified and DNA-sequenced. The neighbor-joining (NJ) analysis indicated three distinct phylogenetic clades, including a novel genotype designated as Ot-Thanjavur-Tamil Nadu (Ot-TJTN, 9 nos. 64.3%); Karp-like (4 nos. 28.6%); and Kuroki-Gilliam type (1 no. 7.1%). Also, phylogenetic analysis of twelve 56 kDa variable domains (VDΙ-ΙΙΙ) of TSA gene sequences revealed a distinctive new genotypic cluster of eight samples (66.6%), and the remaining four (33.4%) were Karp-like genotypes. The Simplot analysis for the similarity and event of recombination testing elucidated the existence of the new genotype of the Ot-TJTN cluster, which was undescribed so far, in the Kato and TA716 lineages. The significant findings recommend further studies to understand the ongoing transmission dynamics of different O. tsutsugamushi strains in vector mites, rodent hosts, and humans in this region. Full article

Scrub typhus is caused by intracellular bacteria belonging to the genus Orientia. Until 2010, the endemic region was thought to be restricted to the Asia–Pacific region. Orientia species have recently been discovered in South America, Africa, Europe, and North America. In accordance with these circumstances, we tried to find new or novel bacterial strains in the Republic of Korea (ROK). We found that a new strain of O. tsutsugamushi formed a unique clade based on a 56-kDa type-specific antigen gene and showed 63.2–77.8% similarity to other strains of the same species. Additionally, we identified another sequence with 99.8% similarity to the O3 strain, which has not been recorded in the ROK and whose pathogenicity remains unknown. These findings confirm the diversity of O. tsutsugamushi strains in the ROK, and highlight the need for continued surveillance and further studies to characterize the pathogenicity of this novel bacterial strain. Full article

While urbanization leads to habitat loss for medium and large mammals, small mammals can survive in fragmented habitats. As they are known to be the primary hosts of chigger mites (Acari: Trombiculidae) that transmit scrub typhus, their habitat can be considered the primary distribution area for chigger mites. This study aims to examine the distribution of small mammals and chigger mites in four habitat types and analyzed species richness, mean intensity (MI), dominance, and infestation rate (IR). A total of six small mammal species were captured, 76.8% of which were identified as Apodemus agrarius. Species richness of small mammals was highest in forests, followed by ecotones, grasslands, and agricultural lands. Apodemus agrarius accounted for 61% of the captures in forests, 80% in ecotones, 84% in grasslands, and 50% in agricultural lands, highlighting its varying dominance across habitat types. The MI of chigger mites was higher in grasslands (215.41 ± 20.70) and ecotones (171.67 ± 30.33) and lower in forests (76.67 ± 32.11). The MI of chigger mites was higher in the fall than that in the spring, and according to the MaxEnt model, they had a narrow, dense distribution in the fall and a wide distribution in the spring. These results suggest that inducing increased species richness of small mammalian hosts by habitat management and vegetation diversification may contribute to a reduction in the MI of chigger mites. Full article

Chiggers are the exclusive vector of Orientia tsutsugamushi, which is the causative agent of scrub typhus. Based on the field surveys in southwest China between 2001 and 2022, this paper retrospectively reported the chigger infestation and distribution on the large-eared field mouse (Apodemus latronum), an endemic rodent species in the region, for the first time. A total of 933 chiggers were collected from 501 mice, and these chiggers were identified as 2 families, 8 genera, and 61 species. The overall infestation prevalence (P_M) and mean abundance (MA) of A. latronum with chiggers reached 19.76% and 1.86 mites/per mouse, respectively. The chigger infestation indices on adult A. latronum (P_M = 38.28%, MA = 5.11) were higher than those on juvenile mice (P_M = 12.63%, MA = 0.97) with p < 0.01, showing an age bias of infestation. The relative fatness (K) was used to reflect the nutrition status of the mouse host. The mouse hosts with good nutrition (K = 3.4 ± 0.89 g/cm³) harbored fewer chiggers than the hosts with poor nutrition (K = 2.2 ± 0.90 g/cm³) (p < 0.01). The infestation indices of chiggers on A. latronum obviously fluctuated along different altitude gradients (p < 0.01). With the increase in altitudes, the β diversity of the chigger community showed a gradually increasing tendency. The spillover chord diagram, which was based on indices of PAC (potential for apparent competition), revealed high spillover potentials of dominant chigger species dispersing from high altitude gradients to the lowest one. The chigger abundance was positively correlated with the mean monthly temperature (tmp), mean monthly humidity (hum), the mean monthly precipitation (pre), and the human footprint (hfp), and it was negatively correlated with the altitude (ele) (p < 0.05). The temperature and humidity are the most important factors which influence the chigger infestation. Full article

Chiggers (chigger mites) are a group of tiny arthropods, and they are the exclusive vector of Orientia tsutsugamushi (Ot), the causative agent of scrub typhus (tsutsugamushi disease). Dehong Prefecture in Yunnan Province of southwest China is located on the China–Myanmar border and is an important focus of scrub typhus. Based on the field surveys in Dehong between 2008 and 2022, the present paper reports the infestation and ecological distribution of chiggers on the body surface of rodents and other sympatric small mammals (shrews, tree shrews, etc.) in the region for the first time. The constituent ratio (C_r), prevalence (P_M), mean abundance (MA), and mean intensity (MI) were routinely calculated to reflect the infestation of small-mammal hosts with chiggers. Additionally, the species richness (S), Shannon–Wiener diversity index (H), Simpson dominance index (D), and Pielou’s evenness index (E) were calculated to illustrate the chigger community structure. Preston’s log-normal model was used to fit the theoretical curve of species abundance distribution, and the Chao 1 formula was used to roughly estimate the expected total species. The “corrplot” package in R software (Version 4.3.1) was used to analyze interspecific relationships, and the online drawing software was used to create a chord diagram to visualize the host–chigger associations. From 1760 small-mammal hosts, a total of 9309 chiggers were identified as belonging to 1 family, 16 genera, and 117 species, with high species diversity. The dominant chigger species were Leptotrombidium deliense, Walchia ewingi, and Gahrliepia longipedalis, with a total C_r = 47.65% (4436/9309), among which L. deliense is the most important vector of Ot in China. The overall infestation indexes (P_M, MA, and MI) and community parameters (S, H, and E) of chiggers in the mountainous areas and outdoors were higher than those in the flatland areas and indoors, with an obvious environmental heterogeneity. Leptotrombidium deliense was the dominant species in the flatland and indoors, while G. longipedalis was the prevalent species in the mountainous and outdoor areas. The species abundance distribution of the chigger community conformed to log-normal distribution with the theoretical curve equation: ${S\left(R\right)}^{\prime }=28e^{{-[0.23(R-0)]}^2}$, indicating the existence of many rare species and only a few dominant species in the community. The expected total number of chigger species was roughly estimated to be 147 species, 30 more than the 117 species actually collected, suggesting that some uncommon species may have been missed in the sampling survey. The host–parasite association analysis revealed that one host species can harbor different chigger species, and one chigger species can parasitize different host species with low host specificity. A positive or negative correlation existed among different chigger species, indicating a cooperative or competitive interspecific relationship. The species diversity of chiggers is high in Dehong on the China–Myanmar border, and a large host sample is recommended to find more uncommon species. There is an obvious environmental heterogeneity of the chigger community, with different species diversity and dominant species in different environments. The low host specificity of chiggers and the occurrence of a large number of L. deliense in Dehong, especially in flatland areas and indoors, would increase the risk of persistent transmission of scrub typhus in the region. Full article

Leptotrombidium imphalum is a species of chigger mites, and it can serve as a transmitting vector of scrub typhus. Southwest China is an important focus of scrub typhus. Based on the field investigation in southwest China from 2001 to 2022, this article presents the first report on the distribution and infestation of L. imphalum on rodents and other sympatric small mammals in the region. A total of 2161 L. imphalum were identified from 218 small mammal hosts in 21 of 114 survey sites. The 17 host species of L. imphalum crossed 13 genera and 5 families in 3 orders (Rodentia, Eulipotyphla, and Scandentia), indicating the low host specificity of the mite. The Asian house rat (Rattus tanezumi) was the dominant host species in the 21 sites where L. imphalum were collected, and 49.38% of mites were found on R. tanezumi. Different small mammals had different susceptibility to the infestation of L. imphalum. The prevalence (P_M = 27.66%), infestation mean abundance (MA = 6 mites/per examined host), and mean intensity (MI = 21.69 mites/per infested host) for L. imphalum on the shrew gymnure (Neotetracus sinensis) were much higher than those on other host species (p < 0.05), indicating N. sinensis had a high susceptibility to the infestation of L. imphalum. The infestation indices for L. imphalum on small mammal hosts varied along different altitude and latitude gradients (p < 0.05), indicating the environmental heterogeneity of the mite infestation. Leptotrombidium imphalum exhibited an aggregated distribution among different individuals of its hosts. Besides the low host specificity of L. imphalum, the prevalence of the mite was positively correlated with the occurrence of scrub typhus, indicating the potential risk of the mite. Full article

Scrub typhus is a re-emerging disease caused by Orientia tsutsugamushi, transmitted by mites belonging to the family Trombiculidae. Humans and rodents acquire the infection by the bite of larval mites/chiggers. Suncus murinus, the Asian house shrew, has been reported to harbor the vector mites and has been naturally infected with O. tsutsugamushi. The present study aimed to localize and record O. tsutsugamushi in the tissues and the host response in shrews naturally infected with O. tsutsugamushi. Sheehan’s modified May–Grunwald Giemsa staining was carried out in 365 tissues from 87 animals, and rickettsiae were documented in 87 tissues from 20 animals. Immunohistochemical (IHC) staining, using polyclonal antibodies raised against selected epitopes of the 56-kDa antigen, was carried out, and 81/87 tissue sections were tested positive for O. tsutsugamushi. By IHC, in addition to the endothelium, the pathogen was also demonstrated by IHC in cardiomyocytes, the bronchiolar epithelium, stroma of the lungs, hepatocytes, the bile duct epithelium, the epithelium and goblet cells of intestine, the tubular epithelium of the kidney, and splenic macrophages. Furthermore, the pathogen was confirmed by real-time PCR using blood (n = 20) and tissues (n = 81) of the IHC-positive animals. None of the blood samples and only 22 out of 81 IHC-positive tissues were tested positive by PCR. By nucleotide sequencing of the 56-kDa gene, Gilliam and Karp strains were found circulating among these animals. Although these bacterial strains are highly virulent and cause a wide range of pathological alterations, hence exploring their adaptive mechanisms of survival in shrews will be of significance. Given that the pathogen localizes in various organs following a transient bacteremia, we recommend the inclusion of tissues from the heart, lung, intestine, and kidney of reservoir animals, in addition to blood samples, for future molecular surveillance of scrub typhus. Full article

Mites are highly prevalent arthropods that infest diverse ecological niches globally. Approximately 55,000 species of mites have been identified but many more are yet to be discovered. Of the ones we do know about, most go unnoticed by humans and animals. However, there are several species from the Acariformes superorder that exert a significant impact on global human health. House dust mites are a major source of inhaled allergens, affecting 10–20% of the world’s population; storage mites also cause a significant allergy in susceptible individuals; chiggers are the sole vectors for the bacterium that causes scrub typhus; Demodex mites are part of the normal microfauna of humans and their pets, but under certain conditions populations grow out of control and affect the integrity of the integumentary system; and scabies mites cause one of the most common dermatological diseases worldwide. On the other hand, recent genome sequences of mites provide novel tools for mite control and the development of new biomaterial with applications in biomedicine. Despite the palpable disease burden, mites remain understudied in parasitological research. By better understanding mite biology and disease processes, researchers can identify new ways to diagnose, manage, and prevent common mite-induced afflictions. This knowledge can lead to improved clinical outcomes and reduced disease burden from these remarkably widespread yet understudied creatures. Full article

Neoschoengastia gallinarum is widely distributed in Asia, preferentially parasitising birds, and heavy infestations have clinical impacts on domestic fowl. In common with other trombiculid mites, the genetic diversity and potential variation in host preferences or pathology induced by N. gallinarum are poorly understood. This study aimed to unravel the geographical variation and population structure of N. gallinarum collected from galliform birds in Peninsular Malaysia and Thailand by inference from concatenated mitochondrial-encoded cytochrome c oxidase subunit I (COI), and nuclear-encoded internal transcribed spacer 2 (ITS2) and 18S ribosomal DNA gene sequences, including a comparison with previously published data from southeastern China. Our multi-locus sequence analysis revealed three monophyletic clades comprising (A) specimens from Peninsular Malaysia, (B) the samples from Thailand together with a minority of Chinese sequences, and (C) the majority of sequences from China. Similarly, most species delimitation approaches divided the specimens into three operational taxonomic units. Analysis of molecular variance revealed 96.41% genetic divergence between Malaysian and Thai populations, further supported by the absence of gene flow (Nm = 0.01). In conclusion, despite the two countries sharing a land border, populations of N. gallinarum from Peninsular Malaysia and Thailand appear to be genetically segregated and may represent distinct cryptic species. Full article