Search Results (27)

Chiggers are common ectoparasites and the exclusive vector of scrub typhus. From November 2020 to October 2021, a 12-month investigation was conducted at Waxi Village of Binchuan County, Yunnan Province of southwest China, a focus of scrub typhus. A total of 217,671 chiggers collected from 1329 small mammal hosts (belonging to 18 species) at the survey site were taxonomically identified as 115 species and 13 genera in the family Trombiculidae with high species diversity. Among the 115 chigger species identified, there were nine vector species. The prevalence (P_M = 69.38%), mean abundance (MA = 163.79 mites/per examined host), and mean intensity (MI = 236.09 mites/per infested host) were high. Three rodent species, Rattus andamanensis, Apodemus chevrieri, and Mus caroli, were the dominant hosts. Three vector chiggers, L. deliense, L. scutellare, and L. imphalum, were the dominant chiggers, with a constituent ratio (C_r) of 60.72%. The indexes of chigger infestation and community showed varying degrees of monthly and seasonal fluctuations. From August (summer) to September and October (autumn), the Margalef richness index (R), Shannon–Wiener diversity index (H), and Pielou evenness (E) of chiggers were at low levels, but the Simpson dominance index (D) was at a high level. The C_r and infestation indexes (MA, MI) of chiggers were high from August to October in summer and autumn, with abundant vector chiggers (such as L. deliense and L. imphalum) appearing in these seasons. The species richness of chigger community was highest in winter, but lowest in summer. The similarity of the chigger community was very high between August (summer) and September to October (autumn). The evenness of the chigger community was highest in spring and lowest in summer. In conclusion, small mammals are susceptible to chigger infestation with coexistence of multiple vector chigger species. Most chigger species have a wide range of hosts with low host specificity. The abundant vector chiggers (especially L. deliense and L. imphalum) in summer and autumn suggests that the surveillance campaign of scrub typhus and vector chiggers should mainly focus on these two seasons at the survey site. Full article

Scrub typhus has emerged as a life-threatening and increasingly prevalent vector-borne disease. While the spatial and temporal distributions of scrub typhus have been studied by the research community, the main driving factors that influence the spatiotemporal patterns of the disease remain under investigation. Using Guangdong Province as a case study, we combined monthly scrub typhus case data from 2010 to 2019 and environmental and vector-related datasets with a Bayesian hierarchical mixed model to elucidate the spatiotemporal characteristics of the disease. This study revealed that the most highly endemic areas of scrub typhus are concentrated in the western and southern parts of Guangdong Province. A distinct bimodal pattern of scrub typhus was observed, with peaks typically occurring from May to July and October to November. The fitted model indicated that forest, cropland, and chigger mites were positively associated with scrub typhus transmission. Furthermore, climate and vectors were identified as key factors shaping the bimodal seasonal patterns of scrub typhus. Despite data-related limitations, including the treatment of population as a time-invariant variable and the binary simplification of vector suitability, sensitivity analyses confirmed the robustness of the model, offering valuable insights for scrub typhus prevention in Guangdong. Full article

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

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

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 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

Chigger mites (Acari) are common ectoparasites on rodents, and they are the exclusive vector of scrub typhus. South China field mouse (Apodemus draco) and Lantsang field mouse (A. ilex) are two sibling rodent species. Based on field investigations in southwest China (2001–2015), this paper compared the infestation of these two mouse species with chiggers. Of 42 chigger species identified from two mouse species, 36 were found on A. draco, 11 on A. ilex and 5 common species on both mice. Jaccard similarity index (J = 0.12, J < 0.25) showed a very different species composition of chiggers on two mouse species, and some parameters of the chigger community were also different. The overall mean intensity of chiggers on A. draco (MI = 4.26) was higher than that on A. ilex (MI = 3.91, p < 0.05). The dominant chigger species on A. draco were Trombiculindus yunnanus, Leptotrombidium scutellare (a major vector species in China) and L. sinicum with a total constituent ratio C_r = 42.9% (106/247). Leptorombidium sinicum and L. scutellare independently occurred on A. draco with an association coefficient V = 0.09 (V ≈ 0). The dominant chigger species on A. ilex were L. rusticum, L. densipunctatum and L. gongshanense, with a total C_r = 58.14% (25/43). Leptorombidium rusticum and L. densipunctatum on A. ilex had a slight positive association (V = 0.49, 0.5 < V < 1). All dominant chigger species were unevenly distributed among different individuals of two mouse species. Chigger infestation showed sex bias on different sexes of two mouse species. The species abundance of the chigger community on A. draco was revealed as a log-normal distribution pattern. Full article

Chigger mites are the exclusive vector of scrub typhus. Based on field investigations of 91 survey sites in 5 provincial regions of Southwest China, this paper reported variations of chigger infestation on the oriental house rat (Rattus tanezumi) along various environmental gradients. A total of 149 chigger species were identified from 2919 R. tanezumi in the 5 provincial regions, and Leptotrombidium deliense (a major vector of scrub typhus in China) was the first dominant chigger species, followed by Ascoschoengastia indica and Walchia ewingi. Rattus tanezumi had a stable overall prevalence (PM = 21.10%), mean abundance (MA = 7.01), and mean intensity (MI = 33.20) of chiggers with the same dominant mites in the whole Southwest China in comparison with a previous report in Yunnan Province, but chigger infestations on R. tanezumi varied along different environmental gradients. Rattus tanezumi in mountainous landscape had a higher infestation load of chiggers with higher species diversity than in flatland landscape. The infestation was higher at lower altitudes and latitudes. A high intensity of vegetation coverage was associated with high infestations. The results reflect the environmental heterogeneity of chiggers on the same host species. Warm climate and high relative humidity are beneficial to chigger infestation on R. tanezumi. Full article