Research Advances of Leptotrombidium scutellare in China.

Leptotrombidium scutellare is one of the 6 main vectors of scrub typhus in China. It has been found in more than 15 provinces of China. Especially in Yunnan, it was found to be mainly distributed in some mountainous areas with high altitude, low temperature and low precipitation. Rodents and some other small mammals were the most common hosts of L. scutellare. To date, more than 40 host species of L. scutellare have been recorded with very low host specificity, and the main hosts varied in different geographical regions. L. scutellare had a strong resistance against the cold environment, and the temperature and humidity were 2 important factors affecting its growth and development. Among different individuals of their rodent hosts, L. scutellare mites often showed an aggregated distribution pattern, which reflected the interspecific cooperation of the mites. The chromosome karyotype of L. scutellare was 2n=16 and all the 8 pairs of chromosomes were short rod-shaped with metacentric or sub-metacentric types. The isozyme spectrum supported that L. scutellare, L. deliense and L. rubellum were in the same species group. Based on the natural infection, experimental transmission and epidemiological evidence, L. scutellare has been eventually confirmed as the second major vector of scrub typhus in China, which is second only to L. deliense.

Epidemiology of tsutsugamushi disease and its relationship with meteorological factors in Xiamen city, China.

Tsutsugamushi disease (TD) is an acute infectious disease caused by Orientia tsutsugamushi. This study aimed to analyze the epidemiological features of TD, investigate chigger mites and their hosts, and investigate the meteorological factors affecting TD incidence and the host of O. tsutsugamushi in Xiamen city, China. Data on reported TD cases were collected from 2006 to 2018. Spearman's correlation test were used for identifying the relationship between meteorological factors and TD incidence and whether meteorological factors affect the host of O. tsutsugamushi. The incidence of reported TD increased gradually from 2006, reached a peak of 4.59 per 100,000 persons in 2014, and then decreased gradually. The TD incidence was seasonal, with epidemic periods occurred mainly in summer and autumn. Patients aged 40-60 years had the highest proportion of cases, accounting for 44.44% of the total cases. Farmers had the largest number of cases among all occupational groups. Rattus Norvegicus was the most common host, accounting for the largest proportion of rats (73.00%), and the highest rat density was observed in March and October every year. There were significant positive correlations between the number of reported cases and average temperature, sunshine duration, and rainfall as well as between rat density and average temperature. On phylogenetic analysis, 7 sequences of hosts and human TD cases obtained from health records demonstrated the highest similarities to the Kato, Karp, and Gilliam strains. No correlations were observed between rat density, and sunshine duration and rainfall. The transmission of TD in Xiamen city, China, was seasonal, and its incidence was affected by several meteorological factors including average temperature, sunshine duration, and rainfall. However, the host of O. tsutsugamushi was only affected by average temperature.

Relative Abundance of a Vector of Scrub Typhus, Leptotrombidium sialkotense, in Southern Yunnan Province, China.

The chigger mite Leptotrombidium sialkotense is one of the 6 main vectors of scrub typhus in China. Before present study, L. sialkotense was found in some parts of Hunan province, China with a narrow geographical distribution. During field investigation 2016-2017, we found L. sialkotense in Jingha, southern Yunnan, China. Of 15 small mammal host species, L. sialkotense were collected from 6 species of the hosts. Rattus brunneusculus was a dominant host of L. sialkotense, from which 98.3% of the mites were collected. The chigger mite showed a relatively high infestation prevalence (PM=11.7%) and mean abundance (MA=0.5) in comparison with the rest 5 host species. These results reveal a certain host specificity of L. sialkotense to a rat R. brunneusculus. The mite L. sialkotense showed an aggregated distribution on the host (P<0.05). A positive correlation observed between L. sialkotense and the body length of hosts. There was a positive interspecific association between L. sialkotense and 2 other dominant vectors, L. deliense and L. scutellare.

Clinical profile, complications and outcome of scrub typhus in children: A hospital based observational study in central Nepal.

BACKGROUND: Scrub typhus, an important cause of unexplained fever, is grossly neglected and often misdiagnosed in low and middle income countries like Nepal. The main aim of this study was to report on the clinical profile and complications of scrub typhus and its outcome in Nepalese children. METHODS: A prospective observational study was carried out in children aged 1-16 years, admitted to a tertiary care hospital of central Nepal in between July 2016- Aug 2017. Scrub typhus was diagnosed with IgM ELISA. RESULTS: All cases of scrub typhus (n = 76) presented with fever and commonly had other symptoms such as headache (75%), myalgia (68.4%), vomiting (64.5%), nausea (59.2%), abdominal pain (57.9%), cough (35.5%), shortness of breath (22.4%), altered sensorium (14.5%), rashes (13.2%) and seizures (11.8%). Important clinical signs noticed were lymphadenopathy (60.5%), hepatomegaly (47.4%), edema (26.3%), jaundice (26.3%), and splenomegaly (15.8%). About 12% (n = 9) had necrotic eschar. Similarly, thrombocytopenia, raised liver enzymes and raised creatinine values were seen in 36.9%, 34.2% and 65.8% respectively. The most common complications were myocarditis (72.4%), hypoalbuminemia (71.1%), severe thrombocytopenia (22.4%), renal impairment (65.8%), hyponatremia (48.7%) and hepatitis (34.2%). Over two-thirds (69.70%) of the cases were treated with doxycycline followed by combination with azithromycin in the remaining 18.4%. Overall, mortality rate in this group was 3.9%. CONCLUSIONS: Scrub typhus should be considered as a differential in any community acquired acute undifferentiated febrile illness regardless of the presence of an eschar. Myocarditis and acute kidney injury are important complications which when addressed early can prevent mortality. Use of doxycycline showed a favorable outcome.

Research Progress on Leptotrombidium deliense.

This article reviews Leptotrombidium deliense, including its discovery and nomenclature, morphological features and identification, life cycle, ecology, relationship with diseases, chromosomes and artificial cultivation. The first record of L. deliense was early in 1922 by Walch. Under the genus Leptotrombidium, there are many sibling species similar to L. deliense, which makes it difficult to differentiate L. deliense from another sibling chigger mites, for example, L. rubellum. The life cycle of the mite (L. deliense) includes 7 stages: egg, deutovum (or prelarva), larva, nymphochrysalis, nymph, imagochrysalis and adult. The mite has a wide geographical distribution with low host specificity, and it often appears in different regions and habitats and on many species of hosts. As a vector species of chigger mite, L. deliense is of great importance in transmitting scrub typhus (tsutsugamushi disease) in many parts of the world, especially in tropical regions of Southeast Asia. The seasonal fluctuation of the mite population varies in different geographical regions. The mite has been successfully cultured in the laboratory, facilitating research on its chromosomes, biochemistry and molecular biology.

A review of the global epidemiology of scrub typhus.

Scrub typhus is a serious public health problem in the Asia-Pacific area. It threatens one billion people globally, and causes illness in one million people each year. Caused by Orientia tsutsugamushi, scrub typhus can result in severe multiorgan failure with a case fatality rate up to 70% without appropriate treatment. The antigenic heterogeneity of O. tsutsugamushi precludes generic immunity and allows reinfection. As a neglected disease, there is still a large gap in our knowledge of the disease, as evidenced by the sporadic epidemiologic data and other related public health information regarding scrub typhus in its endemic areas. Our objective is to provide a systematic analysis of current epidemiology, prevention and control of scrub typhus in its long-standing endemic areas and recently recognized foci of infection.

Comparison of Preferred Bite Sites Between Mites and Ticks on Humans in Korea.

Identification of mite and tick bite sites provides important clinical information. The predominant mite species in Korea associated with scrub typhus are Leptotrombidium pallidum and Leptotrombidium scutellare The most abundant tick species is Haemaphysalis longicornis To date, there has been no comparative study on preferred bite sites between mites and ticks in humans. This study included a review of medical records and a field study. For mite bite sites, eschars were checked on 506 patients with scrub typhus, confirmed by indirect immunofluorescence assay or nested polymerase chain reaction on the 56-kDa type-specific antigen gene of Orientia tsutsugamushi Tick bite sites were identified and marked on a diagram for 91 patients who experienced tick bites within the previous year through a field epidemiological investigation. The mite and tick bite sites in Koreans were compared. The most frequently observed mite bite sites were the anterior chest, including the axillae (29.1%) and the abdominal region, including the inguinal area (26.1%). Tick bite sites were most frequent on the lower extremities (33.0%), followed by the abdominal region, including the inguinal area (26.4%), and upper extremities (26.4%). The distribution was significantly different between mite and tick bite sites (P < 0.001). There was a statistically significant difference in the mite bite (P = 0.001), but not tick bite sites (P = 0.985), between men and women. This is the first report on the differences between tick and mite bite sites, and may help clinicians reach a rapid diagnosis of mite- or tick-borne infection.

Comparative morphology and ultrastructure of the prosomal salivary glands in the unfed larvae Leptotrombidium orientale (Acariformes, Trombiculidae), a possible vector of tsutsugamushi disease agent.

The prosomal salivary glands of the unfed larvae Leptotrombidium orientale (Schluger) were investigated using transmission electron microscopy. In total, four pairs of the prosomal glands were identified--three pairs, the lateral, the medial and the anterior, belong to the podocephalic system, and one pair, the posterior, is separate having an own excretory duct. All glands are simple alveolar/acinous with prismatic cells arranged around a relatively small intra-alveolar lumen with the duct base. The cells of all glands besides the lateral ones contain practically mature electron-dense secretory granules ready to be discharged from the cells. The secretory granules in the lateral glands undergo formation and maturation due to the Golgi body activity. The cells of all gland types contain a large basally located nucleus and variously expressed rough endoplasmic reticulum. Specialized duct-forming cells filled with numerous freely scattered microtubules are situated in the middle zone of each gland's acinus and form the intra-alveolar lumen and the duct base. Both the acinar (secretory) and the duct-forming cells contact each other via gap junctions and septate desmosomes. Axons of nerve cells come close to the basal extensions of the duct-forming cells where they form the bulb-shaped synaptic terminations. The process of secretion is under the control of the nerve system that provides contraction of the duct-forming cells and discharge of secretion from the secretory cells into the intra-alveolar lumen and further to the exterior. Unfed larvae of L. orientale, the potential vector of tsutsugamushi disease agents, contain the most simply organized salivary secretory granules among known trombiculid larvae, and this secretion, besides the lateral glands, does not undergo significant additional maturation. Thus, the larvae are apparently ready to feed on the appropriate host just nearly after hatching.

Emergence of Schoengastiella ligula as the vector of scrub typhus outbreak in Darjeeling: has Leptotrombidium deliense been replaced?

BACKGROUND: Following a suspected outbreak of scrub typhus in Kurseong, Darjeeling, the Armed Forces Medical College, Pune was requested by the National Institute of Epidemiology and the State authorities to undertake investigation of the ongoing scrub typhus outbreak and suggest containment measures. MATERIALS AND METHODS: The epidemic team undertook clinical, entomological and serological studies to understand the local disease pattern and delineate high risk areas, host diversity by rodent trapping using Sherman traps, mite fauna diversity, abundance and vector species identification by phase contrast microscopy for preparation of electronic database and rodent and human serological studies by Weil Felix and PCR. RESULTS: The results indicate no association of scrub typhus with age and sex (P=0.37 and 0.74 respectively). The maximum cases occurred amongst the tea garden workers (73%) in the age group of 25-44 years. The predominant clinical presentation was fever (100%) with headache (75%), lymphadenopathy (45%) and presence of eschar (76.7%). The dominant host species (50% of trapped rodents) was shrew Suncus murinus, the index animal for scrub typhus, which contributed maximally to the vector abundance (52.96%) with a chigger index of 61.56. The trombiculid mite Schoengastiella ligula was the vector species much against the expected mite vector Leptotrombidium deliense, in the area. The study found the presence and abundance of vector species which corroborated well with the occurrence of cases in the various localities within the subdivisions. CONCLUSION: The study thus establishes Schoengastiella ligula as the vector of scrub typhus outbreak in Kurseong, Darjeeling. Preventive and containment measures with emphasis on reduction of man - vector contact were suggested to the state authorities to contain the outbreak.

Correlation between the concentrations of tumor necrosis factor-alpha and the severity of disease in patients infected with Orientia tsutsugamushi.

BACKGROUND: Patients with tsutsugamushi disease sometimes die if they do not receive appropriate chemotherapy. This study measured the concentration of several cytokines both before and after the administration of tetracyclines, and evaluated the changes in cytokine levels in patient serum to investigate the relationship between serum levels of cytokines and disease severity. METHODS: A total of nine patients were infected with Orientia tsutsugamushi. The diagnosis of tsutsugamushi disease was made using an indirect immunoperoxidase antibody test. The serum concentrations of cytokines were measured using enzyme-linked immunosorbent assays. RESULTS: The levels of interleukin (IL)-10 (mean 71.7 pg/ml) and IL-12p40 (mean 588 pg/ml) were elevated in all patients in the acute phase, above the normal upper limits. Tumor necrosis factor-alpha (TNF-alpha) levels (mean 9.20 pg/ml) were elevated in 89% and interferon-gamma (IFN-gamma) levels (mean 41.0 pg/ml) in 44% of patients. The down-regulation of these overproduced cytokines was observed after chemotherapy. There was a significant correlation between the concentrations of TNF-alpha in the acute phase and the severity of disease (r=0.918). CONCLUSION: The concentration of TNF-alpha may predict the severity of tsutsugamushi disease in the acute infectious phase.

Follow-up analysis on the epidemic strains of Orientia tsutsugamushi in the first outbreak of scrub typhus in Henan Province, China.

To obtain knowledge of the genetic characteristics and types of the epidemic strains of Orientia tsutsugamushi in the first outbreak of scrub typhus in Henan Province, genus and type-specific primers were employed to amplify a fragment of the gene of 56 kDa protein. Serotyping demonstrated that, of the 19 patients [15 patients in recovery phase (10-40 days) and 4 of patients in acute phase (1-7 days)], 4 were infected with Gilliam type, 8 with Kato type, 6 with Karp type, and 1 with an unknown type. Successful genotyping was obtained for only 3 patients, indicating that 2 were infected with Karp type and 1 with Taiwan Kato type. Thus the outbreak of scrub typhus in Henan Province was caused by at least two epidemic strains.

Trombiculid mites (Acari: Trombiculidae) and Rickettsia tsutsugamushi isolated from wild rodents in a new endemic area of Japan.

Investigations of trombiculid mites and Rickettsia tsutsugamushi in wild rodents were made in southern Gifu Prefecture where patients infected with tsutsugamushi disease recently have been found. A total of 16,396 trombiculid mites, consisting of 10 species from three genera, was collected from 170 Apodemus speciosus in two locations. Kani-Sakahogi and Kuze. Leptotrombidium scutellare (Nagayo et al.) (44.0%) was most predominant, followed by L. pallidum (Nagayo et al.) (26.9%); L. fuji (Kuwata et al.) (13.6%); and Gahrliepia saduski Womersley (14.2%). These four species constituted the bulk of the chigger mite fauna. L. scutellare was present from October to February with a remarkably high peak in November, whereas pallidum occurred from November to March with the highest peak in December. L. fuji and G. saduski showed their highest peaks in December and moderate peaks in early summer (April and May). Positive identification of Rickettsia tsutsugamushi in wild rodents from Kani-Sakahogi were found to be 50 and 58.3% in November 1985 and 1986, respectively, and 38.5% in November 1986 from Kuze. R. tsutsugamushi was isolated from chigger mites of an L. pallidum-rich group, displaying the highest titer to Karp strain. Serological investigation of rodents to R. tsutsugamushi antibodies were calculated as 41.6 and 50% positive in November 1985 and 1986 in Kani-Sakahogi, respectively, and 50% in November 1986 in Kuze. The Karp strain was dominant in specificity to antibodies. These results indicate that the surveyed areas have a high probability of occurrence of tsutsugamushi disease, and L. scutellare and L. pallidum may serve as the vectors in these areas. Particularly, we suggest that L. scutellare is the most important vector which has caused a recent outbreak of this disease in southern Gifu Prefecture.

A survey of scrub and murine typhus in the Ancol section of Jakarta, Indonesia.

Rickettsia tsutsugamushi was isolated from L. (L.) arenicola chiggers and three species of rats in an area of scrub and sedge along the Bay of Jakarta. This is the only finding in Indonesia of a cycle of the agent of scrub typhus associated with L. (L.) arenicola. A serologic survey of nearly 300 persons living in two kampungs near the site at which rickettsiae were recovered revealed one individual with antibodies to R. tsutsugamushi. Murine typhus, with a seropositivity rate of 6.5%, may be endemic at low levels.