Concomitant leptospirosis-hantavirus co-infection in acute patients hospitalized in Sri Lanka: implications for a potentially worldwide underestimated problem

Two global (re-)emerging zoonoses, leptospirosis and hantavirus infections, are clinically indistinguishable. Thirty-one patients, hospitalized in Sri Lanka for acute severe leptospirosis, were after exclusion of other potentially involved pathogens, prospectively screened with IgM ELISA for both pathogens. Of these, nine (29·0%) were positive for leptospirosis only, one (3·2%) for hantavirus only, seven (22·5%) for both pathogens concomitantly, whereas 13 (41·9%) remained negative for both. Moreover, in a retrospective study of 23 former patients, serologically confirmed for past leptospirosis, six (26·0%) were also positive in two different IgG ELISA hantavirus formats. Surprisingly, European Puumala hantavirus (PUUV) results were constantly higher, although statistically not significantly different, than Asian Hantaan virus (HTNV), suggesting an unexplained cross-reaction, since PUUV is considered absent throughout Asia. Moreover, RT-PCR on all hantavirus IgM ELISA positives was negative. Concomitant leptospirosis-hantavirus infections are probably heavily underestimated worldwide, compromising epidemiological data, therapeutical decisions, and clinical outcome.

Identification of factors for physicians to facilitate early differential diagnosis of scrub typhus, murine typhus, and Q fever from dengue fever in Taiwan

BACKGROUND

Dengue fever, rickettsial diseases, and Q fever are acute febrile illnesses with similar manifestations in tropical areas. Early differential diagnosis of scrub typhus, murine typhus, and Q fever from dengue fever may be made by understanding the distinguishing clinical characteristics and the significance of demographic and weather factors.

METHODS

We conducted a retrospective study to identify clinical, demographic, and meteorological characteristics of 454 dengue fever, 178 scrub typhus, 143 Q fever, and 81 murine typhus cases in three Taiwan hospitals.

RESULTS

Case numbers of murine typhus and Q fever correlated significantly with temperature and rainfall; the scrub typhus case number was only significantly related with temperature. Neither temperature nor rainfall correlated with the case number of dengue fever. The rarity of dengue fever cases from January to June in Taiwan may be a helpful clue for diagnosis in the area. A male predominance was observed, as the male-to-female rate was 2.1 for murine typhus and 7.4 for Q fever. Multivariate analysis revealed the following six important factors for differentiating the rickettsial diseases and Q fever group from the dengue fever group: fever ≥8 days, alanine aminotransferase > aspartate aminotransferase, platelets >63,000/mL, C-reactive protein >31.9 mg/L, absence of bone pain, and absence of a bleeding syndrome.

CONCLUSION

Understanding the rarity of dengue in the first half of a year in Taiwan and the six differentiating factors may help facilitate the early differential diagnosis of rickettsial diseases and Q fever from dengue fever, permitting early antibiotic treatment.

A city park as a potential epidemic site of scrub typhus: a case-control study of an outbreak in Guangzhou, China

BACKGROUND

Scrub typhus is an important public health problem in China, especially in Guangzhou city. Typical outbreaks of scrub typhus have been previously reported in rural areas, affecting mainly farmers. We describe an atypical outbreak of the disease with case fatalities, from a park in Haizhu District, Guangzhou, that could turn out to be a potential scrub typhus epidemic site.

METHODS

From May 2012 to June 2012, a case-control study was conducted to identify source and risk factors of this outbreak. Reported cases of scrub typhus in Xiaogang Park were confirmed by Weil-Felix test or a nested polymerase chain reaction (NPCR). Controls were matched with their neighbors by gender and age. Multivariate conditional logistic regression was used to identify risk factors and protective factors.

RESULTS

A total of 29 cases were confirmed by Weil-Felix test, including 4 deaths by both Weil-Felix test and NPCR. All patients presented with fever (100%), while 28 (96.6%) cases had eschars, 10 (34.5%) headache, 10 (34.5%) chills, 6 (20.7%) lymphadenopathy, 5 (17.2%) rash, 2 (6.9%) vomiting and 1 (3.5%) presented with conjunctival congestion. The proportion of cases with activity history in Xiaogang Park was much higher than the control group (72.4% vs 24.1%, P < 0.001), and morning exercise in park or field was also as a risk factor for scrub typhus (adjusted OR = 3.0, 95% CI: 1.1-8.2). Four factors were significantly associated with the risk of developing scrub typhus: sitting on the lawn (adjusted OR = 8.0, 95% CI: 1.4-44.5), close contact with rats (adjusted OR = 3.3, 95% CI: 1.2-9.6), sitting near the rat holes (OR = 6.8, 95% CI: 1.2-38.1) and wearing long-sleeved clothing when outside (adjusted OR = 0.3, 95% CI: 0.1-0.7).

CONCLUSIONS

We confirmed an atypical outbreak of scrub typhus in a park in Guangzhou city, which has the potential to develop into an important epidemic site. This public health risk should not be neglected and requires more attention from authorities.

Diagnosis of scrub typhus

Scrub typhus is an acute febrile illness that, if untreated, can result in considerable morbidity and mortality. One of the primary reasons for delays in the treatment of this potentially fatal infection is the difficulty in diagnosing the condition. Diagnosis is often complicated because of the combination of non-specific symptoms that overlap with other infections commonly found in endemic areas and the poor available diagnostics. In the majority of the endemic settings, diagnosis still relies on the Weil-Felix test, which is neither sensitive nor specific. Other methods of testing have become available, but at this time, these remain insufficient to provide the rapid point-of-care diagnostics that would be necessary to significantly change the management of this infection by providers in endemic areas. This article reviews the currently available diagnostic tools for scrub typhus and their utility in the clinical setting.

Emerging vector-borne zoonoses: eco-epidemiology and public health implications in India

The diseases originating from animals or associated with man and animals are remerging and have resulted in considerable morbidity and mortality. The present review highlights the re-emergence of emerging mainly zoonotic diseases like chikungunya, scrub typhus, and extension of spatial distribution of cutaneous leishmaniasis from western Rajasthan to Himachal Pradesh, Kerala, and Haryana states; West Nile virus to Assam, and non-endemic areas of Japanese encephalitis (JE) like Maharashtra and JE to Delhi; Crimean-Congo hemorrhagic fever making inroads in Ahmedabad; and reporting fifth parasite of human malaria with possibility of zoonosis have been highlighted, which necessitates further studies for prevention and control. Emphasis has been given on understanding the ecology of reservoir hosts of pathogen, micro niche of vector species, climatic, socioeconomic risk factors, etc. Development of facilities for diagnosis of virus from insects, reservoirs, and human beings (like BSL4, which has been established in NIV, Pune), awareness about symptoms of new emerging viral and other zoonotic diseases, differential diagnosis, risk factors (climatic, ecological, and socioeconomic) and mapping of disease-specific vulnerable areas, and mathematical modeling for projecting epidemiological scenario is needed for preparedness of public health institutes. It is high time to understand the ecological link of zoonotic or anthroponotic diseases for updated risk maps and epidemiological knowledge for effective preventive and control measures. The public health stakeholders in India as well as in Southeast Asia should emphasize on understanding the eco-epidemiology of the discussed zoonotic diseases for taking preventive actions.

Acute encephalitis syndrome following scrub typhus infection

Objective:

The aim was to find the incidence of acute encephalitis syndrome (AES) secondary to scrub infection and to observe the clinical, biochemical, radiological profile, and outcomes in these patients.

Materials and Methods:

A total of 20 consecutive patients of AES were evaluated for scrub infection using scrub typhus immunoglobulin M enzyme linked immuno-sorbant assay positivity along with the presence or absence of an eschar. Clinical profile, routine laboratory tests, cerebrospinal fluid (CSF) analysis, and neuroimaging were analyzed. Patients were treated with doxycycline and followed-up.

Results:

Among 20 consecutive patients with AES, 6 (30%) were due to scrub infection. They presented with acute onset fever, altered sensorium, seizures. Eschar was seen in 50% of patients. CSF done in two of them was similar to consistent with viral meningitis. Magnetic resonance imaging brain revealed cerebral edema, bright lesions in the putamen and the thalamus on T2-weighted and fluid-attenuated inversion recovery sequences. Renal involvement was seen in all patients. All patients responded well to oral doxycycline.

Conclusion:

AES is not an uncommon neurological presentation following scrub typhus infection. It should be suspected in all patients with fever, altered sensorium, and renal involvement. Oral doxycycline should be started as early as possible for better outcomes.

Estimation of the genome sizes of the chigger mites Leptotrombidium pallidum and Leptotrombidium scutellare based on quantitative PCR and k-mer analysis

BACKGROUND

Leptotrombidium pallidum and Leptotrombidium scutellare are the major vector mites for Orientia tsutsugamushi, the causative agent of scrub typhus. Before these organisms can be subjected to whole-genome sequencing, it is necessary to estimate their genome sizes to obtain basic information for establishing the strategies that should be used for genome sequencing and assembly.

METHOD

The genome sizes of L. pallidum and L. scutellare were estimated by a method based on quantitative real-time PCR. In addition, a k-mer analysis of the whole-genome sequences obtained through Illumina sequencing was conducted to verify the mutual compatibility and reliability of the results.

RESULTS

The genome sizes estimated using qPCR were 191 ± 7 Mb for L. pallidum and 262 ± 13 Mb for L. scutellare. The k-mer analysis-based genome lengths were estimated to be 175 Mb for L. pallidum and 286 Mb for L. scutellare. The estimates from these two independent methods were mutually complementary and within a similar range to those of other Acariform mites.

CONCLUSIONS

The estimation method based on qPCR appears to be a useful alternative when the standard methods, such as flow cytometry, are impractical. The relatively small estimated genome sizes should facilitate whole-genome analysis, which could contribute to our understanding of Arachnida genome evolution and provide key information for scrub typhus prevention and mite vector competence.

Scrub typhus complicated by acute respiratory distress syndrome and multiorgan failure; an unrecognized alarming entity in central India: a report of two cases

Scrub typhus is an acute infectious illness, distributed throughout the Asia Pacific rim. In India, it has been reported from northern, eastern, and southern India. However, cases of scrub typhus have not been well-documented from Vidarbha, an eastern region of Maharashtra state in central India. We report two cases of complicated scrub typhus from Vidarbha region. These cases admitted in unconscious state with 8-10 days history of fever, body ache, cough, and progressive breathlessness. The diagnosis in both cases was based on presence of eschar, a positive Weil-Felix test, and a positive rapid diagnostic test (immunochromatographic assay). Both cases were complicated by acute respiratory distress syndrome (ARDS) and multiorgan failure. Both of them presented in their 2^nd week of illness and died during the hospital course in spite of intensive supportive care. The main cause of mortality was delayed referral leading to delay in diagnosis and treatment.

Multiple eschars in scrub typhus

An eschar is highly suggestive of scrub typhus in a case of fever. Multiple eschars are rare in scrub typhus. We present a picture of multiple eschars in scrub typhus.

Transient adrenal insufficiency and post-treatment bradycardia in scrub typhus - a case report

Scrub typhus appears throughout the Asia-Pacific rim. This disease is known for its diverse clinical manifestations and complications. There is no literature on the association of scrub typhus with adrenal insufficiency. Relative bradycardia has been reported in scrub typhus during the febrile phase but not during convalescence. We report the case of a 45- year-old woman with scrub typhus whose blood pressure was persistently low due to acute adrenal insufficiency. Adrenal failure responded to supplementation with steroids. She also developed sinus bradycardia during the afebrile period following treatment.

Meteorological factors and risk of scrub typhus in Guangzhou, southern China, 2006-2012

BACKGROUND

Scrub typhus is becoming the most common vector born disease in Guangzhou, southern China. In this study, we aimed to examine the effect of weather patterns on the incidence of Scrub typhus in the subtropical city of Guangzhou for the period 2006-2012, and assist public health prevention and control measures.

METHODS

Scrub typhus reported cases during the period of 2006-2012 in Guangzhou were obtained from National Notifiable Disease Report System (NNDRS). Simultaneous meteorological data including temperature, relative humidity, atmospheric pressure, sunshine, and rainfall were obtained from the documentation of the Guangzhou Meteorological Bureau. A negative binomial regression was used to identify the relationship between meteorological variables and scrub typhus.

RESULTS

Annual incidence rates of scrub typhus from 2006 to 2012 were 3.25, 2.67, 3.81, 4.22, 4.41, 5.12, and 9.75 (per 100 000) respectively. Each 1°C rise in temperature corresponded to an increase of 14.98% (95% CI 13.65% to 16.33%) in the monthly number of scrub typhus cases, while a 1 hPa rise in atmospheric pressure corresponded to a decrease in the number of cases by 8.03% (95% CI -8.75% to -7.31%). Similarly, a 1 hour rise in sunshine corresponded to an increase of 0.17% or 0.54%, and a 1 millimeter rise in rainfall corresponded to an increase of 0.05% or 0.10%, in the monthly number of scrub typhus cases, depending on the variables considered in the model.

CONCLUSION

Our study provided evidence that climatic factors were associated with occurrence of scrub typhus in Guangzhou city, China. Temperature, duration of sunshine, and rainfall were positively associated with scrub typhus incidence, while atmospheric pressure was inversely associated with scrub typhus incidence. These findings should be considered in the prediction of future patterns of scrub typhus transmission.

Outbreak of scrub typhus in North India: a re-emerging epidemic

Scrub typhus is re-emerging in India. We describe an outbreak of 45 cases from our tertiary care center in north India. This outbreak included city dwellers who had no history of travel to hilly areas. The classical feature of scrub typhus, the eschar, was also noted rarely in these patients. The changing epidemiology of scrub typhus should be kept in mind while attending patients with acute febrile illness.

Genetic variants of Orientia tsutsugamushi in domestic rodents, northern China

We screened Orientia tsutsugamushi from 385 domestic rodents and 19 humans with scrub typhus in rural Tai’an District, Shandong Province, a new scrub typhus epidemic area in northern China. Sequence analysis identified 7 genotypes in the rodents, of which 2 were also identified in the humans.

Rhabdomyolysis in scrub typhus: an unusual presentation

Scrub typhus is the most common zoonosis of public health importance in rural areas of Asia, Northern Australia and Pacific Islands. The clinical spectrum of the disease varies from acute febrile illness to multi-organ involvement with systemic complications. Delay in diagnosis and treatment often lead to increased morbidity and mortality. Rhabdomyolysis is a rare complication seen in an infectious disease. We report a 50-year-old farmer with scrub typhus presented with rhabdomyolysis and acute renal failure who succumbed to the disease in hospital.

Scrub typhus and malaria co-infection causing severe sepsis

We report a case of dual infection of scrub typhus and malaria in a 48-year-old woman.

Central nervous system involvement in scrub typhus

Scrub typhus is an emerging infectious disease in India. Among its protean clinical manifestations, central nervous system involvement is common. In this prospective observational study, altered sensorium, headache, seizures and aseptic meningitis were found to be common central nervous system manifestations. Prompt treatment with doxycycline reduces morbidity and mortality.

Scrub typhus outbreak, northern Thailand, 2006-2007

During a scrub typhus outbreak investigation in Thailand, 4 isolates of O. tsutsugamushi were obtained and established in culture. Phylogenetic analysis based on the 56-kDa type-specific antigen gene demonstrated that the isolates fell into 4 genetic clusters, 3 of which had been previously reported and 1 that represents a new genotype.

Are there spatial and temporal correlations in the incidence distribution of scrub typhus in Korea?

Objectives:

A hierarchical generalized linear model (HGLM) was applied to estimate the transmission pattern of scrub typhus from 2001 to 2011 in the Republic of Korea, based on spatial and temporal correlation.

Methods:

Based on the descriptive statistics of scrub typhus incidence from 2001 to 2011 reported to the Korean Centers for Disease Control and Prevention, the spatial and temporal correlations were estimated by HGLM. Incidences according to age, sex, and year were also estimated by the best-fit model out of nine HGLMs. A disease map was drawn to view the annual regional spread of the disease.

Results:

The total number of scrub typhus cases reported from 2001 to 2011 was 51,136: male, 18,628 (36.4%); female, 32,508 (63.6%). The best-fit model selected was a combination of the spatial model (Markov random-field model) and temporal model (first order autoregressive model) of scrub typhus transmission. The peak incidence was 28.80 per 100,000 persons in early October and the peak incidence was 40.17 per 100,000 persons in those aged 63.3 years old by the best-fit HGLM. The disease map showed the spread of disease from the southern central area to a nationwide area, excepting Gangwon-do (province), Gyeongsangbuk-do (province), and Seoul.

Conclusion:

In the transmission of scrub typhus in Korea, there was a correlation to the incidence of adjacent areas, as well as that of the previous year. According to the disease map, we are unlikely to see any decrease in the incidence in the near future, unless ongoing aggressive measures to prevent the exposure to the vector, chigger mites, in rural areas, are put into place.

Spatial distribution analysis of scrub typhus in Korea

OBJECTIVE

This study analyzes the spatial distribution of scrub typhus in Korea.

METHODS

A spatial distribution of Orientia tsutsugamushi occurrence using a geographic information system (GIS) is presented, and analyzed by means of spatial clustering and correlations.

RESULTS

The provinces of Gangwon-do and Gyeongsangbuk-do show a low incidence throughout the year. Some districts have almost identical environmental conditions of scrub typhus incidence. The land use change of districts does not directly affect the incidence rate.

CONCLUSION

GIS analysis shows the spatial characteristics of scrub typhus. This research can be used to construct a spatial-temporal model to understand the epidemic tsutsugamushi.

Elevated procalcitonin is associated with increased mortality in patients with scrub typhus infection needing intensive care admission

Context:

Procalcitonin is a biomarker of bacterial sepsis. It is unclear if scrub typhus, a rickettsial illness, is associated with elevated procalcitonin levels.

Aim:

To assess if scrub typhus infection is associated with high procalcitonin levels and whether high levels portend a poorer prognosis.

Setting and Design:

Retrospective study of patients with severe scrub typhus infection, admitted to the medical intensive care unit of a tertiary care university affiliated teaching hospital.

Materials and Methods:

Eighty-four patients with severe scrub typhus infection that also had procalcitonin levels were assessed.

Statistical Analysis:

Relationship between procalcitonin and mortality explored using univariate and multivariate analyses.

Results:

The mean (±standard deviation) age was 40.0 ± 15.5 years. Patients were symptomatic for 8.3 ± 4.3 days prior to presentation. The median admission procalcitonin level was 4.0 (interquartile range 1.8 to 8.5) ng/ml; 59 (70.2%) patients had levels >2 ng/ml. Invasive mechanical ventilation was required in 65 patients; 20 patients died. On univariate analysis, admission procalcitonin was associated with increased odds of death [odds ratio (OR) 1.09, 95% confidence interval (CI) 1.03 to 1.18]. On multivariate logistic regression analysis including procalcitonin and APACHE-II score, the APACHE-II score was significantly associated with mortality (OR 1.16, 95% CI 1.06 to 1.30, P = 0.004) while a trend was observed with procalcitonin (OR 1.05, 95%CI 1.01 to 1.13, P = 0.09). The area under the receiver operating characteristic (ROC) curve, AUC, for mortality was 0.77 for procalcitonin and 0.78 for APACHE-II.

Conclusions:

Procalcitonin is elevated in severe scrub typhus infection and may be associated with higher mortality.

Scrub typhus

Scrub typhus is an acute febrile illness caused by orientia tsutsugamushi, transmitted to humans by the bite of the larva of trombiculid mites. It causes a disseminated vasculitic and perivascular inflammatory lesions resulting in significant vascular leakage and end-organ injury. It affects people of all ages and even though scrub typhus in pregnancy is uncommon, it is associated with increased foetal loss, preterm delivery, and small for gestational age infants. After an incubation period of 6-21 days, onset is characterized by fever, headache, myalgia, cough, and gastrointestinal symptoms. A primary papular lesion which later crusts to form a flat black eschar, may be present. If untreated, serious complications may occur involving various organs. Laboratory studies usually reveal leukopenia, thrombocytopenia, deranged hepatic and renal function, proteinuria and reticulonodular infiltrate. Owing to the potential for severe complications, diagnosis, and decision to initiate treatment should be based on clinical suspicion and confirmed by serologic tests. A therapeutic trial of tetracycline or chloramphenicol is indicated in patients in whom the diagnosis of scrub typhus is suspected. The recommended treatment regimen for scrub typhus is doxycycline. Alternative regimens include tetracycline, chloramphenicol, azithromycin, ciprofloxacin, rifampicin, and roxithromycin. Treatment of pregnant women with azithromycin was successfully done without relapse and with favorable pregnancy outcomes. Hence, early diagnosis and treatment are essential in order to reduce the mortality and the complications associated with the disease. We searched the English-language literature for reports of scrub typhus in children, pregnant women, and non-pregnant patients with scrub typhus, using the MEDLINE/PubMed database, which includes citations from 1945 to the present time. We used the search terms 'scrub typhus', 'scrub typhus' and 'pregnancy', 'scrub typhus' and 'children', 'scrub typhus' and 'complications', 'scrub typhus' and 'treatment'.

Natural Scrub Typhus Antibody Suppresses HIV CXCR4(X4) Viruses

Viral load generally rises in HIV-infected individuals with a concomitant infection, but falls markedly in some individuals with scrub typhus (ST), a common Asian rickettsial infection. ST infection appears to shift the viral population from CXCR4-using (X4) to CCR5-utilizing (R5) strains, and there is evidence of cross-reactivity between ST-specific antibodies and HIV-1. We examined the mechanism of ST suppression of HIV by measuring the effects of ST infection on X4 and R5 viruses in vivo and in vitro, and assessing the relative contributions of antibodies and chemokines to the inhibitory effect. In vivo, a single scrub typhus plasma infusion markedly reduced the subpopulation of HIV-1 viruses using the X4 co-receptor in all 8 recipients, and eliminated X4 viruses 6 patients. In vitro, the 14 ST sera tested all inhibited the replication of an X4 but not an R5 virus. This inhibitory effect was maintained if ST sera were depleted of chemokines but was lost upon removal of antibodies. Sera from STinfected mice recognized a target that co-localized with X4 HIV gp120 in immunofluorescent experiments. These in vivo and in vitro data suggest that acute ST infection generates cross-reactive antibodies that produce potent suppression of CXCR4- but not CCR5-using HIV-1 viruses. ST suppression of HIV replication could reveal novel mechanisms that could be exploited for vaccination strategies, as well as aid in the development of fusion inhibitors and other new therapeutic regimens. This also appears to be the first instance where one pathogen is neutralized by antibody produced in response to infection by a completely unrelated organism.

Trends in the incidence of scrub typhus: the fastest growing vector-borne disease in Korea

Scrub typhus, also called tsutsugamushi disease, is classified as a Group 3 disease in Korea according to the National Notifiable Diseases Surveillance Systems. It is an infectious disease transmitted to humans through the bite of mites that are infected with an intracellular parasite called Orientia tsutsugamushi (Family: Rickettsiaceae). This study aims to identify the demographic characteristics of the infected cases according to profession, region, gender, and onset period and provide a basic data for prevention and control of the disease in the infected patients. Between 2001 and 2010, 16,741 men (36.3%) and 29,373 women (63.7%) were reported to have been infected with scrub typhus, with men being 1.6 times less infected than women. When classified according to age, it was found that 4421 persons (9.6%) were under 40 years of age; 6601 (13.1%) in their 40s; 9714 (21.1%) in their 50s; 13,067 (28.3%) in 60s; 10,128 (22.0%) in their 70s; and 2723 (5.9%) aged 80 or more. The elderly (60 years or older) represented more than half of the infected cases. When the infections were classified according to region, it was found that the county residents had the major share of infection, with a total of 1583 infected cases (59.85).

Approaches to vaccines against Orientia tsutsugamushi

Scrub typhus is a severe mite-borne infection caused by Orientia tsutsugamushi, an obligately intracellular bacterium closely related to Rickettsia. The disease explains a substantial proportion of acute undifferentiated febrile cases that require hospitalization in rural areas of Asia, the North of Australia, and many islands of the Pacific Ocean. Delayed antibiotic treatment is common due to the lack of effective commercially available diagnostic tests and the lack of specificity of the early clinical presentation. The systemic infection of endothelial cells that line the vasculature with Orientia can lead to many complications and fatalities. In survivors, immunity does not last long, and is poorly cross-reactive among numerous strains. In addition, chronic infections are established in an unknown number of patients. All those characteristics justify the pursuit of a prophylactic vaccine against O. tsutsugamushi; however, despite continuous efforts to develop such a vaccine since World War II, the objective has not been attained. In this review, we discuss the history of vaccine development against Orientia to provide a clear picture of the challenges that we continue to face from the perspective of animal models and the immunological challenges posed by an intracellular bacterium that normally triggers a short-lived immune response. We finish with a proposal for development of an effective and safe vaccine for scrub typhus through a new approach with a strong focus on T cell-mediated immunity, empirical testing of the immunogenicity of proteins encoded by conserved genes, and assessment of protection in relevant animal models that truly mimic human scrub typhus.