Strategies for detecting rickettsiae and diagnosing rickettsial diseases

Leptospira spp. and Rickettsia spp. as pathogens with zoonotic potential causing acute undifferentiated febrile illness in a central-eastern region of Peru

OBJETIVE

this study was to determine the relationship between acute febrile illness and bacterial pathogens with zoonotic potential that cause emerging and re-emerging diseases in a central-eastern region of Peru.

RESULTS

Out of the 279 samples analyzed, 23 (8.2%) tested positive for infection by Rickettsia spp., while a total of 15 (5.4%) tested positive for Leptospira spp. Women had a higher frequency of infection by Rickettsia spp., with 13 cases (53.3%), while men had a higher frequency of infection by Leptospira spp., with 10 cases (66.7%). The most frequently reported general symptom was headache, with 100.0% (n = 23) of patients with Rickettsia (+) and 86.7% (n = 13) of patients with Leptospira (+) experiencing it. Arthralgia was the second most frequent symptom, reported by 95.6% (n = 22) and 60% (n = 9) of patients with Rickettsia (+) and Leptospira (+), respectively. Myalgia was reported by 91.3% (n = 21) and 66.7% (n = 10) of patients with Rickettsia (+) and Leptospira (+), respectively. Retroocular pain, low back pain, and skin rash were also present, but less frequently. Among the positives, no manifestation of bleeding was recorded, although only one positive case for Leptospira spp. presented a decrease in the number of platelets.

A proof of concept for a targeted enrichment approach to the simultaneous detection and characterization of rickettsial pathogens from clinical specimens

Infection with either Rickettsia prowazekii or Orientia tsutsugamushi is common, yet diagnostic capabilities are limited due to the short window for positive identification. Until now, although targeted enrichment had been applied to increase sensitivity of sequencing-based detection for various microorganisms, it had not been applied to sequencing of R. prowazekii in clinical samples. Additionally, hybridization-based targeted enrichment strategies had only scarcely been applied to qPCR of any pathogens in clinical samples. Therefore, we tested a targeted enrichment technique as a proof of concept and found that it dramatically reduced the limits of detection of these organisms by both qPCR and high throughput sequencing. The enrichment methodology was first tested in contrived clinical samples with known spiked-in concentrations of R. prowazekii and O. tsutsugamushi DNA. This method was also evaluated using clinical samples, resulting in the simultaneous identification and characterization of O. tsutsugamushi directly from clinical specimens taken from sepsis patients. We demonstrated that the targeted enrichment technique is helpful by lowering the limit of detection, not only when applied to sequencing, but also when applied to qPCR, suggesting the technique could be applied more broadly to include other assays and/or microbes for which there are limited diagnostic or detection modalities.

Bat-associated microbes: Opportunities and perils, an overview

The potential biotechnological uses of bat-associated bacteria are discussed briefly, indicating avenues for biotechnological applications of bat-associated microbes. The uniqueness of bats in terms of their lifestyle, genomes and molecular immunology may predispose bats to act as disease reservoirs. Molecular phylogenetic analysis has shown several instances of bats harbouring the ancestral lineages of bacterial (Bartonella), protozoal (Plasmodium, Trypanosoma cruzi) and viral (SARS-CoV2) pathogens infecting humans. Along with the transmission of viruses from bats, we also discuss the potential roles of bat-associated bacteria, fungi, and protozoan parasites in emerging diseases. Current evidence suggests that environmental changes and interactions between wildlife, livestock, and humans contribute to the spill-over of infectious agents from bats to other hosts. Domestic animals including livestock may act as intermediate amplifying hosts for bat-origin pathogens to transmit to humans. An increasing number of studies investigating bat pathogen diversity and infection dynamics have been published. However, whether or how these infectious agents are transmitted both within bat populations and to other hosts, including humans, often remains unknown. Metagenomic approaches are uncovering the dynamics and distribution of potential pathogens in bat microbiomes, which might improve the understanding of disease emergence and transmission. Here, we summarize the current knowledge on bat zoonoses of public health concern and flag the gaps in the knowledge to enable further research and allocation of resources for tackling future outbreaks.

Isothermal amplification technology (IAT) for rapid diagnosis of Rickettsioses: scope, overview, existing evidence, and the way forward

Rickettsioses, a category of zoonosis primarily caused by Rickettsia and Orientia, is a huge cause of public health concern worldwide. Diseases like murine typhus, scrub typhus, Mediterranean spotted fever and rocky mountain spotted fever are major contributors of Rickettsioses globally, with peculiar distributions in south-east Asia, Africa, Arabia and the Americas. With the innovations in molecular diagnostics, Isothermal Amplification Technology is gaining popularity for its fidelity, rapidity and cost-effectiveness. Compared to commercial assays, they are easily adaptable for point-of-care (PoC) settings. Due to nonspecific presentation as an acute undifferentiated febrile illness, diagnosis of Rickettsioses poses a great challenge. Certain isothermal amplification assays have proven to be highly efficient in diagnosing vector borne diseases like dengue, malaria, and chikungunya. The purpose of this review is to provide readers the current advancements, scope, challenges, and future prospects of isothermal amplification technologies in the detection of zoonotic pathogens like Rickettsia and Orientia.

Geographical distribution of scrub typhus and risk of Orientia tsutsugamushi infection in Indonesia: Evidence mapping

BACKGROUND

Scrub typhus is a potentially fatal acute febrile illness caused by bacteria in the genus Orientia. Though cases have been documented, a comprehensive body of evidence has not previously been compiled to give an overview of scrub typhus in Indonesia. This study aimed to address this key knowledge gap by mapping and ranking geographic areas based on existing data on the presence or absence of the pathogen in humans, vectors, and host animals.

METHODOLOGY/PRINCIPAL FINDINGS

We performed searches on local and international electronic databases, websites, libraries, and collections including Embase, Medline, and Scopus to gather relevant evidence (including grey literature). After extracting data on the presence and absence of the pathogen and its vectors, we ranked the evidence based on the certainty for the presence of human infection risk. The country was divided into subnational units, and each were assigned a score based on the evidence available for that unit. We presented this in an evidence map. Orientia tsutsugamushi presence has been identified on all the main islands (Sumatra, Java, Borneo, Celebes, Papua). About two thirds of the data points were collected before 1946. South Sumatra and Biak had the strongest evidence for sustaining infectious vectors. There was only one laboratory confirmed case in a human identified but 2,780 probable cases were documented. The most common vector was Leptotrombidium deliense.

CONCLUSIONS/SIGNIFICANCE

Our review highlights the concerning lack of data on scrub typhus in Indonesia, the fourth most populous country in the world. The presence of seropositive samples, infected vectors and rodents confirm O. tsutsugamushi is widespread in Indonesia and likely to be causing significant morbidity and mortality. There is an urgent need to increase surveillance to better understand the burden of the disease across the archipelago and to inform national empirical fever treatment guidelines.

Molecular detection of Rickettsia, Anaplasma, and Bartonella in ticks from free-ranging sheep in Gansu Province, China

Ticks pose a serious threat to public health as carriers and often vectors of zoonotic pathogens. There are few systematic studies on the prevalence and genetic diversity of tick-borne bacterial pathogens in Western China. In this study, 465 ticks were collected from free-ranging sheep in Gansu Province in China. Ticks were divided into 113 pools and tick DNA was extracted from these ticks. PCR assays were performed using specific primers to screen for tick-borne pathogens as well as sequence analysis based on the 16S rRNA (rrs), ompB, gltA, ompA genes for Rickettsia, rrs, groEL genes for Anaplasma, and ssrA and rpoB genes for Bartonella. The PCR results showed that the minimum infection rates with Rickettsia, Anaplasma, and Bartonella were 16.8% (78/465), 18.9% (88/465), and 0.9% (4/465), respectively. Sequence analysis based on the concatenated sequences of rrs-ompB-gltA-ompA indicated that the Rickettsia species identified in the ticks belonged to Rickettsia raoultii, Rickettsia slovaca, and Rickettsia sibirica, respectively; phylogenetic analysis based on the groEL gene showed that all Anaplasma strains identified were Anaplasma ovis; and phylogenetic analysis based on the ssrA and rpoB genes indicated that all Bartonella strains in the ticks belonged to Bartonella melophagi. The results of this study showed that ticks in Gansu Province harbored multiple pathogens that may cause rickettsial diseases and bartonellosis. These diseases were neglected in the area and physicians and public health workers need to pay attention to their diagnoses to prevent human infection.

Clinical usefulness of metagenomic next-generation sequencing for Rickettsia and Coxiella burnetii diagnosis

Rickettsia and Coxiella burnetii are zoonotic tick-borne pathogens that cause febrile illnesses in humans. Metagenomic next-generation sequencing (mNGS) is a new technology used to diagnose infectious diseases. However, clinical experience with applying the test to rickettsioses and Q fever is relatively limited. Therefore, this study aimed to explore the diagnostic performance of mNGS in detecting Rickettsia and C. burnetii. We retrospectively studied patients with rickettsioses or Q fever between August 2021 and July 2022. Peripheral blood mNGS and polymerase chain reaction (PCR) were performed for all patients. Clinical data were retrieved for analysis. Thirteen patients were included in this study (eleven confirmed cases and two suspected cases). Signs and symptoms included fever (13, 100%), rash (7, 53.8%), muscle soreness (5, 38.5%), headache (4, 30.8%), skin eschar (3, 23.1%), and disturbance of consciousness (2, 15.4%). In addition, eight patients (61.6%) had thrombocytopenia, ten (76.9%) had liver function impairment, and two (15.4%) had renal function impairment. The results of mNGS revealed seven patients with R. japonica (53.8%), five with C. burneti (38.5%), two with R. heilongjiangensis (15.4%), and one with R. honei (7.7%). PCR results were positive in 11 patients (84.6%). After receiving doxycycline-based treatment, 12 (92.3%) patients returned to a normal temperature within 72 h. All patients were discharged in better health. Therefore, mNGS can help diagnose Rickettsia and C. burnetii and shorten the diagnosis time, especially for patients with atypical clinical manifestations and unclear epidemiologic evidence of a tick bite or exposure.

Transovarial transmission of pathogenic protozoa and rickettsial organisms in ticks

Transovarial transmission (TOT) is an efficient vertical transmission of pathogens that is observed in many arthropod vectors. This method seems to be an evolutionarily unique development observed only in Babesia sensu stricto (clade VI) and Rickettsia spp., whereas transstadial transmission is the common/default way of transmission. Transovarial transmission does not necessarily contribute to the amplification of tick-borne pathogens but does contribute to the maintenance of disease in the environment. This review aims to provide an updated summary of previous reports on TOT of tick-borne pathogens.

Diversity of Rickettsiales bacteria in five species of ticks collected from Jinzhai County, Anhui Province, China in 2021-2022

The order Rickettsiales in the class Alphaproteobacteria comprises vector-borne pathogens of both medical and veterinary importance. Ticks, as a group, are second only to mosquitoes as vectors of pathogens to humans, playing a critical role in the transmission of rickettsiosis. In the present study, 880 ticks collected from Jinzhai County, Lu'an City, Anhui Province, China in 2021-2022 were identified as belonging to five species from three genera. DNA extracted from individual ticks was examined using nested polymerase chain reaction targeting the 16S rRNA gene (rrs), and the gene fragments amplified were sequenced to detect and identify Rickettsiales bacteria in the ticks. For further identification, the rrs-positive tick samples were further amplified by PCR targeting the gltA and groEL gene and sequenced. As a result, 13 Rickettsiales species belonging to the genera Rickettsia, Anaplasma, and Ehrlichia were detected, including three tentative species of Ehrlichia. Our results reveal the extensive diversity of Rickettsiales bacteria in ticks from Jinzhai County, Anhui Province. There, emerging rickettsial species may be pathogenic and cause under-recognized diseases. Detection of several pathogens in ticks that are closely related to human diseases may indicate a potential risk of infection in humans. Therefore, additional studies to assess the potential public health risks of the Rickettsiales pathogens identified in the present study are warranted.

Geography and prevalence of rickettsial infections in Northern Tamil Nadu, India: a cross-sectional study

Rickettsial infections and Q fever are a common cause of acute febrile illness globally. Data on the role of climate and altitude on the prevalence of these infections in lacking from Southern India. In this study, we determined the sero-prevalence of scrub typhus (ST), spotted fever (SF), murine typhus (MT) and Q Fever (QF) in 8 eight geographical regions of North Tamil Nadu by detecting IgG antibodies using ELISA. Totally we tested 2565 people from 86 localities. Among the 27.3% positives, approximately 5% were IgG positive for two or more infections. Sero-prevalence to rickettsioses and Q fever was highest for individuals from rural areas and increased with age (> 30 years). Those in the Nilgiris highlands (wetter and cooler) and Erode, which has the most land under irrigation, demonstrated the least exposure to rickettsioses and Q fever. Lowland plains (AOR: 8.4-22.9; 95% CI 3.1-55.3) and highland areas up to 1000 m (AOR: 6.1-10.3; 95% CI 2.4-23.9) showed the highest risk of exposure to scrub typhus. For spotted fever, the risk of exposure was highest in Jawadhi (AOR:10.8; 95% CI 2.6-44.3) and Kalrayan (AOR:16.6; 95% CI 4.1-66.2). Q fever positivity was most likely to be encountered in Salem (AOR: 5.60; 95% CI 1.01-31.08) and Kalrayan hills (AOR:12.3; 95% CI 2.9-51.6). Murine typhus risk was significant only in Tiruvannamalai (AOR:24.2; 95% CI 3.3-178.6). Our study suggests that prevalence of rickettsial infections and Q fever is low in areas which receive rainfall of ≥ 150 cm/year, with average minimum and maximum temperatures between 15 and 25 °C and elevation in excess of 2000 m. It is also less in well irrigated lowlands with dry climate. These preliminary findings need confirmation by active surveillance in these areas.

A community approach for pathogens and their arthropod vectors (ticks and fleas) in cats of sub-Saharan Africa

Background

Arthropod-borne pathogens and their vectors are present throughout Africa. They have been well studied in livestock of sub-Saharan Africa, but poorly studied in companion animals. Given their socioeconomic importance, the African Small Companion Animal Network (AFSCAN), as part of the WSAVA Foundation, initiated a standardized multi-country surveillance study.

Methods

In six countries (Ghana, Kenya, Nigeria, Tanzania, Uganda, and Namibia) in both rural and urban settings, 160 infested cats were sampled to assess their ectoparasite community (ticks and fleas), as well as the micro-parasite prevalence within those ectoparasites (60 and 118 pools of ticks and fleas, respectively) and blood (276 cats, including 116 non-infested).

Results

Almost two thirds of all infested cats originated from Tanzania and Kenya. Despite the large macro-geographical variation, no consistent difference was found in ectoparasite diversity and numbers between East and West Africa. Far more flea-infested than tick-infested cats were found. The most dominant ectoparasite was Ctenocephalides felis. Among the ticks, the exophilic Haemaphysalis spp. were the commonest, including species that are not typically linked with companion animals (Haemaphysalis spinulosa and Haemaphysalis elliptica). The most prevalent pathogens found in the blood and fleas were Bartonella henselae and Mycoplasma haemofelis. In the ticks, the dog-associated Hepatozoon canis was most commonly found. A high degree of co-parasitism was found in all countries and habitats.

Conclusions

Our continent-wide standardized field study highlights the cat’s potential to serve as a reservoir of pathogens that can be transmitted to humans or livestock, especially when cats are expected to become more commonly kept in African villages and towns.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05436-y.

Diagnostic Value of IgA Antibody Measurement in Tick-Borne Spotted Fever (Astrakhan Rickettsial Fever)

Tick-borne spotted fevers caused by Rickettsia occur worldwide. The symptoms of this bacterial infection are similar to those of viral infection, and thus, diagnostic accuracy has special clinical importance. One of the commonly used methods for the diagnosis of tick-borne spotted fever is enzyme-linked immunosorbent assay (ELISA), which is based on estimation of the presence of specific IgM antibodies in blood. However, IgA analysis has not been used for the diagnosis of rickettsial diseases thus far. We investigated the diagnostic value of IgA antibody determination using patient sera collected in the Astrakhan region of Russia, where an isolated site of Astrakhan rickettsial fever (ARF) caused by Rickettsia conorii subsp. caspia is located. Our investigation was performed on serum samples collected from 185 patients diagnosed with Astrakhan rickettsial fever from May to October 2019. Western blot analysis revealed that specific IgA antibodies, as well as IgM antibodies, from patient sera bind to high-molecular-weight pathogen proteins with similar masses. The obtained data show that the determination of IgM alone allows for serological confirmation of diagnosis in only 46.5% of cases but that the determination of both IgM and IgA increases this rate to 66.5%. Taken together, the findings show an important diagnostic value of IgA evaluation for tick-borne spotted fever rickettsiosis. IMPORTANCE Tick-borne spotted fevers caused by Rickettsia occur worldwide. The symptoms of this bacterial infection are similar to the symptoms of viral infection, and thus, diagnostic accuracy has special clinical importance. The most serious spotted fever group rickettsiosis is Rocky Mountain fever in the United States, which is caused by Rickettsia rickettsii, and disease complications can lead to hemiparesis, blindness, or amputation. Rickettsia conorii subsp. caspia causes a rickettsial spotted fever named Astrakhan rickettsial fever (ARF). One of the commonly used methods for the diagnosis of tick-borne spotted fevers is ELISA, which is based on estimation of the presence of specific IgM antibodies in blood, though IgA has not been used for the diagnosis of rickettsial diseases thus far. In this study, we showed that both IgA and IgM should be analyzed in the blood serum samples of patients to significantly enhance the accuracy of diagnostics of tick-borne spotted fever rickettsiosis.

Systematic Surveillance of Rickettsial Diseases in 27 Hospitals from 26 Provinces throughout Vietnam

In Vietnam, the public health burden of rickettsial infections continues to be underestimated due to knowledge gaps in the epidemiology of these diseases. We conducted a systematic study among 27 hospitals from 26 provinces in eight ecological regions throughout Vietnam to investigate the prevalence, distribution, and clinical characteristics of rickettsial diseases. We recruited 1834 patients in the study from April 2018 to October 2019. The findings showed that rickettsial diseases were common among undifferentiated febrile patients, with 564 (30.8%) patients positive by qPCR for scrub typhus, murine typhus or spotted fever. Scrub typhus (484, 85.8%) was the most common rickettsial disease, followed by murine typhus (67, 11.9%) and spotted fever (10, 1.8%). Rickettsial diseases were widely distributed in all regions of Vietnam and presented with nonspecific clinical manifestations.

Utility of ultra-rapid real-time PCR for detection and prevalence of Rickettsia spp. in ticks

Background

Rickettsia spp. are important tick-borne pathogens that cause various human and animal diseases worldwide. A tool for rapid and accurate detection of the pathogens from its vectors is necessary for prevention of Rickettsioses propagation in humans and animals, which are infested by ticks. Therefore, this study was conducted to evaluate a molecular tool, ultra-rapid real-time PCR (UR-qPCR), for rapid and accurate detection of Rickettsia spp. from 5644 ticks in 408 pools collected from livestock and their surrounding environments in Gangwon and Jeju province in South Korea.

Results

The UR-qPCR of Rickettsia DNA showed a limit of detection of 2.72 × 10¹ copies of Rickettsia DNA and no cross reaction with other tick-borne pathogens, namely Anaplasma phagocytophilum, Ehrlichia chaffeensis, E. canis, Toxoplasma gondii, and Borrelia burgdorferi. In addition, the PCR assay also showed possibility of various Rickettsia species detection including R. monacensis, “Candidatus R. longicornii”, R. japonica, R. roultii, and R. tamurae. The collected ticks were identified with major species belonged to Haemaphysalis longicornis (81.62%), followed by H. flava (15.19%), and Ixodes nipponensis (3.19%). Rickettsia detection from tick samples using the UR-qPCR showed that the minimum infection rate (MIR) of Rickettsia in collected ticks was 1.24‰ and that all positive pools contained H. longicornis, equal to the MIR of 1.39‰ of this species. Additionally, MIR of Rickettsia spp. detected in ticks collected in Gangwon and Jeju was 1.53‰ and 0.84‰, respectively. Furthermore, the sequencing results of the 17 kDa protein antigen gene and ompA gene showed that Rickettsia spp. sequences from all pools were related to “Candidatus R. longicornii” and “Candidatus R. jingxinensis”.

Conclusions

The UR-qPCR system was demonstrated to be useful tool for accurate and rapid detection of Rickettsia from its vector, ixodid ticks, within 20 min. The data on Rickettsia spp. in ticks detected in this study provide useful information on the distribution of Rickettsia in previously unstudied Korean provinces, which are important for the prevention and control of the spread of rickettsioses in both animals and humans in the country.

Development of a New Genus-Specific Quantitative Real-Time PCR Assay for the Diagnosis of Scrub Typhus in South America

Scrub typhus is a potentially severe rickettsiosis, caused by Orientia tsutsugamushi in the Asia-Pacific region. Recently, however, two distinct pathogens, “Candidatus Orientia chuto” and “Candidatus Orientia chiloensis”, have been discovered in the Middle East and South America, respectively. Since the novel pathogens differ significantly from O. tsutsugamushi, many established diagnostic methods are unreliable. This work describes the development and validation of a new quantitative real-time PCR (qPCR) assay (Orien16S) for the detection of all known Orientia species. Based on a 94 bp sequence of the 16S rRNA gene (rrs), Orien16S recognized DNA samples from O. tsutsugamushi (n = 41), Ca. O. chiloensis (n = 5), and Ca. O. chuto (n = 1), but was negative for DNA preparations from closely related rickettsiae and other members of the order Rickettsiales (n = 22) as well as unrelated bacterial species (n = 11). After its implementation in Chile, the assay was verified, correctly identifying all tested eschar and buffy coat samples (n = 28) of clinical suspected cases. Furthermore, Orien16S detected Orientia DNA in trombiculid mites collected in endemic regions in southern Chile. The presented novel qPCR assay provides a useful tool for detecting Orientia and diagnosing scrub typhus from all geographical regions.

Risk factors analysis for neglected human rickettsioses in rural communities in Nan province, Thailand: A community-based observational study along a landscape gradient

In this study, we estimated exposure for Scrub typhus (STG), Typhus (TG) and Spotted fever groups (SFG) rickettsia using serology at a fine scale (a whole sub-district administration level) of local communities in Nan Province, Thailand. Geographical characteristics of the sub-district were divided into two landscape types: lowland agricultural area in an urbanized setting (lowland-urbanized area) and upland agricultural area located close to a protected area of National Park (upland-forested area). This provided an ideal contrast between the two landscapes with low and high levels of human-altered habitats to study in differences in disease ecology. In total, 824 serum samples of participants residing in the eight villages were tested by screening IgG ELISA, and subsequently confirmed by the gold standard IgG Immunofluorescent Assay (IFA). STG and TG IgG positivity were highest with seroprevalence of 9.8% and 9.0%, respectively; whereas SFG positivity was lower at 6.9%. Inhabitants from the villages located in upland-forested area demonstrated significantly higher STG exposure, compared to those villages in the lowland-urbanized area (chi-square = 51.97, p < 0.0001). In contrast, TG exposure was significantly higher in those villagers living in lowland-urbanized area (chi-square = 28.26, p < 0.0001). In addition to the effect of landscape types, generalized linear model (GLM) analysis identified socio-demographic parameters, i.e., gender, occupation, age, educational level, domestic animal ownership (dog, cattle and poultry) as influential factors to explain the level of rickettsial exposure (antibody titers) in the communities. Our findings raise the public health awareness of rickettsiosis as a cause of undiagnosed febrile illness in the communities.

Evidence of human exposures to rickettsial pathogens were reported from a cross-sectional study at a whole sub-district scale of local communities in Nan Province, Thailand. Seroprevalence and level of rickettsial exposures demonstrated differences between the habitat types, ecological aspects and socio-demographic factors. In addition, abundance of domestic animals in the community appeared to be one of significant factors influencing levels of human exposure to rickettsial pathogens. Our findings will benefit the local public health by raising awareness of rickettsial infections as one of potential health concerns in the community. Inclusion of rickettsioses in routine laboratory diagnosis would help to differentiate unknown febrile illness and guide appropriate treatment. Further studies are required, particularly in the fields of disease ecology as well as medical and veterinary entomology, in order to better understand epidemiology and potential zoonotic transmission of these neglected rickettsioses in endemic areas.

Changing spectrum of acute encephalitis syndrome in India and a syndromic approach

Acute encephalitis syndrome (AES) refers to an acute onset of fever and clinical neurological manifestation that includes mental confusion, disorientation, delirium, or coma, which may occur because of infectious or non-infectious causes. Cerebrospinal fluid (CSF) pleocytosis generally favors infectious etiology, and a normal CSF favors an encephalopathy or non-infectious AES. Among the infectious AES, viral, bacterial, rickettsial, fungal, and parasitic causes are the commonest. Geographical and seasonal clustering and other epidemiological characteristics are important in clinical decision making. Clinical markers like eschar, skin rash, myalgia, hepatosplenomegaly, thrombocytopenia, liver and kidney dysfunction, elevated serum CK, fronto-temporal or thalamic involvement on MRI, and anterior horn cell involvement are invaluable clues for the etiological diagnosis. Categorizing the AES cases into neurologic [Herpes simplex encephalitis (HSE), Japanese encephalitis (JE), and West Nile encephalitis (WNE)] and systemic (scrub typhus, malaria, dengue, and Chikungunya) helps in rational utilization of diagnostic and management resources. In neurological AES, cranial CT/MRI revealing frontotemporal lesion is consistent with HSE, and thalamic and basal ganglia lesions are consistent with JE. Cerebrospinal fluid nucleic acid detection test or IgM antibody for JE and HSE are confirmatory. Presence of frontotemporal involvement on MRI indicates acyclovir treatment pending virological confirmation. In systemic AES, CT/MRI, PCR for HSE and JE, and acyclovir therapy may not be useful, rather treatable etiologies such as malaria, scrub typhus, and leptospirosis should be looked for. If smear or antigen for malaria is positive, should receive antimalarial, if negative doxycycline and ceftriaxone should be started pending serological confirmation of scrub typhus, leptospira, or dengue. A syndromic approach of AES based on the prevalent infection in a geographical region may be developed, which may be cost-effective.

Comparative evaluation of serological tests used for the diagnosis of rickettsial diseases prevalent in the temperate region of North India

PURPOSE

The clinical manifestations of rickettsial diseases mimic other endemic infections with similar presentations thus posing a serious challenge to clinicians for their diagnosis. For the diagnosis of rickettsial disease serological tests like Weil Felix, ELISA and IFA are used. There are limited studies that have evaluated different serological tests for the diagnosis of rickettsial diseases. Therefore, the present study was undertaken to evaluate the ELISA and Weil Felix test for the diagnosis of rickettsial diseases prevalent in this region.

METHODS

Samples from 281 patients clinically suspected of rickettsial diseases were tested for spotted fever group (SFG), typhus group (TG) and scrub typhus group (STG) by Weil Felix, ELISA and IFA was taken as the gold standard. Baseline titers and cut-off ODs were calculated by taking samples from healthy blood donors.

RESULTS

The sensitivity, specificity, positive and negative predictive value of Weil Felix test ranged from 30% to 44%, 83.46%-97.86%, 9%-77%, 92-96% respectively. The sensitivity and specificity, positive and negative predictive value of ELISA ranged from 80.77% to 96.15%, 96.33%-98.43%, 70.21%-88.64%, 92.89%-99.60% respectively. Maximum cross-reactions were observed between SFG and STG by the Weil Felix test and between STG and TG by ELISA.

CONCLUSIONS

ELISA was found to be sensitive and specific for the diagnosis of rickettsial diseases. It is easy to perform, does not require a technical expert for result interpretation and a large number of samples can be processed at a time.

Microorganisms associated with the North African hedgehog Atelerix algirus and its parasitizing arthropods in Algeria

Hedgehogs are small mammals. They are potential reservoirs of various zoonotic agents. This study was conducted in Bouira, a north-central region of Algeria. A total of 21 Atelerix algirus corpses were picked up on roadsides and gardens. Hedgehog kidneys, spleens and ectoparasites were collected. Twelve hedgehogs were infested with ectoparasites, including Archaeopsylla erinacei, Rhipicephalus sanguineus s.l. and Haemaphysalis erinacei. Hedgehog organs and randomly selected arthropods were screened for microorganisms using molecular methods. Coxiella burnetii was detected in kidneys, spleens, A. erinacei, Hae. erinacei and Rh. sanguineus s.l. Leptospira interrogans was detected in kidneys. Rickettsia felis and Rickettsia massiliae were detected respectively in A. erinacei and in Rh. sanguineus s.l. DNA of an uncultivated Rickettsia spp. was found in Hae. erinacei. Wolbachia spp. DNA was detected in fleas. The DNA of potential new Bartonella and Ehrlichia species were found respectively in fleas and ticks. This study highlights the presence of DNA from a broad range of microorganisms in hedgehogs and their ectoparasites that may be responsible for zoonoses in Algeria.

An Update on the Laboratory Diagnosis of Rickettsia spp. Infection

Rickettsia species causing human illness are present globally and can cause significant disease. Diagnosis and identification of this intracellular bacteria are challenging with many available diagnostic modalities suffering from several shortcomings. Detection of antibodies directed against Rickettsia spp. via serological methods remains widely used with a broad range of sensitivity and specificity values reported depending on the assay. Molecular methods, including polymerase chain reaction (PCR) testing, enables species-specific identification with a fast turnaround time; however, due to resource requirements, use in some endemic settings is limited. Reports on the use of next-generation sequencing (NGS) and metagenomics to diagnose Rickettsia spp. infection have been increasing. Despite offering several potential advantages in the diagnosis and surveillance of disease, genomic approaches are currently only limited to reference and research laboratories. Continued development of Rickettsia spp. diagnostics is required to improve disease detection and epidemiological surveillance, and to better understand transmission dynamics.

Spotted fever diagnosis: Experience from a South Indian center

Spotted fever (SF) is an important treatable cause of acute febrile illness (AFI) with rash and has reemerged in India. A prospective AFI with rash study was undertaken at a South Indian hospital to correlate specific clinical findings with laboratory confirmation of spotted fever. During the study period (December 2017 to May 2019), 175 patients with fever and rash were suspected to have spotted fever. Molecular assays for scrub typhus and spotted fever (47 kDa and ompA qPCR) and serology (IgM ELISA) was performed on the 96 individuals recruited. Laboratory confirmed SF cases (ompA qPCR positive) were 21, whereas laboratory supported SF cases (ompA negative but sero-positive by SF IgM ELISA) were 27. Among the 48 spotted fever (SF) cases, 70% of had maculopapular rash, 12.5% had macular rash, purpuric/petechial rash (severe rash) was seen in 8 patients (16.7%). Presence of rash on the palms and soles was associated with a relative risk (RR) of 4.36 (95% CI: 2.67-7.10; p < 0.001). Our study suggests that ompA qPCR though useful for confirming the diagnosis of spotted fever is not always positive. A positive SF IgM ELISA in febrile individuals with palmo-plantar rash supports the diagnosis of spotted fever especially when other causes of febrile rash have been excluded. Multi-centric prospective studies employing the serological reference standard, IFA (immunofluorescence assay) in addition to the assays used in this study are needed to validate these findings.

Ecological and behavioural risk factors of scrub typhus in central Vietnam: a case-control study

Background

The risk factors for scrub typhus in Vietnam remain unknown. Scrub typhus caused by Orientia tsutsugamushi often presents as an undifferentiated febrile illness and remains under appreciated due to the limited availability of diagnostic tests. This tropical rickettsial illness is increasingly recognized as an important cause of non-malaria acute undifferentiated fever in Asia. This study aimed to investigate behavioural and ecological related risk factors of scrub typhus to prevent this potentially life-threatening disease in Vietnam.

Methods

We conducted a clinical hospital-based active surveillance study, and a retrospective residence-enrolment date-age-matched case–control study in Khanh Hoa province, Vietnam, from August 2018 to March 2020. Clinical examinations, polymerase chain reaction and enzyme-linked immunosorbent assay IgM tests were applied to define cases and controls. All enrolled participants filled out a questionnaire including demographic socio-economic status, personal behaviors/protective equipment, habitat connections, land use, and possible exposure to the vector. Multivariable conditional logistic regression was used to define the scrub typhus associated risk factors.

Results

We identified 44 confirmed cases and matched them with 152 controls. Among cases and controls, the largest age group was the 41–50 years old and males accounted for 61.4% and 42.8%, respectively. There were similarities in demographic characteristics between the two groups, with the exception of occupation. Several factors were significantly associated with acquisition of scrub typhus, including sitting/laying directly on household floor [adjusted OR (aOR) = 4.9, 95% CI: 1.6–15.1, P = 0.006], household with poor sanitation/conditions (aOR = 7.9, 95% CI: 1.9–32.9, P = 0.005), workplace environment with risk (aOR = 3.0, 95% CI: 1.2–7.6, P = 0.020), always observing mice around home (aOR = 3.7, 95% CI: 1.4–9.9, P = 0.008), and use of personal protective equipment in the field (aOR = 0.4, 95% CI: 0.1–1.1, P = 0.076).

Conclusions

Ecological and household hygiene-related factors were more associated with scrub typhus infection, than individual-level exposure activities in the hyper-endemic area. These findings support local education and allow people to protect themselves from scrub typhus, especially in areas with limitations in diagnostic capacity.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s40249-021-00893-6.

SERS-based serodiagnosis of acute febrile diseases using plasmonic nanopopcorn microarray platforms

We report a surface-enhanced Raman scattering (SERS)-based immunoassay platform for the rapid diagnosis of scrub typhus and murine typhus, which are the most common acute febrile diseases in South Korea. A microarray device, composed of multiple gold nanopopcorn substrates capable of detecting ultra-sensitive biomarkers, was used as a multiplex SERS-based assay platform. Sequentially diluted titers of Orientia tsutsugamushi and Rickettsia typhi specific human IgG/IgM antibodies, which are biomarkers of two typhus diseases, were analyzed by Raman spectroscopy, and the peak intensity was plotted against the different titer concentration range (0-2048 and 0-1024 for O. tsutsugamushi IgG/IgM and 0-8192 and 0-256 for R. typhi IgG/IgM) to generate calibration curves. The sensitivities and limits of detection (LODs) determined for four different IgG/IgM antibodies were significantly lower than those for the ELISA method. The LODs of titer concentrations for O. tsutsugamushi IgG/IgM and R. typhi IgG/IgM are determined to be 20.4, 7.03, 16.8 and 12.5, respectively. The LOD values were all lower than the cut-off values (256, 16, 128, and 64) used for clinical diagnosis, which means that this assay platform can diagnose two typhus diseases with high sensitivity. When the microarray sensors are combined with portable Raman spectrophotometers, which are commercially available worldwide, it is also possible to directly diagnose a patient in the field without sending their blood sample to a hospital.

Spotted Fever Group Rickettsiae among Children with Acute Febrile Illness, in Gorakhpur, India

Seasonal outbreaks of acute encephalitis syndrome have been occurring in Gorakhpur division in the Indian state of Uttar Pradesh during monsoon and post-monsoon months. Orientia tsutsugamushi was identified as the major aetiology of these outbreaks. Orientia tsutsugamushi was also identified as one of the important aetiology of febrile illness among children attending peripheral health facilities. The present study was undertaken to detect antibodies against spotted fever group rickettsiae (SFGR) and typhus group rickettsiae (TGR) among children with acute febrile illness presenting at peripheral health facilities in Gorakhpur district. Of the 224 blood samples tested, SFGR infection was detected in 13 (6%) patients. None of the samples tested positive for TGR.

Serological Evidence of Exposure to Spotted Fever Group and Typhus Group Rickettsiae in Australian Wildlife Rehabilitators

Rickettsioses are arthropod-borne zoonotic diseases, several of which occur in Australia. This study aimed to assess the exposure levels and risk factors for Rickettsia spp. among Australian wildlife rehabilitators (AWRs) using serology, PCR and a questionnaire. Antibody titres against Spotted Fever Group (SFG), Typhus Group (TG) and Scrub Typhus Group (STG) antigens were determined using an immunofluorescence assay. PCR targeting the gltA gene was performed on DNA extracts from whole blood and serum. Logistic regression was used to identify risk factors associated with seropositivity. Of the 27 (22.1%; 27/122) seropositive participants all were seropositive for SFG, with 5/27 (4.1%) also positive for TG. Of the 27 positive sera, 14.8% (4/27) were further classified as exposure to R. australis, 3.7% (1/27) to R. honei, 3.7% (1/27) to R. felis and 77.8% (21/27) were classified as ‘indeterminate’—most of which (85.7%; 18/21) were indeterminate R. australis/R. honei exposures. Rickettsia DNA was not detected in whole blood or serum. Rehabilitators were more likely to be seropositive if more than one household member rehabilitated wildlife, were older than 50 years or had occupational animal contact. These findings suggest that AWRs are at increased risk of contracting Rickettsia-related illnesses, however the source of the increased seropositivity remains unclear.

Current tools for the diagnosis and detection of spotted fever group Rickettsia

Spotted fever group (SFG) rickettsiae causes a number of diseases in humans worldwide, which can range from mild to highly lethal. Since the clinical presentations of rickettsioses caused by SFG rickettsiae are variable and may be similar to the diseases caused by other rickettsiae, such as Orientia tsutsugamushi (agent for scrub typhus), Coxiella burnetii (agent for Q fever) and the typhus group rickettsiae (agents for epidemic and murine typhus), the accurate diagnosis of infections caused by SFG Rickettsia remains challenging especially in resource-poor settings in developing countries. This review summarizes the various diagnostic and detection tools that are currently available for the confirmation of infections by SFG rickettsiae. The advantages and challenges pertaining to the different serological and molecular detections methods, as well as new assays in development, are discussed. The utility of the detection tools contributing to the surveillance of SFG rickettsiae in arthropods and animals are reviewed.

Occurrence of Anti-Rickettsia spp. Antibodies in Hospitalized Patients with Undifferentiated Febrile Illness in the Southern Region of Kazakhstan

Undifferentiated febrile illness still represents a demanding medical problem all over the world, but primarily in low- and middle-income countries. Scientific and clinical investigations related to undifferentiated febrile illness and rickettsial diseases in Kazakhstan are lacking. This study reflects the investigation of antibodies against spotted fever group (SFG) and typhus group (TG) rickettsiae in patients with undifferentiated febrile illness in the southern region of Kazakhstan (Almaty and Kyzylorda oblasts). Paired serum samples were gathered from 13 hospitals in these two oblasts and explored for the presence of IgM and IgG antibodies against typhus group and IgG antibodies against spotted fever group rickettsiae using ELISA. Patient's questionnaires were statistically analyzed. In total, 802 inpatients from Almaty (N = 9) and Kyzylorda (N = 4) hospitals were included in this research. Based on ELISA results, 250 patients out of 802 (31.2%) from both oblasts had IgG antibodies against SFG rickettsiae. Results from 11 (1.4%) patients indicated acute infection with tick-borne rickettsiosis. Regarding TG rickettsiae (R. typhi), a past infection was detected in 248 (30.9%) febrile patients and acute infection in 22 (2.7%) patients in the two selected oblasts. The data indicated that SFG and TG rickettsioses are present in Kazakhstan. Kazakh physicians should be aware of these emerging diseases in both investigated oblasts because the occurrence of these diseases is not suspected during day-to-day clinical practice. The identification of rickettsial pathogens and implementation of modern laboratory methods for the diagnostics of rickettsioses are in need throughout Kazakhstan.

New records of bacteria in different species of fleas from France and Spain

In this study, we assessed the presence of vector-borne microorganisms in different species of fleas collected from different hosts in diverse areas of South-Western Europe by molecular methods. A total of 319 fleas belonging to eight different species was tested for the presence of eight microorganisms. Wolbachia spp. endosymbionts were detected in Ctenocephalides felis, Pulex irritans, Archaeopsylla erinacei and Ctenophthalmus baeticus boisseauorum specimens. Rickettsia felis, an emerging pathogen, was detected in C. felis, A. erinacei and Ct. b. boisseauorum. Rickettsia typhi, the agent of murine typhus was detected for the first time in A. erinacei and Mycobacterium spp. were detected for the first time in fleas (C. felis, P. irritans and A. erinacei). Lastly, five different species of Bartonella were detected in fleas' DNA in this study, including a possible new bacterium belonging to this genus. With this study, we updated the knowledge of the flea-borne bacteria present in the South-West of Europe reinforcing the idea about the necessity to expand and increase the current knowledge on flea-borne pathogens.

International Rickettsia Disease Surveillance: An Example of Cooperative Research to Increase Laboratory Capability and Capacity for Risk Assessment of Rickettsial Outbreaks Worldwide

Cooperative research that addresses infectious disease surveillance and outbreak investigations relies heavily on availability and effective use of appropriate diagnostic tools, including serological and molecular assays, as exemplified by the current COVID-19 pandemic. In this paper, we stress the importance of using these assays to support collaborative epidemiological studies to assess risk of rickettsial disease outbreaks among international partner countries. Workforce development, mentorship, and training are important components in building laboratory capability and capacity to assess risk of and mitigate emerging disease outbreaks. International partnerships that fund cooperative research through mentoring and on-the-job training are successful examples for enhancing infectious disease surveillance. Cooperative research studies between the Naval Medical Research Center's Rickettsial Diseases Research Program (RDRP) and 17 institutes from nine countries among five continents were conducted to address the presence of and the risk for endemic rickettsial diseases. To establish serological and molecular assays in the collaborative institutes, initial training and continued material, and technical support were provided by RDRP. The laboratory methods used in the research studies to detect and identify the rickettsial infections included (1) group-specific IgM and IgG serological assays and (2) molecular assays. Twenty-six cooperative research projects performed between 2008 and 2020 enhanced the capability and capacity of 17 research institutes to estimate risk of rickettsial diseases. These international collaborative studies have led to the recognition and/or confirmation of rickettsial diseases within each of the partner countries. In addition, with the identification of specific pathogen and non-pathogen Rickettsia species, a more accurate risk assessment could be made in surveillance studies using environmental samples. The discoveries from these projects reinforced international cooperation benefiting not only the partner countries but also the scientific community at large through presentations (n = 40) at international scientific meetings and peer-reviewed publications (n = 18). The cooperative research studies conducted in multiple international institutes led to the incorporation of new SOPs and trainings for laboratory procedures; biosafety, biosurety, and biosecurity methods; performance of rickettsia-specific assays; and the identification of known and unknown rickettsial agents through the introduction of new serologic and molecular assays that complemented traditional microbiology methods.

Tick-borne rickettsiae in Midwestern region of Republic of Korea

To identify spotted fever group (SFG) rickettsiae among ticks collected by dragging at eight sites in three provinces of the midwestern region of the Republic of Korea (ROK), genus- and species-specific quantitative real-time PCR (qPCR) assays and sequencing were performed. DNA was extracted from a total of 2,312 ticks that were assayed individually (n=140) or in pools (n=444), resulting in a total of 584 individual and pooled tick samples. The 584 tick samples were screened with the genus-specific qPCR assay (Rick17b) and produced 265 (45.38%) positive reactions [individual (n=64) and pooled (n=101) samples]. Of these genus-specific positive samples, 57 (21.51%) were identified as Candidatus Rickettsia longicornii and 48 (18.11%) were identified as R. monacensis by species-specific qPCR assays. Subsequently, nested PCR (nPCR) was performed with 120 samples, which tested positive samples for genus-specific, but not species-specific, qPCR assays. The sequences of ompA and ompB genes showed how many close relatedness to Ca. R. longicornii and Ca. R. jingxinensis isolate Xian Hl-79, uncultured Rickettsia sp. Y27-1, Ca. R. tasmanensis strain T152, R. endosymbiont of H. longicornis tick 47, and R. koreansis strain CNH17-7. In conclusion, we successfully detected specific rickettsial agents using qPCR and a sequence-based analysis approach that demonstrated the prevalence of various tick-borne Rickettsia spp. in midwestern ROK.

Diagnostic accuracy of an in-house Scrub Typhus enzyme linked immunoassay for the detection of IgM and IgG antibodies in Laos

Scrub typhus is a major cause of morbidity and mortality in Southeast Asia. Diagnosis of scrub typhus is difficult due to a lack of accessible validated diagnostic tools. Despite its objectivity, the diagnostic accuracy of ELISA tests is influenced by methodological and patient factors. This study aims to evaluate the performance of a novel in-house ELISA developed in the Mahidol Oxford Tropical Medicine Research Unit (MORU) for anti-scrub typhus group IgM and IgG compared to the “gold standard” reference IFA and PCR, and to determine whether the in-house ELISA can be used as a seroepidemiological screening tool and/or stand-alone test for scrub typhus. A total of 1,976 admission and 1,438 participant follow-up sera collected in the Lao PDR (Laos) were tested with ELISA for IgM and IgG. Samples with an ELISA OD≥0.50 were tested with IFA for IgM and/or IgG. A strong positive relationship was present between ELISA ODs and IFA titers for admission IgM (r²: 0.70, p <0.005) and IgG (r²: 0.76, p<0.005), and for follow-up IgM and IgG (both r²: 0.76, p<0.005) samples. The best compromise between sensitivity and specificity for the ELISA OD cut-off is likely to be between 0.8–1.0 for IgM antibodies and 1.2–1.8 for IgG antibodies. These results demonstrate that the diagnostic accuracy of the MORU in-house scrub typhus group ELISA is comparable to that of IFA, with similar results as reported for the commonly used InBios Scrub Typhus Detect ELISA, validating the use of the in-house ELISA. The optimal ELISA cut-off would depend on the use of the test, and the desired sensitivity and specificity. Further studies are required to authenticate the use of these cut-offs in other endemic regions. This in-house ELISA has the potential to replace the imperfect IFA, which could ultimately reduce the burden of scrub typhus by improving the rate of scrub typhus diagnoses in endemic low-resource areas.

Scrub typhus is a mite-borne infectious disease, caused by the Orientia tsutsugamushi bacterium, resulting in considerable morbidity and mortality in the Asia-Pacific region. Diagnosis is difficult since it does not present with any distinctive clinical signs compared to other febrile illnesses in this region, except for a necrotic skin lesion (eschar) in some patients. Laboratory tests are therefore crucial to identify scrub typhus. Reliable laboratory tests need significant infrastructure and experienced staff, making access to accurate tests very limited in the low-resource endemic regions. This study aimed to evaluate the accuracy of less expensive and easier-to-use in-house Enzyme Linked Immunoassays (ELISAs) detecting immunoglobulin IgM and IgG antibodies against scrub typhus infection compared to the “gold-standard” Immunofluorescence Assays (IFAs). There was a strong positive relationship between ELISA and IFA antibody levels for both IgM and IgG. If the ELISA would be used as a stand-alone test for scrub typhus diagnosis in Laos, an ideal balance between sensitivity and specificity would likely be around an ELISA optical density (OD) of 0.8–1.0 for IgM and 1.2–1.8 for IgG. There is a need to investigate the use of these cut-offs in other endemic regions, which could improve the rate of scrub typhus diagnosis in low-resource settings.

A Brief History of the Major Rickettsioses in the Asia-Australia-Pacific Region: A Capstone Review for the Special Issue of TMID

The rickettsioses of the "Far East" or Asia-Australia-Pacific region include but are not limited to endemic typhus, scrub typhus, and more recently, tick typhus or spotted fever. These diseases embody the diversity of rickettsial disease worldwide and allow us to interconnect the various contributions to this special issue of Tropical Medicine and Infectious Disease. The impact of rickettsial diseases-particularly of scrub typhus-was substantial during the wars and "police actions" of the last 80 years. However, the post-World War II arrival of effective antibiotics reduced their impact, when recognized and adequately treated (chloramphenicol and tetracyclines). Presently, however, scrub typhus appears to be emerging and spreading into regions not previously reported. Better diagnostics, or higher population mobility, change in antimicrobial policies, even global warming, have been proposed as possible culprits of this phenomenon. Further, sporadic reports of possible antibiotic resistance have received the attention of clinicians and epidemiologists, raising interest in developing and testing novel diagnostics to facilitate medical diagnosis. We present a brief history of rickettsial diseases, their relative importance within the region, focusing on the so-called "tsutsugamushi triangle", the past and present impact of these diseases within the region, and indicate how historically, these often-confused diseases were ingeniously distinguished from each another. Moreover, we will discuss the importance of DNA-sequencing efforts for Orientia tsutsugamushi, obtained from patient blood, vector chiggers, and rodent reservoirs, particularly for the dominant 56-kD type-specific antigen gene (tsa56), and whole-genome sequences, which are increasing our knowledge of the diversity of this unique agent. We explore and discuss the potential of sequencing and other effective tools to geographically trace rickettsial disease agents, and develop control strategies to better mitigate the rickettsioses.

Diagnosis of scrub typhus: recent advancements and challenges

Scrub typhus is a mite-borne, acute febrile illness caused by the bacterium Orientia tsutsugamushi. It is a re-emerging infectious disease of the tsutsugamushi triangle. Scrub typhus is transmitted through bites of contaminated chiggers (larval stage). Diagnosis of scrub typhus is challenging as its symptoms mimic with other acute febrile illnesses. Several methods are effectual for diagnosis of scrub typhus that includes enzyme-linked immunosorbent assay (ELISA), immunofluorescence assay (IFA), immunochromatographic test (ICT), Weil-Felix, polymerase chain reaction (PCR) and loop-mediated isothermal amplification (LAMP). Weil-Felix test was initially used for the diagnosis of scrub typhus in underdeveloped countries but not preferred due to a lack of both specificity and sensitivity. Other immuno-based methods like IFA and ELISA are most outrank for detection of scrub typhus due to their higher sensitivity and specificity, but not vigorous to lay bare the infection at early stages and need the convalescent sampling for verification of positive samples. On another deed, PCR based methods becoming acceptable over era due to its dexterity of early-stage diagnosis with higher specificity and sensitivity but lack its applicability in circumstances of scrub typhus due to the variegated genetic makeup of Orientia tsutsugamushi among its serotypes. The present review focused on various detection methods along with their advantages and disadvantages used in the diagnosis of scrub typhus. A comparison between available methods of diagnosis with challenges in the detection of scrub typhus is also summarized.

Optimization and Evaluation of a Multiplex Quantitative PCR Assay for Detection of Nucleic Acids in Human Blood Samples from Patients with Spotted Fever Rickettsiosis, Typhus Rickettsiosis, Scrub Typhus, Monocytic Ehrlichiosis, and Granulocytic Anaplasmosis

Spotted fever group rickettsioses (SFGR), typhus group rickettsioses (TGR), scrub typhus (caused by Orientia tsutsugamushi), ehrlichiosis, and anaplasmosis often present as undifferentiated fever but are not treated by agents (penicillins and cephalosporins) typically used for acute febrile illness. Inability to diagnose these infections when the patient is acutely ill leads to excess morbidity and mortality. Failure to confirm these infections retrospectively if a convalescent blood sample is not obtained also impairs epidemiologic and clinical research. We designed a multiplex real-time quantitative PCR (qPCR) assay to detect SFGR, TGR, O. tsutsugamushi, and infections caused by Anaplasma phagocytophilum and Ehrlichia chaffeensis with the ompA, 17-kDa surface antigen gene, tsa56, msp2 (p44), and vlpt gene targets, respectively. Analytical sensitivity was ≥2 copies/μl (linear range, 2 to 2 × 10⁵) and specificity was 100%. Clinical sensitivities for SFGR, TGR, and O. tsutsugamushi were 25%, 20%, and 27%, respectively, and specificities were 98%, 99%, and 100%, respectively. Clinical sensitivities for A. phagocytophilum and E. chaffeensis were 93% and 84%, respectively, and specificities were 99% and 98%, respectively. This multiplex qPCR assay could support early clinical diagnosis and treatment, confirm acute infections in the absence of a convalescent-phase serum sample, and provide the high-throughput testing required to support large clinical and epidemiologic studies. Because replication of SFGR and TGR in endothelial cells results in very low bacteremia, optimal sensitivity of qPCR for these rickettsioses will require use of larger volumes of input DNA, which could be achieved by improved extraction of DNA from blood and/or extraction of DNA from a larger initial volume of blood.

Scrub Typhus: Historic Perspective and Current Status of the Worldwide Presence of Orientia Species

Scrub typhus and its etiological agents, Orientia species, have been around for a very long time. Historical reference to the rickettsial disease scrub typhus was first described in China (313 AD) by Hong Ge in a clinical manual (Zhouhofang) and in Japan (1810 AD) when Hakuju Hashimoto described tsutsuga, a noxious harmful disease in the Niigata prefecture. Other clinicians and scientists in Indonesia, Philippines, Taiwan, Australia, Vietnam, Malaysia, and India reported on diseases most likely to have been scrub typhus in the early 1900s. All of these initial reports about scrub typhus were from an area later designated as the Tsutsugamushi Triangle-an area encompassing Pakistan to the northwest, Japan to the northeast and northern Australia to the south. It was not until the 21st century that endemic scrub typhus occurring outside of the Tsutsugamushi Triangle was considered acceptable. This report describes the early history of scrub typhus, its distribution in and outside the Tsutsugamushi Triangle, and current knowledge of the causative agents, Orientia species.

Determination of Optimal Diagnostic Cut-Offs for the Naval Medical Research Center Scrub Typhus IgM ELISA in Chiang Rai, Thailand

In this diagnostic accuracy study, we evaluated data from 135 febrile patients from Chiang Rai, to determine the optimal optical density (OD) cutoffs for an in-house scrub typhus IgM ELISA. Receiver operating characteristic curves were generated using a panel of reference assays, including an IgM immunofluorescence assay (IFA), PCR, in vitro isolation, presence of an eschar, or a combination of these. Altogether, 33 patients (24.4%) were diagnosed as having scrub typhus. Correlation between positivity by IFA and increasing OD values peaked at a cutoff of 2.0, whereas there was little association between positivity by culture or eschar with increasing ELISA cutoffs—cutoffs of 3.0 and 4.0 were demonstrated to be optimal for the total absorbance of the OD at dilutions 1:100, 1:400, 1:1,600, and 1:6,400, for admission and convalescent samples, respectively. The optimal cutoff at a 1:100 dilution was found to be between 1.85 and 2.22 for admission samples and convalescent-phase samples, respectively. Sensitivities for the cutoffs varied from 57.1% to 90.0% depending on the reference test and sample timing, whereas specificities ranged from 85.2% to 99.0%. We therefore recommend a cutoff of around 2.0, depending on the sensitivity and specificity desired in clinical or epidemiological settings. The results demonstrate the ELISA to be a valuable diagnostic tool, suitable for use in resource-limited endemic regions, especially when used in combination with other diagnostic modalities such as the presence of an eschar.

Clinical Manifestations and Molecular Diagnosis of Scrub Typhus and Murine Typhus, Vietnam, 2015-2017

Scrub typhus was the predominant rickettsial disease diagnosed among hospitalized patients with acute undifferentiated fever in northern Vietnam.

Rickettsioses are endemic to Vietnam; however, only a limited number of clinical studies have been performed on these vectorborne bacteria. We conducted a prospective hospital-based study at 2 national referral hospitals in Hanoi to describe the clinical characteristics of scrub typhus and murine typhus in northern Vietnam and to assess the diagnostic applicability of quantitative real-time PCR assays to diagnose rickettsial diseases. We enrolled 302 patients with acute undifferentiated fever and clinically suspected rickettsiosis during March 2015–March 2017. We used a standardized case report form to collect clinical information and laboratory results at the time of admission and during treatment. We confirmed scrub typhus in 103 (34.1%) patients and murine typhus in 12 (3.3%) patients. These results highlight the need for increased emphasis on training for healthcare providers for earlier recognition, prevention, and treatment of rickettsial diseases in Vietnam.

Biosafety and biosecurity requirements for Orientia spp. diagnosis and research: recommendations for risk-based biocontainment, work practices and the case for reclassification to risk group 2

Scrub typhus is an important arthropod-borne disease causing significant acute febrile illness by infection with Orientia spp.Using a risk-based approach, this review examines current practice, the evidence base and regulatory requirements regarding matters of biosafety and biosecurity, and presents the case for reclassification from Risk Group 3 to Risk Group 2 along with recommendations for safe working practices of risk-based activities during the manipulation of Orientia spp. in the laboratory.We recommend to reclassify Orientia spp. to Risk Group 2 based on the classification for RG2 pathogens as being moderate individual risk, low community risk. We recommend that low risk activities, can be performed within a biological safety cabinet located in a Biosafety Level (BSL) 2 core laboratory using standard personal protective equipment. But when the risk assessment indicates, such as high concentration and volume, or aerosol generation, then a higher biocontainment level is warranted. For, the majority of animal activities involving Orientia spp., Animal BSL 2 (ABSL2) is recommended however where high risk activities are performed including necropsies, Animal BSL (ABSL3) is recommended.

Molecular identification of vector-borne organisms in Ehrlichia seropositive Nicaraguan horses and first report of Rickettsia felis infection in the horse

Certain vector-borne organisms serve as etiological agents of equine disease. After previously identifying a new Ehrlichia species in horses from Mérida, we aimed to determine the infection frequency and screen for a wide range of vector-borne organisms from 93 tick-exposed, Ehrlichia seropositive horses in this region. PCR assays were performed to identify infection by organisms within the following genera: Anaplasma, Babesia, Bartonella, Ehrlichia, Leishmania, Mycoplasma, Neorickettsia, Rickettsia and Theileria. Overall, 90/93 horses (96.8%) were infected with one or more vector-borne organisms. Ninety (96.8%) horses were infected with Theileria equi and 21 (26.8%) with Babesia caballi. Nine (9.7%) horses were infected with the novel Ehrlichia species previously designated H7, reported in horses from Nicaragua and Brazil. Two horses (2.2%) were infected with Rickettsia felis. Anaplasma, Bartonella, Leishmania, Mycoplasma, or Neorickettsia species DNA was not amplified from any horse. Ticks collected from horses infected with vector-borne organisms were identified as Amblyomma cajennense sensu lato and Dermacentor nitens. Horses in Mérida are infected by a range of vector-borne organisms, including B. caballi, T. equi, Ehrlichia species H7, and R. felis. To the authors' knowledge, this constitutes the first report of molecular detection of R. felis in horses.

Distribution and Ecological Drivers of Spotted Fever Group Rickettsia in Asia

Spotted fever group and related rickettsia (SFGR) are a neglected group of pathogens that belong to the genus Rickettsia. SFGR are zoonotic and are transmitted by arthropod vectors, primarily ticks, fleas and mites to accidental hosts. These emerging and re-emerging infections are widely distributed throughout the world. Land-use change and increasing human-wildlife conflict compound the risk of SFGR infection to local people in endemic areas and travelers to these regions. In this article, we discuss the rickettsial organisms causing spotted fever and related diseases, their arthropod vectors in Asia and the impact of land-use change on their spread.

Optimized fixation of actin filaments for improved indirect immunofluorescence staining of rickettsiae

Objective

The objective was to investigate fixative solutions: 3.7% formaldehyde, 4% paraformaldehyde, 4% paraformaldehyde in the cytoskeletal buffer and 4% paraformaldehyde in PHEM buffer (containing PIPES, HEPES, EGTA and MgCl₂), applicable for immunofluorescence assay.

Results

Herein we optimized this serological technique, testing four fixative solutions, for the sensitive detection of rickettsial antigens, and preservation of intracellular structures of the host cells, particularly filamentous actin. Rickettsial antigens were presented equally well both with formaldehyde and all paraformaldehyde-based fixations, but only protocol with 4% paraformaldehyde in PHEM buffer allowed accurate imaging of actin filaments, and simultaneously allows monitoring of rickettsiae using actin-based motility during infection inside the host cells.

Diagnosis of spotted fever group Rickettsia infections: the Asian perspective

Spotted fever group rickettsiae (SFG) are a neglected group of bacteria, belonging to the genus Rickettsia, that represent a large number of new and emerging infectious diseases with a worldwide distribution. The diseases are zoonotic and are transmitted by arthropod vectors, mainly ticks, fleas and mites, to hosts such as wild animals. Domesticated animals and humans are accidental hosts. In Asia, local people in endemic areas as well as travellers to these regions are at high risk of infection. In this review we compare SFG molecular and serological diagnostic methods and discuss their limitations. While there is a large range of molecular diagnostics and serological assays, both approaches have limitations and a positive result is dependent on the timing of sample collection. There is an increasing need for less expensive and easy-to-use diagnostic tests. However, despite many tests being available, their lack of suitability for use in resource-limited regions is of concern, as many require technical expertise, expensive equipment and reagents. In addition, many existing diagnostic tests still require rigorous validation in the regions and populations where these tests may be used, in particular to establish coherent and worthwhile cut-offs. It is likely that the best strategy is to use a real-time quantitative polymerase chain reaction (qPCR) and immunofluorescence assay in tandem. If the specimen is collected early enough in the infection there will be no antibodies but there will be a greater chance of a PCR positive result. Conversely, when there are detectable antibodies it is less likely that there will be a positive PCR result. It is therefore extremely important that a complete medical history is provided especially the number of days of fever prior to sample collection. More effort is required to develop and validate SFG diagnostics and those of other rickettsial infections.

Prevalence of Orientia tsutsugamushi, Anaplasma phagocytophilum and Leptospira interrogans in striped field mice in Gwangju, Republic of Korea

This study investigated the prevalence of Orientia tsutsugamushi, Anaplasma phagocytophilum, and Leptospira interrogans in wild rodents through molecular detection using organ samples and through serological assay using blood samples of mice collected from two distinct sites in Gwangju Metropolitan City, Republic of Korea (ROK). A total of 47 wild rodents, identified as Apodemus agrarius (A. agrarius), were captured from June to August 2016. The seroprevalence of antibodies against bacterial pathogens in A. agrarius sera was analyzed; 17.4% (8/46) were identified as O. tsutsugamushi through indirect immunofluorescence assay and 2.2% (1/46) were identified as Leptospira species through passive hemagglutination assay. Using polymerase chain reaction, the spleen, kidney and blood samples were investigated for the presence of O. tsutsugamushi, A. phagocytophilum, and L. interrogans. Out of the 47 A. agrarius, 19.1% (9/47) were positive for A. phagocytophilum and 6.4% (3/47) were positive for L. interrogans, while none were positive for O. tsutsugamushi. Four out of 46 (8.7%) blood samples, six out of 45 (13.3%) spleen samples, and one out of 47 (2.1%) kidney samples were positive for A. phagocytophilum. Three out of 47 (6.4%) kidney samples were positive for L. interrogans. The sequencing results of PCR positive samples demonstrated > 99% similarity with A. phagocytophilum and L. interrogans sequences. A. phagocytophilum was mostly detected in the spleen, whereas L. interrogans was mostly detected in the kidneys. Notably, A. phagocytophilum and L. interrogans were detected in A. agrarius living in close proximity to humans in the metropolitan suburban areas. The results of this study indicate that rodent-borne bacteria may be present in wild rodents in the metropolitan suburban areas of ROK.

Cellulitis of the face associated with SENLAT caused by Rickettsia slovaca detected by qPCR on scalp eschar swab sample: An unusual case report and review of literature

BACKGROUND

Tick-borne rickettsioses are infectious diseases caused by obligate intracellular Gram-negative bacteria belonging to the spotted fever groupof Rickettsia.

METHODS

We describe an unusual case of SENLAT (Scalp eschar and neck lymphadenopathy after tick bite), caused byRickettsia slovaca, associated with a cellulitis of the face in a 70-year-old woman, and diagnosed using qPCR on a scalp eschar swab. We review the literature regarding cases of SENLAT-associated-cellulitis and case of SENLAT diagnosed by qPCR on scalp eschar swabs.

RESULTS

We found only one previous report of SENLAT associated with a cellulitis of the face. It was a nine-year-old French girl diagnosed by seroconversion for Rickettsia sp. Our review of the literature showed that qPCR on eschar swab samples is a less invasive method than performing cutaneous biopsy of the eschar and has good sensitivity and specificity (90% and 100%, respectively).

CONCLUSIONS

We report the second case of cellulitis of the face associated with the SENLAT syndrome. Detection of Rickettsia by qPCR on swab sample of the scalp eschar is a simple, noninvasive technique allowing rapid diagnosis and treatment when SENLAT is suspected.

Development of multiplex PCR for neglected infectious diseases

Scrub typhus, murine typhus, and leptospirosis are widely neglected infectious diseases caused by Orientia tsutsugamushi, Rickettsia typhi, and pathogenic Leptospira spp., respectively. Patients usually present with non-specific symptoms and therefore are commonly diagnosed with acute undifferentiated febrile illness. Consequently, patients face delayed treatment and increased mortality. Antibody-based serological test currently used as gold standard has limitations due to insufficient antibody titers, especially in the early phase of infection. In this study, we aimed to develop multiplex PCR to combine 3 primer pairs that target specific genes encoding 56-kDa TSA of O. tsutsugamushi, 17-kDa antigen of R. typhi, and LipL32 of L. Interrogans and evaluate its performance in comparison to the standard serological tests. Using EDTA blood samples of known patients, the sensitivity and specificity of our multiplex PCR was 100% and 70%, respectively. In addition, the assay was able to diagnose the co-infection of scrub typhus and leptospirosis. The assay may be useful in identifying causative agents during the early phase of these diseases, enabling prompt and appropriate treatment.

Scrub typhus, murine typhus, and leptospirosis are diagnosed as acute undifferentiated febrile illness. Diagnostic tests for these diseases depend on antibody detection. However, antibody detection is still limited by its tendency to return negative results during the early phase of aforementioned diseases. In this study, a novel multiplex PCR has been developed for detecting Orientia tsutsugamushi, Rickettsia typhi, and Leptospira interrogans that are simultaneously amplified in a single tube. The results have shown that multiplex PCR could be used as a diagnostic tool for detecting bacteria during the early phase of scrub typhus, murine typhus, and leptospirosis, allowing for administration of appropriate treatment.

Evaluation of scrub typhus diagnosis in China: analysis of nationwide surveillance data from 2006 to 2016

Background

Scrub typhus is a life-threatening disease caused by Orientia tsutsugamushi, and specific antimicrobial medicine is available. Early and accurate diagnosis is essential for reducing the risk of severe complications and death. In this study, we aimed to evaluate the case diagnosis situation among medical care institutions and geographical regions in China, and the results will benefit both clinical practice and the disease surveillance system.

Methods

We extracted individual scrub typhus case data 2006–2016 from a national disease surveillance system in China. The diagnosis category and interval time from illness onset to diagnosis were compared among three levels of medical care institutions and provinces. The descriptive analysis method was performed in our study.

Results

During the 11-year study period, 93 481 scrub typhus cases, including 57 deaths, were recorded in the nationwide surveillance system. The overall proportion of laboratory-confirmed cases was only 4.7%, and this proportion varied greatly among primary medical centres (2.8%), county level hospitals (4.2%), and city level hospitals (6.3%). Notably, the proportion of laboratory-confirmed cases has consistently decreased from 16.3% in 2006 to 2.6% in 2016, and the same decreasing trend was found among all three levels of medical care institutions. The interval from illness onset to case diagnosis (T_diag) for all cases was 5 days (interquartile range [IQR]: 2–9 days) and decreased from 7 days (IQR: 3–11 days) in 2006 to 5 days (IQR: 2–8 days) in 2016. The risk of death for patients with a T_diag of > 7 days was 2.2 times higher (OR = 2.21, 95% CI: 1.05–5.21) than that of patients with a T_diag of < 2 days.

Conclusions

The interval time from illness onset to diagnosis for scrub typhus cases decreased greatly in China; however, the diagnosis rate of cases with laboratory-confirmed results must be increased among all levels of medical care institutions to reduce both the risk of death and the misuse of antibiotics associated with scrub typhus.

Electronic supplementary material

The online version of this article (10.1186/s40249-019-0566-0) contains supplementary material, which is available to authorized users.