Human seroepidemiology of Rickettsia and Orientia species in Chile - A cross-sectional study in five regions

Eco-epidemiological study of seropositivity against Rickettsia and Leptospira agents in rural areas of Urabá, Colombia

Rickettsioses and leptospirosis are infectious diseases that are often underdiagnosed due to a lack of knowledge about their epidemiology, pathophysiology, diagnosis, management, among others.

Objetive

to characterize the seroprevalence and seroincidence of both Rickettsia and Leptospira agents and determine the risk factors for these outcomes in rural areas of Urabá, Antioquia.

Methods

a secondary data analysis using information on Rickettsia and Leptospira exposure from a prior prospective study that explored sociocultural and ecological aspects of Rickettsia infection in rural Urabá, Colombia. A multinomial mixed logistic regression model was employed to analyze factors linked to seroprevalent cases of Rickettsia, Leptospira and both, along with descriptive analyses of seroincident cases.

Results

the concomitant seroprevalence against Rickettsiaand Leptospira was 9.38% [95%CI 6.08%-13.37%] (56/597). The factors associated with this seroprevalence were age (ORa= 1.02 [95%CI 1.007-1.03]), male gender (ORa= 3.06 [95%CI 1.75-5.37]), fever history (ORa= 1.71 [95%CI 1.06-2.77]) the presence of breeding pigs (ORa= 2.29 [95%CI 1.36-3.88]), peridomicile yucca crops(ORa= 2.5 [95%CI 1.1-5.62]), and deforestation practices(ORa= 1.74 [95%CI 1.06-2.87]). The concomitant seroincidence against Rickettsia and Leptospira was 1.09% (3/274) [95%CI 0.29%-4.05%], three cases were female, with a median age of 31.83 years-old (IQR 8.69-56.99). At the household level, all the seroincident cases had households built partially or totally with soil floors, wooden walls, and zinc roofs. Two seroincident cases described the presence of equines, canines, and domestic chickens in intra or peri-domicile. Finally, two cases were exposed to synanthropic rodents, and one case to tick infestation.

Conclusion

there is evidence of seroprevalent and seroincident cases of seropositivity against both Rickettsia and Leptospira in rural areas of Urabá, Colombia. These findings can help improve public health surveillance systems in preventing, detecting, and attending to the different clinical cases caused by these pathogens.

A seminested recombinase polymerase amplification assay to detect rickettsial pathogens in clinical samples

Treatment at the early stage of onset is vital for the prognosis of rickettsioses. But the absence of specific clinical symptoms complicates the diagnosis of this condition. Herein we established a seminested recombinase polymerase amplification assay (snRPA-nfo) that enables quick detection and differentiation of rickettsial pathogens in clinical samples with high sensitivity and specificity. The conserved 17-kDa protein gene of Rickettsia sibirica and the 47-kDa protein gene of Orientia tsutsugamushi were targeted for the duplex RPA-nfo assay. The snRPA-nfo assay exhibited an increased LOD in spiked blood samples, up to 1000-fold in comparison to standard RPA-nfo, and a better detection rate (83.3%, 5/6) than TaqMan PCR (16.6%, 1/6, Ct ≤ 35) in clinically confirmed patient blood samples. Thus, snRPA-nfo assay represents a promising alternative to TaqMan PCR in the early diagnosis of rickettsioses for point-of-care testing as well as in resource-limited settings.

Etiologies of Zoonotic Tropical Febrile Illnesses That Are Not Part of the Notifiable Diseases in Colombia

In Colombia, tropical febrile illnesses represent one of the most important causes of clinical attention. Febrile illnesses in the tropics are mainly zoonotic and have a broad etiology. The Colombian surveillance system monitors some notifiable diseases. However, several etiologies are not monitored by this system. In the present review, we describe eleven different etiologies of zoonotic tropical febrile illnesses that are not monitored by the Colombian surveillance system but have scientific, historical, and contemporary data that confirm or suggest their presence in different regions of the country: Anaplasma, Arenavirus, Bartonella, relapsing fever group Borrelia, Coxiella burnetii, Ehrlichia, Hantavirus, Mayaro virus, Orientia, Oropouche virus, and Rickettsia. These could generate a risk for the local population, travelers, and immigrants, due to which they should be included in the mandatory notification system, considering their importance for Colombian public health.

Alterations in germinal center formation and B cell activation during severe Orientia tsutsugamushi infection in mice

Scrub typhus is a poorly studied but life-threatening disease caused by the intracellular bacterium Orientia tsutsugamushi (Ot). Cellular and humoral immunity in Ot-infected patients is not long-lasting, waning as early as one-year post-infection; however, its underlying mechanisms remain unclear. To date, no studies have examined germinal center (GC) or B cell responses in Ot-infected humans or experimental animals. This study was aimed at evaluating humoral immune responses at acute stages of severe Ot infection and possible mechanisms underlying B cell dysfunction. Following inoculation with Ot Karp, a clinically dominant strain known to cause lethal infection in C57BL/6 mice, we measured antigen-specific antibody titers, revealing IgG2c as the dominant isotype induced by infection. Splenic GC responses were evaluated by immunohistology, co-staining for B cells (B220), T cells (CD3), and GCs (GL-7). Organized GCs were evident at day 4 post-infection (D4), but they were nearly absent at D8, accompanied by scattered T cells throughout splenic tissues. Flow cytometry revealed comparable numbers of GC B cells and T follicular helper (Tfh) cells at D4 and D8, indicating that GC collapse was not due to excessive death of these cell subtypes at D8. B cell RNAseq analysis revealed significant differences in expression of genes associated with B cell adhesion and co-stimulation at D8 versus D4. The significant downregulation of S1PR2 (a GC-specific adhesion gene) was most evident at D8, correlating with disrupted GC formation. Signaling pathway analysis uncovered downregulation of 71% of B cell activation genes at D8, suggesting attenuation of B cell activation during severe infection. This is the first study showing the disruption of B/T cell microenvironment and dysregulation of B cell responses during Ot infection, which may help understand the transient immunity associated with scrub typhus.

Gastrointestinal parasites in wild rodents in Chiloé Island-Chile

Gastrointestinal parasites are well-documented in small mammals from north-central Chile, but little is known about endoparasites of rodents in southern Chile. A survey was conducted between January and February 2018 to evaluate gastrointestinal parasites and risk factors of wild rodents that live in rural areas in Northern Chiloé Island, Chile. A total of 174 fecal samples from rodents of six native and one introduced species were collected and examined using the Mini-FLOTAC method. Also, 41 individuals of four native wild rodent species were examined furtherly to determinate adult parasites from gastrointestinal tracts. The overall prevalence of endoparasites was 89.65% (156). Helminth egg types included: Rodentolepis spp., Capillariidae, Trichuris sp., Syphacia sp., oxyurid-type eggs, Strongyloides sp., Spirurid-type eggs, Strongilid-type eggs, Moniliformis sp., and an unidentified nematode egg and larvae. Protozoa comprised coccidia, amoeba, and unidentified cysts. From necropsies, adult parasites involved Syphacia sp. Trichuris sp., Protospirura sp. and Physaloptera sp. In Abrothrix olivacea, individuals with low-body-mass index exhibited reduced infection probability for Spirurid-type and Strongilid-type eggs. Some parasites in this study may affect human health. In rural settings where environmental conditions are changing, more research should be undertaken to understand parasitic infections in wildlife and implications for public health and conservation.

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.

Antibody Prevalence and Risk Factors Associated with Rickettsia spp. in a Pediatric Cohort: SFGR Remains Underdiagnosed and Underreported in El Salvador

Spotted fever group rickettsioses (SFGR) are caused by a group of tick-borne pathogens that are increasing in incidence globally. These diseases are typically underreported and undiagnosed in low- and middle-income countries, and thus, have been classified as neglected bacterial pathogens. Countries with high poverty, low human development index score, and limited health infrastructure—like El Salvador in Central America—lack necessary surveillance for SFGR and other tick-borne pathogens. This paucity of baseline SFGR infection prevalence leaves vulnerable populations at risk of misdiagnosis. Further, tick-borne disease burdens in El Salvador are severely limited. To lay the foundation for tick-borne disease epidemiology in El Salvador, our team conducted two different enzyme-linked immunosorbent assays (ELISA) on banked human sera samples from a cohort of approximately 1000 pediatric participants from a high-risk vector-borne disease population. Eleven percent of all tested banked pediatric sera were positive for at least one ELISA assay at the time of enrollment: 10.7% were positive for only IgM antibodies (acute SFGR infection), and 2.5% were positive for IgG antibodies (a past SFGR infection). Older, male, children enrolled during the wet season, with a household history of infectious disease and higher maternal education level had higher odds of SFGR antibodies. Additionally, children from households with domestic poultry birds and previous knowledge of other vector-borne diseases had significantly reduced odds of SFGR antibodies. The large percentage of acute SFGR infections indicates that it continues to remain an underreported and undiagnosed issue in El Salvador and the Central American region. Much is still unknown regarding the complexity of the tick, animal host, and human host ecology transmission cycle of SFGR in El Salvador.

Molecular Description of a Novel Orientia Species Causing Scrub Typhus in Chile

Scrub typhus is a potentially fatal rickettsiosis caused by Orientia species intracellular bacteria of the genus Orientia. Although considered to be restricted to the Asia Pacific region, scrub typhus has recently been discovered in southern Chile. We analyzed Orientia gene sequences of 16S rRNA (rrs) and 47-kDa (htrA) from 18 scrub typhus patients from Chile. Sequences were ≥99.7% identical among the samples for both amplified genes. Their diversity was 3.1%–3.5% for rrs and 11.2%–11.8% for htrA compared with O. tsusugamushi and 3.0% for rrs and 14.8% for htrA compared with Candidatus Orientia chuto. Phylogenetic analyses of both genes grouped the specimens from Chile in a different clade from other Orientia species. Our results indicate that Orientia isolates from Chile constitute a novel species, which, until they are cultivated and fully characterized, we propose to designate as Candidatus Orientia chiloensis, after the Chiloé Archipelago where the pathogen was identified.

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.

Pattern Recognition Receptors in Innate Immunity to Obligate Intracellular Bacteria

Host pattern recognition receptors (PRRs) are crucial for sensing pathogenic microorganisms, launching innate responses, and shaping pathogen-specific adaptive immunity during infection. Rickettsia spp., Orientia tsutsugamushi, Anaplasma spp., Ehrlichia spp., and Coxiella burnetii are obligate intracellular bacteria, which can only replicate within host cells and must evade immune detection to successfully propagate. These five bacterial species are zoonotic pathogens of clinical or agricultural importance, yet, uncovering how immune recognition occurs has remained challenging. Recent evidence from in-vitro studies and animal models has offered new insights into the types and kinetics of PRR activation during infection with Rickettsia spp., A. phagocytophilum, E. chaffeensis, and C. burnetii, respectively. However, much less is known in these regards for O. tsutsugamushi infection, until the recent discovery for the role of the C-type lectin receptor Mincle during lethal infection in mice and in primary macrophage cultures. This review gives a brief summary for clinical and epidemiologic features of these five bacterial infections, focuses on fundamental biologic facets of infection, and recent advances in host recognition. In addition, we discuss knowledge gaps for innate recognition of these bacteria in the context of disease pathogenesis.