Detection of Candidatus Neoehrlichia mikurensis in Norway up to the northern limit of Ixodes ricinus distribution using a novel real time PCR test targeting the groEL gene

Neoehrlichia mikurensis is uncommon in rheumatological patients receiving tumour necrosis factor inhibitors and in blood donors: a retrospective cohort study

INTRODUCTION

Neoehrlichia mikurensis is a tick-borne bacterium that primarily causes disease in immunocompromised patients. The bacterium has been detected in ticks throughout Europe, with a 0%-25% prevalence. N. mikurensis infection presents unspecific symptoms, which can easily be mistaken for inflammatory disease activity. We aimed to determine the prevalence of N. mikurensis in rheumatological patients receiving tumour necrosis factor inhibitors (TNFi) and a cohort of healthy individuals.

MATERIALS AND METHODS

This retrospective cohort study included 400 rheumatological patients treated with TNFi and 400 healthy blood donors. Plasma samples were retrieved from the Danish Rheumatological Biobank and the Danish Blood Donor Study between 2015 and 2022. Age, sex, diagnosis and duration of TNFi treatment were recovered from the Danish Rheumatological Database, DANBIO. Data on age and sex were available for the blood donors. One plasma sample per individual was tested for N. mikurensis DNA-specific real-time PCR targeting the groEL gene.

RESULTS

In the rheumatological patients, the median age was 61 years (IQR 55-68 years), 62% were women, and 44% had a diagnosis of seropositive rheumatoid arthritis. In total, 54% of the patients were treated with infliximab. The median time from TNFi initiation to blood sampling was 20 months (IQR, 5-60 months). N. mikurensis DNA was not detected in any samples from patients or blood donors.

CONCLUSION

N. mikurensis infection does not appear to represent a prevalent risk in Danish rheumatological patients receiving TNFi or in blood donors.

Rickettsia species in Dermacentor reticulatus ticks feeding on human skin and clinical manifestations of tick-borne infections after tick bite

Dermacentor reticulatus ticks are sporadically removed from human skin and therefore the medical consequences of their feeding are neglected compared to Ixodes ricinus. We investigated the prevalence of pathogens in D. reticulatus removed from human skin and possible clinical manifestations suggestive of tick-borne diseases after a tick bite. A total of 2153 ticks were studied and of these only 34 were D. reticulatus. The mean prevalence of Rickettsia in D. reticulatus was 50.0% and R. raoultii was identified in 82.4% of infected D. reticulatus ticks. We confirmed the first case of R. aeschlimannii infection in D. reticulatus ticks. Among participants bitten by D. reticulatus, 13.3% reported reddening around the tick bite site and flu-like symptoms, including lymphadenopathy and 3.3% reported eschar on the tick site bite. All of the participants with flu-like symptoms after tick removal were bitten by ticks infected with R. raoultii. The results of this study indicate that even though D. reticulatus ticks bite humans sporadically, pathogenic Rickettsia have a remarkably high prevalence in this tick species. We can expect that the incidence of tick-borne lymphadenopathy might increase with the reported expansion of the D. reticulatus into new areas and its growing abundance in Central Europe.

Tick-borne diseases under the radar in the North Sea Region

The impact of tick-borne diseases caused by pathogens such as Anaplasma phagocytophilum, Neoehrlichia mikurensis, Borrelia miyamotoi, Rickettsia helvetica and Babesia species on public health is largely unknown. Data on the prevalence of these pathogens in Ixodes ricinus ticks from seven countries within the North Sea Region in Europe as well as the types and availability of diagnostic tests and the main clinical features of their corresponding diseases is reported and discussed. Raised awareness is needed to discover cases of these under-recognized types of tick-borne disease, which should provide valuable insights into these diseases and their clinical significance.

Neoehrlichia mikurensis in Danish immunocompromised patients: a retrospective cohort study

BACKGROUND

The tick-borne bacterium, Neoehrlichia mikurensis (N. mikurensis) can cause severe febrile illness and thromboembolic complications in immunocompromised individuals. We investigated the presence of N. mikurensis DNA in retrospectively collected plasma from a well-characterized cohort of Danish immunocompromised patients.

METHODS

Plasma samples from 239 patients with immune dysfunction related to hematological or rheumatological disease or due to immunosuppressive therapy, were retrieved from a transdisciplinary biobank (PERSIMUNE) at Rigshospitalet, Copenhagen, Denmark. Serving as immunocompetent controls, plasma samples from 192 blood donors were included. All samples were collected between 2015 and 2019. Real-time PCR targeting the groEL gene was used to detect N. mikurensis DNA. Sequencing was used for confirmation. Borrelia burgdorferi sensu lato IgG antibodies were detected by ELISA as a proxy of tick exposure. Prevalence was compared using Fisher's exact test.

RESULTS

Neoehrlichia mikurensis DNA was detected in 3/239 (1.3%, 95% confidence interval (CI): 0.3 - 3.6%) patients, all of whom primarily had a hematological disease. Follow-up samples of these patients were negative. N. mikurensis DNA was not detected in any of the blood donor samples. IgG antibodies against B. burgdorferi s.l. were detected with similar prevalence in immunocompromised patients and blood donors, i.e., 18/239 (7.5%, 95% CI: 4.8-11.5%) and 11/192 (5.7%, 95%: CI 3.2-10.0%).

CONCLUSION

In this study, patients with N. mikurensis were not identified by clinical indication and N. mikurensis may therefore be underdiagnosed in Danish patients. Further investigations are needed to explore the clinical significance and implications of this infection.

Herbivores in Arctic ecosystems: Effects of climate change and implications for carbon and nutrient cycling

Arctic terrestrial herbivores influence tundra carbon and nutrient dynamics through their consumption of resources, waste production, and habitat-modifying behaviors. The strength of these effects is likely to change spatially and temporally as climate change drives shifts in herbivore abundance, distribution, and activity timing. Here, we review how herbivores influence tundra carbon and nutrient dynamics through their consumptive and nonconsumptive effects. We also present evidence for herbivore responses to climate change and discuss how these responses may alter the spatial and temporal distribution of herbivore impacts. Several current knowledge gaps limit our understanding of the changing functional roles of herbivores; these include limited characterization of the spatial and temporal variability in herbivore impacts and of how herbivore activities influence the cycling of elements beyond carbon. We conclude by highlighting approaches that will promote better understanding of herbivore effects on tundra ecosystems, including their integration into existing biogeochemical models, new applications of remote sensing techniques, and the continued use of distributed experiments.

No molecular detection of tick-borne pathogens in the blood of patients with erythema migrans in Belgium

Background

A number of tick-borne pathogens circulate in the Belgian tick population in addition to the causative agent of Lyme borreliosis. However, so far, only a few patients with tick-borne diseases other than Lyme borreliosis have been reported in Belgium. The aim of this study was to investigate the occurrence of other human tick-borne infections in Belgium and their possible clinical manifestation.

Methods

Patients with fever (> 37.5 °C) after a tick bite or those with erythema migrans (EM) were included in the study. EDTA-blood samples were screened for the presence of DNA from Borrelia burgdorferi sensu lato, Borrelia miyamotoi, Anaplasma phagocytophilum, Neoehrlichia mikurensis, spotted fever group rickettsiae (genus Rickettsia), Babesia spp., Bartonella spp., Spiroplasma ixodetis and tick-borne encephalitis virus, using multiplex PCR methods. A questionnaire on, among others, demographics and clinical symptoms, was also filled in.

Results

Over a period of 3 years, 119 patients with EM and 14 patients with fever after a recent tick bite were enrolled in the study. Three samples initially tested positive for N. mikurensis by quantitative PCR (qPCR), but the results could not be confirmed by other PCR methods, and repetition of the DNA extraction procedure and qPCR test was not successful. The qPCR test results for the other tick-borne pathogens were negative.

Conclusions

In general, only a few patients with fever after a tick bite could be identified. Although no tick-borne pathogens were detected, their occurrence cannot be excluded based on the limited number of patients and the limitations inherent to current methodologies. This study underscores the possibility of false-positive PCR results and the necessity for the development of multiple independent tools for the sensitive and specific detection of emerging tick-borne pathogens.

Graphical Abstract

Neoehrlichiosis: A Case Study of the Tick-Borne Pathogen That Can Cause Thromboembolic Events

Candidatus Neoehrlichia mikurensis is a gram-negative bacterium carried and spread by Ixodes ricinus ticks often found in Europe and Asia. It causes a disease process called neoehrlichiosis, which can result in vasculitis and thromboembolic events. This pathogen does not grow in typical culture medium, and most laboratories do not carry the specific polymerase chain reaction (PCR) test needed to detect neoehrlichiosis. If a patient presents to an emergency department complaining of a recent tick bite and symptoms of a deep vein thrombosis or pulmonary embolism, consider that these symptoms may be related. Treat the tick bite with doxycycline for 3 weeks and manage the thromboembolic event according to standard treatment of care.

Biting insects in a rapidly changing Arctic

Biting insects have a long-standing reputation for being an extreme presence in the Arctic, but it is unclear how they are responding to the rapid environmental changes currently taking place in the region. We review recent advances in our understanding of climate change responses by several key groups of biting insects, including mosquitoes, blackflies, and warble/botflies, and we highlight the significant knowledge gaps on this topic. We also discuss how changes in biting insect populations could impact humans and wildlife, including disease transmission and the disruption of culturally and economically important activities. Future work should integrate scientific with local and traditional ecological knowledge to better understand global change responses by biting insects in the Arctic and the associated consequences for the environmental security of Arctic communities.

Unbiased Characterization of the Microbiome and Virome of Questing Ticks

Due to their vector capacity, ticks are ectoparasites of medical and veterinary significance. Modern sequencing tools have facilitated tick-associated microbiota studies, but these have largely focused on bacterial pathogens and symbionts. By combining 16S rRNA gene sequencing with total RNA-sequencing methods, we aimed to determine the complete microbiome and virome of questing, female Ixodes holocyclus recovered from coastal, north-eastern New South Wales (NSW), Australia. We present, for the first time, a robust and unbiased method for the identification of novel microbes in ticks that enabled us to identify bacteria, viruses, fungi and eukaryotic pathogens. The dominant bacterial endosymbionts were Candidatus Midichloria sp. Ixholo1 and Candidatus Midichloria sp. Ixholo2. Candidatus Neoehrlichia australis and Candidatus Neoehrlichia arcana were also recovered, confirming that these bacteria encompass I. holocyclus’ core microbiota. In addition, seven virus species were detected—four previously identified in I. holocyclus and three novel species. Notably, one of the four previously identified virus species has pathogenic potential based on its phylogenetic relationship to other tick-associated pathogens. No known pathogenic eukaryotes or fungi were identified. This study has revealed the microbiome and virome of female I. holocyclus from the environment in north-eastern NSW. We propose that future tick microbiome and virome studies utilize equivalent methods to provide an improved representation of the microbial diversity in ticks globally.

Spatial patterns of pathogen prevalence in questing Ixodes ricinus nymphs in southern Scandinavia, 2016

Tick-borne pathogens cause diseases in animals and humans, and tick-borne disease incidence is increasing in many parts of the world. There is a need to assess the distribution of tick-borne pathogens and identify potential risk areas. We collected 29,440 tick nymphs from 50 sites in Scandinavia from August to September, 2016. We tested ticks in a real-time PCR chip, screening for 19 vector-associated pathogens. We analysed spatial patterns, mapped the prevalence of each pathogen and used machine learning algorithms and environmental variables to develop predictive prevalence models. All 50 sites had a pool prevalence of at least 33% for one or more pathogens, the most prevalent being Borrelia afzelii, B. garinii, Rickettsia helvetica, Anaplasma phagocytophilum, and Neoehrlichia mikurensis. There were large differences in pathogen prevalence between sites, but we identified only limited geographical clustering. The prevalence models performed poorly, with only models for R. helvetica and N. mikurensis having moderate predictive power (normalized RMSE from 0.74-0.75, R2 from 0.43-0.48). The poor performance of the majority of our prevalence models suggest that the used environmental and climatic variables alone do not explain pathogen prevalence patterns in Scandinavia, although previously the same variables successfully predicted spatial patterns of ticks in the same area.

Spatial data of Ixodes ricinus instar abundance and nymph pathogen prevalence, Scandinavia, 2016-2017

Ticks carry pathogens that can cause disease in both animals and humans, and there is a need to monitor the distribution and abundance of ticks and the pathogens they carry to pinpoint potential high risk areas for tick-borne disease transmission. In a joint Scandinavian study, we measured Ixodes ricinus instar abundance at 159 sites in southern Scandinavia in August-September, 2016, and collected 29,440 tick nymphs at 50 of these sites. We additionally measured abundance at 30 sites in August-September, 2017. We tested the 29,440 tick nymphs in pools of 10 in a Fluidigm real-time PCR chip to screen for 17 different tick-associated pathogens, 2 pathogen groups and 3 tick species. We present data on the geolocation, habitat type and instar abundance of the surveyed sites, as well as presence/absence of each pathogen in all analysed pools from the 50 collection sites and individual prevalence for each site. These data can be used alone or in combination with other data for predictive modelling and mapping of high-risk areas.

Tick-Borne Pathogens Detected in the Blood of Immunosuppressed Norwegian Patients Living in a Tick-Endemic Area

BACKGROUND

The knowledge regarding the occurrence and the clinical implications of tick-borne infections in immunosuppressed patients living in tick-endemic areas is limited.

METHODS

Adult patients with autoimmune conditions requiring immunosuppressive treatment such as infliximab and rituximab, were invited to participate in the study when they attended the hospital for treatment and/or control of the disease. Whole blood samples were analysed by real-time PCR for Borrelia burgdorferi s.l., Borrelia miyamotoi, Anaplasma phagocytophilum, Rickettsia spp., Candidatus Neoehrlichia mikurensis and Babesia spp.

RESULTS

The occurrence of tick-borne pathogens in the blood of patients (n=163) with autoimmune conditions requiring immunosuppressive treatment were evaluated. Pathogen DNA was detected in 8.6% (14/163) of the patients. The predominant pathogen was Candidatus Neoehrlichia mikurensis (12/14), which was carried in the blood of infected patients for 10-59 days until treatment with doxycycline. Borrelia burgdorferi sensu lato and Rickettsia spp. were detected in one patient each. The B. burgdorferi-infected patient presented with fever, whereas the remaining patients were judged to have subclinical infections. Borrelia miyamotoi, Anaplasma phagocytophilum, and Babesia spp. were not detected in any patient.

CONCLUSIONS

Patients treated with biologicals and living in a tick-endemic area seem to have a high risk of contracting Ca. Neoehrlichia mikurensis infection which if left untreated could result in thromboembolic complications.

Tick-borne pathogens in Ixodes ricinus ticks collected from migratory birds in southern Norway

Birds are important hosts for the first life stages of the Ixodes ricinus tick and they can transport their parasites over long distances. The aim of this study was to investigate the prevalence of Borrelia burgdorferi sensu lato, Anaplasma phagocytophilum, Neoehrlichia mikurensis and Rickettsia helvetica in ticks collected from migratory birds in Norway. A total of 815 Ixodes ricinus ticks from 216 birds trapped at Lista Bird Observatory in southern Norway during spring and autumn migration in 2008 were analysed by real-time PCR. B. burgdorferi s. l. was the most prevalent pathogen, detected in 6.1% of the ticks. The prevalence of N. mikurensis, A. phagocytophilum and R. helvetica was 1.2%, 0.9% and 0.4% respectively. In addition, one sample (0.1%) was positive for B. miyamotoi. In total, 8.2% of the ticks were infected with at least one pathogen. Co-infection with B. burgdorferi s. l. and N. mikurensis or A. phagocytophilum was found in 6.0% of the infected ticks. Our results show that all the known major tick-borne bacterial pathogens in Norway are subject to transport by migratory birds, potentially allowing spread to new areas. Our study showed a surprisingly high number of samples with PCR inhibition (57%). These samples had been extracted using standard methodology (phenol-chloroform extraction). This illustrates the need for inhibition controls to determine true prevalence rates.

Distribution of Neoehrlichia mikurensis in Ixodes ricinus ticks along the coast of Norway: The western seaboard is a low-prevalence region

Neoehrlichia mikurensis is a tick-borne pathogen widespread among ticks and rodents in Europe and Asia. A previous study on Ixodes ricinus ticks in Norway suggested that N. mikurensis was scarce or absent on the south-west coast of Norway, but abundant elsewhere. The aim of this study was to further investigate the prevalence and distribution of N. mikurensis along the western seaboard of Norway in comparison with more eastern and northern areas. The second aim of the study was to examine seasonal variation of the bacterium in one specific location in the south-eastern part of Norway. Questing I. ricinus were collected from 13 locations along the coast of Norway, from Brønnøysund in Nordland County to Spjaerøy in Østfold County. In total, 11,113 nymphs in 1,113 pools and 718 individual adult ticks were analysed for N. mikurensis by real-time PCR. The mean prevalence of N. mikurensis in adult ticks was 7.9% while the estimated pooled prevalence in nymphs was 3.5%. The prevalence ranged from 0% to 25.5%, with the highest prevalence in the southernmost and the northernmost locations. The pathogen was absent, or present only at low prevalence (<5%), at eight locations, all located in the west, from 58.9°N to 64.9°N. The prevalence of N. mikurensis was significantly different between counties (p < .0001). No significant seasonal variation of N. mikurensis prevalence was observed in the period May to October 2015. Our results confirm earlier findings of a low prevalence of N. mikurensis in the western seaboard of Norway.