Occurrence and Identification of Ixodes ricinus Borne Pathogens in Northeastern Italy

Surveillance of Tick-Borne Pathogens in Ticks from Humans in the Province of Verona, Italy (2018-2022): A Prospective Study

In Italy, the epidemiology of tick-borne pathogens is still poorly characterized. This prospective study was conducted at the IRCCS Sacro Cuore Don Calabria Hospital in Negrar di Valpolicella (Verona), northeastern Italy, from 2018 to 2022. Ticks from asymptomatic individuals visiting the hospital after a recent tick bite were characterized using microscopy and tested for pathogens using molecular tests. A total of 317 ticks collected from 280 subjects were analyzed, with most identified as Ixodes species (95.6%), followed by Rhipicephalus spp. (0.6%) and Dermacentor spp. (0.3%). Molecular analysis was performed on 257 single ticks and 23 pooled samples. Overall, 15.4% tested positive for at least one pathogen. The most frequently detected pathogen was Borrelia spp. (n = 22, 7.8%), including B. afzeli (n = 8), B. miyamotoi (n = 6), B. valaisiana (n = 2), B. garinii (n = 2), Borrelia spp. (n = 2), B. burgdorferi sensu stricto (n = 1), and B. spielmanii (n = 1). Rickettsia spp. was detected in 20 samples (7.1%), comprising R. helvetica (n = 11), R. monacensis (n = 7), and Rickettsia spp. (n = 2). Other pathogens included Anaplasma phagocytophilum (n = 5, 1.8%), Babesia venatorum (n = 2, 0.7%), and tick-borne encephalitis virus (n = 1, 0.4%). This study calls for enhanced surveillance in the province of Verona to clarify these pathogens' clinical impact.

Identifying and Mapping Ticks on Wild Boars from Romania

Globally, due to climate change, urbanization, and the intensification of interactions between humans and animals, tick populations have increased, and areas where these arthropod vectors can develop and transmit diseases have expanded. Ixodidae ticks infect a wide variety of species and serve as major vectors for zoonotic pathogens of veterinary importance. This study aimed to identify and map ticks collected from boar tails in six Romanian counties. A total of 141 ticks were identified and differentiated on the basis of their morphological characteristics via stereomicroscopy and electron microscopy. Among the 141 ticks examined, five species, Ixodes ricinus, Haemaphysalis concinna, Haemaphysalis erinacei, Dermacentor reticulatus, and Dermacentor marginatus, were identified. The identification and mapping of ticks present on wild boars is beneficial for both veterinary and human medicine due to the pathogens they can transmit. The results of our study indicate that parasitism with different tick species in wildlife-in this case, wild boar-is present in the Romanian counties under study. This is one of the most recent tick identification and mapping studies. Tick parasitism represents a threat to the health of wild/domestic animals, and frequent monitoring is necessary.

Co-infections of rickettsiales in clinically healthy, Leishmania infantum seropositive and seronegative dogs: a systematic literature review and new findings from Southern Italy

Canine leishmaniosis (CanL), caused by Leishmania infantum, is a widespread vector-borne disease. In Italy, an endemic region for CanL, overlapping transmission of L. infantum and tick-borne pathogens (TBPs) like Anaplasma phagocytophilum and Ehrlichia canis is increasingly reported. Dogs with clinical leishmaniosis often show higher co-infection rates and pronounced clinicopathological abnormalities. This study presents a systematic literature review and new findings from southern Italy, focusing on co-infections with E. canis and A. phagocytophilum in clinically healthy L. infantum seropositive and seronegative dogs. The systematic review identified two eligible studies. The first reported 34/488 (7%) dogs L. infantum seropositive, with 11.8% also seropositive for A. phagocytophilum. Among 454 seronegative dogs, 3% were seropositive for A. phagocytophilum and 2.4% for E. canis. The second study identified 154/1260 (12.2%) dogs L. infantum seropositive, with co-infection rates of 0.6% and 1.9% for A. phagocytophilum and E. canis, respectively. Among 1106 seronegative dogs, 1.3% were seropositive for A. phagocytophilum and 2.3% for E. canis. In the retrospective study from southern Italy, 90/154 (58.4%) dogs were L. infantum seropositive, with co-infection rates of 4.4% for A. phagocytophilum and 2.2% for A. phagocytophilum and E. canis. Among 64 seronegative dogs, 1.6% showed similar co-infections. This is the first systematic review in Italy, documenting low and comparable co-infection rates with A. phagocytophilum and E. canis in clinically healthy dogs, regardless of L. infantum serostatus. These findings suggest that co-infections may occur independently, offering insights into vector-borne disease dynamics in endemic areas.

Temporal Changes in Tick-Borne Pathogen Prevalence in Questing Ixodes ricinus Across Different Habitats in the North-Eastern Italian Alps

Changes in land use, climate, and host community are leading to increased complexity in eco-epidemiological relationships and the emergence of zoonoses. This study investigates the changes in the prevalence of several Ixodes ricinus-transmitted pathogens in questing ticks over a 10-year interval (2011-2013, 2020) in natural and agricultural habitats of the Autonomous Province of Trento (North-eastern Alps), finding an average prevalence of infection of 27.1%. Analysis of 2652 ticks, investigating four infectious agents (Borrelia burgdorferi sensu lato, Anaplasma spp., Rickettsia spp., and Babesia spp.), revealed the circulation of 11 different zoonotic pathogens, with varying infection rates across different years and habitats. In 2020, we found a decrease in Anaplasma phagocytophilum, associated with agricultural habitats, and Rickettsia spp., found in all habitats. In the same year, Babesia spp. increased in both habitats, similar to Borrelia burgdorferi sensu stricto, which was related to natural habitats. Co-infections were identified in 8% of positive-tested ticks with different spatiotemporal associations, primarily in natural settings. Our results provide new evidence that the risk of infection with tick-borne pathogens in the Alpine region varies over time and in different environments, broadening the current information on co-infection rates and the circulation of zoonotic pathogens, previously not reported in this area.

Genome sequence of Ehrlichia muris from Ixodes ricinus collected in Italy on a migratory bird provides epidemiological and evolutionary insights

Ticks are prominent vectors of several zoonotic diseases. Tick-borne pathogens include the members of the genus Ehrlichia, which are obligate intracellular bacteria infecting immune and hematopoietic cells. Ehrlichia muris predominantly affects rodents, but was also reported to be a human pathogen. The known geographical distribution of this bacterium ranges from Asia, to the USA and eastern Europe. In the present work, we report the finding of E. muris in an Ixodes ricinus tick collected from a migratory bird (Turdus iliacus) in Italy, southern Europe. We sequenced the total DNA from this tick sample, and, thanks to a dedicated bioinformatic pipeline, selectively assembled the genome of the bacterium, which represents the first one for E. muris from Europe. Phylogenetic and comparative genomic analyses were then performed. Accounting for tick species distribution, bird migratory routes, and molecular phylogeny of the bacterium, it is likely that this bird transported the tick to Italy from an endemic area of E. muris, such as eastern Europe. In addition, comparative genomic analyses highlighted that E. muris and other Ehrlichia spp. display copy number variations in two families of membrane proteins, likely due to recent gene duplication, deletion and recombination events. These differences are probably a source of variability for surface antigens to evade host immunity, with a potential role in host adaptation and specificity. The present results underline the impact of migratory birds on the spread of tick-borne pathogens towards non-endemic areas, highlighting the need for further epidemiological surveillance at bird ringing stations in Italy, and advocating further investigations on possible local transmission of E. muris in competent mammalian hosts.

Habitat Suitability of Ixodes ricinus Ticks Carrying Pathogens in North-East Italy

Ixodes ricinus ticks are ubiquitous in Europe, including in North-East Italy. These ticks are important vectors of several zoonotic pathogens of public health relevance. In this study, the habitat suitability range of I. ricinus ticks infected with zoonotic pathogens was predicted in North-East Italy, and relevant spatial predictors were identified. In 2015-2021, ticks were collected at 26 sampling sites in the study area. The collected ticks were screened for the presence of pathogens using PCR assays. For Borrelia, Rickettsia and Anaplasma/Ehrlichia species, data allowed for ecological niche modelling using Maxent. Environmental determinants potentially related to tick habitat suitability were used as model inputs. Predicted suitable habitat distributions revealed hotspots of the probability of pathogen presence in I. ricinus ticks mainly in the central and upper parts of the study area. Key environmental predictors were temperature, rainfall and altitude, and vegetation index for specific pathogens (Rickettsia and Anaplasma/Ehrlichia species). Increased risk of exposure to tick-borne pathogens upon tick bites in the predicted hotspot areas can, therefore, be expected. This provides useful information for public health risk managers in this and other similar regions.

Ticks and Tick-Borne Pathogens: Occurrence and Host Associations over Four Years of Wildlife Surveillance in the Liguria Region (Northwest Italy)

Tick-borne diseases (TBDs) are a considerable public health problem worldwide. The occurrence of Anaplasma spp., Borrelia burgdorferi s.l., Coxiella burnetii, Rickettsia spp., and tick-borne encephalitis virus (TBEv) was investigated via PCR and sequencing in 683 ticks collected from 105 roe deer, 61 wild boars, 49 fallow deer, and 2 chamois, in the Liguria region, northwest Italy, between 2019 and 2022. The ticks were morphologically identified. Four different tick species were found: Ixodes ricinus (66.8% of the collected ticks), Dermacentor marginatus (15.8%), Rhipicephalus sanguineus s.s. (15.7%), and Haemaphysalis punctata (0.9%). Six ticks (0.9%) were only identified as Rhipicephalus spp. Of the 222 pools analyzed, 27.9% were positive. Most pools (n = 58, 26.1% of pools analyzed) were positive for Rickettsia spp., and several species were found: Rickettsia slovaca was the dominant species (15.3%), followed by R. monacensis (8.1%), while R. helvetica (1.8%), R. massiliae (0.5%), and R. raoultii (0.5%) were found only sporadically. Anaplasma phagocytophilum was identified in three pools and B. burgdorferi s.l. in one pool. All samples were negative for C. burnetii and TBEv. Significant associations were found between I. ricinus and roe deer, D. marginatus and wild boar, and between R. monacensis and I. ricinus. The prevalence of Rickettsia spp. differed significantly between tick and host species. This updated picture of tick species and TBPs in wild ungulates in Liguria, where the population of these animals is increasing, shows a widespread presence of potentially zoonotic Rickettsia spp. Continuous monitoring and public information on preventive measures are needed.

Prevalence of Lyme Disease and Relapsing Fever Borrelia spp. in Vectors, Animals, and Humans within a One Health Approach in Mediterranean Countries

The genus Borrelia has been divided into Borreliella spp., which can cause Lyme Disease (LD), and Borrelia spp., which can cause Relapsing Fever (RF). The distribution of genus Borrelia has broadened due to factors such as climate change, alterations in land use, and enhanced human and animal mobility. Consequently, there is an increasing necessity for a One Health strategy to identify the key components in the Borrelia transmission cycle by monitoring the human-animal-environment interactions. The aim of this study is to summarize all accessible data to increase our understanding and provide a comprehensive overview of Borrelia distribution in the Mediterranean region. Databases including PubMed, Google Scholar, and Google were searched to determine the presence of Borreliella and Borrelia spp. in vectors, animals, and humans in countries around the Mediterranean Sea. A total of 3026 were identified and screened and after exclusion of papers that did not fulfill the including criteria, 429 were used. After examination of the available literature, it was revealed that various species associated with LD and RF are prevalent in vectors, animals, and humans in Mediterranean countries and should be monitored in order to effectively manage and prevent potential infections.

Italian peninsula as a hybridization zone of Ixodes inopinatus and I. ricinus and the prevalence of tick-borne pathogens in I. inopinatus, I. ricinus, and their hybrids

BACKGROUND

Ixodes inopinatus was described from Spain on the basis of morphology and partial sequencing of 16S ribosomal DNA. However, several studies suggested that morphological differences between I. inopinatus and Ixodes ricinus are minimal and that 16S rDNA lacks the power to distinguish the two species. Furthermore, nuclear and mitochondrial markers indicated evidence of hybridization between I. inopinatus and I. ricinus. In this study, we tested our hypothesis on tick dispersal from North Africa to Southern Europe and determined the prevalence of selected tick-borne pathogens (TBPs) in I. inopinatus, I. ricinus, and their hybrids.

METHODS

Ticks were collected in Italy and Algeria by flagging, identified by sequencing of partial TROSPA and COI genes, and screened for Borrelia burgdorferi s.l., B. miyamotoi, Rickettsia spp., and Anaplasma phagocytophilum by polymerase chain reaction and sequencing of specific markers.

RESULTS

Out of the 380 ticks, in Italy, 92 were I. ricinus, 3 were I. inopinatus, and 136 were hybrids of the two species. All 149 ticks from Algeria were I. inopinatus. Overall, 60% of ticks were positive for at least one TBP. Borrelia burgdorferi s.l. was detected in 19.5% of ticks, and it was significantly more prevalent in Ixodes ticks from Algeria than in ticks from Italy. Prevalence of Rickettsia spotted fever group (SFG) was 51.1%, with significantly greater prevalence in ticks from Algeria than in ticks from Italy. Borrelia miyamotoi and A. phagocytophilum were detected in low prevalence (0.9% and 5.2%, respectively) and only in ticks from Italy.

CONCLUSIONS

This study indicates that I. inopinatus is a dominant species in Algeria, while I. ricinus and hybrids were common in Italy. The higher prevalence of B. burgdorferi s.l. and Rickettsia SFG in I. inopinatus compared with that in I. ricinus might be due to geographical and ecological differences between these two tick species. The role of I. inopinatus in the epidemiology of TBPs needs further investigation in the Mediterranean Basin.

Biting Back: Advances in Fighting Ticks and Understanding Tick-Borne Pathogens

Ticks are blood-feeding arthropods and obligate ectoparasites of virtually all animal species (except fish) and humans [...].

High-throughput screening of pathogens in Ixodes ricinus removed from hosts in Lombardy, northern Italy

Ticks are important vectors of many pathogens in Europe, where the most impactful species is Ixodes ricinus. Recently, the geographical distribution of this tick species has been expanding, resulting in an increased risk of human exposure to tick bites. With the present study, we aimed to screen 350 I. ricinus specimens collected from humans and wild animals (mainly ungulates), to have a broader understanding of the tick-borne pathogens circulating in the Lombardy region, in northern Italy. To do so, we took advantage of a high-throughput real-time microfluidic PCR approach to screen ticks in a cost-effective and time-saving manner. Molecular analysis of the dataset revealed the presence of four genera of bacteria and two genera of protozoa: in ungulates, 77 % of collected ticks carried Anaplasma phagocytophilum, while the most common pathogen species in ticks removed from humans were those belonging to Borrelia burgdorferi sensu lato group (7.6 %). We also detected other pathogenic microorganisms, such as Rickettisa monacensis, Rickettsia helvetica, Neoehrlichia mikurensis, Babesia venatorum, and Hepatozoon martis. Besides, we also reported the presence of the pathogenic agent Borrelia miyamotoi in the area (1.4 % overall). The most common dual co-infection detected in the same tick individual involved A. phagocytophilum and Rickettsia spp. Our study provided evidence of the circulation of different tick-borne pathogens in a densely populated region in Italy.

Wild ungulates as sentinels of flaviviruses and tick-borne zoonotic pathogen circulation: an Italian perspective

BACKGROUND

Vector-borne zoonotic diseases are a concerning issue in Europe. Lyme disease and tick-borne encephalitis virus (TBEV) have been reported in several countries with a large impact on public health; other emerging pathogens, such as Rickettsiales, and mosquito-borne flaviviruses have been increasingly reported. All these pathogens are linked to wild ungulates playing roles as tick feeders, spreaders, and sentinels for pathogen circulation. This study evaluated the prevalence of TBEV, Borrelia burgdorferi sensu lato, Rickettsia spp., Ehrlichia spp., and Coxiella spp. by biomolecular screening of blood samples and ticks collected from wild ungulates. Ungulates were also screened by ELISA and virus neutralization tests for flaviviral antibody detection.

RESULTS

A total of 274 blood samples were collected from several wild ungulate species, as well as 406 Ixodes ricinus, which were feeding on them. Blood samples tested positive for B. burgdorferi s.l. (1.1%; 0-2.3%) and Rickettsia spp. (1.1%; 0-2.3%) and showed an overall flaviviral seroprevalence of 30.6% (22.1-39.2%): 26.1% (17.9-34.3%) for TBEV, 3.6% (0.1-7.1%) for Usutu virus and 0.9% (0-2.7%) for West Nile virus. Ticks were pooled when possible and yielded 331 tick samples that tested positive for B. burgdorferi s.l. (8.8%; 5.8-11.8%), Rickettsia spp. (26.6%; 21.8-31.2%) and Neoehrlichia mikurensis (1.2%; 0-2.4%). TBEV and Coxiella spp. were not detected in either blood or tick samples.

CONCLUSIONS

This research highlighted a high prevalence of several tick-borne zoonotic pathogens and high seroprevalence for flaviviruses in both hilly and alpine areas. For the first time, an alpine chamois tested positive for anti-TBEV antibodies. Ungulate species are of particular interest due to their sentinel role in flavivirus circulation and their indirect role in tick-borne diseases and maintenance as Ixodes feeders and spreaders.

Distribution of ticks in the Western Palearctic: an updated systematic review (2015-2021)

BACKGROUND

The distributions of ticks and tick-borne pathogens are thought to have changed rapidly over the last two decades, with their ranges expanding into new regions. This expansion has been driven by a range of environmental and socio-economic factors, including climate change. Spatial modelling is being increasingly used to track the current and future distributions of ticks and tick-borne pathogens and to assess the associated disease risk. However, such analysis is dependent on high-resolution occurrence data for each species. To facilitate such analysis, in this review we have compiled georeferenced tick locations in the Western Palearctic, with a resolution accuracy under 10 km, that were reported between 2015 and 2021 METHODS: The PubMed and Web of Science databases were searched for peer-reviewed papers documenting the distribution of ticks that were published between 2015 and 2021, using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The papers were then screened and excluded in accordance with the PRISMA flow chart. Coordinate-referenced tick locations along with information on identification and collection methods were extracted from each eligible publication. Spatial analysis was conducted using R software (version 4.1.2).

RESULTS

From the 1491 papers identified during the initial search, 124 met the inclusion criteria, and from these, 2267 coordinate-referenced tick records from 33 tick species were included in the final dataset. Over 30% of articles did not record the tick location adequately to meet inclusion criteria, only providing a location name or general location. Among the tick records, Ixodes ricinus had the highest representation (55%), followed by Dermacentor reticulatus (22.1%) and Ixodes frontalis (4.8%). The majority of ticks were collected from vegetation, with only 19.1% collected from hosts.

CONCLUSIONS

The data presented provides a collection of recent high-resolution, coordinate-referenced tick locations for use in spatial analyses, which in turn can be used in combination with previously collated datasets to analyse the changes in tick distribution and research in the Western Palearctic. In the future it is recommended that, where data privacy rules allow, high-resolution methods are routinely used by researchers to geolocate tick samples and ensure their work can be used to its full potential.

Effective Methods of Estimation of Pathogen Prevalence in Pooled Ticks

Since tick-borne diseases (TBDs) incidence, both in human and animal populations, is increasing worldwide, there is the need to assess the presence, distribution and prevalence of tick-borne pathogens. Reliable estimates on tick-borne pathogens (TBPs) prevalence represent the public health foundation to create risk maps and take effective prevention and control actions against TBDs. Tick surveillance consists of collecting and testing (usually in pools) thousands of specimens. Construction and analysis of tick pools represent a challenge due to the complexity of tick-borne pathogens and tick-borne diseases ecology. The aim of this study is to provide a practical guideline on appropriate pooling strategies and statistical analysis of infection prevalence through: (i) reporting the different pooling strategies and statistical methodologies commonly used to calculate pathogen prevalence in tick populations and (ii) practical comparison between statistical methods utilising a real dataset of infection prevalence in ticks collected in Northern Italy. Reporting detailed information on tick pool composition and size is as important as the correct TBPs prevalence estimation. Among the prevalence indexes, we suggest using maximum-likelihood estimates of pooled prevalence instead of minimum infection rate or pool positivity rate given the merits of the method and availability of software.

High Prevalence of Tick-Borne Zoonotic Rickettsia slovaca in Ticks from Wild Boars, Northeastern Italy

Simple Summary

Tick-borne rickettsioses are emerging diseases that have become widespread in many European countries, particularly in those facing the Mediterranean basin. Although Rickettsia conorii was traditionally thought to be the most threatening species, in recent decades, thanks to the improvements in biomolecular tools, other zoonotic species have been identified, such as Rickettsia slovaca, the etiological agent of scalp eschar and neck lymphadenopathy after tick bite (SENLAT), as well as other neglected species. These pathogens are present in Italy, but few data are available. This research aimed to improve the epidemiological knowledge of rickettsial infections in tick and wild boar populations in the Euganean Hills Regional Park, an enclosed area in northeastern Italy. Both tick and wild boar blood samples were tested using biomolecular methods to detect and identify Rickettsia species. Only ticks tested positive, and Rickettsia slovaca was the most frequently detected species, showing a high prevalence, followed by Rickettsia monacensis and Rickettsia helvetica. These data highlight a non-negligible presence of these pathogens in northern Italy and outline that rickettsial infections deserve further investigation.

Abstract

Tick-borne rickettsiae are emerging pathogens that are becoming widespread in Europe. Rickettsiae are endemic in Italy, but epidemiological data are currently scarce. This study aimed to improve our knowledge about rickettsial infections in tick and wild boar populations. Blood and ticks were collected from 102 wild boars in 2010 and 2018. Ticks were also collected from the vegetation in the area. All of the samples were examined using real-time PCR targeting the gltA gene to detect Rickettsia DNA. Positivity was confirmed by PCR amplifying the gltA and/or ompB genes. A total of 254 ticks and 89 blood samples were analyzed. Zoonotic rickettsiae were detected in the ticks but not in the blood samples. Rickettsia slovaca (R. slovaca) was the most prevalent in ticks and was found in 23.7% of Dermacentor marginatus (D. marginatus) and in 3.4% of Ixodes ricinus (I. ricinus). Other zoonotic species were identified, such as Rickettsia monacensis, which was detected in 12% of I. ricinus ticks, and Rickettsia helvetica which was found in 3.4% of questing I. ricinus ticks and in 1.1% of D. marginatus collected from wild boars. This study highlights a high prevalence of zoonotic rickettsiae, particularly that of R. slovaca, in northeastern Italy. As rickettsioses are underreported and underdiagnosed in human medicine, both clinicians and researchers should pay more attention to this topic.

Looking for Dog Blood Donors in an Endemic Area for Vector-Borne Infections of Central Italy

Simple Summary

Dogs have proved to be competent reservoir hosts for several vector-borne pathogens, whose prevalence varies according to the area and over time due to the increased movement of people and their pets, climate changes, and vector adaptation strategies. The purpose of this study was to determine the prevalence of some vector-borne pathogens in dog blood donors, living in central Italy. Blood samples of 126 donors included were tested for a broad screening panel for infectious pathogens. The differences in pathogens prevalence according to age, sex, and breeds were tested. Overall, 50 animals tested positive for at least one pathogen. A tendency of hemoplasmas to be more prevalent in older dogs (41.2%) was noted. We highlight the difficulties of selecting healthy blood donor dogs in an endemic area for vector-borne infections. Close collaboration between specialists is important in the interpretation of positive test results. Finally, we underline the important role of blood donors as an epidemiological tool for active surveillance against canine infectious diseases.

Abstract

Dogs are proved to be competent reservoir hosts for several vector-borne pathogens. Their prevalence varies according to the geographical area. Many vector-borne pathogens may be transmitted by blood transfusion. The purpose of this study was to determine the serological and molecular prevalence of some vector-borne pathogens in dog blood donors, living in central Italy. Blood samples of 126 donors (19 breeds) included were tested for a broad serological and DNA-base tests panel. The differences in pathogen prevalence according to age, sex, and breeds were tested (chi-square test, Fisher’s exact test). Overall, 50 animals (39.7%) tested positive at PCR (polymerase chain reaction) and/or serology (IFAT, indirect fluorescent antibody test) for at least one pathogen. Three dogs were positive at both serology and PCR. A tendency of hemoplasmas to be more prevalent in older dogs (41.2%) compared to the younger ones (25.7%) was noted. We highlight the difficulties of selecting healthy blood donor dogs in an endemic area for vector-borne infections. It is important to choose the serological and biomolecular investigations panel that is most suited to the donor’s environment. Close collaboration between clinician and parasitologists is important in the interpretation of IFAT and PCR results. Finally, we underline the important role of blood donors as an epidemiological tool for active surveillance against canine vector-borne diseases.

Human Co-Infections between Borrelia burgdorferi s.l. and Other Ixodes-Borne Microorganisms: A Systematic Review

When it comes to tick-borne diseases, co-infections are often mentioned. This concept includes several entities. On the one hand, tick vectors or vertebrate reservoir host can harbor several microorganisms that can be pathogenic for humans. On the other hand, human co-infections can also be understood in different ways, ranging from seropositivity without clinical symptoms to co-disease, i.e., the simultaneous clinical expression of infections by two tick-borne microorganisms. The latter, although regularly speculated, is not often reported. Hence, we conducted a systematic review on co-infections between B. burgdorferi s.l., the etiological agent of Lyme borreliosis, and other microorganisms potentially transmitted to humans by Ixodes spp. ticks. A total of 68 relevant articles were included, presenting 655 cases of possible co-infections. Most cases of co-infections corresponded to patients with one tick-borne disease and presenting antibody against another tick-borne microorganism. Co-disease was particularly frequent in two situations: patients with clinical symptoms of high fever and erythema migrans (EM), and patients with neurological symptoms linked to the TBEv or a neuroborreliosis. No impact on severity was evidenced. Further studies are needed to better appreciate the frequency and the impact of co-infections between several tick-borne microorganisms.