ABSTRACT Obligate endosymbionts relying on transovarial transmission must coordinate with host reproduction, yet the regulatory mechanisms remain poorly understood. Here we show that the vitellogenesis pathway of the tick Ixodes scapularis regulates the transcriptional state of its endosymbiont Rickettsia buchneri ( Rb ), separately from its abundance. In males, Rb DNA remained detectable, but bacterial transcription was strongly reduced across all examined genes, with markedly lower RNA/DNA ratios. In females, Rb was restricted to ovarian tissues (developing oocytes and interstitial cells), with no detection in salivary glands or midgut by TEM, FISH, or PCR. After blood feeding, Rb density within size-matched early-stage oocytes was significantly reduced. We further characterized two gene families mediating vitellogenesis: vitellogenin synthesis genes (Vgs, n = 20) and vitellogenin receptor genes (Vgr, n = 15). Vgs proteins showed conserved domain organization, whereas Vgr paralogs showed greater structural diversification. RNAi silencing of Vgs20 or Vgr12 altered Rb transcriptional profiles in both tick cells and ticks, although changes in bacterial load were not consistent between the two systems. Antibiotic depletion of Rb increased expression of both host genes. Together, these findings show that tick vitellogenesis pathways contribute to Rb regulation during reproduction and identify the I. scapularis - Rb system as a useful model for studying host control of obligate endosymbionts. IMPORTANCE Maternally inherited bacterial symbionts are commonly characterized by bacterial abundance. This study shows that bacterial abundance alone does not necessarily reflect symbiont functional state. In the blacklegged tick, the inherited symbiont Rickettsia buchneri persists in males but exhibits little transcriptional activity. In females, the host reproductive pathway determines whether the symbiont is active: silencing one component of this pathway changed bacterial gene expression without changing bacterial abundance. Hosts therefore regulate not only the abundance of inherited symbionts, but also their functional state. The same bacterial abundance can correspond to very different functional states. Understanding inherited symbioses therefore requires considering bacterial function alongside bacterial abundance.

Background/Objectives: Incidence of vector-borne diseases, including rickettsioses and anaplasmosis, has been increasing in many parts of the world. The obligate intracellular nature of rickettsial pathogens has hindered the development of robust genetic tools for the study of gene function and the identification of therapeutic targets. Transposon mutagenesis has contributed to recent progress in the identification of virulence factors in this important group of pathogens. Methods: Combining the efficiency of the himar1 transposon method with a recombinase-mediated system, we aimed to develop a genetic tool enabling the exchange of the transposon with a cassette encoding non-native sequences. Results: This approach was used in Rickettsia parkeri to insert a himar1 transposon encoding fluorescent protein and antibiotic resistance genes for visualization and selection, flanked by mismatched loxP sites to enable subsequent recombinase-mediated cassette exchange (RMCE). RMCE mediated by a plasmid-encoded Cre recombinase was then employed to replace the transposon with a different cassette containing alternate fluorescent and selection markers and epitopes of Anaplasma phagocytophilum antigens. The resulting genetically modified R. parkeri was trialed as a live-attenuated vaccine against spotted fever rickettsiosis and anaplasmosis in mice. Conclusions: The use of this system provides a well-established and relatively efficient way of inserting non-native sequences into the rickettsial genome, with applications for the study of gene function and vaccine development.

Tick cell lines have emerged as a valuable tool in many research areas concerning ticks and tick-borne diseases. This has established a useful model for investigating interactions between ticks and pathogenic agents, as various economically significant tick-borne pathogens can be isolated and propagated in tick cell lines. However, tick cell lines are relatively fragile compared to more common cell types and demand higher maintenance culture conditions. Here, we describe the basic methods for tick cell culture using ISE6, a cell line derived from the embryos of the Ixodes scapularis tick species, to showcase its morphological features. Moreover, this approach can be adapted for in vitro cultivation of viral and bacterial pathogens.

Rickettsia parkeri, an intracellular bacterium transmitted by Amblyomma maculatum ticks, causes a febrile illness associated with eschar formation in humans. As a less virulent member of the spotted fever group within the Rickettsia genus, R. parkeri serves as an ideal model for studying interactions between rickettsial pathogens, their vectors, and hosts. Our previous research showed that R. parkeri modulates mitochondrial-dependent apoptosis in tick cells, enhancing its intracellular survival and replication; however, the underlying mechanisms remain unclear. To investigate further, we employed a Himar1-based transposon mutagenesis system to identify R. parkeri genes involved in apoptosis. Using the modified plasmid pLoxHimar, we introduced a transposon into the R. parkeri Tate's Hell strain and selected a mutant with an insertion in RPATATE_1266, a hypothetical protein with homology to exopolyphosphatase/guanosine pentaphosphate phosphohydrolase (Ppx/Gppa) family proteins, using mCherry fluorescence and spectinomycin/streptomycin resistance. The mutant genotype and single insertion site were confirmed by insertion site sequencing and inverse PCR. We found that the RPATATE_1266 mutant had reduced infection rates, growth, and plaque formation compared to wild-type R. parkeri in tick and mammalian cells. Moreover, the mutant showed upregulation of genes associated with ppx/gppa gene regulation networks (GRNs) and exhibited a marked inhibition of apoptosis in tick cells, including decreased expression of apoptosis-related genes, reduced mitochondrial membrane potential, and less DNA fragmentation. Restoration of RPATATE_1266 resulted in significant recovery of later-phase apoptosis, as measured by Caspase 3/7 activity. These findings suggest that RPATATE_1266 is a critical regulator of apoptosis in tick cells and could be a potential target for controlling R. parkeri infection and replication. This research enhances our understanding of how vector responses to pathogen infection influence pathogen replication and transmission. IMPORTANCE:Rickettsia parkeri infections, though less severe than other rickettsioses, are becoming increasingly significant due to the expanding geographic range of their tick vector and their role in shaping our understanding of rickettsial biology. Advancing knowledge of the molecular mechanisms that regulate R. parkeri infection and replication is important for the field of vector-pathogen interactions. This study identifies the RPATATE_1266 gene (a hypothetical protein with homology to exopolyphosphatase/guanosine pentaphosphate phosphohydrolase [Ppx/Gppa] family proteins) as a key regulator of mitochondrial-dependent apoptosis in tick cells, a process critical for rickettsial intracellular survival. By elucidating the role of this gene, we provide new insights into the molecular interactions between rickettsial pathogens and their vectors. These findings not only enhance our understanding of pathogen-vector dynamics but also highlight potential directions for developing future strategies to manage rickettsial diseases beyond those caused by R. parkeri.

Invasive mosquitoes continue to spread, increasing the threat of mosquito-borne disease. Ongoing mosquito surveillance is necessary to track the introduction and establishment of these species in new areas and implement appropriate public health and vector control measures. Contributions from citizen science initiatives have been an important component in detecting, controlling, and raising awareness of invasive mosquitoes. The open-access biodiversity platform iNaturalist is an extensive source of human observations of wildlife, including arthropod vectors, and can be a useful supplementary tool for passive vector surveillance. In this study, the utility of iNaturalist data to support invasive mosquito surveillance was assessed by examining the distribution and seasonal data on four invasive Aedes species (IAS) in Europe and neighbouring countries. Almost 16,000 iNaturalist observations of mosquitoes were examined across 62 countries; 13% were identified as IAS, with a further 2% considered probable IAS. These included 16 observations of Aedes aegypti, 1582 Aedes albopictus, 373 Aedes japonicus, and 58 Aedes koreicus. iNaturalist observations of IAS were present in most known areas of establishment, but potential new regions of spread were also identified. These results further support the use of iNaturalist data as a low-cost source of arthropod data to assist existing vector surveillance.

Abstract Culex (Barraudius) modestus is an important vector of West Nile virus (WNV) in Europe and it has the potential to play a bridge vector role in future WNV transmission in the UK. Here we provide an update on the known distribution of the species in England based on adult and larval data, characterise the preferred Cx. modestus larval habitats, and present adult and larval data from sites where the species is known to occur. Culex modestus is primarily found in the south-east of England, particularly in North Kent, the Thames Estuary, and along the Essex coast, and as far east as Orford Ness, Suffolk, and in Rainham Marshes, Essex, in the West. Adult numbers peak in mid-late July, with larval numbers highest in late August / early September. Preferred habitats in North Kent are warm, shallow, narrow ditches, with an abundance of marginal, submerged, and floating vegetation. Such environmental data on the distribution, seasonality and habitat preference of Cx. modestus are critical for informing WNV surveillance programmes, identifying at risk areas (associated with this species) and providing information for a targeted control strategy in the event of WNV transmission.

Mosquitoes (Diptera: Culicidae) and the pathogens they transmit represent a threat to human and animal health. Low-cost and effective surveillance methods are necessary to enable sustainable monitoring of mosquito distributions, diversity, and human interactions. This study examined the use of iNaturalist, an online, community-populated biodiversity recording database, for passive mosquito surveillance in the United Kingdom (UK) and Ireland, countries under threat from the introduction of invasive mosquitoes and emerging mosquito-borne diseases. The Mozzie Monitors UK & Ireland iNaturalist project was established to collate mosquito observations in these countries. Data were compared with existing long-term mosquito UK datasets to assess representativeness of seasonal and distribution trends in citizen scientist-recorded observations. The project collected 738 observations with the majority recorded 2020-2022. Records were primarily associated with urban areas, with the most common species Culex pipiens and Culiseta annulata significantly more likely to be observed in urban areas than other species. Analysis of images uploaded to the iNaturalist project also provided insights into human-biting behavior. Our analyses indicate that iNaturalist provides species composition, seasonal occurrence, and distribution figures consistent with existing datasets and is therefore a useful surveillance tool for recording information on human interactions with mosquitoes and monitoring species of concern.

Abstract The absence of habitat-based guidance for wetland managers on the British mosquito assemblages has in recent years prevented development of the ecological aspect of medical entomology in the UK. This has been particularly relevant in the context of emerging mosquito-borne disease and the creation of wetlands for biodiversity and flood-alleviation goals. This study aimed to provide empirically derived habitat-based predictions in order to assess the suitability of English wetland habitats for mosquitoes. Entomological field data on mosquito density and diversity were collected at 12 English wetlands in 2017 and 2018 using immature and adult mosquito surveys. Wetlands were chosen representing a number of wetland categories that included coastal, urban, wet woodland and established freshwater wetlands to identify key species and functional groups to inform predictions of mosquitoes by aquatic habitat type. Nineteen species were recorded from eight functional groups, totalling 38,577 adult female (19 mosquito species groups) and ~2,000 immature mosquitoes in 13 aquatic habitat types. Approximately 90% of all trapped mosquitoes were attributed to one of five species groups. The most common species were: Aedes (Och.) caspius (Pallas, 1771) (~35% of all mosquitoes), associated with coastal estuarine and flooded grassland sites, Ae. cantans/annulipes (19.7%) in wet woodland field sites, Anopheles claviger (16.2%) and Coquillettidia richiardii (12.6%) with the widest occurrence, found in nearly all field sites, and Ae. detritus (6.9%) in brackish field sites. Across the study, adult mosquito activity increased from week 21 with wet woodland Aedes mosquitoes, until week 40 with open-flood water species, with greatest diversity of species during weeks 23–30. The resulting data inform efforts towards developing predictive tools for non-entomologists to accurately predict the presence and abundance of British mosquitoes in a given habitat, using local knowledge of seasonal aquatic habitats.

Babesiosis, a disease in humans and animals is caused by piroplasms from the genus Babesia and is transmitted by ixodid ticks. Bovine babesiosis, commonly called redwater fever, is reported in cattle from many regions of the British Isles. The presence of Babesia in questing ticks in the United Kingdom (UK) and its potential impact on public and animal health has not been widely studied. Therefore, this study aimed to assess the presence of Babesia spp. in England and Wales using ticks collected over a six-year period. Questing Ixodes ricinus nymphs were collected at 20 recreational areas between 2014 and 2019 and screened for Babesia. Of 3912 nymphs tested, Babesia spp. were detected in 15, giving an overall prevalence of 0.38% [95%CI: 0.21–0.63%]. A number of Babesia species were identified including B. venatorum (n = 9), B. divergens/capreoli (n = 5) and B. odocoilei-like species (n = 1). Based on the low prevalence of Babesia detected in questing I. ricinus nymphs in the recreational areas studied, the likelihood of exposure to Babesia-infected ticks is lower compared to other pathogens more widely studied in the UK (e.g. Borrelia burgdorferi s.l.). However, localized areas of elevated risk may occur in pockets in England and Wales.

Arthropod-borne pathogens are responsible for hundreds of millions of infections in humans each year. The blacklegged tick, Ixodes scapularis, is the predominant arthropod vector in the United States and is responsible for transmitting several human pathogens, including the Lyme disease spirochete Borrelia burgdorferi and the obligate intracellular rickettsial bacterium Anaplasma phagocytophilum, which causes human granulocytic anaplasmosis. However, tick metabolic response to microbes and whether metabolite allocation occurs upon infection remain unknown. Here we investigated metabolic reprogramming in the tick ectoparasite I. scapularis and determined that the rickettsial bacterium A. phagocytophilum and the spirochete B. burgdorferi induced glycolysis in tick cells. Surprisingly, the endosymbiont Rickettsia buchneri had a minimal effect on bioenergetics. An unbiased metabolomics approach following A. phagocytophilum infection of tick cells showed alterations in carbohydrate, lipid, nucleotide and protein metabolism, including elevated levels of the pleiotropic metabolite β-aminoisobutyric acid. We manipulated the expression of genes associated with β-aminoisobutyric acid metabolism in I. scapularis, resulting in feeding impairment, diminished survival and reduced bacterial acquisition post haematophagy. Collectively, we discovered that metabolic reprogramming affects interspecies relationships and fitness in the clinically relevant tick I. scapularis.

ABSTRACT Approximately 80 identified tick species are recognized as vectors and impact global public health by transmitting a wide range of pathogens; however, little is known about the interactions of ticks with the microbiome that they harbor, let alone their bacterial symbionts. In this study, we used the black-legged tick, Ixodes scapularis Say (Acari: Ixodidae), a vector of seven human pathogens in the United States, and utilized Rickettsia buchneri sensu stricto ISO7T (Rickettsiales: Rickettsiaceae), a spotted fever group (SFG) rickettsia that is an endosymbiont of I. scapularis, to investigate the role of autophagy in symbiont and tick interactions. We found that the expression profile of most autophagy family member proteins (ATGs) is down-regulated after R. buchneri infection in tick cell cultures. The autophagic process was observed by assessment of autophagosome formation and maturation in vitro (tick cell culture) and in vivo (tick ovary) in the presence of R. buchneri, whereas apoptosis was not induced. We further showed that R. buchneri infection triggered the accumulation of plasma membranes within cells. Suppressing autophagy via Atg8 siRNA interference inhibited intracellular rickettsial replication. This research indicates that autophagy regulation is important for the maintenance of R. buchneri in its I. scapularis tick host and provides more clues to solve the tick-symbiont interaction puzzle. IMPORTANCE Ticks are second only to mosquitoes in their importance as vectors of disease agents; however, tick-borne diseases (TBDs) account for the majority of all vector-borne disease cases in the United States (approximately 76.5%), according to Centers for Disease Control and Prevention reports. Newly discovered tick species and their associated disease-causing pathogens, and anthropogenic and demographic factors also contribute to the emergence and re-emergence of TBDs. Thus, incorporating different tick control approaches based on a thorough knowledge of tick biology has great potential to prevent and eliminate TBDs in the future. Here we demonstrate that replication of a transovarially transmitted rickettsial endosymbiont depends on the tick’s autophagy machinery but not on apoptosis. Our findings improve our understanding of the role of symbionts in tick biology and the potential to discover tick control approaches to prevent or manage TBDs.

Alongside active surveillance at ports and land transport sites, the UK Health Security Agency runs a passive mosquito surveillance scheme: The Mosquito Recording Scheme (MRS). The MRS is a citizen-science scheme, it receives and identifies mosquitoes submitted by members of the public, including in response to nuisance biting incidents. The aims of the scheme are to detect unusual or invasive species, provide a log of reportable incidents of nuisance mosquito biting, and gain insight into the seasonality of British mosquito biting. Between 2005 and 2021, 286 submissions of mosquitoes were submitted to the MRS, all of which were native UK species, 23 specifically reported nuisance biting, with 92.7% of submissions from England. In total 16 species were submitted with Culiseta annulata (39%) and Culex pipiens s.l. (26% of submissions) the most common, with records of these species throughout the years. Case studies giving examples of a range of submissions and a flow chart of the workflow when receiving a submission are described. Reasons for the low incidence of submissions compared to comparable schemes in Europe are discussed and recommendations on how to improve the scheme is given.

Chen, L., Xiao, Q., Shi, M., Cheng, J., Wu, J. Detecting Wolbachia strain wAlbB in Aedes albopictus cell lines. Journal of Visualized Experiments. (184), e63662 (2022). Haziqah-Rashid, A. et al. Determining temperature preference of mosquitoes and other ectotherms. Journal of Visualized Experiments. (187), e64356 (2022). Huang, D. et al. Mosquito-associated virus isolation from field-collected mosquitoes. Journal of Visualized Experiments. (186), e63852 (2022). Khoo, B., Cull, B., Oliver, J. D. Tick artificial membrane feeding for Ixodes scapularis. Journal of Visualized Experiments. 64553 (2022). Leal-Galvan, B., Harvey, C., Thomas, D., Saelao, P., Oliva Chavez, A. S. Isolation of microRNAs from tick ex vivo salivary gland cultures and extracellular vesicles. Journal of Visualized Experiments. (182), e63618 (2022). Liang, Q. et al. Control of Aedes albopictus mosquito larvae with Carpesium abrotanoides L. Journal of Visualized Experiments. (186), e63976 (2022). Wang, F. et al. Experimental viral infection in adult mosquitoes by oral feeding and microinjection. Journal of Visualized Experiments. (185), e63830 (2022). Wang, X. R., Burkhardt, N. Y., Price, L. D., Munderloh, U. G. An electroporation method to transform Rickettsia spp. with a fluorescent protein-expressing shuttle vector in tick cell lines. Journal of Visualized Experiments. (188), e64562 (2022).

The density of Borrelia burgdorferi-infected Ixodes ricinus nymphs (DIN) was investigated during 2013-2017 across a Lyme disease-endemic landscape in southern England. The density of nymphs (DON), nymph infection prevalence (NIP), and DIN varied across five different natural habitats, with the highest DIN in woodland edge and high biodiversity woodlands. DIN was significantly lower in scrub grassland compared to the woodland edge, with low DON and no evidence of infection in ticks in non-scrub grassland. Over the 5 years, DON, NIP and DIN were comparable within habitats, except in 2014, with NIP varying three-fold and DIN significantly lower compared to 2015-2017. Borrelia garinii was most common, with bird-associated Borrelia (B. garinii/valaisiana) accounting for ~70% of all typed sequences. Borrelia burgdorferi sensu stricto was more common than B. afzelii. Borrelia afzelii was more common in scrub grassland than woodland and absent in some years. The possible impact of scrub on grazed grassland, management of ecotonal woodland margins with public access, and the possible role of birds/gamebirds impacting NIP are discussed. Mean NIP was 7.6%, highlighting the potential risk posed by B. burgdorferi in this endemic area. There is a need for continued research to understand its complex ecology and identify strategies for minimizing risk to public health, through habitat/game management and public awareness.

Recent increases in the incidence and geographic range of tick-borne diseases in North America are linked to the range expansion of medically important tick species, including Ixodes scapularis, Amblyomma americanum, and Amblyomma maculatum. Passive tick surveillance programs have been highly successful in collecting information on tick distribution, seasonality, host-biting activity, and pathogen infection prevalence. These have demonstrated the power of citizen or community science participation to collect country-wide, epidemiologically relevant data in a resource-efficient manner. This study examined tick observations from the online image-based biological recording platform iNaturalist to evaluate its use as an effective tool for monitoring the distributions of A. americanum, A. maculatum, I. scapularis, and Dermacentor in the United States and Canada. The distribution and seasonality of iNaturalist tick observations were found to accurately represent those of the studied species. County-level iNaturalist tick occurrence data showed good agreement with other data sources in documented areas of I. scapularis and A. americanum establishment, and highlighted numerous previously unreported counties with iNaturalist observations of these species. This study supports the use of iNaturalist data as a highly cost-effective passive tick surveillance method that can complement existing surveillance strategies to update tick distributions and identify new areas of tick establishment.

Tick-borne disease risk is intrinsically linked to the distribution of tick vector species. To assess risk and anticipate disease emergence, an understanding of tick distribution, host associations, and seasonality is needed. This can be achieved, to some extent, using passive surveillance supported by engagement with the public, animal health, and public health experts. The Tick Surveillance Scheme (TSS) collects data and maps tick distribution across the United Kingdom (UK). Between 2017 and 2020, 3720 tick records were received and 39 tick species were detected. Most records were acquired in the UK, with a subset associated with recent overseas travel. The dominant UK acquired species was Ixodes ricinus (Ixodida: Ixodidae, Linnaeus), the main vector of Lyme borreliosis. Records peaked during May and June, highlighting a key risk period for tick bites. Other key UK species were detected, including Dermacentor reticulatus (Ixodida: Ixodidae, Fabricius) and Haemaphysalis punctata (Ixodida: Ixodidae, Canestrini & Fanzago) as well as several rarer species that may present novel tick-borne disease risk to humans and other animals. Updated tick distribution maps highlight areas in the UK where tick exposure has occurred. There is evidence of increasing human tick exposure over time, including during the COVID-19 pandemic, but seasonal patterns remain unchanged.

Ticks and their associated diseases are an important topic of study due to their public health and veterinary burden. However, the feeding requirements of ticks during both study and rearing can limit experimental questions or the ability of labs to research ticks and their associated pathogens. An artificial membrane feeding system can reduce these problems and open up new avenues of research that may not have been possible with traditional animal feeding systems. This study describes an artificial membrane feeding system that has been refined for feeding and engorgement success for all Ixodes scapularis life stages. Moreover, the artificial membrane feeding system described in this study can be modified for use with other tick species through simple refinement of the desired membrane thickness. The benefits of an artificial membrane feeding system are counterbalanced by the labor intensiveness of the system, the additional environmental factors that may impact feeding success, and the need to refine the technique for each new species and life stage of ticks.

Ixodes scapularis is the primary vector of tick-borne pathogens in North America but notably does not transmit pathogenic Rickettsia species. This tick harbors the transovarially transmitted endosymbiont Rickettsia buchneri, which is widespread in I. scapularis populations, suggesting that it confers a selective advantage for tick survival such as providing essential nutrients. The R. buchneri genome includes genes with similarity to those involved in antibiotic synthesis. There are two gene clusters not found in other Rickettsiaceae, raising the possibility that these may be involved in excluding pathogenic bacteria from the tick. This study explored whether the R. buchneri antibiotic genes might exert antibiotic effects on pathogens associated with I. scapularis. Markedly reduced infectivity and replication of the tick-borne pathogens Anaplasma phagocytophilum, R. monacensis, and R. parkeri were observed in IRE11 tick cells hosting R. buchneri. Using a fluorescent plate reader assay to follow infection dynamics revealed that the presence of R. buchneri in tick cells, even at low infection rates, inhibited the growth of R. parkeri by 86–100% relative to R. buchneri-free cells. In contrast, presence of the low-pathogenic species R. amblyommatis or the endosymbiont R. peacockii only partially reduced the infection and replication of R. parkeri. Addition of host-cell free R. buchneri, cell lysate of R. buchneri-infected IRE11, or supernatant from R. buchneri-infected IRE11 cultures had no effect on R. parkeri infection and replication in IRE11, nor did these treatments show any antibiotic effect against non-obligate intracellular bacteria E. coli and S. aureus. However, lysate from R. buchneri-infected IRE11 challenged with R. parkeri showed some inhibitory effect on R. parkeri infection of treated IRE11, suggesting that challenge by pathogenic rickettsiae may induce the antibiotic effect of R. buchneri. This research suggests a potential role of the endosymbiont in preventing other rickettsiae from colonizing I. scapularis and/or being transmitted transovarially. The confirmation that the observed inhibition is linked to R. buchneri's antibiotic clusters requires further investigation but could have important implications for our understanding of rickettsial competition and vector competence of I. scapularis for rickettsiae.

Understanding the effects of local habitat and wider landscape connectivity factors on tick presence, nymph density and Borrelia species (spp.) prevalence in the tick population is important for identifying the public health risk from Lyme borreliosis. This multi-city study collected data in three southern England cities (Bath, Bristol, and Southampton) during spring, summer, and autumn in 2017. Focusing specifically on urban green space used for recreation which were clearly in urbanised areas, 72 locations were sampled. Additionally, geospatial datasets on urban green space coverage within 250 m and 1 km of sampling points, as well as distance to woodland were incorporated into statistical models. Distance to woodland was negatively associated with tick presence and nymph density, particularly during spring and summer. Furthermore, we observed an interaction effect between habitat and season for tick presence and nymph density, with woodland habitat having greater tick presence and nymph density during spring. Borrelia spp. infected Ixodes ricinus were found in woodland, woodland edge and under canopy habitats in Bath and Southampton. Overall Borrelia spp. prevalence in nymphs was 2.8%, similar to wider UK studies assessing prevalence in Ixodes ricinus in rural areas. Bird-related Borrelia genospecies dominated across sites, suggesting bird reservoir hosts may be important in urban green space settings for feeding and infecting ticks. Whilst overall density of infected nymphs across the three cities was low (0.03 per 100 m2), risk should be further investigated by incorporating data on tick bites acquired in urban settings, and subsequent Lyme borreliosis transmission.

Tick-borne diseases are a significant threat to human and animal health throughout the world. How tick-borne pathogens successfully infect and disseminate in both their vertebrate and invertebrate hosts is only partially understood. Pathogens have evolved several mechanisms to combat host defense systems, and to avoid and modulate host immunity during infection, therefore benefitting their survival and replication. In the host, pathogens trigger responses from innate and adaptive immune systems that recognize and eliminate invaders. Two important innate defenses against pathogens are the programmed cell death pathways of apoptosis and autophagy. This Mini Review surveys the current knowledge of apoptosis and autophagy pathways in tick-pathogen interactions, as well as the strategies evolved by pathogens for their benefit. We then assess the limitations to studying both pathways and discuss their participation in the network of the tick immune system, before highlighting future perspectives in this field. The knowledge gained would significantly enhance our understanding of the defense responses in vector ticks that regulate pathogen infection and burden, and form the foundation for future research to identify novel approaches to the control of tick-borne diseases.