Tick Artificial Membrane Feeding for <em>Ixodes scapularis</em>

Ticks and their associated diseases are an important topic of study due to their public health and veterinary burden. However, the feeding requirements of ...

Methods for the Study of Ticks, Mosquitoes, and their Transmitted Pathogens: Toward a Greater Understanding of Vector Biology and Arthropod-Microbe Interactions

ARTICLES DISCUSSED:
Chen, L., Xiao, Q., Shi, M., Cheng, J., Wu, J. Detecting&#160;Wolbachia&#160;strain wAlbB in&#160;Aedes albopictus&#160;cell lines. ...

University of Minnesota

Apoptosis is an innate immune response induced by infection in eukaryotes that contributes significantly to protection from pathogens. However, little is known about the role of apoptosis in the interactions of arthropod vectors with the rickettsiae that they transmit.  spp. are vector-borne obligately intracellular bacteria and display different degrees of virulence in their eukaryotic hosts. In this study, we found that infection with  () activated the apoptosis pathway in an  tick cell line (AAE2), as evidenced by the loss of phospholipid membrane asymmetry and DNA fragmentations. Additionally, infection with  also led to apoptosis activation in cell lines of different tick species. Interestingly, suppressing apoptosis decreased  infection and replication, while the activation of apoptosis increased  accumulation at the early stage of infection. Moreover, mitochondrion-dependent apoptosis was essential for  infection and replication in vector cells, and apoptosis induction required intracellular rickettsia replication. We further showed that  utilizes two different survival strategies to modulate apoptosis in the arthropod vectors and mammalian host cells. There was no direct correlation between apoptosis activation in vector cells and rickettsial pathogenicity. These novel findings indicate a possible mechanism whereby apoptosis facilitates infection and replication of a  sp. in an arthropod vector. These results contribute to our understanding of how the vector's responses to pathogen infection affect pathogen replication and therefore transmission. Rickettsioses, infections caused by the genus , are among the oldest known infectious diseases. Ticks are essential arthropod vectors for rickettsiae, and knowledge about the interactions between ticks, their hosts, and pathogens is fundamental for identifying drivers of tick-borne rickettsioses. Despite the rapid development in apoptosis research with rickettsiae, little is known regarding the role of apoptosis in the interactions between  spp., vertebrate hosts, and arthropod vectors. Here, we demonstrated that mitochondrion-dependent apoptosis is essential for rickettsial infection and replication in vector cells and that apoptosis induction requires intracellular rickettsial replication. However, rickettsial pathogenicity is not linked with apoptosis activation in tick cells. Our findings improve understanding of the apoptosis mechanism in arthropods exploited by rickettsiae and also the potential to discover specific targets for new vaccines and drugs to prevent or treat rickettsial infections.

Mitochondrion-Dependent Apoptosis Is Essential for Rickettsia parkeri Infection and Replication in Vector Cells.

Voluntary contributions by citizen scientists can gather large datasets covering wide geographical areas, and are increasingly utilized by researchers for multiple applications, including arthropod vector surveillance. Online platforms such as iNaturalist accumulate crowdsourced biological observations from around the world and these data could also be useful for monitoring vectors. The aim of this study was to explore the availability of observations of important vector taxa on the iNaturalist platform and examine the utility of these data to complement existing vector surveillance activities. Of ten vector taxa investigated, records were most numerous for mosquitoes (Culicidae; 23,018 records, 222 species) and ticks (Ixodida; 16,214 records, 87 species), with most data from 2019-2020. Case studies were performed to assess whether images associated with records were of sufficient quality to identify species and compare iNaturalist observations of vector species to the known situation at the state, national and regional level based on existing published data. Firstly, tick data collected at the national (United Kingdom) or state (Minnesota, USA) level were sufficient to determine seasonal occurrence and distribution patterns of important tick species, and were able to corroborate and complement known trends in tick distribution. Importantly, tick species with expanding distributions (Haemaphysalis punctata in the UK, and Amblyomma americanum in Minnesota) were also detected. Secondly, using iNaturalist data to monitor expanding tick species in Europe (Hyalomma spp.) and the USA (Haemaphysalis longicornis), and invasive Aedes mosquitoes in Europe, showed potential for tracking these species within their known range as well as identifying possible areas of expansion. Despite known limitations associated with crowdsourced data, this study shows that iNaturalist can be a valuable source of information on vector distribution and seasonality that could be used to supplement existing vector surveillance data, especially at a time when many surveillance programs may have been interrupted by COVID-19 restrictions.

Potential for online crowdsourced biological recording data to complement surveillance for arthropod vectors.

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

The  Symbiont  Inhibits Growth of Pathogenic Rickettsiaceae in Tick Cells: Implications for Vector Competence.

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.

Apoptosis and Autophagy: Current Understanding in Tick-Pathogen Interactions.

Human granulocytic anaplasmosis and tick-borne fever, affecting livestock, are diseases caused by an infection with the bacterium Anaplasma phagocytophilum. Its transmission dynamics between vertebrate hosts and ticks remain largely unknown and the potential impact on public health in the United Kingdom is unclear. This study aimed to assess the distribution and estimate the prevalence of A. phagocytophilum in questing Ixodes ricinus at recreational locations across England and Wales over six years. An additional objective was to investigate possible associations between prevalence, habitat and presence of ruminant hosts. Ixodes ricinus ticks were collected each spring at 20 recreational locations across England and Wales between 2014 and 2019. Nymphs were tested for infection with A. phagocytophilum by detection of bacterial genome in DNA extracts, targeting the msp2 gene locus. Positive samples were further investigated for the presence of different ecotypes based on the GroEL region. Of 3,919 nymphs tested, the mean infection prevalence was 3.6% [95%CI: 3.1-4.3] and ranged from 0 to 20.4%. Northern England had a higher overall prevalence (4.7% [95%CI: 3.4-6.4]) compared to Southern England (1.8% [95%CI: 1.3-2.5]) and the presence of sheep was associated with higher A. phagocytophilum prevalence (8.4% [95%CI: 6.9-10.1] vs 1.2% [95%CI: 0.8-1.7] when absent). There was also a negative correlation with the prevalence of Borrelia burgdorferi s.l. (causing Lyme borreliosis). When investigating the diversity of A. phagocytophilum, ecotype I accounted for 86.8% of samples and ecotype II for 13.2%. Our study presents an overview of A. phagocytophilum prevalence in questing I. ricinus in recreational areas across England and Wales and discusses the potential public and veterinary health relevance.

Prevalence of Anaplasma phagocytophilum in questing Ixodes ricinus nymphs across twenty recreational areas in England and Wales.

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 , , and  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 , , , and  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  and  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.

Benjamin Cull

Department of Entomology,
College of Food,
Agricultural and Natural Resources,
Department of Entomology, College of Food, Agricultural and Natural Resources

University of Minnesota

Tick Artificial Membrane Feeding for Ixodes scapularis

Methods for the Study of Ticks, Mosquitoes, and their Transmitted Pathogens: Toward a Greater Understanding of Vector Biology and Arthropod-Microbe Interactions

Benjamin Cull

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Entomology,College of Food,Agricultural and Natural Resources,Department of Entomology, College of Food, Agricultural and Natural Resources

University of Minnesota

Tick Artificial Membrane Feeding for Ixodes scapularis

Methods for the Study of Ticks, Mosquitoes, and their Transmitted Pathogens: Toward a Greater Understanding of Vector Biology and Arthropod-Microbe Interactions

Department of Entomology,
College of Food,
Agricultural and Natural Resources,
Department of Entomology, College of Food, Agricultural and Natural Resources