Publications by authors named "Sukanya Narasimhan"

49 Publications

Grappling with the tick microbiome.

Trends Parasitol 2021 May 4. Epub 2021 May 4.

Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06420, USA.

Ixodes scapularis and Ixodes pacificus are the predominant vectors of multiple human pathogens, including Borrelia burgdorferi, one of the causative agents of Lyme disease in North America. Differences in the habitats and host preferences of these closely related tick species present an opportunity to examine key aspects of the tick microbiome. While advances in sequencing technologies have accelerated a descriptive understanding of the tick microbiome, molecular and mechanistic insights into the tick microbiome are only beginning to emerge. Progress is stymied by technical difficulties in manipulating the microbiome and by biological variables related to the life cycle of Ixodid ticks. This review highlights these challenges and examines avenues to understand the significance of the tick microbiome in tick biology.
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http://dx.doi.org/10.1016/j.pt.2021.04.004DOI Listing
May 2021

Acquired tick resistance: The trail is hot.

Parasite Immunol 2021 May 15;43(5):e12808. Epub 2020 Dec 15.

Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA.

Acquired tick resistance is a phenomenon wherein the host elicits an immune response against tick salivary components upon repeated tick infestations. The immune responses, potentially directed against critical salivary components, thwart tick feeding, and the animal becomes resistant to subsequent tick infestations. The development of tick resistance is frequently observed when ticks feed on non-natural hosts, but not on natural hosts. The molecular mechanisms that lead to the development of tick resistance are not fully understood, and both host and tick factors are invoked in this phenomenon. Advances in molecular tools to address the host and the tick are beginning to reveal new insights into this phenomenon and to uncover a deeper understanding of the fundamental biology of tick-host interactions. This review will focus on the expanding understanding of acquired tick resistance and highlight the impact of this understanding on anti-tick vaccine development efforts.
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http://dx.doi.org/10.1111/pim.12808DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8058238PMC
May 2021

Fractionation of tick saliva reveals proteins associated with the development of acquired resistance to Ixodes scapularis.

Vaccine 2020 12 7;38(51):8121-8129. Epub 2020 Nov 7.

Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06420, USA; Howard Hughes Medical Institute, Chevy Chase MD-20815, USA. Electronic address:

Tick-borne diseases pose a global medical problem. As transmission of tick-borne pathogens to their hosts occurs during tick feeding, development of vaccines thwarting this process could potentially prevent transmission of multiple tick-borne pathogens. The idea of tick vaccines is based on the phenomenon of acquired tick immunity, rejection of ticks feeding on hosts which were repeatedly infested by ticks. Recently, we demonstrated that saliva of the blacklegged tick Ixodes scapularis, which is the main vector of tick-borne pathogens in northeast USA, is sufficient for induction of tick immunity in the guinea pig model and that immunity directed against tick glycoproteins is important in this phenomenon. Nevertheless, immunity elicited against individual tick salivary antigens, which have been identified and tested so far, provided only modest tick rejection. We therefore now tested fractions of tick saliva produced by liquid chromatography for their ability to induce tick immunity in the guinea pig model. Immunization with all individual fractions elicited antibodies that reacted with tick saliva, however only some fractions displayed the ability to induce robust protective tick immunity. Mass spectrometry analysis led to identification of 24 proteins present only in saliva fractions which were able to induce tick immunity, suggesting suitable candidates for development of a tick vaccine.
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http://dx.doi.org/10.1016/j.vaccine.2020.10.087DOI Listing
December 2020

Repeat tick exposure elicits distinct immune responses in guinea pigs and mice.

Ticks Tick Borne Dis 2020 11 2;11(6):101529. Epub 2020 Aug 2.

Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520, USA; Howard Hughes Medical Institute. Chevy Chase, MD 20815, USA. Electronic address:

Ticks deposit salivary proteins into the skin during a bite to mediate acquisition of a blood meal. Acquired resistance to tick bites has been demonstrated to prevent Borrelia burgdorferi sensu lato (s.l.) transmission. However, the mechanism of resistance, as well as the protective antigens, have remained elusive. To address these unknowns, we utilized a guinea pig model of tick resistance and a mouse model of permissiveness. Guinea pigs developed immunity after multiple Ixodes scapularis tick infestations, characterized by rapid tick detachment and impaired feeding. In comparison, mice tolerated at least 6 infestations with no significant impact on feeding. We analyzed the bite sites by RNA-sequencing and histology, identifying several inflammatory pathways in tick immune animals, such as FcεRI signaling and complement activation, and activation of coagulation pathways that could impair local blood flow. Together, these results identify important pathways altered during tick rejection and potential tick proteins that could serve as vaccine candidates.
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http://dx.doi.org/10.1016/j.ttbdis.2020.101529DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7530331PMC
November 2020

An Ixodes scapularis Protein Disulfide Isomerase Contributes to Borrelia burgdorferi Colonization of the Vector.

Infect Immun 2020 11 16;88(12). Epub 2020 Nov 16.

Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.

causes Lyme disease, the most common tick-transmitted illness in North America. When feed on an infected vertebrate host, spirochetes enter the tick gut along with the bloodmeal and colonize the vector. Here, we show that a secreted tick protein, rotein isulfide somerase (IsPDIA3), enhances colonization of the tick gut. ticks in which has been knocked down using RNA interference have decreased spirochete colonization of the tick gut after engorging on -infected mice. Moreover, administration of IsPDIA3 antiserum to -infected mice reduced the ability of spirochetes to colonize the tick when feeding on these animals. We show that IsPDIA3 modulates inflammatory responses at the tick bite site, potentially facilitating spirochete survival at the vector-host interface as it exits the vertebrate host to enter the tick gut. These data provide functional insights into the complex interactions between and its arthropod vector and suggest additional targets to interfere with the spirochete life cycle.
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http://dx.doi.org/10.1128/IAI.00426-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7671890PMC
November 2020

Interactions between Borrelia burgdorferi and ticks.

Nat Rev Microbiol 2020 10 10;18(10):587-600. Epub 2020 Jul 10.

Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA.

Borrelia burgdorferi is the causative agent of Lyme disease and is transmitted to vertebrate hosts by Ixodes spp. ticks. The spirochaete relies heavily on its arthropod host for basic metabolic functions and has developed complex interactions with ticks to successfully colonize, persist and, at the optimal time, exit the tick. For example, proteins shield spirochaetes from immune factors in the bloodmeal and facilitate the transition between vertebrate and arthropod environments. On infection, B. burgdorferi induces selected tick proteins that modulate the vector gut microbiota towards an environment that favours colonization by the spirochaete. Additionally, the recent sequencing of the Ixodes scapularis genome and characterization of tick immune defence pathways, such as the JAK-STAT, immune deficiency and cross-species interferon-γ pathways, have advanced our understanding of factors that are important for B. burgdorferi persistence in the tick. In this Review, we summarize interactions between B. burgdorferi and I. scapularis during infection, as well as interactions with tick gut and salivary gland proteins important for establishing infection and transmission to the vertebrate host.
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http://dx.doi.org/10.1038/s41579-020-0400-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7351536PMC
October 2020

Ixodes scapularis saliva components that elicit responses associated with acquired tick-resistance.

Ticks Tick Borne Dis 2020 05 3;11(3):101369. Epub 2020 Jan 3.

Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06420, United States; Howard Hughes Medical Institute. Chevy Chase, MD, 20815, United States. Electronic address:

Ticks and tick-borne diseases are on the rise world-wide and vaccines to prevent transmission of tick-borne diseases is an urgent public health need. Tick transmission of pathogens to the mammalian host occurs during tick feeding. Therefore, it is reasoned that vaccine targeting of tick proteins essential for feeding would thwart tick feeding and consequently prevent pathogen transmission. The phenomenon of acquired tick-immunity, wherein, repeated tick infestations of non-natural hosts results in the development of host immune responses detrimental to tick feeding has served as a robust paradigm in the pursuit of tick salivary antigens that may be vaccine targeted. While several salivary antigens have been identified, immunity elicited against these antigens have only provided modest tick rejection. This has raised the possibility that acquired tick-immunity is directed against tick components other than tick salivary antigens. Using Ixodes scapularis, the blacklegged tick, that vectors several human pathogens, we demonstrate that immunity directed against tick salivary glycoproteins is indeed sufficient to recapitulate the phenomenon of tick-resistance. These observations emphasize the utility of tick salivary glycoproteins as viable vaccine targets to thwart tick feeding and direct our search for anti-tick vaccine candidates.
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http://dx.doi.org/10.1016/j.ttbdis.2019.101369DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7382422PMC
May 2020

Protective Immunity and New Vaccines for Lyme Disease.

Clin Infect Dis 2020 04;70(8):1768-1773

Department of Medicine, Rutgers New Jersey Medical School, Newark, New Jersey, USA.

Lyme disease, caused by some Borrelia burgdorferi sensu lato, is the most common tick-borne illness in the Northern Hemisphere and the number of cases, and geographic spread, continue to grow. Previously identified B. burgdorferi proteins, lipid immunogens, and live mutants lead the design of canonical vaccines aimed at disrupting infection in the host. Discovery of the mechanism of action of the first vaccine catalyzed the development of new strategies to control Lyme disease that bypassed direct vaccination of the human host. Thus, novel prevention concepts center on proteins produced by B. burgdorferi during tick transit and on tick proteins that mediate feeding and pathogen transmission. A burgeoning area of research is tick immunity as it can unlock mechanistic pathways that could be targeted for disruption. Studies that shed light on the mammalian immune pathways engaged during tick-transmitted B. burgdorferi infection would further development of vaccination strategies against Lyme disease.
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http://dx.doi.org/10.1093/cid/ciz872DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7155782PMC
April 2020

The role of Mannose Binding Lectin in the immune response against Borrelia burgdorferi sensu lato.

Sci Rep 2019 02 5;9(1):1431. Epub 2019 Feb 5.

Amsterdam UMC, University of Amsterdam, Center for Experimental and Molecular Medicine, Meibergdreef 9, Amsterdam, Netherlands.

The causative agents of Lyme borreliosis, spirochetes belonging to the Borrelia burgdorferi sensu lato group, have developed several ways to protect themselves against killing by the host complement system. In addition, it has been shown that serum sensitive isolates are (partially) protected by the Ixodes Tick Salivary Lectin Pathway Inhibitor (TSLPI) protein; a salivary gland protein that inhibits the function of Mannose Binding Lectin (MBL). MBL is a C-type lectin that recognizes oligosaccharides on pathogens and activates the complement system via the lectin pathway. MBL deficiency has been linked to a more severe course of several infectious diseases and humans with detectable antibodies against B. burgdorferi are significantly more often MBL deficient compared to humans without antibodies against B. burgdorferi. Here we set out to investigate the role of MBL in the immune response against B. burgdorferi in more detail. We demonstrate that B. burgdorferi N40 needle-infected C57BL/6 MBL deficient mice harbored significantly higher B. burgdorferi numbers in skin tissue during the early course of infection. In line with these findings they also developed higher anti-B. burgdorferi IgG serum antibodies compared to WT controls. In contrast, B. burgdorferi loads in distant tissue such as heart, joints or bladder at later time points were similar for both mouse strains. These in vivo findings were corroborated using a B. burgdorferi N40-infected I. scapularis infestation model. We showed that MBL is capable of binding B. burgdorferi through its carbohydrate recognition domains, but in vitro complement killing assays, peritoneal macrophage and whole blood stimulations, phagocytosis assays and an in vivo migration experiment did not reveal the mechanism by which MBL facilitates early clearance of B. burgdorferi. To conclude, we show a protective role of MBL in the early stages of B. burgdorferi infection, yet the underlying mechanism warrants further investigation.
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http://dx.doi.org/10.1038/s41598-018-37922-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6363739PMC
February 2019

Host-specific expression of Ixodes scapularis salivary genes.

Ticks Tick Borne Dis 2019 02 3;10(2):386-397. Epub 2018 Dec 3.

Section of Infectious Diseases, New Haven, CT, 06520, USA; Howard Hughes Medical Institute, Chevy Chase, Maryland, 20815, USA.

Ixodes scapularis vectors several pathogens including Borrelia burgdorferi, the agent of Lyme disease. Nymphal and larval stages, and the pathogens transmitted by I. scapularis are maintained in a zoonotic cycle involving rodent reservoir hosts, predominantly Peromyscus leucopus. Humans are not reservoir hosts, however, accidental encounters of infected ticks with humans, results in pathogen transmission to the human host. Laboratory models of non-reservoir hosts such as guinea pigs develop a strong immune response to tick salivary proteins and reject ticks upon repeated tick infestations. Anecdotal and scientific evidence suggests that humans that get frequent tick bites might also develop resistance to ticks. Mus musculus, the laboratory model of natural host, does not develop resistance to I. scapularis upon repeated tick infestations. Addressing this dichotomy in vector-host interaction, we present data that suggest that the salivary transcriptome and proteome composition is different in mouse and guinea pig-fed I. scapularis, and that these differences might contribute to differences in host immune responses. These findings reveal a new insight into vector-host interactions and offer a functional paradigm to better understand the phenomenon of acquired tick-resistance.
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http://dx.doi.org/10.1016/j.ttbdis.2018.12.001DOI Listing
February 2019

Visualization of Microbiota in Tick Guts by Whole-mount In Situ Hybridization.

J Vis Exp 2018 06 1(136). Epub 2018 Jun 1.

Department of Internal Medicine, Yale University School of Medicine;

Infectious diseases transmitted by arthropod vectors continue to pose a significant threat to human health worldwide. The pathogens causing these diseases, do not exist in isolation when they colonize the vector; rather, they likely engage in interactions with resident microorganisms in the gut lumen. The vector microbiota has been demonstrated to play an important role in pathogen transmission for several vector-borne diseases. Whether resident bacteria in the gut of the Ixodes scapularis tick, the vector of several human pathogens including Borrelia burgdorferi, influence tick transmission of pathogens is not determined. We require methods for characterizing the composition of the bacteria associated with the tick gut to facilitate a better understanding of potential interspecies interactions in the tick gut. Using whole-mount in situ hybridization to visualize RNA transcripts associated with particular bacterial species allows for the collection of qualitative data regarding the abundance and distribution of the microbiota in intact tissue. This technique can be used to examine changes in the gut microbiota milieu over the course of tick feeding and can also be applied to analyze expression of tick genes. Staining of whole tick guts yield information about the gross spatial distribution of target RNA in the tissue without the need for three-dimensional reconstruction and is less affected by environmental contamination, which often confounds the sequencing-based methods frequently used to study complex microbial communities. Overall, this technique is a valuable tool that can be used to better understand vector-pathogen-microbiota interactions and their role in disease transmission.
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http://dx.doi.org/10.3791/57758DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6101453PMC
June 2018

Human Borrelia miyamotoi infection in California: Serodiagnosis is complicated by multiple endemic Borrelia species.

PLoS One 2018 8;13(2):e0191725. Epub 2018 Feb 8.

Department of Environmental Science, Policy and Management, University of California, Berkeley, CA, United States of America.

To determine whether human Borrelia miyamotoi infection occurs in the far-western United States, we tested archived sera from northwestern California residents for antibodies to this emerging relapsing fever spirochete. These residents frequently were exposed to I. pacificus ticks in a region where B. miyamotoi tick infection has been reported. We used a two-step B. miyamotoi rGlpQ assay and a B. miyamotoi whole-cell lysate (WCL) assay to detect B. miyamotoi antibody. We also employed Borrelia hermsii and Borrelia burgdorferi WCL assays to examine if these Borrelia induce cross reacting antibody to B. miyamotoi. Sera were collected from 101 residents in each of two consecutive years. The sera of 12 and 14 residents in years one and two, respectively, were B. miyamotoi rGlpQ seroreactive. Sufficient sera were available to test 15 of the 26 seropositive samples using B. miyamotoi and B. hermsii WCL assays. Two residents in year one and seven residents in year two were seroreactive to both Borrelia antigens. Although discernible differences in seroreactivity were evident between the B. miyamotoi and B. hermsii WCL assays, infection with one or the other could not be determined with certainty. Sera from two Borrelia burgdorferi /B. miyamotoi seropositive subjects reacted strongly against B. miyamotoi and B. hermsii WCL antigens. Ecological, epidemiological, and clinical data implicated B. miyamotoi as the probable cause of infection among those whose sera reacted against both antigens. Our findings suggest that human B. miyamotoi infection occurs in northern California and that B. hermsii and B. burgdorferi infections produce antibodies that cross-react with B. miyamotoi antigens. Health care professionals in the far-western United States should be aware that B. miyamotoi disease may occur throughout the geographic distribution of I. pacificus and that improved relapsing fever group spirochete antibody assays are urgently needed.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0191725PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5805228PMC
March 2018

Modulation of the tick gut milieu by a secreted tick protein favors Borrelia burgdorferi colonization.

Nat Commun 2017 08 4;8(1):184. Epub 2017 Aug 4.

Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, 06420, USA.

The Lyme disease agent, Borrelia burgdorferi, colonizes the gut of the tick Ixodes scapularis, which transmits the pathogen to vertebrate hosts including humans. Here we show that B. burgdorferi colonization increases the expression of several tick gut genes including pixr, encoding a secreted gut protein with a Reeler domain. RNA interference-mediated silencing of pixr, or immunity against PIXR in mice, impairs the ability of B. burgdorferi to colonize the tick gut. PIXR inhibits bacterial biofilm formation in vitro and in vivo. Abrogation of PIXR function in vivo results in alterations in the gut microbiome, metabolome and immune responses. These alterations influence the spirochete entering the tick gut in multiple ways. PIXR abrogation also impairs larval molting, indicative of its role in tick biology. This study highlights the role of the tick gut in actively managing its microbiome, and how this impacts B. burgdorferi colonization of its arthropod vector. Borrelia burgdorferi, the causative agent of Lyme disease, is transmitted by the tick Ixodes scapularis. Here, the authors show that a tick secreted protein (PIXR) modulates the tick gut microbiota and facilitates B. burgdorferi colonization.
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http://dx.doi.org/10.1038/s41467-017-00208-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5543126PMC
August 2017

Pathogen-mediated manipulation of arthropod microbiota to promote infection.

Proc Natl Acad Sci U S A 2017 01 17;114(5):E781-E790. Epub 2017 Jan 17.

Section of Infectious Disease, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06510;

Arthropods transmit diverse infectious agents; however, the ways microbes influence their vector to enhance colonization are poorly understood. Ixodes scapularis ticks harbor numerous human pathogens, including Anaplasma phagocytophilum, the agent of human granulocytic anaplasmosis. We now demonstrate that A. phagocytophilum modifies the I. scapularis microbiota to more efficiently infect the tick. A. phagocytophilum induces ticks to express Ixodes scapularis antifreeze glycoprotein (iafgp), which encodes a protein with several properties, including the ability to alter bacterial biofilm formation. IAFGP thereby perturbs the tick gut microbiota, which influences the integrity of the peritrophic matrix and gut barrier-critical obstacles for Anaplasma colonization. Mechanistically, IAFGP binds the terminal d-alanine residue of the pentapeptide chain of bacterial peptidoglycan, resulting in altered permeability and the capacity of bacteria to form biofilms. These data elucidate the molecular mechanisms by which a human pathogen appropriates an arthropod antibacterial protein to alter the gut microbiota and more effectively colonize the vector.
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http://dx.doi.org/10.1073/pnas.1613422114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5293115PMC
January 2017

Hard Tick Relapsing Fever Caused by Borrelia miyamotoi in a Child.

Pediatr Infect Dis J 2016 12;35(12):1352-1354

From the *Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, †Department of Internal Medicine, Yale School of Medicine, New Haven, Connecticut, ‡Northampton Area Pediatrics, Northampton, Massachusetts; and §Laboratory of Medical Zoology, Department of Microbiology, University of Massachusetts, Amherst, Massachusetts.

A 5-year-old Massachusetts resident developed hard tick-borne relapsing fever caused by Borrelia miyamotoi. A partially engorged Ixodes scapularis tick was removed from her scalp and identified as infected with B. miyamotoi using polymerase chain reaction. Two weeks later, she developed an illness compatible with B. miyamotoi infection that included fatigue and recurrent fever. The diagnosis was confirmed by B. miyamotoi seroconversion.
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http://dx.doi.org/10.1097/INF.0000000000001330DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5106309PMC
December 2016

Variable Major Proteins as Targets for Specific Antibodies against Borrelia miyamotoi.

J Immunol 2016 05 13;196(10):4185-95. Epub 2016 Apr 13.

Center for Experimental and Molecular Medicine, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, the Netherlands;

Borrelia miyamotoi is a relapsing fever spirochete in Ixodes ticks that has been recently identified as a human pathogen causing hard tick-borne relapsing fever (HTBRF) across the Northern Hemisphere. No validated serologic test exists, and current serologic assays have low sensitivity in early HTBRF. To examine the humoral immune response against B. miyamotoi, we infected C3H/HeN mice with B. miyamotoi strain LB-2001 expressing variable small protein 1 (Vsp1) and demonstrated that spirochetemia was cleared after 3 d, coinciding with anti-Vsp1 IgM production. Clearance was also observed after passive transfer of immune sera to infected SCID mice. Next, we showed that anti-Vsp1 IgG eliminates Vsp1-expressing B. miyamotoi, selecting for spirochetes expressing a variable large protein (VlpC2) resistant to anti-Vsp1. The viability of Asian isolate B. miyamotoi HT31, expressing Vlp15/16 and Vlp18, was also unaffected by anti-Vsp1. Finally, in nine HTBRF patients, we demonstrated IgM reactivity to Vsp1 in two and against Vlp15/16 in four ∼1 wk after these patients tested positive for B. miyamotoi by PCR. Our data show that B. miyamotoi is able to express various variable major proteins (VMPs) to evade humoral immunity and that VMPs are antigenic in humans. We propose that serologic tests based on VMPs are of additional value in diagnosing HTBRF.
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http://dx.doi.org/10.4049/jimmunol.1600014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5008243PMC
May 2016

Ixodes scapularis dystroglycan-like protein promotes Borrelia burgdorferi migration from the gut.

J Mol Med (Berl) 2016 Mar 23;94(3):361-70. Epub 2015 Nov 23.

Center for Experimental and Molecular Medicine, Academic Medical Center, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands.

The causative agent of Lyme borreliosis, Borrelia burgdorferi, is transmitted by Ixodes ticks. During tick feeding, B. burgdorferi migrates from the tick gut to the salivary glands from where transmission to the host occurs. B. burgdorferi-interacting tick proteins might serve as vaccine targets to thwart B. burgdorferi transmission. A previous screening for B. burgdorferi-interacting Ixodes scapularis gut proteins identified an I. scapularis putative dystroglycan protein (ISCW015049). Here, we describe the ISCW015049's protein structure and its cellular location in the tick gut in relation to B. burgdorferi migration. Secondly, in vivo B. burgdorferi-tick attachment murine models were performed to study the role of ISCW015049 during B. burgdorferi migration and transmission. In silico analysis confirmed that ISCW015049 is similar to dystroglycan and was named I. scapularis dystroglycan-like protein (ISDLP). Confocal microscopy of gut tissue showed that ISDLP is expressed on the surface of gut cells, is upregulated during tick feeding, and is expressed significantly higher in infected ticks compared to uninfected ticks. Inhibition of ISDLP by RNA interference (RNAi) resulted in lower B. burgdorferi transmission to mice. In conclusion, we have identified a dystroglycan-like protein in I. scapularis gut that can bind to B. burgdorferi and promotes B. burgdorferi migration from the tick gut. Key messages: B. burgdorferi exploits tick proteins to orchestrate its transmission to the host. B. burgdorferi is able bind to an I. scapularis dystroglycan-like protein (ISDLP). Inhibition of ISDLP in ticks results in lower B. burgdorferi transmission to mice. ISDLP is a potential target to prevent Lyme borreliosis.
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http://dx.doi.org/10.1007/s00109-015-1365-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4803822PMC
March 2016

Tick microbiome: the force within.

Trends Parasitol 2015 Jul 27;31(7):315-23. Epub 2015 Apr 27.

Section of Infectious Diseases, Department of Internal Medicine, Yale University, New Haven, CT, USA; The Howard Hughes Medical Institute, Chevy Chase, MD, USA. Electronic address:

Ticks are obligate blood-feeders and serve as vectors of human and livestock pathogens worldwide. Defining the tick microbiome and deciphering the interactions between the tick and its symbiotic bacteria in the context of tick development and pathogen transmission will likely reveal new insights and spawn new paradigms to control tick-borne diseases. Descriptive observations on the tick microbiome that began almost a century ago serve as forerunners to the gathering momentum to define the tick microbiome in greater detail. This review will focus on the current efforts to address the microbiomes of diverse ticks, and the evolving understanding of tick microbiomes. There is hope that these efforts will bring a holistic understanding of pathogen transmission by ticks.
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http://dx.doi.org/10.1016/j.pt.2015.03.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4492851PMC
July 2015

A tick gut protein with fibronectin III domains aids Borrelia burgdorferi congregation to the gut during transmission.

PLoS Pathog 2014 Aug 7;10(8):e1004278. Epub 2014 Aug 7.

Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, United States of America; Howard Hughes Medical Institute, Chevy Chase, Maryland, United States of America.

Borrelia burgdorferi transmission to the vertebrate host commences with growth of the spirochete in the tick gut and migration from the gut to the salivary glands. This complex process, involving intimate interactions of the spirochete with the gut epithelium, is pivotal to transmission. We utilized a yeast surface display library of tick gut proteins to perform a global screen for tick gut proteins that might interact with Borrelia membrane proteins. A putative fibronectin type III domain-containing tick gut protein (Ixofin3D) was most frequently identified from this screen and prioritized for further analysis. Immunization against Ixofin3D and RNA interference-mediated reduction in expression of Ixofin3D resulted in decreased spirochete burden in tick salivary glands and in the murine host. Microscopic examination showed decreased aggregation of spirochetes on the gut epithelium concomitant with reduced expression of Ixofin3D. Our observations suggest that the interaction between Borrelia and Ixofin3D facilitates spirochete congregation to the gut during transmission, and provides a "molecular exit" direction for spirochete egress from the gut.
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http://dx.doi.org/10.1371/journal.ppat.1004278DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4125277PMC
August 2014

Borrelia miyamotoi sensu lato seroreactivity and seroprevalence in the northeastern United States.

Emerg Infect Dis 2014 Jul;20(7):1183-90

Borrelia miyamotoi sensu lato, a relapsing fever Borrelia sp., is transmitted by the same ticks that transmit B. burgdorferi (the Lyme disease pathogen) and occurs in all Lyme disease-endemic areas of the United States. To determine the seroprevalence of IgG against B. miyamotoi sensu lato in the northeastern United States and assess whether serum from B. miyamotoi sensu lato-infected persons is reactive to B. burgdorferi antigens, we tested archived serum samples from area residents during 1991-2012. Of 639 samples from healthy persons, 25 were positive for B. miyamotoi sensu lato and 60 for B. burgdorferi. Samples from ≈10% of B. miyamotoi sensu lato-seropositive persons without a recent history of Lyme disease were seropositive for B. burgdorferi. Our results suggest that human B. miyamotoi sensu lato infection may be common in southern New England and that B. burgdorferi antibody testing is not an effective surrogate for detecting B. miyamotoi sensu lato infection.
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http://dx.doi.org/10.3201/eid2007.131587DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4073859PMC
July 2014

Long term effect of gut microbiota transfer on diabetes development.

J Autoimmun 2014 Sep 22;53:85-94. Epub 2014 Apr 22.

Section of Endocrinology, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520, USA. Electronic address:

The composition of the gut microbiome represents a very important environmental factor that influences the development of type 1 diabetes (T1D). We have previously shown that MyD88-deficient non-obese diabetic (MyD88-/-NOD) mice, that were protected from T1D development, had a different composition of gut microbiota compared to wild type NOD mice. The aim of our study was to investigate whether this protection could be transferred. We demonstrate that transfer of gut microbiota from diabetes-protected MyD88-deficient NOD mice, reduced insulitis and significantly delayed the onset of diabetes. Gut bacteria from MyD88-deficient mice, administered over a 3-week period, starting at 4 weeks of age, stably altered the family composition of the gut microbiome, with principally Lachnospiraceae and Clostridiaceae increased and Lactobacillaceae decreased. The transferred mice had a higher concentration of IgA and TGFβ in the lumen that was accompanied by an increase in CD8(+)CD103(+) and CD8αβ T cells in the lamina propria of the large intestine. These data indicate not only that gut bacterial composition can be altered after the neonatal/weaning period, but that the composition of the microbiome affects the mucosal immune system and can delay the development of autoimmune diabetes. This result has important implications for the development of probiotic treatment for T1D.
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http://dx.doi.org/10.1016/j.jaut.2014.03.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4361177PMC
September 2014

Gut microbiota of the tick vector Ixodes scapularis modulate colonization of the Lyme disease spirochete.

Cell Host Microbe 2014 Jan;15(1):58-71

Section of Infectious Diseases, Department of Internal Medicine, Yale University, New Haven, CT 06520, USA; The Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA. Electronic address:

Arthopods such as Ixodes scapularis ticks serve as vectors for many human pathogens. The arthropod gut presents a pivotal microbial entry point and determines pathogen colonization and survival. We show that the gut microbiota of I. scapularis, a major vector of the Lyme disease spirochete Borrelia burgdorferi, influence spirochete colonization of ticks. Perturbing the gut microbiota of larval ticks reduced Borrelia colonization, and dysbiosed larvae displayed decreased expression of the transcription factor signal transducer and activator of transcription (STAT). Diminished STAT expression corresponded to lower expression of peritrophin, a key glycoprotein scaffold of the glycan-rich mucus-like peritrophic matrix (PM) that separates the gut lumen from the epithelium. The integrity of the I. scapularis PM was essential for B. burgdorferi to efficiently colonize the gut epithelium. These data elucidate a functional link between the gut microbiota, STAT-signaling, and pathogen colonization in the context of the gut epithelial barrier of an arthropod vector.
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http://dx.doi.org/10.1016/j.chom.2013.12.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3905459PMC
January 2014

Characterization of Ixophilin, a thrombin inhibitor from the gut of Ixodes scapularis.

PLoS One 2013 9;8(7):e68012. Epub 2013 Jul 9.

Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, United States of America.

Ixodes scapularis, the black-legged tick, vectors several human pathogens including Borrelia burgdorferi, the agent of Lyme disease in North America. Pathogen transmission to the vertebrate host occurs when infected ticks feed on the mammalian host to obtain a blood meal. Efforts to understand how the tick confronts host hemostatic mechanisms and imbibes a fluid blood meal have largely focused on the anticoagulation strategies of tick saliva. The blood meal that enters the tick gut remains in a fluid state for several days during the process of feeding, and the role of the tick gut in maintaining the blood-meal fluid is not understood. We now demonstrate that the tick gut produces a potent inhibitor of thrombin, a key enzyme in the mammalian coagulation cascade. Chromatographic fractionation of engorged tick gut proteins identified one predominant thrombin inhibitory activity associated with an approximately 18 kDa protein, henceforth referred to as Ixophilin. The ixophilin gene was preferentially transcribed in the guts of feeding nymphs. Expression began after 24 hours of feeding, coincident with the flow of host blood into the tick gut. Immunity against Ixophilin delayed tick feeding, and decreased feeding efficiency significantly. Surprisingly, immunity against Ixophilin resulted in increased Borrelia burgdorferi transmission to the host, possibly due to delayed feeding and increased transmission opportunity. These observations illuminate the potential drawbacks of targeting individual tick proteins in a functional suite. They also underscore the need to identify the "anticoagulome" of the tick gut, and to prioritize a critical subset of anticoagulants that could be targeted to efficiently thwart tick feeding, and block pathogen transmission to the vertebrate host.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0068012PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3706618PMC
February 2014

Vaccination against Lyme disease: past, present, and future.

Front Cell Infect Microbiol 2013 12;3. Epub 2013 Feb 12.

Division of Bacteriology and Parasitology, Tulane National Primate Research Center, Covington, LA, USA.

Lyme borreliosis is a zoonotic disease caused by Borrelia burgdorferi sensu lato bacteria transmitted to humans and domestic animals by the bite of an Ixodes spp. tick (deer tick). Despite improvements in diagnostic tests and public awareness of Lyme disease, the reported cases have increased over the past decade to approximately 30,000 per year. Limitations and failed public acceptance of a human vaccine, comprised of the outer surface A (OspA) lipoprotein of B. burgdorferi, led to its demise, yet current research has opened doors to new strategies for protection against Lyme disease. In this review we discuss the enzootic cycle of B. burgdorferi, and the unique opportunities it poses to block infection or transmission at different levels. We present the correlates of protection for this infectious disease, the pros and cons of past vaccination strategies, and new paradigms for future vaccine design that would include elements of both the vector and the pathogen.
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http://dx.doi.org/10.3389/fcimb.2013.00006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3569838PMC
October 2014

Ixodes scapularis JAK-STAT pathway regulates tick antimicrobial peptides, thereby controlling the agent of human granulocytic anaplasmosis.

J Infect Dis 2012 Oct 2;206(8):1233-41. Epub 2012 Aug 2.

Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.

Ixodes scapularis transmits the agent of human granulocytic anaplasmosis, among other pathogens. The mechanisms used by the tick to control Anaplasma phagocytophilum are not known. We demonstrate that the I. scapularis Janus kinase (JAK)-signaling transducer activator of transcription (STAT) pathway plays a critical role in A. phagocytophilum infection of ticks. The A. phagocytophilum burden increases in salivary glands and hemolymph when the JAK-STAT pathway is suppressed by RNA interference. The JAK-STAT pathway exerts its anti-Anaplasma activity presumably through STAT-regulated effectors. A salivary gland gene family encoding 5.3-kDa antimicrobial peptides is highly induced upon A. phagocytophilum infection of tick salivary glands. Gene expression and electrophoretic mobility shift assays showed that the 5.3-kDa antimicrobial peptide-encoding genes are regulated by tick STAT. Silencing of these genes increased A. phagocytophilum infection of tick salivary glands and transmission to mammalian host. These data suggest that the JAK-STAT signaling pathway plays a key role in controlling A. phagocytophilum infection in ticks by regulating the expression of antimicrobial peptides.
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http://dx.doi.org/10.1093/infdis/jis484DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3448968PMC
October 2012

Activation of the RpoN-RpoS regulatory pathway during the enzootic life cycle of Borrelia burgdorferi.

BMC Microbiol 2012 Mar 23;12:44. Epub 2012 Mar 23.

Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.

Background: The maintenance of Borrelia burgdorferi in its complex tick-mammalian enzootic life cycle is dependent on the organism's adaptation to its diverse niches. To this end, the RpoN-RpoS regulatory pathway in B. burgdorferi plays a central role in microbial survival and Lyme disease pathogenesis by up- or down-regulating the expression of a number of virulence-associated outer membrane lipoproteins in response to key environmental stimuli. Whereas a number of studies have reported on the expression of RpoS and its target genes, a more comprehensive understanding of when activation of the RpoN-RpoS pathway occurs, and when induction of the pathway is most relevant to specific stage(s) in the life cycle of B. burgdorferi, has been lacking.

Results: Herein, we examined the expression of rpoS and key lipoprotein genes regulated by RpoS, including ospC, ospA, and dbpA, throughout the entire tick-mammal infectious cycle of B. burgdorferi. Our data revealed that transcription of rpoS, ospC, and dbpA is highly induced in nymphal ticks when taking a blood meal. The RpoN-RpoS pathway remains active during the mammalian infection phase, as indicated by the sustained transcription of rpoS and dbpA in B. burgdorferi within mouse tissues following borrelial dissemination. However, dbpA transcription levels in fed larvae and intermolt larvae suggested that an additional layer of control likely is involved in the expression of the dbpBA operon. Our results also provide further evidence for the downregulation of ospA expression during mammalian infection, and the repression of ospC at later phases of mammalian infection by B. burgdorferi.

Conclusion: Our study demonstrates that the RpoN-RpoS regulatory pathway is initially activated during the tick transmission of B. burgdorferi to its mammalian host, and is sustained during mammalian infection.
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http://dx.doi.org/10.1186/1471-2180-12-44DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3320556PMC
March 2012

Persistence of Borrelia burgdorferi in rhesus macaques following antibiotic treatment of disseminated infection.

PLoS One 2012 11;7(1):e29914. Epub 2012 Jan 11.

Divisions of Bacteriology & Parasitology, Tulane National Primate Research Center, Tulane University Health Sciences Center, Covington, Louisiana, United States of America.

The persistence of symptoms in Lyme disease patients following antibiotic therapy, and their causes, continue to be a matter of intense controversy. The studies presented here explore antibiotic efficacy using nonhuman primates. Rhesus macaques were infected with B. burgdorferi and a portion received aggressive antibiotic therapy 4-6 months later. Multiple methods were utilized for detection of residual organisms, including the feeding of lab-reared ticks on monkeys (xenodiagnosis), culture, immunofluorescence and PCR. Antibody responses to the B. burgdorferi-specific C6 diagnostic peptide were measured longitudinally and declined in all treated animals. B. burgdorferi antigen, DNA and RNA were detected in the tissues of treated animals. Finally, small numbers of intact spirochetes were recovered by xenodiagnosis from treated monkeys. These results demonstrate that B. burgdorferi can withstand antibiotic treatment, administered post-dissemination, in a primate host. Though B. burgdorferi is not known to possess resistance mechanisms and is susceptible to the standard antibiotics (doxycycline, ceftriaxone) in vitro, it appears to become tolerant post-dissemination in the primate host. This finding raises important questions about the pathogenicity of antibiotic-tolerant persisters and whether or not they can contribute to symptoms post-treatment.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0029914PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3256191PMC
May 2012