Maria A. Diuk-Wasser

Coinfection by Ixodes Tick-Borne Pathogens: Ecological, Epidemiological, and Clinical Consequences.

Ixodes ticks maintain a large and diverse array of human pathogens in the enzootic cycle, including Borrelia burgdorferi and Babesia microti. Despite the poor ecological fitness of B. microti, babesiosis has recently emerged in areas endemic for Lyme disease. Studies in ticks, reservoir hosts, and humans indicate that coinfection with B. burgdorferi and B. microti is common, promotes transmission and emergence of B. microti in the enzootic cycle, and causes greater disease severity and duration in humans. These interdisciplinary studies may serve as a paradigm for the study of other vector-borne coinfections. Identifying ecological drivers of pathogen emergence and host factors that fuel disease severity in coinfected individuals will help guide the design of effective preventative and therapeutic strategies.

Closely-related Borrelia burgdorferi (sensu stricto) strains exhibit similar fitness in single infections and asymmetric competition in multiple infections

BackgroundWild hosts are commonly co-infected with complex, genetically diverse, pathogen communities. Competition is expected between genetically or ecologically similar pathogen strains which may influence patterns of coexistence. However, there is little data on how specific strains of these diverse pathogen species interact within the host and how this impacts pathogen persistence in nature. Ticks are the most common disease vector in temperate regions with Borrelia burgdorferi, the causative agent of Lyme disease, being the most common vector-borne pathogen in North America. Borrelia burgdorferi is a pathogen of high public health concern and there is significant variation in infection phenotype between strains, which influences predictions of pathogen dynamics and spread.MethodsIn a laboratory experiment, we investigated whether two closely-related strains of B. burgdorferi (sensu stricto) showed similar transmission phenotypes, how the transmission of these strains changed when a host was infected with one strain, re-infected with the same strain, or co-infected with two strains. Ixodes scapularis, the black-legged tick, nymphs were used to sequentially infect laboratory-bred Peromyscus leucopus, white-footed mice, with one strain only, homologous infection with the same stain, or heterologous infection with both strains. We used the results of this laboratory experiment to simulate long-term persistence and maintenance of each strain in a simple simulation model.ResultsStrain LG734 was more competitive than BL206, showing no difference in transmission between the heterologous infection groups and single-infection controls, while strain BL206 transmission was significantly reduced when strain LG734 infected first. The results of the model show that this asymmetry in competition could lead to extinction of strain BL206 unless there was a tick-to-host transmission advantage to this less competitive strain.ConclusionsThis asymmetric competitive interaction suggests that strain identity and the biotic context of co-infection is important to predict strain dynamics and persistence.

There is inadequate evidence to support the division of the genus Borrelia

There are surely scientific, genetic or ecological arguments which show that differences exist between the relapsing fever (RF) spirochaetes and the Lyme borreliosis (LB) group of spirochaetes, both of which belong to the genus Borrelia. In a recent publication, Adeolu and Gupta [1] proposed dividing the genus Borrelia into two genera on the basis of genetic differences revealed by comparative genomics. The new genus name for the LB group of spirochaetes, Borreliella, has subsequently been entered in the GenBank database for some species of the group and in a validation list (List of new names and new combinations previously effectively, but not validly, published) [2]. However, rapidly expanding scientific knowledge and considerable conflicting evidence combined with the adverse consequences of splitting the genus Borrelia make such a drastic step somewhat premature. In our opinion, the basis of this division rests on preliminary evidence and should be rescinded for the following reasons:

Identification of Novel Viruses in Amblyomma americanum, Dermacentor variabilis, and Ixodes scapularis Ticks

The incidence of tick-borne disease is increasing, driven by rapid geographical expansion of ticks and the discovery of new tick-associated pathogens. The examination of the tick microbiome is essential in order to understand the relationship between microbes and their tick hosts and to facilitate the identification of new tick-borne pathogens. Genomic analyses using unbiased high-throughput sequencing platforms have proven valuable for investigations of tick bacterial diversity, but the examination of tick viromes has historically not been well explored. By performing a comprehensive virome analysis of the three primary tick species associated with human disease in the United States, we gained substantial insight into tick virome diversity and can begin to assess a potential role of these viruses in the tick life cycle. ABSTRACT Ticks carry a wide range of known human and animal pathogens and are postulated to carry others with the potential to cause disease. Here we report a discovery effort wherein unbiased high-throughput sequencing was used to characterize the virome of 2,021 ticks, including Ixodes scapularis (n = 1,138), Amblyomma americanum (n = 720), and Dermacentor variabilis (n = 163), collected in New York, Connecticut, and Virginia in 2015 and 2016. We identified 33 viruses, including 24 putative novel viral species. The most frequently detected viruses were phylogenetically related to members of the Bunyaviridae and Rhabdoviridae families, as well as the recently proposed Chuviridae. Our work expands our understanding of tick viromes and underscores the high viral diversity that is present in ticks. IMPORTANCE The incidence of tick-borne disease is increasing, driven by rapid geographical expansion of ticks and the discovery of new tick-associated pathogens. The examination of the tick microbiome is essential in order to understand the relationship between microbes and their tick hosts and to facilitate the identification of new tick-borne pathogens. Genomic analyses using unbiased high-throughput sequencing platforms have proven valuable for investigations of tick bacterial diversity, but the examination of tick viromes has historically not been well explored. By performing a comprehensive virome analysis of the three primary tick species associated with human disease in the United States, we gained substantial insight into tick virome diversity and can begin to assess a potential role of these viruses in the tick life cycle.

Co-feeding transmission facilitates strain coexistence in Borrelia burgdorferi, the Lyme disease agent

Coexistence of multiple tick-borne pathogens or strains is common in natural hosts and can be facilitated by resource partitioning of the host species, within-host localization, or by different transmission pathways. Most vector-borne pathogens are transmitted horizontally via systemic host infection, but transmission may occur in the absence of systemic infection between two vectors feeding in close proximity, enabling pathogens to minimize competition and escape the host immune response. In a laboratory study, we demonstrated that co-feeding transmission can occur for a rapidly-cleared strain of Borrelia burgdorferi, the Lyme disease agent, between two stages of the tick vector Ixodes scapularis while feeding on their dominant host, Peromyscus leucopus. In contrast, infections rapidly became systemic for the persistently infecting strain. In a field study, we assessed opportunities for co-feeding transmission by measuring co-occurrence of two tick stages on ears of small mammals over two years at multiple sites. Finally, in a modeling study, we assessed the importance of co-feeding on R0, the basic reproductive number. The model indicated that co-feeding increases the fitness of rapidly-cleared strains in regions with synchronous immature tick feeding. Our results are consistent with increased diversity of B. burgdorferi in areas of higher synchrony in immature feeding – such as the midwestern United States. A higher relative proportion of rapidly-cleared strains, which are less human pathogenic, would also explain lower Lyme disease incidence in this region. Finally, if co-feeding transmission also occurs on refractory hosts, it may facilitate the emergence and persistence of new pathogens with a more limited host range.

Genomic insights into the ancient spread of Lyme disease across North America

Lyme disease is the most prevalent vector-borne disease in North America and continues to spread. The disease was first clinically described in the 1970s in Lyme, Connecticut, but the origins and history of spread of the Lyme disease bacteria, Borrelia burgdorferi sensu stricto (s.s.), are unknown. To explore the evolutionary history of B. burgdorferi in North America, we collected ticks from across the USA and southern Canada from 1984 to 2013 and sequenced the, to our knowledge, largest collection of 146 B. burgdorferi s.s. genomes. Here, we show that B. burgdorferi s.s. has a complex evolutionary history with previously undocumented levels of migration. Diversity is ancient and geographically widespread, well pre-dating the Lyme disease epidemic of the past ~40 years, as well as the Last Glacial Maximum ~20,000 years ago. This means the recent emergence of human Lyme disease probably reflects ecological change—climate change and land use changes over the past century—rather than evolutionary change of the bacterium.Lyme disease, spread by ticks infected with the bacteria Borrelia burgdorferi, was first described in the 1970s, but its origins are obscure. Genomics of North American ticks points to an origin pre-dating the Last Glacial Maximum.

Transplacental transmission of tick-borne Babesia microti in its natural host Peromyscus leucopus

BackgroundBabesia microti is an emerging tick-borne pathogen and the causative agent of human babesiosis. Mathematical modeling of the reproductive rate of B. microti indicates that it cannot persist in nature by horizontal tick-host transmission alone. We hypothesized that transplacental transmission in the reservoir population contributes to B. microti persistence and emergence in North American rodent populations.MethodsPeromyscus leucopus were collected from Connecticut and Block Island, Rhode Island and analyzed using a highly specific quantitative PCR (qPCR) assay for infection with B. microti.ResultsIn April, 100% (n = 103) of mice were infected with B. microti. Females exhibited significantly higher parasitemia than their offspring (P < 0.0001) and transplacental transmission was observed in 74.2% of embryos (n = 89). Transplacental transmission of B. microti is thus a viable and potentially important infectious pathway in naturally infected rodent species and should be considered in future theoretical and empirical studies.ConclusionsTo our knowledge, this study is the first to report transplacental transmission of B. microti occurring in its natural reservoir host, P. leucopus, in the United States and the only study that provides a quantitative estimate of parasitemia. This vector-independent pathway could contribute to the increased geographic range of B. microti or increase its abundance in endemic areas.

Polymorphic factor H-binding activity of CspA protects Lyme borreliae from the host complement in feeding ticks to facilitate tick-to-host transmission.

Borrelia burgdorferi sensu lato (Bbsl), the causative agent of Lyme disease, establishes an initial infection in the host’s skin following a tick bite, and then disseminates to distant organs, leading to multisystem manifestations. Tick-to-vertebrate host transmission requires that Bbsl survives during blood feeding. Complement is an important innate host defense in blood and interstitial fluid. Bbsl produces a polymorphic surface protein, CspA, that binds to a complement regulator, Factor H (FH) to block complement activation in vitro. However, the role that CspA plays in the Bbsl enzootic cycle remains unclear. In this study, we demonstrated that different CspA variants promote spirochete binding to FH to inactivate complement and promote serum resistance in a host-specific manner. Utilizing a tick-to-mouse transmission model, we observed that a cspA-knockout B. burgdorferi is eliminated from nymphal ticks in the first 24 hours of feeding and is unable to be transmitted to naïve mice. Conversely, ectopically producing CspA derived from B. burgdorferi or B. afzelii, but not B. garinii in a cspA-knockout strain restored spirochete survival in fed nymphs and tick-to-mouse transmission. Furthermore, a CspA point mutant, CspA-L246D that was defective in FH-binding, failed to survive in fed nymphs and at the inoculation site or bloodstream in mice. We also allowed those spirochete-infected nymphs to feed on C3-/- mice that lacked functional complement. The cspA-knockout B. burgdorferi or this mutant strain complemented with cspA variants or cspA-L246D was found at similar levels as wild type B. burgdorferi in the fed nymphs and mouse tissues. These novel findings suggest that the FH-binding activity of CspA protects spirochetes from complement-mediated killing in fed nymphal ticks, which ultimately allows Bbsl transmission to mammalian hosts.

Additional file 2: of Transplacental transmission of tick-borne Babesia microti in its natural host Peromyscus leucopus

Table S2. Babesia microti infection prevalence in reproductive tissues (ES, embryonic sac). (DOCX 14 kb)

Corrigendum: There is inadequate evidence to support the division of the genus Borrelia

Author affiliations: National Reference Centre for Borrelia, Bavarian Health and Food Safety Authority, Veterin€ arstr. 2, 85764 Oberschleißheim, Germany; European Programme for Public Health Microbiology Training, European Centre of Disease Prevention and Control (ECDC), Stockholm, Sweden; School of Health Sport and Bioscience, University of East London, Water Lane, London, UK; Department of Zoology, Slovak Academy of Sciences, Bratislava, Slovakia; Department of Ecology, Evolution and Environmental Biology, Columbia University, 1200 Amsterdam Avenue, New York, NY 10027, USA; SmartGene Services SARL, Innovation Park, Building C, EPFL-Ecublens, CH-1015 Lausanne, Switzerland; Yale School of Public Health, Laboratory of Epidemiology and Public Health, 60 College Street, New Haven, CT 06510, USA; Emeritus Professor of Animal Parasitology, University College Dublin, Dublin, Ireland; Members of the Steering Committee of the ESCMID Study Group for Borrelia (ESGBOR); Zentralinstitut für Labormedizin, Mikrobiologie and Krankenhaushygiene, Krankenhaus Nordwest, Akademisches Lehrkrankenhaus der Johann Wolfgang GoetheUniversit€ at, Steinbacher Hohl 2-26, D-60488 Frankfurt am Main, Frankfurt, Germany; Laboratoire de Bact eriologie, CNR des Borrelia, Plateau Technique de Microbiologie, Hôpitaux Universitaires de Strasbourg et Facult e de M edecine de Strasbourg, 1 rue Koeberl e, Strasbourg 67000, France; tick-radar GmbH, Haderslebener Str. 9, Berlin 12163, Germany; Molecular Genetics Lab (www.dnk-ural.ru) Biology Department, Ural Federal University named after the first President of Russia B.N.Yeltsin, Lenin Avenue, Yekaterinburg 620000, Russia; Institute of Medical Microbiology and Infection Control, University Hospital Frankfurt, Paul-Ehrlich-Str, Frankfurt/Main 40, 60596, Germany; Environmental Science, Policy and Management, University of California Berkeley, 130 Mulford Hall, Berkeley CA 94720, California, USA; Borrelia Laboratory for the National Reference Centre of Tick Diseases (CNRT/ NRZK), ADMed Microbiology, La Chaux-de-Fonds 2303, Switzerland; Division of Medical Microbiology, Department of Clinical and Experimental Medicine, Faculty of Health Sciences, Linköping University, Linköping, Sweden; Director, Public Health Risk Sciences Division, National Microbiology Laboratory, @ Saint-Hyacinthe and Guelph, Public Health Agency of Canada, Saint-Hyacinthe, Canada; Clinical and Experimental Infectious Medicine Section, Department of Clinical Sciences, Lund University, Sweden; Klinikum Dachau, Abt. Neurology u. Schlafmedizinisches Zentrum, Krankenhausstr. 15, 8521 Dachau, Germany; Department of Microbiology and Immunology, School of Medicine, New York Medical College, Basic Sciences Building, Valhalla, NY 10595, USA; Chair Bacteriology and Mykology, Department of Veterinary Science, Veterinary Faculty, LMU Munich, Veterin€ arstraße, München 13, 80539, Gemany; Department of Infectious Diseases, University Medical Centre Ljubljana, Ljubljana, Slovenia; Universit e de Neuchâtel, Institut de Biologie, Laboratoire d’Ecologie et Evolution des Parasites, Rue Emile-Argand 11, CH-2000, Neuchâtel, Switzerland; Fondazione Edmund Mach, Research and Innovation Centre, Via Mach, 1, San Michele all’Adige, Trento, Italy; Department of Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, MS421 Chandler Medical Center, Lexington, Kentucky, 40536-0298, USA. *Correspondence: G. Margos, Gabriele.margos@lgl.bayern.de CORRIGENDUM