Natalia Fedorova

Genetic Diversity of Borrelia burgdorferi and Detection of B. bissettii-Like DNA in Serum of North-Coastal California Residents

ABSTRACT In North America, Lyme borreliosis (LB) is a tick-borne disease caused by infection with the spirochete Borrelia burgdorferi. We studied the genetic diversity of LB spirochetes in north-coastal California residents. Spirochete DNA was detected in 23.7% (27/114) of the study subjects using a PCR protocol optimized for increased sensitivity in human sera. Californians were most commonly infected with B. burgdorferi ospC genotype A, a globally widespread spirochete associated with high virulence in LB patients. Sequence analysis of rrf-rrl and p66 loci in 11% (3/27) of the PCR-positive study subjects revealed evidence of infection with an organism closely related to B. bissettii. This spirochete, heretofore associated with LB only in Europe, is widely distributed among ticks and wildlife in North America. Further molecular testing of sera from residents in areas where LB is endemic is warranted to enhance our understanding of the geographic distribution and frequency of occurrence of B. bissettii-like infections.

Population Structure of the Lyme Borreliosis Spirochete Borrelia burgdorferi in the Western Black-Legged Tick (Ixodes pacificus) in Northern California

ABSTRACT Factors potentially contributing to the lower incidence of Lyme borreliosis (LB) in the far-western than in the northeastern United States include tick host-seeking behavior resulting in fewer human tick encounters, lower densities of Borrelia burgdorferi-infected vector ticks in peridomestic environments, and genetic variation among B. burgdorferi spirochetes to which humans are exposed. We determined the population structure of B. burgdorferi in over 200 infected nymphs of the primary bridging vector to humans, Ixodes pacificus, collected in Mendocino County, CA. This was accomplished by sequence typing the spirochete lipoprotein ospC and the 16S-23S rRNA intergenic spacer (IGS). Thirteen ospC alleles belonging to 12 genotypes were found in California, and the two most abundant, ospC genotypes H3 and E3, have not been detected in ticks in the Northeast. The most prevalent ospC and IGS biallelic profile in the population, found in about 22% of ticks, was a new B. burgdorferi strain defined by ospC genotype H3. Eight of the most common ospC genotypes in the northeastern United States, including genotypes I and K that are associated with disseminated human infections, were absent in Mendocino County nymphs. ospC H3 was associated with hardwood-dominated habitats where western gray squirrels, the reservoir host, are commonly infected with LB spirochetes. The differences in B. burgdorferi population structure in California ticks compared to the Northeast emphasize the need for a greater understanding of the genetic diversity of spirochetes infecting California LB patients.

A spatially-explicit model of acarological risk of exposure to Borrelia burgdorferi-infected Ixodes pacificus nymphs in northwestern California based on woodland type, temperature, and water vapor.

In the far-western United States, the nymphal stage of the western black-legged tick, Ixodes pacificus, has been implicated as the primary vector to humans of Borrelia burgdorferi sensu stricto (hereinafter referred to as B. burgdorferi), the causative agent of Lyme borreliosis in North America. In the present study, we sought to determine if infection prevalence with B. burgdorferi in I. pacificus nymphs and the density of infected nymphs differ between dense-woodland types within Mendocino County, California, and to develop and evaluate a spatially-explicit model for density of infected nymphs in dense woodlands within this high-incidence area for Lyme borreliosis. In total, 4.9% (264) of 5431 I. pacificus nymphs tested for the presence of B. burgdorferi were infected. Among the 78 sampling sites, infection prevalence ranged from 0 to 22% and density of infected nymphs from 0 to 2.04 per 100 m(2). Infection prevalence was highest in woodlands dominated by hardwoods (6.2%) and lowest for redwood (1.9%) and coastal pine (0%). Density of infected nymphs also was higher in hardwood-dominated woodlands than in conifer-dominated ones that included redwood or pine. Our spatial risk model, which yielded an overall accuracy of 85%, indicated that warmer areas with less variation between maximum and minimum monthly water vapor in the air were more likely to include woodlands with elevated acarological risk of exposure to infected nymphs. We found that 37% of dense woodlands in the county were predicted to pose an elevated risk of exposure to infected nymphs, and that 94% of the dense-woodland areas that were predicted to harbor elevated densities of infected nymphs were located on privately-owned land.

Borrelia burgdorferi sensu lato spirochetes in wild birds in northwestern California: associations with ecological factors, bird behavior and tick infestation.

Although Borrelia burgdorferi sensu lato (s.l.) are found in a great diversity of vertebrates, most studies in North America have focused on the role of mammals as spirochete reservoir hosts. We investigated the roles of birds as hosts for subadult Ixodes pacificus ticks and potential reservoirs of the Lyme disease spirochete B. burgdorferi sensu stricto (s.s.) in northwestern California. Overall, 623 birds representing 53 species yielded 284 I. pacificus larvae and nymphs. We used generalized linear models and zero-inflated negative binomial models to determine associations of bird behaviors, taxonomic relationships and infestation by I. pacificus with borrelial infection in the birds. Infection status in birds was best explained by taxonomic order, number of infesting nymphs, sampling year, and log-transformed average body weight. Presence and counts of larvae and nymphs could be predicted by ground- or bark-foraging behavior and contact with dense oak woodland. Molecular analysis yielded the first reported detection of Borrelia bissettii in birds. Moreover, our data suggest that the Golden-crowned Sparrow (Zonotrichia atricapilla), a non-resident species, could be an important reservoir for B. burgdorferi s.s. Of 12 individual birds (9 species) that carried B. burgdorferi s.l.-infected larvae, no birds carried the same genospecies of B. burgdorferi s.l. in their blood as were present in the infected larvae removed from them. Possible reasons for this discrepancy are discussed. Our study is the first to explicitly incorporate both taxonomic relationships and behaviors as predictor variables to identify putative avian reservoirs of B. burgdorferi s.l. Our findings underscore the importance of bird behavior to explain local tick infestation and Borrelia infection in these animals, and suggest the potential for bird-mediated geographic spread of vector ticks and spirochetes in the far-western United States.

Detection of Borrelia burgdorferi sensu stricto ospC alleles associated with human lyme borreliosis worldwide in non-human-biting tick Ixodes affinis and rodent hosts in Southeastern United States.

ABSTRACT Comparative analysis of ospC genes from 127 Borrelia burgdorferi sensu stricto strains collected in European and North American regions where Lyme disease is endemic and where it is not endemic revealed a close relatedness of geographically distinct populations. ospC alleles A, B, and L were detected on both continents in vectors and hosts, including humans. Six ospC alleles, A, B, L, Q, R, and V, were prevalent in Europe; 4 of them were detected in samples of human origin. Ten ospC alleles, A, B, D, E3, F, G, H, H3, I3, and M, were identified in the far-western United States. Four ospC alleles, B, G, H, and L, were abundant in the southeastern United States. Here we present the first expanded analysis of ospC alleles of B. burgdorferi strains from the southeastern United States with respect to their relatedness to strains from other North American and European localities. We demonstrate that ospC genotypes commonly associated with human Lyme disease in European and North American regions where the disease is endemic were detected in B. burgdorferi strains isolated from the non-human-biting tick Ixodes affinis and rodent hosts in the southeastern United States. We discovered that some ospC alleles previously known only from Europe are widely distributed in the southeastern United States, a finding that confirms the hypothesis of transoceanic migration of Borrelia species.

Eco-epidemiological factors contributing to the low risk of human exposure to ixodid tick-borne borreliae in southern California, USA

Little is known about the eco-epidemiology of Lyme disease in southern California, a region where the incidence is much lower than it is in northern California. Here, we sought to discover the previously unknown microhabitats of nymphs of the primary vector, the western black-legged tick (Ixodes pacificus), in 3 moderately to heavily-utilized state parks in the Santa Monica Mountains in Los Angeles County; to elucidate the seasonal distribution and abundance of adults of I. pacificus and another human-biter, the Pacific Coast tick (Dermacentor occidentalis); and to determine what Lyme-disease or relapsing-fever group borreliae are present in questing nymphs or adult ticks. I. pacificus nymphs were collected infrequently at various times of day in 2 chaparral or 7 woodland litter areas by dragging (combined mean=0.4 nymphs per hour). The western fence lizard (Sceloporus occidentalis) was a choice sentinel animal for detecting the presence of I. pacificus nymphs (and larvae) in diverse biotopes even when dragging litter in them was fruitless. The abundance and seasonality of I. pacificus and D. occidentalis adults resembled what had been documented previously for these ticks in northern California. Overall, zero of 27 free-living and 118 lizard-infesting I. pacificus nymphs, 7 (0.29%) of 2392 I. pacificus adults and 2 (0.22%) of 896 D. occidentalis adults were infected with Borrelia burgdorferi sensu lato (Bb sl), but none of them harbored B. miyamotoi, a relapsing-fever group spirochete implicated recently as a zoonotic pathogen in Russia. Borrelia americana and the human pathogen B. burgdorferi sensu stricto were each detected in one (0.04%), and uncharacterized Bb sl in 5 adult I. pacificus (0.21%) that clustered with B. americana. Both PCR-positive D. occidentalis adults contained B. burgdorferi sensu stricto. We conclude that the acarologic risk of being bitten by a B. burgdorferi sensu lato-infected ixodid tick in the habitats studied is slight, which offers a plausible explanation for the low reported incidence of Lyme disease in south coastal California.

Remarkable diversity of tick or mammalian-associated Borreliae in the metropolitan San Francisco Bay Area, California.

The diversity of Lyme disease (LD) and relapsing fever (RF)-group spirochetes in the metropolitan San Francisco Bay area in northern California is poorly understood. We tested Ixodes pacificus, I. spinipalpis, and small mammals for presence of borreliae in Alameda County in the eastern portion of San Francisco Bay between 2009 and 2012. Analyses of 218 Borrelia burgdorferi sensu lato (Bb sl) culture or DNA isolates recovered from host-seeking I. pacificus ticks revealed that the human pathogen Bb sensu stricto (hereinafter, B. burgdorferi) had the broadest habitat distribution followed by B. bissettii. Three other North American Bb sl spirochetes, B. americana, B. californiensis and B. genomospecies 2, also were detected at lower prevalence. OspC genotyping of the resultant 167 B. burgdorferi isolates revealed six ospC alleles (A, D, E3, F, H and K) in I. pacificus. A novel spirochete belonging to the Eurasian Bb sl complex, designated CA690, was found in a questing I. spinipalpis nymph. Borrelia miyamotoi, a relapsing-fever (RF) group spirochete recently implicated as a human pathogen, was detected in 24 I. pacificus. Three rodent species were infected with Bb sl: the fox squirrel (Sciurus niger) with B. burgdorferi, and the dusky-footed wood rat (Neotoma fuscipes) and roof rat (Rattus rattus) with B. bissettii. Another spirochete that clustered phylogenetically with the Spanish R57 Borrelia sp. in a clade distinct from both the LD and RF groups infected some of the roof rats. Together, eight borrelial genospecies were detected in ticks or small mammals from a single Californian county, two of which were related phylogenetically to European spirochetes.

Differences in prevalence of Borrelia burgdorferi and Anaplasma spp. infection among host-seeking Dermacentor occidentalis, Ixodes pacificus, and Ornithodoros coriaceus ticks in northwestern California.

Previous studies revealed that the Pacific Coast tick (Dermacentor occidentalis) is infected occasionally with the agents of Lyme disease (Borrelia burgdorferi) or human granulocytic anaplasmosis (Anaplasma phagocytophilum) and that it is an inefficient experimental vector of B. burgdorferi. The relationship of the pajahuello tick (Ornithodoros coriaceus) to each of these bacterial zoonotic agents has not been reported. The primary bridging vector of both bacterial zoonotic agents to humans is the western black-legged tick (Ixodes pacificus). Because of the spatial and temporal overlap of D. occidentalis and O. coriaceus populations with those of I. pacificus in natural foci of B. burgdorferi and A. phagocytophilum in northwestern California, we conducted field and laboratory studies to determine if the Pacific Coast tick or the pajahuello tick potentially may serve as secondary vectors of either bacterium. Our findings reconfirmed that wild-caught D. occidentalis ticks are infected infrequently with B. burgdorferi or A. phagocytophilum, but some adult ticks from dense woodlands or chaparral were found to contain 2 important veterinary pathogens for the first time (Anaplasma bovis, A. ovis). The high prevalence of A. bovis infection (4.3%, n=185 ticks) within chaparral-derived ticks suggests that D. occidentalis could be an efficient vector of this rickettsia. Experimental attempts to transmit borreliae or Anaplasma spp. that may have been present in >100 wild-caught D. occidentalis adults to naïve rabbits were unsuccessful. Anaplasma spp. were not detected in O. coriaceus, but one (4.3%) of 23 nymphs was infected with B. bissettii. This finding and an antecedent report of a B. burgdorferi-like spirochete from the same tick species demonstrate that O. coriaceus sometimes acquires and transstadially passes Lyme disease group spirochetes. I. pacificus nymphs inhabiting a woodland nidus of B. burgdorferi and A. phagocytophilum had a 5-fold higher prevalence of borreliae than adult ticks from the same generational cohort. In contrast to the results of preceding studies carried out at the same site, none of the nymphal or adult ticks was PCR-positive for A. phagocytophilum. This suggests that the distribution of this rickettsia is highly focal or variable from year-to-year within this particular woodland.

Borrelia bissettiae sp. nov. and Borrelia californiensis sp. nov. prevail in diverse enzootic transmission cycles

Two species of the genus Borrelia, Borrelia bissettiae sp. nov. and Borrelia californiensis sp. nov., were first described by Postic and co-workers on the basis of genetic analyses of several loci. Multilocus sequence analysis of eight housekeeping loci confirmed that these two Borrelia genomospecies are distinct members of the Borrelia burgdorferi sensu lato complex. B. bissettiae sp. nov. was initially described in transmission cycles involving Neotoma fuscipes wood rats and Ixodes pacificus ticks in California, and Neotoma mexicana and Ixodes spinipalpis in Colorado. The preferred host of B. californiensis sp. nov. appears to be the California kangaroo rat, Dipodomys californicus; Ixodes jellisoni, I. spinipalipis and I. pacificus ticks are naturally infected with it. Thus, the ecological associations of the two genomospecies and their genetic distance from all other known Borrelia genomospecies species justify their description as separate genomospecies: B. bissettiae sp. nov. (type strain DN127T = DSM 17990T =  CIP 109136T) and B. californiensis (type strain CA446T = DSM 17989T = ATCC BAA-2689T).

Unique strain of Borrelia miyamotoi in Ixodes pacificus Ticks, California, USA

Author(s): Cook, Vanessa J; Fedorova, Natalia; Macdonald, Warren P; Lane, Robert S; Barbour, Alan G