Borrelia lusitaniae OspA gene heterogeneity in Mediterranean basin area

Development of a sequence-based in silico OspA typing method for Borrelia burgdorferi sensu lato

Lyme disease (LD), caused by spirochete bacteria of the genus Borrelia burgdorferi sensu lato, remains the most common vector-borne disease in the northern hemisphere. Borrelia outer surface protein A (OspA) is an integral surface protein expressed during the tick cycle, and a validated vaccine target. There are at least 20 recognized Borrelia genospecies, that vary in OspA serotype. This study presents a new in silico sequence-based method for OspA typing using next-generation sequence data. Using a compiled database of over 400 Borrelia genomes encompassing the 4 most common disease-causing genospecies, we characterized OspA diversity in a manner that can accommodate existing and new OspA types and then defined boundaries for classification and assignment of OspA types based on the sequence similarity. To accommodate potential novel OspA types, we have developed a new nomenclature: OspA in silico type (IST). Beyond the ISTs that corresponded to existing OspA serotypes 1-8, we identified nine additional ISTs that cover new OspA variants in B. bavariensis (IST9-10), B. garinii (IST11-12), and other Borrelia genospecies (IST13-17). The IST typing scheme and associated OspA variants are available as part of the PubMLST Borrelia spp. database. Compared to traditional OspA serotyping methods, this new computational pipeline provides a more comprehensive and broadly applicable approach for characterization of OspA type and Borrelia genospecies to support vaccine development.

Evolutionary dynamics and geographical dispersal of Borrelia lusitaniae

Background

Borrelia lusitaniae is a species within the complex Borrelia burgdorferi sensu lato, associated with lizards as reservoirs and Ixodes ricinus as its main vector. Borrelia lusitaniae is predominantly distributed in Central and Southeast Europe, and in countries of the Mediterranean basin, such as Portugal, Morocco, Tunisia, and Italy where this spirochete appears to infect vector ticks more frequently than other genospecies. Evolution of this zoonotic tick-borne microparasite is shaped by different environmental factors. Comprehensive phylogenetic analysis may give insight into how B. lusitaniae spreads to new geographic locations.

Aim

We applied Bayesian statistical methods to B. lusitaniae multilocus sequence typing (MLST) data to study the migration routes of B. lusitaniae and its potential for further spread.

Results

The discrete phylogeographic analysis placed origins of B. lusitaniae in Southeast Europe and identified at least two introductions of B. lusitaniae from Europe to North Africa. Estimated effective reproductive potential (Re), as a key indicator for a pathogen spread, suggested potential for further spread.

Conclusion

The results of this study can provide beneficial information about the potential for further spread of B. lusitaniae in Europe and North Africa and estimation of necessity for the development of strategies to monitor and control Lyme borreliosis.

Investigation of Tick-Borne Pathogens in Ixodes ricinus in a Peri-Urban Park in Lombardy (Italy) Reveals the Presence of Emerging Pathogens

Ticks are important vectors of a great range of pathogens of medical and veterinary importance. Lately, the spread of known tick-borne pathogens has been expanding, and novel ones have been identified as (re)emerging health threats. Updating the current knowledge on tick-borne pathogens in areas where humans and animals can be easily exposed to ticks represents a starting point for epidemiological studies and public awareness. A PCR screening for tick-borne pathogens was carried out in Ixodes ricinus ticks collected in a peri-urban recreational park in Ticino Valley, Italy. The presence of Rickettsia spp., Borrelia burgdorferi senso latu complex, Anaplasma spp. and Babesia spp. was evaluated in a total of 415 I. ricinus specimens. Rickettsia spp. (R monacensis and R. helvetica) were detected in 22.96% of the samples, while B. burgdorferi s.l. complex (B. afzelii and B. lusitaniae) were present in 10.94%. Neoehrlichia mikurensis (1.99%) and Babesia venatorum (0.73%) were reported in the area of study for the first time. This study confirmed the presence of endemic tick-borne pathogens and highlighted the presence of emerging pathogens that should be monitored especially in relation to fragile patients, the difficult diagnosis of tick-borne associated diseases and possible interactions with other tick-borne pathogens.

The Population Structure of Borrelia lusitaniae Is Reflected by a Population Division of Its Ixodes Vector

Populations of vector-borne pathogens are shaped by the distribution and movement of vector and reservoir hosts. To study what impact host and vector association have on tick-borne pathogens, we investigated the population structure of Borrelia lusitaniae using multilocus sequence typing (MLST). Novel sequences were acquired from questing ticks collected in multiple North African and European locations and were supplemented by publicly available sequences at the Borrelia Pubmlst database (accessed on 11 February 2020). Population structure of B. lusitaniae was inferred using clustering and network analyses. Maximum likelihood phylogenies for two molecular tick markers (the mitochondrial 16S rRNA locus and a nuclear locus, Tick-receptor of outer surface protein A, trospA) were used to confirm the morphological species identification of collected ticks. Our results confirmed that B. lusitaniae does indeed form two distinguishable populations: one containing mostly European samples and the other mostly Portuguese and North African samples. Of interest, Portuguese samples clustered largely based on being from north (European) or south (North African) of the river Targus. As two different Ixodes species (i.e., I. ricinus and I. inopinatus) may vector Borrelia in these regions, reference samples were included for I. inopinatus but did not form monophyletic clades in either tree, suggesting some misidentification. Even so, the trospA phylogeny showed a monophyletic clade containing tick samples from Northern Africa and Portugal south of the river Tagus suggesting a population division in Ixodes on this locus. The pattern mirrored the clustering of B. lusitaniae samples, suggesting a potential co-evolution between tick and Borrelia populations that deserve further investigation.

Diversity of Lyme borreliosis spirochetes isolated from ticks in Serbia

Spirochetes from the Borrelia burgdorferi sensu lato (s.l.). (Spirochaetales: Spirochaetaceae) species complex, including the causative agents of Lyme borreliosis, have been isolated from ticks, vertebrate reservoirs and humans. Previous analyses based on direct molecular detection in ticks indicated a considerable diversity of B. burgdorferi s.l. complex in Serbia. The present study aimed (a) to isolate borrelia strains from Serbia; (b) to determine their genotypic characteristics; and (c) to establish a collection of viable B. burgdorferi s.l. strains for further biological, ecological and genetic studies. For the present study, 231 adult Ixodes ricinus (Ixodida: Ixodidae) ticks from 16 ecologically different localities in Serbia were individually processed to cultivate B. burgdorferi s.l. This led to the isolation of 36 strains. A hbb gene quantitative real-time polymerase chain reaction (PCR) based on melting temperature determination and ospA gene sequencing were used to genotype the isolated spirochetes. The species identified based on the hbb gene real-time PCR were: Borrelia lusitaniae (44.4%), Borrelia afzelii (36.1%), Borrelia garinii (13.9%) and Borrelia valaisiana (5.6%), whereas the ospA sequence analysis revealed the occurrence of Borrelia bavariensis. This is the first report of the isolation of B. lusitaniae, B. garinii, B. bavariensis and B. valaisiana strains in Serbia.

Lyme borreliosis spirochetes and spotted fever group rickettsiae in ixodid ticks from Pianosa island, Tuscany Archipelago, Italy

A study on tick fauna and tick-borne pathogens was undertaken in Pianosa, an island in the Tuscany Archipelago that constitutes an important stopping and nesting point for migratory birds. Ticks were removed from feral cats and a few terrestrial birds, and host-seeking ticks were collected by dragging. A total of 89 ticks were found on animals: 57 Ixodes ventalloi Gil Collado, 1936 and 32 Ixodes acuminatus Neumann, 1901. Host-seeking ticks were 354 Hyalomma spp. larvae and 18 Hyalomma spp. adults, identified as Hyalomma marginatum C.L. Koch, 1844 (n=11) and 7 Hyalomma detritum Schulze, 1919 (n=7). A sample of adult ticks was subjected to molecular analyses to look for Rickettsia spp. and Borrelia burgdorferi sensu lato (s.l.). Sequence analysis of the 5S-23S intergenic spacer region and OspA gene of B. burgdorferi s.l.-positive samples showed the presence of Borrelia spielmanii (n=3; 3.7%, 95% confidence interval [CI] 0.08-10.4) and Borrelia valaisiana (n=13; 13.6%, 95% CI 7.0-23.0) in Ixodes ticks from cats and terrestrial birds. Ixodes spp. were also infected by Rickettsia helvetica (n=19; 23.4%, 95% CI 14.7-34.2). Finally, we detected Rickettsia aeschlimannii in 3 out of 12 host-seeking Hyalomma spp. adults tested (25%, 95% CI 5.5-57.2). Our study shows the presence of several tick-borne pathogens in Pianosa. Hyalomma spp. and Ixodes ticks other than I. ricinus seem to be involved in their epidemiological cycle, and birds could contribute to the pathogen dispersal along their migration routes. This is the first finding of B. spielmanii in Italy. We hypothesize the involvement of peridomestic rodents or hedgehogs in its maintenance in Pianosa.

Lyme borreliosis, Po River Valley, Italy

We aimed to determine the presence of Ixodes ricinus ticks in heavily populated areas of the Po River Valley after report of a Lyme disease case. Eighteen percent of ticks examined from 3 locations were positive for Lyme disease borreliae. Lyme disease was diagnosed for 3 workers at risk for tick bite.

Fine-scale phylogeographic structure of Borrelia lusitaniae revealed by multilocus sequence typing

Borrelia lusitaniae is an Old World species of the Lyme borreliosis (LB) group of tick-borne spirochetes and prevails mainly in countries around the Mediterranean Basin. Lizards of the family Lacertidae have been identified as reservoir hosts of B. lusitaniae. These reptiles are highly structured geographically, indicating limited migration. In order to examine whether host geographic structure shapes the evolution and epidemiology of B. lusitaniae, we analyzed the phylogeographic population structure of this tick-borne bacterium using a recently developed multilocus sequence typing (MLST) scheme based on chromosomal housekeeping genes. A total of 2,099 questing nymphal and adult Ixodes ricinus ticks were collected in two climatically different regions of Portugal, being approximately 130 km apart. All ticks were screened for spirochetes by direct PCR. Attempts to isolate strains yielded 16 cultures of B. lusitaniae in total. Uncontaminated cultures as well as infected ticks were included in this study. The results using MLST show that the regional B. lusitaniae populations constitute genetically distinct populations. In contrast, no clear phylogeographic signals were detected in sequences of the commonly used molecular markers ospA and ospC. The pronounced population structure of B. lusitaniae over a short geographic distance as captured by MLST of the housekeeping genes suggests that the migration rates of B. lusitaniae are rather low, most likely because the distribution of mediterranean lizard populations is highly parapatric. The study underlines the importance of vertebrate hosts in the geographic spread of tick-borne microparasites.