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opencc-zeroDec 2017View details →

Data from: Abiotic and habitat drivers of tick vector abundance, diversity, phenology and human encounter risk in southern California

The distribution, abundance and seasonal activity of vector species, such as ticks and mosquitoes, are key determinants of vector-borne disease risk, and are strongly influenced by abiotic and habitat conditions. Despite the numerous species of tick vectors in the heavily populated North American West Coast, all but Ixodes pacificus, the primary vector of the Lyme disease spirochete, is poorly characterized with regard to seasonal activity patterns and fine scale drivers of distribution and abundance, particularly in heavily populated regions of southern California. This lack of knowledge inhibits both scientific understanding and public health efforts to minimize vector exposure and risk of pathogen transmission to humans. Here we address this gap by characterizing the abiotic and habitat drivers of the distribution, abundance, and diversity of the vector tick community using fine scale temporal surveys over two seasons (2014 and 2015) across coastal and inland regions of Santa Barbara County, CA. We also characterize patterns of seasonal activity of the more common vector species to understand seasonality in risk of vector exposure, and specifically focus on human encounter risk using standardized tick drags as our method of collection. Leveraging plot-level habitat and abiotic variables in partial least squares regression analysis, we find the seven different vector species collected in this study have divergent drivers of activity and abundance. For example, I. pacificus is strongly associated with dense forest habitats and cool and moist microclimates, while Dermacentor occidentalis and Dermacentor variabilis, competent vectors of Rocky Mountain Spotted Fever, were found to be more tolerant of higher average temperatures and more open habitats. These results suggest that I. pacificus may be expected to experience reductions in geographic distribution and seasonal activity under projected land cover and climate change in coastal southern California, while D. occidentalis may experience more limited effects. We discuss implications for changing tick-borne disease risk associated with pathogens transmitted by Ixodes as well as Dermacentor species ticks in the western US, and contrast these predictions with eastern North America.

Data from: Tick infestation of chicks in a seabird colony varies with local breeding synchrony, local nest density and habitat structure

Parasites are a major risk for group-living animals and seabirds are notoriously susceptible to ectoparasite infestations because they commonly nest in dense colonies. Ticks parasitize seabirds across all biogeographical regions and they can be particularly harmful to nestlings, but the ecological factors that affect their transmission to chicks are little studied and poorly understood. Here we show that abundance of tick larvae in blue-footed booby (Sula nebouxii) broods varies with local nest synchrony and density, and also with habitat structure: abundance increased with local breeding synchrony, was linearly and quadratically related to local nest density, and was highest toward the southern end of the study area which has suitable (boulder-rich) habitat for ticks. Also, with increasing chick age infestation first increased and then declined. The results of this study highlight how local physical and social environmental factors influence infestation of seabird nestlings by ticks.

opencc-zeroDec 2011View details →

Data from: Infection intensity and infectivity of the tick-borne pathogen Borrelia afzelii

The 'trade-off' hypothesis for virulence evolution assumes that between-host transmission rate is a positive and saturating function of pathogen exploitation and virulence, but there are as yet few tests of this assumption, in particular for vector-borne pathogens. Here, I show that the infectivity (probability of transmission) of the tick-borne bacterium Borrelia afzelii from two of its natural rodent hosts (bank vole and yellow-necked mouse) to its main tick vector increases asymptotically with increasing exploitation (measured as bacterial load in skin biopsies). Hence, this result provides support for one of the basic assumptions of the 'trade-off hypothesis'. Moreover, there was no difference in infectivity between bank voles and yellow-necked mice despite bacterial loads being on average an order of magnitude higher in bank voles, most likely because ticks took larger blood meals from mice. This shows that interspecific variation in host resistance does not necessarily translate into a difference in infectivity.

Data from: Decreased small mammal and on-host tick abundance in association with invasive red imported fire ants (Solenopsis invicta)

Invasive species may impact pathogen transmission by altering the distributions and interactions among native vertebrate reservoir hosts and arthropod vectors. Here, we examined the direct and indirect effects of the red imported fire ant (Solenopsis invicta) on the native tick, small mammal and pathogen community in southeast Texas. Using a replicated large-scale field manipulation study, we show that small mammals were more abundant on treatment plots where S. invicta populations were experimentally reduced. Our analysis of ticks on small mammal hosts demonstrated a threefold increase in the ticks caught per unit effort on treatment relative to control plots, and elevated tick loads (a 27-fold increase) on one common rodent species. We detected only one known human pathogen (Rickettsia parkeri), present in 1.4% of larvae and 6.7% of nymph on-host Amblyomma maculatum samples but with no significant difference between treatment and control plots. Given that host and vector population dynamics are key drivers of pathogen transmission, the reduced small mammal and tick abundance associated with S. invicta may alter pathogen transmission dynamics over broader spatial scales.

Data from: The genetic signature of range expansion in a disease vector - the black-legged tick

Monitoring and predicting the spread of emerging infectious diseases requires that we understand the mechanisms of range expansion by its vectors. Here, we examined spatial and temporal variation of genetic structure among 13 populations of the Lyme disease vector, the black-legged tick, in southern Quebec, where this tick species is currently expanding and Lyme disease is emerging. Our objective was to identify the primary mode of tick movement into Canada based on observed spatial and temporal genetic patterns. Upon genotyping ten microsatellite loci from 613 tick specimens, we found multiple genetic signatures of frequent long-distance dispersal events, supporting the hypothesis that migratory birds are the primary carriers of black-legged ticks into southern Quebec. When we compared results from analyses of pairwise differences among ticks collected from eight different sites at different years between 2011 and 2014, we found that genetic variation observed among tick individuals appeared to be better explained by collection year than sampling locality. This suggests that while cohorts of black-legged ticks can rapidly invade large areas across southern Quebec, they also appear to be undergoing frequent turnover. Finally, the amount of genetic variation in tick populations across our study area appeared to be related to their degree of establishment, with established populations displaying a lower amount of temporal genetic variation than adventitious ones. Given that Lyme disease infection risk in a region can be influenced by the relative presence of established and/or adventitious tick populations, our results are useful for understanding both the seasonality and spatial variation of Lyme disease.

Data from: Microbiome changes through ontogeny of a tick pathogen vector

Blacklegged ticks (Ixodes scapularis) are one of the most important pathogen vectors in the United States, responsible for transmitting Lyme disease and other tick-borne diseases. The structure of a host's microbial community has the potential to affect the ecology and evolution of the host. We employed high-throughput sequencing of the 16S rRNA gene V3-V4 hypervariable regions in the first study to investigate the tick microbiome across all developmental stages (larvae, nymphs, adults). In addition to field-collected life stages, newly hatched laboratory-reared larvae were studied to determine the baseline microbial community structure and to assess transovarial transmission. We also targeted midguts and salivary glands due to their importance in pathogen maintenance and transmission. Over 100 000 sequences were produced per life stage replicate. Rickettsia was the most abundant bacterial genus across all sample types matching mostly the Ixodes rickettsial endosymbionts, and its proportion decreased as developmental stage progressed, with the exception of adult females that harboured a mean relative abundance of 97.9%. Laboratory-reared larvae displayed the lowest bacterial diversity, containing almost exclusively Rickettsia. Many of the remaining bacteria included genera associated with soil, water and plants, suggesting environmental acquisition while off-host. Female organs exhibited significantly different β-diversity than the whole tick from which they were derived. Our results demonstrate clear differences in both α- and β-diversity among tick developmental stages and between tick organs and the tick as a whole. Furthermore, field-acquired bacteria appear to be very important to the overall internal bacterial community of this tick species, with influence from the host bloodmeal appearing limited.

Data from: Invasion of two tick-borne diseases across New England: harnessing human surveillance data to capture underlying ecological invasion processes

Modelling the spatial spread of vector-borne zoonotic pathogens maintained in enzootic transmission cycles remains a major challenge. The best available spatio-temporal data on pathogen spread often take the form of human disease surveillance data. By applying a classic ecological approach—occupancy modelling—to an epidemiological question of disease spread, we used surveillance data to examine the latent ecological invasion of tick-borne pathogens. Over the last half-century, previously undescribed tick-borne pathogens including the agents of Lyme disease and human babesiosis have rapidly spread across the northeast United States. Despite their epidemiological importance, the mechanisms of tick-borne pathogen invasion and drivers underlying the distinct invasion trajectories of the co-vectored pathogens remain unresolved. Our approach allowed us to estimate the unobserved ecological processes underlying pathogen spread while accounting for imperfect detection of human cases. Our model predicts that tick-borne diseases spread in a diffusion-like manner with occasional long-distance dispersal and that babesiosis spread exhibits strong dependence on Lyme disease.

FIGURES 18–23. Ixodes myrmecobii Male. 18 Spiracular plate, 19 in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 18–23. Ixodes myrmecobii Male. 18 Spiracular plate, 19 Coxae and trochanters, 20 Tarsus I, 21 Tarsus II, 22 Tarsus III, 23 Tarsus IV. (PP = pregenital plate; MP = median plate; ADP = adanal plate; ANP = anal plate)

FIGURES 14–17. Ixodes myrmecobii Male. 14 Dorsal view, 15 Ventral view, 16 Dorsal capitulum, 17 in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 14–17. Ixodes myrmecobii Male. 14 Dorsal view, 15 Ventral view, 16 Dorsal capitulum, 17 Ventral capitulum. (PP = pregenital plate; MP = median plate; ADP = adanal plate; ANP = anal plate)

FIGURES 12–13. Ixodes myrmecobii Female scanning electron micrographs. 12 Dorsal view, 13 in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 12–13. Ixodes myrmecobii Female scanning electron micrographs. 12 Dorsal view, 13 Ventral view.

FIGURES 38–40 in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 38–40. Scanning electron micrographs of the trochanters of Sternalixodes males. 38 Ixodes holocyclus, 39 Ixodes myrmecobii, 40 Ixodes cornuatus.

FIGURES 36–37. Ixodes myrmecobii nymph scanning electron micrographs. 36 Dorsal view, 37 in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 36–37. Ixodes myrmecobii nymph scanning electron micrographs. 36 Dorsal view, 37 Ventral view.

FIGURES 41–42. 41 in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 41–42. 41 Phylogenetic relationships of Ixodes myrmecobii isolates obtained in this study (T4, T12, T15 and T16) with published reference material available at the CO1 locus. Evolutionary history was inferred using the neighbour-joining method supported with bootstrap test of 1000 replicates (values> 50% shown). Rhipicephalus sanguineus is included as the out group, 42 Phylogenetic relationships of Ixodes myrmecobii isolates obtained in this study (T4, T12, T15 and T16) with published reference material available at the ITS2 locus. Evolutionary history was inferred using the neighbour-joining method supported with bootstrap test of 1000 replicates (values> 50% shown). Rhipicephalus sanguineus is included as the out group.

FIGURES 31–35. Ixodes myrmecobii Nymph. 31 Scutum, 32 Tarsus I, 33 Tarsus II, 34 Tarsus III, 35 Tarsus IV in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 31–35. Ixodes myrmecobii Nymph. 31 Scutum, 32 Tarsus I, 33 Tarsus II, 34 Tarsus III, 35 Tarsus IV.

FIGURES 1–4. Ixodes myrmecobii Female. 1 Dorsal view, 2 Ventral view, 3 Dorsal capitulum, 4 in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 1–4. Ixodes myrmecobii Female. 1 Dorsal view, 2 Ventral view, 3 Dorsal capitulum, 4 Ventral capitulum.

FIGURES 26–30. Ixodes myrmecobii Nymph. 26 Dorsal view, 27 Ventral view, 28 in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 26–30. Ixodes myrmecobii Nymph. 26 Dorsal view, 27 Ventral view, 28 Coxae and trochanters, 29 Dorsal capitulum, 30 Ventral capitulum.

FIGURES 5–11. Ixodes myrmecobii Female. 5 Scutum, 6 in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 5–11. Ixodes myrmecobii Female. 5 Scutum, 6 Coxae and trochanters, 7 Spiracular plate, 8 Tarsus I, 9 Tarsus II, 10 Tarsus III, 11 Tarsus IV.

FIGURES 24–25. Ixodes myrmecobii male scanning electron micrographs. 24 Dorsal view, 25 in Redescription of the numbat tick Ixodes (Sternalixodes) myrmecobii Roberts, 1962 (Acari: Ixodidae) with descriptions of the male and nymph, and new host records

FIGURES 24–25. Ixodes myrmecobii male scanning electron micrographs. 24 Dorsal view, 25 Ventral view.

opencc-zeroNov 2023View details →

Supplementary material 12 from: Paez-Triana L, Herrera G, Vega L, Garcia-Corredor D, Pulido Medellín MO, Paniz-Mondolfi A, Muñoz M, Ramírez JD (2023) Metagenomic exploration of endosymbionts and pathogens in the tropical lineage of Rhipicephalus sanguineus sensu lato (s.l.) ticks in Colombia. Metabarcoding and Metagenomics 7: e109085. https://doi.org/10.3897/mbmg.7.109085

p-values obtained between departments and sexes within each department using the Wilcoxon test on the relative abundances of pathogens and endosymbionts