Disentangling tick-borne diseases dynamics: an integrative approach
I am very interested in understanding why human cases of tick-borne diseases (TBDs) are unevenly distributed in nature (some geographic areas with a lot of cases, and others with only a few) given that ticks and pathogens are more widely distributed. In this context, part of my dissertation focussed on studying population genomics and microbiome of ticks. I integrated different lines of evidence to better understand TBDs dynamics.
Among the tick species present in the eastern United States, Amblyomma americanum (lone star tick) and Dermacentor variabilis (American dog tick) are two of the most important from a health and economic perspective. They are involved in the transmission of a wide variety of human and animal pathogens, including the causative agents of diseases such as anaplasmosis, rickettsiosis, ehrlichiosis, and STARI. For my dissertation work, I generated genetic data (using NGS technologies) for both species, and I explored their population genetic structure, microbiome, and demographic history.
During 2017-19 I collected adult ticks from numerous locations across the US. Additionally, I received invaluable help from collaborators from various institutions, and citizens, through a small citizen science project I started on twitter. After three successful collecting seasons my sampling included lone stars from ~17 states and American dog ticks from ~24 states.
I am very grateful to the American Philosophical Society for funding part of my fieldwork. I was a Lewis and Clark field scholar in 2018-2019. I would not have been able to collect at all the locations I did without those funds, so thank you!!.
Among the tick species present in the eastern United States, Amblyomma americanum (lone star tick) and Dermacentor variabilis (American dog tick) are two of the most important from a health and economic perspective. They are involved in the transmission of a wide variety of human and animal pathogens, including the causative agents of diseases such as anaplasmosis, rickettsiosis, ehrlichiosis, and STARI. For my dissertation work, I generated genetic data (using NGS technologies) for both species, and I explored their population genetic structure, microbiome, and demographic history.
During 2017-19 I collected adult ticks from numerous locations across the US. Additionally, I received invaluable help from collaborators from various institutions, and citizens, through a small citizen science project I started on twitter. After three successful collecting seasons my sampling included lone stars from ~17 states and American dog ticks from ~24 states.
I am very grateful to the American Philosophical Society for funding part of my fieldwork. I was a Lewis and Clark field scholar in 2018-2019. I would not have been able to collect at all the locations I did without those funds, so thank you!!.
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PROJECTS |
Is Dermacentor variabilis a single species?
After successfully collecting, preserving (with the help of awesome collaborators) specimens from the west coast states, generating and analyzing genetic data, our results suggest that populations western and eastern of the Rockies belong to two different species. In our publication, we present this evidence and describe a new Dermacentor sp., Dermacentor similis
Evolutionary history of the genus Dermacentor and the arrival of this genus to the New World.
There are many gaps related to the origin and subsequent dispersion routes of different ticks’ genera. I was particularly interested in the origin and dispersion of the genus Dermacentor. Where did the genus originated? How did Dermacentor ticks dispersed after their origin? And last but not least: how did the genus Dermacentor arrive to the New World? What dispersion route/routes were employed? We got very interesting results from this project, and they are now published! Read more in Lado and Klompen 2019, Biological Journal of the Linnean Society.
Is the species name faithful to reality? How variable is D. variabilis?
A look into its genetic variation.
D. variabilis is found -generally speaking- from Canada to Mexico, and thus, it’s a widely distributed species. As such, we expected to find genetic variability between populations from different areas, and population structuring between populations or groups of populations. For this project, we used NGS techniques to analyze the population genetic structure of different D. variabilis populations across the US, and to explore this species genetic diversity. This project was done as part of a NSF REU (research experience for undergraduates) project at OSU. Three undergraduate students (Caleb Cox, Kya Wideman, and Andrea Hernandez) participated in this project and coauthored the publication (Lado et al. 2019, Annals of the Entomological Society of America).
Amblyomma americanum demographic history and historic distribution in the US.
What’s the deal with A. americanum? Were lone stars common in New England in the past? Are New England populations recent colonizations? The distribution of this species in norther and northeastern locations has been questioned many times in the past, with records including and excluding same geographic areas as part of the geographic distribution. For this project we looked at the population genetic structure and demographic history of A. americanum using NGS data, and we also explored the habitat suitability for this species across its geographic range. Exciting results!!
(Lado et al. 2020, Molecular Ecology).
(Lado et al. 2020, Molecular Ecology).
Is Dermacentor variabilis a single species?
I have a deep interest on the process of speciation, and how to delimit species using integrative taxonomy. In the United States, D. variabilis has a discontinuous geographic distribution. It is present eastwards of a line drawn from Montana to southern Texas, and a few disjoint populations west of the Rockies, and in the intermountain region. Previous studies, using different sets of molecular markers, suggest
that both groups (east and west of the Rocky Mountains) may correspond to different species. To determine whether we are dealing with one or two species more genetic data, especially from western populations is needed. After successfully collecting, preserving (with the help of awesome collaborators) specimens from the west coast states, and generating genetic data, I am currently analyzing the results of this project. Interesting results…stay tunned!
that both groups (east and west of the Rocky Mountains) may correspond to different species. To determine whether we are dealing with one or two species more genetic data, especially from western populations is needed. After successfully collecting, preserving (with the help of awesome collaborators) specimens from the west coast states, and generating genetic data, I am currently analyzing the results of this project. Interesting results…stay tunned!
Check out this interview about my microbiome research!
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MORE RESEARCH |
Insights to the microbiome of Haemaphysalis lemuris, a tick that parasitizes lemurs in different areas of Madagascar (Lado et al. 2018, Ticks and Tick-borne Diseases)
Abstract:
Lemurs are primate species that are endemic to Madagascar. At present, about 90% of lemur species are endangered, and 5 species are among the 25 most endangered primates worldwide. Health status is a major factor impacting the viability of wild populations of many endangered species including lemurs. Given this context, we analyzed the microbiome of 24 specimens of Haemaphysalis lemuris, the most common tick parasitizing lemurs in their native habitats. Ticks were collected from 6 lemur species and microbiomes analyzed using next-generation sequencing. Our results show that the H. lemuris microbiome is highly diverse, including over 500 taxa, 267 of which were identified to genus level. Analysis of the microbiome also shows that there is a distinct "host" (lemur species) component when explaining the differences among and between microbial communities of H. lemuris. This "host" component seems to overwhelm any "locality" (geographic origin of the sample) component. In addition to the microbiome data, targeted PCR was used to test for the presence of three pathogens recently detected in the blood of wild lemurs: Borrelia sp., Candidatus Neoehrlichia sp., and Babesia sp. Overall, the presence of DNA of Rickettsia spp., Bartonella spp., Francisella spp., and a Babesia sp., in H. lemuris, is consistent with the hypothesis that these ectoparasites may act as vector for these pathogens. Further studies assessing vector competence are needed to confirm this hypothesis
Lemurs are primate species that are endemic to Madagascar. At present, about 90% of lemur species are endangered, and 5 species are among the 25 most endangered primates worldwide. Health status is a major factor impacting the viability of wild populations of many endangered species including lemurs. Given this context, we analyzed the microbiome of 24 specimens of Haemaphysalis lemuris, the most common tick parasitizing lemurs in their native habitats. Ticks were collected from 6 lemur species and microbiomes analyzed using next-generation sequencing. Our results show that the H. lemuris microbiome is highly diverse, including over 500 taxa, 267 of which were identified to genus level. Analysis of the microbiome also shows that there is a distinct "host" (lemur species) component when explaining the differences among and between microbial communities of H. lemuris. This "host" component seems to overwhelm any "locality" (geographic origin of the sample) component. In addition to the microbiome data, targeted PCR was used to test for the presence of three pathogens recently detected in the blood of wild lemurs: Borrelia sp., Candidatus Neoehrlichia sp., and Babesia sp. Overall, the presence of DNA of Rickettsia spp., Bartonella spp., Francisella spp., and a Babesia sp., in H. lemuris, is consistent with the hypothesis that these ectoparasites may act as vector for these pathogens. Further studies assessing vector competence are needed to confirm this hypothesis
Systematics and phylogenetics of the Amblyomma maculatum ticks complex:
The Amblyomma maculatum Koch, 1844 (Acari: Ixodidae) group of ticks:
phenotypic plasticity or incipient speciation? (Lado et al. 2018, Parasites and Vectors)
Abstract:
Background: The goal of this study was to reassess the taxonomic status of A. maculatum, A. triste and A. tigrinum by phylogenetic analysis of five molecular markers [four mitochondrial: 12S rDNA, 16S rDNA, the control region (DL) and cytochrome c oxidase 1 (cox1), and one nuclear: ribosomal intergenic transcribed spacer 2 (ITS2)]. In addition, the phenotypic diversity of adult ticks identified as A. maculatum and A. triste from geographically distinct populations was thoroughly re-examined.
Results: Microscopic examination identified four putative morphotypes distinguishable by disjunct geographical ranges, but very scant fixed characters. Analysis of the separated mitochondrial datasets mostly resulted in conflicting tree topologies. Nuclear gene sequences were almost identical throughout the geographical ranges of the two species, suggesting a very recent, almost explosive radiation of the terminal operational taxonomic units. Analysis of concatenated molecular datasets was more informative and indicated that, although genetically very close to the A. maculatum - A. triste lineage, A. tigrinum was a monophyletic separate entity. Within the A. maculatum - A. triste cluster, three main clades were supported. The two morphotypes, corresponding to the western North American and eastern North American populations, consistently grouped in a single monophyletic clade with many shared mitochondrial sequences among ticks of the two areas. Ticks from the two remaining morphotypes, south-eastern South America and Peruvian, corresponded to two distinct clades. Conclusions: Given the paucity of morphological characters, the minimal genetic distance separating morphotypes, and more importantly the fact that two morphotypes are genetically indistinguishable, our data suggest that A. maculatum and A. triste should be synonymized and that morphological differences merely reflect very recent local adaptation to distinct environments in taxa that might be undergoing the first steps of speciation but have yet to complete lineage sorting. Nonetheless, future investigations using more sensitive nuclear markers and/or crossbreeding experiments might reveal the occurrence of very rapid speciation events in this group of taxa. Tentative node dating revealed that the A. tigrinum and A. maculatum - A. triste clades split about 2 Mya, while the A. maculatum - A.triste cluster radiated no earlier than 700,000 years ago.
Background: The goal of this study was to reassess the taxonomic status of A. maculatum, A. triste and A. tigrinum by phylogenetic analysis of five molecular markers [four mitochondrial: 12S rDNA, 16S rDNA, the control region (DL) and cytochrome c oxidase 1 (cox1), and one nuclear: ribosomal intergenic transcribed spacer 2 (ITS2)]. In addition, the phenotypic diversity of adult ticks identified as A. maculatum and A. triste from geographically distinct populations was thoroughly re-examined.
Results: Microscopic examination identified four putative morphotypes distinguishable by disjunct geographical ranges, but very scant fixed characters. Analysis of the separated mitochondrial datasets mostly resulted in conflicting tree topologies. Nuclear gene sequences were almost identical throughout the geographical ranges of the two species, suggesting a very recent, almost explosive radiation of the terminal operational taxonomic units. Analysis of concatenated molecular datasets was more informative and indicated that, although genetically very close to the A. maculatum - A. triste lineage, A. tigrinum was a monophyletic separate entity. Within the A. maculatum - A. triste cluster, three main clades were supported. The two morphotypes, corresponding to the western North American and eastern North American populations, consistently grouped in a single monophyletic clade with many shared mitochondrial sequences among ticks of the two areas. Ticks from the two remaining morphotypes, south-eastern South America and Peruvian, corresponded to two distinct clades. Conclusions: Given the paucity of morphological characters, the minimal genetic distance separating morphotypes, and more importantly the fact that two morphotypes are genetically indistinguishable, our data suggest that A. maculatum and A. triste should be synonymized and that morphological differences merely reflect very recent local adaptation to distinct environments in taxa that might be undergoing the first steps of speciation but have yet to complete lineage sorting. Nonetheless, future investigations using more sensitive nuclear markers and/or crossbreeding experiments might reveal the occurrence of very rapid speciation events in this group of taxa. Tentative node dating revealed that the A. tigrinum and A. maculatum - A. triste clades split about 2 Mya, while the A. maculatum - A.triste cluster radiated no earlier than 700,000 years ago.
Amblyomma parvum Aragão, 1908 (Acari: Ixodidae):
Phylogeography and systematic considerations (Lado et al. 2016, Ticks and tick-borne Diseases)
Abstract:
The geographical distribution of Amblyomma parvum Aragão 1908 in the New World is disjunct, with two main clusters separated from each other by the Amazon basin. The main objectives of this study were to further investigate the systematic relationships within A. parvum, to determine whether or not populations from different geographical areas might represent cryptic species, and to reconstruct the phylogeographical evolutionary history of the species. The genetic diversity of A. parvum collected throughout its distributional range was analyzed by using 6 molecular markers: 5 mitochondrial [the small and the large ribosomal subunits 12rDNA and 16SrDNA, the cytochrome oxidase I (COI) and II (COII) and the control region or d-loop (DL)], and one nuclear (ITS2, Inter transcribed spacer 2). Phylogenetic trees were inferred by using maximum parsimony and Bayesian analyses. In addition, node dating was attempted for the main lineages identified phylogenetically. Although mitochondrial and nuclear topologies were not totally congruent, they all identified at least two main supported clusters, a Central American lineage, and a Brazilian-Argentinian lineage. Clade support and divergence values strongly suggest that the two lineages correspond to different taxonomic entities. Node dating placed the split between the Central American and the Brazilian-Argentinian lineages at approximately 5.8-4.9 Mya, just after the progressive replacement of the dry areas that occupied the northern part of South America by the Amazon Basin in the early-mid Miocene. This event might be the cause of fragmentation and putative speciation within the ancestral relatively xerophilic A. parvum population.
The geographical distribution of Amblyomma parvum Aragão 1908 in the New World is disjunct, with two main clusters separated from each other by the Amazon basin. The main objectives of this study were to further investigate the systematic relationships within A. parvum, to determine whether or not populations from different geographical areas might represent cryptic species, and to reconstruct the phylogeographical evolutionary history of the species. The genetic diversity of A. parvum collected throughout its distributional range was analyzed by using 6 molecular markers: 5 mitochondrial [the small and the large ribosomal subunits 12rDNA and 16SrDNA, the cytochrome oxidase I (COI) and II (COII) and the control region or d-loop (DL)], and one nuclear (ITS2, Inter transcribed spacer 2). Phylogenetic trees were inferred by using maximum parsimony and Bayesian analyses. In addition, node dating was attempted for the main lineages identified phylogenetically. Although mitochondrial and nuclear topologies were not totally congruent, they all identified at least two main supported clusters, a Central American lineage, and a Brazilian-Argentinian lineage. Clade support and divergence values strongly suggest that the two lineages correspond to different taxonomic entities. Node dating placed the split between the Central American and the Brazilian-Argentinian lineages at approximately 5.8-4.9 Mya, just after the progressive replacement of the dry areas that occupied the northern part of South America by the Amazon Basin in the early-mid Miocene. This event might be the cause of fragmentation and putative speciation within the ancestral relatively xerophilic A. parvum population.
For older projects (rickettsiosis in Uruguay, fish trematodes, etc), please refer to the publications section of this website. If you are interested on chatting about any of the projects, would like more information, please contact me and I will be happy to help you with that!.
If you are interested in collaborating, please contact me.
If you are interested in collaborating, please contact me.