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Christopher D Paddock - One of the best experts on this subject based on the ideXlab platform.

Shahid Karim - One of the best experts on this subject based on the ideXlab platform.

  • Amblyomma maculatum SECIS binding protein 2 and putative selenoprotein P are indispensable for pathogen replication and tick fecundity.
    Insect biochemistry and molecular biology, 2017
    Co-Authors: Khemraj Budachetri, Gary Crispell, Shahid Karim
    Abstract:

    Selenium, a vital trace element, is incorporated into selenoproteins to produce selenocysteine. Our previous studies have revealed an adaptive co-evolutionary process that has enabled the spotted fever-causing tick-borne pathogen Rickettsia parkeri to survive by manipulating an antioxidant defense system associated with selenium, which includes a full set of selenoproteins and other antioxidants in ticks. Here, we conducted a systemic investigation of SECIS binding protein 2 (SBP2) and putative selenoprotein P (SELENOP) by transcript silencing in adult female Gulf-coast ticks (Amblyomma maculatum). Knockdown of the SBP2 and SELENOP genes depleted the respective transcript levels of these tick selenogenes, and caused differential regulation of other antioxidants. Importantly, the selenium level in the immature and mature tick stages increased significantly after a blood meal, but the selenium level decreased in ticks after the SBP2 and SELENOP knockdowns. Moreover, the SBP2 knockdown significantly impaired both transovarial transmission of R. parkeri to tick eggs and egg hatching. Overall, our data offer new insight into the relationship between the SBP2 selenoprotein synthesis gene and the putative tick SELENOP gene. It also augments our understanding of selenoprotein synthesis, selenium maintenance and utilization, and bacterial colonization of a tick vector.

  • Catalase is a determinant of the colonization and transovarial transmission of Rickettsia parkeri in the Gulf Coast tick Amblyomma maculatum
    Insect molecular biology, 2017
    Co-Authors: Khemraj Budachetri, Deepak Kumar, Shahid Karim
    Abstract:

    The Gulf Coast tick (Amblyomma maculatum) has evolved as a competent vector of the spotted-fever group rickettsia, Rickettsia parkeri. In this study, the functional role of catalase, an enzyme responsible for the degradation of toxic hydrogen peroxide, in the colonization of the tick vector by R. parkeri and transovarial transmission of this pathogen to the next tick generation, was investigated. Catalase gene (CAT) expression in midgut, salivary glands and ovarian tissues exhibited a 2–11-fold increase in transcription level upon R. parkeri infection. Depletion of CAT transcripts using an RNA-interference approach significantly reduced R. parkeri infection levels in midgut and salivary gland tissues by 53–63%. The role of CAT in transovarial transmission of R. parkeri was confirmed by simultaneously blocking the transcript and the enzyme by injecting double-stranded RNA for CAT and a catalase inhibitor (3-amino-1,2,4-triazole) into gravid females. Simultaneous inhibition of the CAT transcript and the enzyme significantly reduced the egg conversion ratio with a 44% reduction of R. parkeri transovarial transmission. These data suggest that catalase is required for rickettsial colonization of the tick vector and transovarial transmission to the next generation.

  • Knockdown of Selenocysteine-Specific Elongation Factor in Amblyomma maculatum Alters the Pathogen Burden of Rickettsia parkeri with Epigenetic Control by the Sin3
    2016
    Co-Authors: Histone Deacetylase, Rebecca E Browning, Steven W Adamson, Khemraj Budachetri, Jose M C Ribeiro, Corepressor Complex, Shahid Karim
    Abstract:

    Selenocysteine is the 21st naturally-occurring amino acid. Selenoproteins have diverse functions and many remain uncharacterized, but they are typically associated with antioxidant activity. The incorporation of selenocysteine into the nascent polypeptide chain recodes the TGA stop codon and this process depends upon a number of essential factors including the selenocysteine elongation factor (SEF). The transcriptional expression of SEF did not change significantly in tick midguts throughout the blood meal, but decreased in salivary glands to 20 % at the end of the fast feeding phase. Since selenoprotein translation requires this specialized elongation factor, we targeted this gene for knockdown by RNAi to gain a global view of the role selenoproteins play in tick physiology. We found no significant differences in tick engorgement and embryogenesis but detected no antioxidant capacity in tick saliva. The transcriptional profile of selenoproteins in R. parkeri-infected Amblyomma maculatum revealed declined activity of selenoprotein M and catalase and increased activity of selenoprotein O, selenoprotein S, and selenoprotein T. Furthermore, the pathogen burden was significantly altered in SEF-knockdowns. We then determined the global impact of SEF-knockdown by RNA-seq, and mapped huge shifts in secretory gene expression that could be th

  • Rickettsia parkeri colonization in Amblyomma maculatum: the role of superoxide dismutases
    Parasites & Vectors, 2016
    Co-Authors: Gary Crispell, Khemraj Budachetri, Shahid Karim
    Abstract:

    Background The Gulf Coast tick ( Amblyomma maculatum ) is an arthropod vector of Rickettsia parkeri , the causative agent of American boutonneuse fever and an infectious agent of public health significance. In this study, we evaluated the biological significance of the superoxide dismutases (SODs) of A. maculatum in hematophagy and R. parkeri colonization within the tick host. Methods An RNA interference approach was used to measure the functional roles of tick SODs ( Cu/Zn-SOD and Mn-SOD ) in R. parkeri colonization of the tick vector. Total microbial load, R. parkeri infection rate, and compensatory mechanisms by tick genes were examined using quantitative polymerase chain reaction (PCR) and quantitative reverse-transcriptase PCR assays. SOD enzymatic activity assays and malondialdehyde (MDA) lipid peroxidation were employed to determine the redox states in the tick tissues. Results Knockdown of the Cu/Zn-SOD gene caused the upregulation of Mn-SOD in transcript levels. Single and dual knockdowns of the SOD genes caused an increase in MDA lipid peroxidation while SOD enzymatic activities did not show a significant change. Mn-SOD knockdown resulted in a substantial increase in the microbial load; however, Cu/Zn-SOD transcript depletion prompted an upsurge in the midgut bacterial load, and significantly decreased the bacterial load in salivary gland tissues. Additionally, Cu/Zn-SOD transcript silencing led to significantly fewer R. parkeri DNA copy numbers in both tick tissues (midguts and salivary glands). Conclusions SOD enzymes play an important function in the regulation of bacterial communities associated with tick vectors and also in the defense mechanisms against the damage caused by reactive oxygen species within the tick. Knockdown experiments increased the levels of total oxidative stress in ticks, revealing the interplay between SOD isozymes that results in the transcriptional regulation of tick antioxidants. Moreover, the tick's Cu/Zn-SOD aids in the colonization of  R. parkeri in tick tissues providing evidence of A. maculatum's vectorial success for a spotted fever group rickettsial pathogen.

  • Rickettsia parkeri colonization in Amblyomma maculatum: the role of superoxide dismutases.
    Parasites & vectors, 2016
    Co-Authors: Gary Crispell, Khemraj Budachetri, Shahid Karim
    Abstract:

    The Gulf Coast tick (Amblyomma maculatum) is an arthropod vector of Rickettsia parkeri, the causative agent of American boutonneuse fever and an infectious agent of public health significance. In this study, we evaluated the biological significance of the superoxide dismutases (SODs) of A. maculatum in hematophagy and R. parkeri colonization within the tick host. An RNA interference approach was used to measure the functional roles of tick SODs (Cu/Zn-SOD and Mn-SOD) in R. parkeri colonization of the tick vector. Total microbial load, R. parkeri infection rate, and compensatory mechanisms by tick genes were examined using quantitative polymerase chain reaction (PCR) and quantitative reverse-transcriptase PCR assays. SOD enzymatic activity assays and malondialdehyde (MDA) lipid peroxidation were employed to determine the redox states in the tick tissues. Knockdown of the Cu/Zn-SOD gene caused the upregulation of Mn-SOD in transcript levels. Single and dual knockdowns of the SOD genes caused an increase in MDA lipid peroxidation while SOD enzymatic activities did not show a significant change. Mn-SOD knockdown resulted in a substantial increase in the microbial load; however, Cu/Zn-SOD transcript depletion prompted an upsurge in the midgut bacterial load, and significantly decreased the bacterial load in salivary gland tissues. Additionally, Cu/Zn-SOD transcript silencing led to significantly fewer R. parkeri DNA copy numbers in both tick tissues (midguts and salivary glands). SOD enzymes play an important function in the regulation of bacterial communities associated with tick vectors and also in the defense mechanisms against the damage caused by reactive oxygen species within the tick. Knockdown experiments increased the levels of total oxidative stress in ticks, revealing the interplay between SOD isozymes that results in the transcriptional regulation of tick antioxidants. Moreover, the tick's Cu/Zn-SOD aids in the colonization of R. parkeri in tick tissues providing evidence of A. maculatum's vectorial success for a spotted fever group rickettsial pathogen.

Holly Gaff - One of the best experts on this subject based on the ideXlab platform.

  • Comparative population genetics of Amblyomma maculatum and Amblyomma americanum in the mid-Atlantic United States.
    Ticks and tick-borne diseases, 2020
    Co-Authors: Sara A. Benham, Holly Gaff, Zachary Bement, Christian Blaise, Hannah Cummins, Rebecca Ferrara, Joshua Moreno, Erika Parker, Anna Phan, Tori Rose
    Abstract:

    Abstract The Gulf Coast tick, Amblyomma maculatum, is undergoing a northward expansion along the United States East Coast, most recently establishing populations in Virginia, Maryland, and Delaware. This expansion has human health implications, as A. maculatum is the primary natural vector of the bacterium Rickettsia parkeri, which causes a spotted fever-type rickettsiosis. Newly established populations of A. maculatum in Virginia tend to have high prevalence of R. parkeri, compared to lower infection rates in the historical range. The factors contributing to high R. parkeri prevalence in Virginia are not known. Investigating connectivity between sites colonized with A. maculatum can help determine whether sites with higher prevalence are isolated or well-connected through migration, thus serving as a source of infected individuals. We characterized 16S rRNA haplotypes of A. maculatum and, for comparison, the congeneric Amblyomma americanum collected from sites where these species co-occur. We then explored connectivity and genetic structure among Virginia populations using pairwise ΦST and AMOVA analyses. Our study identified one recently restored native grassland site with low A. maculatum haplotype diversity and strong evidence of a founder effect, whereas most sites are haplotypically diverse but with no clear genetic structure or connectivity between sites. These findings contrast with high connectivity and a slight mainland/island structure among A. americanum populations. Our results suggest that A. maculatum populations occasionally arise following long-distance drop-offs of few individual ticks in suitable habitat, but no clear migration patterns were observed. The distinct population genetic patterns between species might result from differences in host utilization.

  • Survey of Rickettsia parkeri and Amblyomma maculatum associated with small mammals in southeastern Virginia.
    Ticks and tick-borne diseases, 2020
    Co-Authors: Alexandra N. Cumbie, Robyn M. Nadolny, Wayne L. Hynes, Christina Espada, Robert K. Rose, Raymond D. Dueser, Holly Gaff
    Abstract:

    Abstract Small mammals are often parasitized by the immature stages of hard-bodied ticks (family Ixodidae) and may serve as reservoir hosts of tick-borne pathogens. Amblyomma maculatum, the Gulf Coast tick, is the primary vector of Rickettsia parkeri, the causative agent of R. parkeri rickettsiosis. This hard-bodied tick species is expanding its historical range from the Gulf Coast of the U.S. up the Mid-Atlantic coast. In Mid-Atlantic states, such as Virginia, R. parkeri prevalence is higher in these ticks than those found in its historical range. This high prevalence may be explained in part by small mammal populations. In this study, small mammals were trapped and checked for the presence of immature A. maculatum. The ticks as well as tissue samples from these mammals were tested for the presence of R. parkeri. This study found six rodent species acting as hosts to immature A. maculatum and three species that may play a role in the enzootic cycle of R. parkeri in Virginia.

  • Assessing the underwater survival of two tick species, Amblyomma americanum and Amblyomma maculatum.
    Ticks and tick-borne diseases, 2018
    Co-Authors: Lindsey Bidder, Kristine M. Asmussen, Sean E. Campbell, Katerina A. Goffigan, Holly Gaff
    Abstract:

    Abstract The hard (ixodid) ticks Amblyomma americanum and Amblyomma maculatum are found throughout the southeastern United States. To study the effects of water inundation, which is an increasingly common phenomenon in many coastal areas, unfed adult A. americanum and A. maculatum ticks were tested for survival by submergence in three water conditions: freshwater, brackish water, and saltwater. The results demonstrated a significant difference in survival between the two species in all three water conditions, with A. maculatum ticks surviving a shorter time underwater than A. americanum ticks. There is also a significant difference in A. americanum survival among the different water conditions, with the highest mortality in saltwater and the lowest in freshwater. Amblyomma americanum ticks survived the longest in freshwater (70 d), followed by brackish water (64 d), and the shortest survival was in saltwater (46 d), while the longest any A. maculatum tick survived was 24 d in freshwater. These findings demonstrate that any short-term flooding events, e.g., less than a week, would not likely eliminate these species of ticks in the flooded area.

  • Natural history of Amblyomma maculatum in Virginia.
    Ticks and tick-borne diseases, 2017
    Co-Authors: Robyn M. Nadolny, Holly Gaff
    Abstract:

    The Gulf Coast tick Amblyomma maculatum Koch is increasingly relevant to medical and veterinary communities as human infection rates of Rickettsia parkeri rise, the risk of introduction of Ehrlichia ruminantium increases, and the range of this tick expands into the densely populated Mid-Atlantic region of the United States. We report on the results of five years of field surveillance to better describe the ecology of A. maculatum in newly established populations in southeastern Virginia. We document habitat preferences, host preferences, and the phenology of the adult human-biting life stage. We discuss key ecological factors needed for A. maculatum establishment and the influence of the successional process and anthropogenic activities on the persistence of A. maculatum populations in Virginia.

  • rickettsia parkeri transmission to Amblyomma americanum by cofeeding with Amblyomma maculatum acari ixodidae and potential for spillover
    Journal of Medical Entomology, 2015
    Co-Authors: Chelsea L. Wright, Daniel E. Sonenshine, Holly Gaff, Wayne L. Hynes
    Abstract:

    Amblyomma americanum (L.) is a human-biting ixodid tick distributed throughout much of the southeastern United States. Rickettsia parkeri is a member of the spotted fever group rickettsiae and causes a febrile illness in humans commonly referred to as "Tidewater spotted fever" or "R. parkeri rickettsiosis." Although the Gulf Coast tick, Amblyomma maculatum Koch, is the primary vector of R. parkeri, a small proportion of A. americanum have also been shown to harbor R. parkeri. The purpose of this investigation was to determine whether R. parkeri is spilling over into A. americanum in eastern Virginia and also to determine through laboratory experiments, whether A. americanum can acquire R. parkeri by cofeeding alongside infected ticks. Of 317 wild-caught, flat adult A. americanum tested from 29 counties and independent cities in coastal Virginia, a single female A. americanum was positive for R. parkeri, suggesting that R. parkeri is spilling over into this species, but at very low rates (<1.0%). Laboratory studies using guinea pigs indicated that nymphal A. americanum were able to acquire R. parkeri while feeding alongside infected A. maculatum and then transstadially maintain the infection. Nymphal A. americanum infected with Rickettsia amblyommii, however, were less likely to acquire R. parkeri, suggesting that infection with R. amblyommii may prevent R. parkeri from establishing infection in A. americanum.

Wayne L. Hynes - One of the best experts on this subject based on the ideXlab platform.

  • Survey of Rickettsia parkeri and Amblyomma maculatum associated with small mammals in southeastern Virginia.
    Ticks and tick-borne diseases, 2020
    Co-Authors: Alexandra N. Cumbie, Robyn M. Nadolny, Wayne L. Hynes, Christina Espada, Robert K. Rose, Raymond D. Dueser, Holly Gaff
    Abstract:

    Abstract Small mammals are often parasitized by the immature stages of hard-bodied ticks (family Ixodidae) and may serve as reservoir hosts of tick-borne pathogens. Amblyomma maculatum, the Gulf Coast tick, is the primary vector of Rickettsia parkeri, the causative agent of R. parkeri rickettsiosis. This hard-bodied tick species is expanding its historical range from the Gulf Coast of the U.S. up the Mid-Atlantic coast. In Mid-Atlantic states, such as Virginia, R. parkeri prevalence is higher in these ticks than those found in its historical range. This high prevalence may be explained in part by small mammal populations. In this study, small mammals were trapped and checked for the presence of immature A. maculatum. The ticks as well as tissue samples from these mammals were tested for the presence of R. parkeri. This study found six rodent species acting as hosts to immature A. maculatum and three species that may play a role in the enzootic cycle of R. parkeri in Virginia.

  • rickettsia parkeri transmission to Amblyomma americanum by cofeeding with Amblyomma maculatum acari ixodidae and potential for spillover
    Journal of Medical Entomology, 2015
    Co-Authors: Chelsea L. Wright, Daniel E. Sonenshine, Holly Gaff, Wayne L. Hynes
    Abstract:

    Amblyomma americanum (L.) is a human-biting ixodid tick distributed throughout much of the southeastern United States. Rickettsia parkeri is a member of the spotted fever group rickettsiae and causes a febrile illness in humans commonly referred to as "Tidewater spotted fever" or "R. parkeri rickettsiosis." Although the Gulf Coast tick, Amblyomma maculatum Koch, is the primary vector of R. parkeri, a small proportion of A. americanum have also been shown to harbor R. parkeri. The purpose of this investigation was to determine whether R. parkeri is spilling over into A. americanum in eastern Virginia and also to determine through laboratory experiments, whether A. americanum can acquire R. parkeri by cofeeding alongside infected ticks. Of 317 wild-caught, flat adult A. americanum tested from 29 counties and independent cities in coastal Virginia, a single female A. americanum was positive for R. parkeri, suggesting that R. parkeri is spilling over into this species, but at very low rates (<1.0%). Laboratory studies using guinea pigs indicated that nymphal A. americanum were able to acquire R. parkeri while feeding alongside infected A. maculatum and then transstadially maintain the infection. Nymphal A. americanum infected with Rickettsia amblyommii, however, were less likely to acquire R. parkeri, suggesting that infection with R. amblyommii may prevent R. parkeri from establishing infection in A. americanum.

  • Rickettsia parkeri Transmission to Amblyomma americanum by Cofeeding with Amblyomma maculatum (Acari: Ixodidae) and Potential for Spillover
    Journal of medical entomology, 2015
    Co-Authors: Chelsea L. Wright, Daniel E. Sonenshine, Holly Gaff, Wayne L. Hynes
    Abstract:

    Amblyomma americanum (L.) is a human-biting ixodid tick distributed throughout much of the southeastern United States. Rickettsia parkeri is a member of the spotted fever group rickettsiae and causes a febrile illness in humans commonly referred to as "Tidewater spotted fever" or "R. parkeri rickettsiosis." Although the Gulf Coast tick, Amblyomma maculatum Koch, is the primary vector of R. parkeri, a small proportion of A. americanum have also been shown to harbor R. parkeri. The purpose of this investigation was to determine whether R. parkeri is spilling over into A. americanum in eastern Virginia and also to determine through laboratory experiments, whether A. americanum can acquire R. parkeri by cofeeding alongside infected ticks. Of 317 wild-caught, flat adult A. americanum tested from 29 counties and independent cities in coastal Virginia, a single female A. americanum was positive for R. parkeri, suggesting that R. parkeri is spilling over into this species, but at very low rates (

  • Experimental vertical transmission of Rickettsia parkeri in the Gulf Coast tick, Amblyomma maculatum.
    Ticks and tick-borne diseases, 2015
    Co-Authors: Chelsea L. Wright, Daniel E. Sonenshine, Holly Gaff, Wayne L. Hynes
    Abstract:

    Rickettsia parkeri, an obligate intracellular bacterium, is a member of the spotted fever group of rickettsiae (SFGR), and is transmitted to humans and other animals by invertebrate vectors. In the United States, the primary vector of R. parkeri is the Gulf Coast tick, Amblyomma maculatum Koch. This study investigates the vertical transmission dynamics of R. parkeri within a field-derived, naturally infected colony of A. maculatum. Transovarial and transstadial transmission of the pathogen was observed over three generations, with transovarial transmission efficiency averaging 83.7% and transstadial transmission rates approaching 100%. Fitness costs were determined by comparing reproduction values of the R. parkeri-infected A. maculatum colony to values from a R. parkeri-free colony. No significant reproductive fitness costs to the host ticks were detected in the R. parkeri-infected A. maculatum colony. Significantly fewer engorged F1 nymphs and F2 larvae of the R. parkeri-free colony succeeded in molting, suggesting that there may be some advantage to survival conferred by R. parkeri. The results of this study indicate that R. parkeri is maintained in A. maculatum populations efficiently by transovarial and transstadial transmission without any noticeable effects on tick reproduction or survival.

  • In vitro propagation of Candidatus Rickettsia andeanae isolated from Amblyomma maculatum.
    FEMS immunology and medical microbiology, 2011
    Co-Authors: Alison Luce-fedrow, Chelsea L. Wright, Daniel E. Sonenshine, Wayne L. Hynes, Holly Gaff, Allen L. Richards
    Abstract:

    Candidatus Rickettsia andeanae was identified during an investigation of a febrile outbreak in northwestern Peru (2002). DNA sequencing from two ticks (Amblyomma maculatum, Ixodes boliviensis) collected during the investigation revealed a novel Rickettsia agent with similarity to the spotted fever group rickettsiae. Since then, Candidatus R. andeanae has been detected in A. maculatum ticks collected in the southeastern and southcentral United States, Argentina, and Peru. To date, Candidatus R. andeanae has not been successfully cultivated in the laboratory. We present evidence for the continuous cultivation in three cell lines of Candidatus R. andeanae isolated from an A. maculatum tick (Portsmouth, Virginia).

Andrea S. Varela-stokes - One of the best experts on this subject based on the ideXlab platform.

  • Amblyomma maculatum-associated rickettsiae in vector tissues and vertebrate hosts during tick feeding
    Experimental and Applied Acarology, 2019
    Co-Authors: Jung Keun Lee, John V. Stokes, Robert W. Wills, Gail M. Moraru, Amanda N. Benton, Haley P. Nabors, Catherine L. Smith, Amanda M. Lawrence, Bridget V. Willeford, Andrea S. Varela-stokes
    Abstract:

    Rickettsia parkeri , a causative agent of spotted fever rickettsiosis, is transmitted by Amblyomma maculatum (Gulf Coast tick), a tick that may also carry a non-pathogenic spotted fever group Rickettsia , “ Candidatus Rickettsia andeanae”. Here, we evaluated R. parkeri and “ Candidatus R. andeanae” in tissues from A. maculatum prior to, during, and after blood feeding on rabbits. Using colony-reared A. maculatum that were capillary-fed uninfected cells, R. parkeri, “Candidatus R. andeanae”, or both rickettsiae, we detected higher levels of Rickettsia spp. in the respective treatment groups. Rickettsial levels increased during blood feeding for both R. parkeri and “Candidatus R. andeanae”, with a greater increase in R. parkeri in co-infected ticks compared to singly-infected ticks. We detected transovarial transmission of “Candidatus R. andeanae” in egg and larval cohorts and confirmed vertical transmission of R. parkeri in one group of larvae. Rabbits from all Rickettsia -exposed groups seroconverted on immunofluorescent antibody testing using R. parkeri antigen. Visualization of “Candidatus R. andeanae” in tick salivary glands suggested potential transmission via tick feeding. Here, rickettsial levels in artificially infected ticks demonstrate changes during feeding and transovarial transmission that may be relevant for interpreting rickettsial levels detected in wild A. maculatum .

  • Transmission of Amblyomma maculatum-Associated Rickettsia spp. During Cofeeding on Cattle.
    Vector borne and zoonotic diseases (Larchmont N.Y.), 2018
    Co-Authors: Jung Keun Lee, Gail Miriam Moraru, John V. Stokes, Robert W. Wills, Catherine L. Smith, Amanda B. Harper, Andrea S. Varela-stokes
    Abstract:

    Amblyomma maculatum is the primary vector for the spotted fever group rickettsiae, Rickettsia parkeri, a known pathogen, and "Candidatus Rickettsia andeanae," currently considered nonpathogenic. Spotted fever group rickettsiae are typically endothelial cell associated and rarely circulate in the blood. Horizontal transmission to naive ticks through blood feeding from an infected host is likely rare. Cofeeding provides an opportunity for rickettsial transmission to naive ticks in the absence of circulating rickettsiae. We evaluated R. parkeri transmission through cofeeding between A. maculatum adults and nymphs on beef calves. Six calves in each of two trials were infested with A. maculatum that had been capillary fed R. parkeri. Four days later, calves each received recipient A. maculatum that were either capillary fed "Ca. R. andeanae" or not capillary fed before infestation. Trials differed by whether we included a barrier to minimize adjacent feeding between recipient and donor ticks. After cofeeding, we detected R. parkeri in 27% of "Ca. R. andeanae"-free recipient ticks, whereas R. parkeri was not detected in any recipient ticks that were capillary fed "Ca. R. andeanae." Rickettsia parkeri transmission efficiency to naive ticks was greater when ticks freely cofed in proximity. No rickettsial DNA was detected in calf blood. Results confirm cofeeding as a method of horizontal transmission of R. parkeri in the absence of host rickettsemia and suggest no evidence of transmission by cofeeding when recipient ticks are first exposed to "Ca. R. andeanae" through capillary feeding. While cofeeding may provide an opportunity for maintaining the pathogen, R. parkeri, the mechanisms driving any potential effect of "Ca. R. andeanae" on R. parkeri transmission are unclear.

  • Tick microbial communities within enriched extracts of Amblyomma maculatum.
    Ticks and tick-borne diseases, 2018
    Co-Authors: Andrea S. Varela-stokes, John V. Stokes, Gail M. Moraru, Si Hong Park, Nancy A. Gavron, S.i. Lee, Steven C. Ricke
    Abstract:

    Abstract Our objective of this study was to explore the bacterial microbiome in fresh or fresh-frozen adult Amblyomma maculatum (Gulf Coast ticks) using extracts enriched for microbial DNA. We collected 100 questing adult A. maculatum, surface disinfected them, and extracted DNA from individual ticks collected the same day or after storage at −80 °C. Because only extracts with microbial DNA concentrations above 2 ng/μL were considered suitable for individual analysis, we expected fewer samples to meet these requirements. Of individual ticks extracted, 48 extracts met this minimum concentration. We pooled 20 additional extracts that had lower concentrations to obtain seven additional pools that met the minimum DNA concentration. Libraries created from these 55 samples were sequenced using an Illumina MiSeq platform, and data sets were analyzed using QIIME to identify relative abundance of microorganisms by phylum down to genus levels. Proteobacteria were in greatest abundance, followed by Actinobacteria, Firmicutes, and Bacteroidetes, at levels between 1.9% and 6.4% average relative abundance. Consistent with the Francisella-like endosymbiont known to be present in A. maculatum, the genus Francisella was detected at highest relative abundance (72.9%; SE 0.02%) for all samples. Among the top ten genera identified (relative abundance ≥ 0.5%) were potential extraction kit contaminants, Sphingomonas and Methylobacterium, the soil bacterium Actinomycetospora, and the known A. maculatum-associated genus, Rickettsia. Four samples had Rickettsia at greater than 1% relative abundance, while nine additional samples had Rickettsia at low (0.01–0.04%) relative abundance. In this study, we used the entire microbe-enriched DNA extract for whole ticks for microbiome analysis. A direct comparison of the microbiome in microbe-enriched DNA and total genomic DNA extracts from halves of the same tick would be useful to determine the utility of this extraction method in this system. We anticipate that future tick microbiome studies will be valuable to explore the influence of microbial diversity on pathogen maintenance and transmission, and to evaluate niche-specific microbiomes within individual tick tissues.

  • Rickettsia parkeri and "Candidatus Rickettsia andeanae" in Questing Amblyomma maculatum (Acari: Ixodidae) From Mississippi.
    Journal of medical entomology, 2017
    Co-Authors: Jung Keun Lee, Gail Miriam Moraru, John V. Stokes, Robert W. Wills, E. Mitchell, E. Unz, B. Moore-henderson, A. B. Harper, Andrea S. Varela-stokes
    Abstract:

    Amblyomma maculatum Koch (Acari: Ixodidae), the primary vector for Rickettsia parkeri , may also be infected with a rickettsia of unknown pathogenicity, “ Candidatus Rickettsia andeanae.” Infection rates with these rickettsiae vary geographically, and coinfected ticks have been reported. In this study, infection rates of R. parkeri and “ Ca . R. andeanae” were evaluated, and rickettsial DNA levels quantified, in 335 questing adult A. maculatum collected in 2013 ( n  = 95), 2014 ( n  = 139), and 2015 ( n  = 101) from Oktibbeha County, MS. Overall infection rates of R. parkeri and “ Ca. R. andeanae” were 28.7% and 9.3%, respectively, with three additional A. maculatum (0.9%) coinfected. While R. parkeri- infected ticks were detected all three years (34.7% in 2013; 13.7% in 2014; 43.6% in 2015), “ Ca. R. andeanae” was not detected in 2013, and was detected at rates of 10.8% in 2014, and 15.8% in 2015. Interestingly, rickettsial DNA levels in singly-infected ticks were significantly lower in “ Ca. R. andeanae”-infected ticks compared to R. parkeri- infected ticks ( P  

  • Ultrastructure of Presumed “Candidatus Rickettsia Andeanae” in Amblyomma maculatum (Acari: Ixodidae)
    Journal of medical entomology, 2014
    Co-Authors: Flavia A.g. Ferrari, Christopher D Paddock, Jerome Goddard, Andrea S. Varela-stokes
    Abstract:

    Amblyomma maculatum Koch, 1844 (also known as the Gulf Coast tick) is found in parts of the Americas, including the central and southern United States. Its primary importance is as the vector of Rickettsia parkeri, a spotted fever group rickettsia that causes an illness similar to, but milder than, Rocky Mountain spotted fever. A second spotted fever group rickettsia, "Candidatus Rickettsia andeanae," was detected in Gulf Coast ticks approximately 10 yr ago. However, the significance of this organism, including pathogenicity, has not yet been well-characterized. Here, we use transmission electron microscopy to describe bacteria within the tissues of A. maculatum ticks that were positive by polymerase chain reaction assay for "Ca. R. andeanae." In ultrathin sections of unfed A. maculatum adult females, we found evidence of bacteria with morphological features consistent with spotted fever group rickettsiae, including small size (≈0.3 by 0.9 μm), a halo zone (electron-lucent layer around the bacterium), and a trilaminar cell wall. In female ticks, bacteria were present in granular salivary glands and ducts, foregut, Malpighian tubules, nerve trunks, and reproductive tissue. These findings demonstrate evidence of "Ca. R. andeanae" in situ and contribute to our understanding of this novel rickettsia in A. maculatum.