Skip directly to site content Skip directly to page options Skip directly to A-Z link Skip directly to A-Z link Skip directly to A-Z link
Volume 26, Number 8—August 2020
Research Letter

Heartland Virus in Lone Star Ticks, Alabama, USA

Brent C. NewmanComments to Author , William B. Sutton, Abelardo C. Moncayo, Holly R. Hughes, Ali Taheri, Thomas C. Moore, Callie J. Schweitzer, and Yong Wang
Author affiliations: Tennessee State University, Nashville, Tennessee, USA (B.C. Newman, W.B. Sutton, A. Taheri); Tennessee Department of Health, Nashville (A.C. Moncayo, T.C. Moore); Centers for Disease Control and Prevention, Fort Collins, Colorado, USA (H.R. Hughes); US Department of Agriculture, Huntsville, Alabama, USA (C.J. Schweitzer); Alab; ma Agricultural and Mechanical University, Huntsville (Y. Wang)

Cite This Article

Abstract

We detected Heartland virus (HRTV) in lone star nymphs collected in 2018 in northern Alabama, USA. Real-time reverse transcription PCR selective for the small segment of the HRTV genome and confirmatory sequencing of positive samples showed high identity with HRTV strains sequenced from Tennessee and Missouri.

Figure

Thumbnail of Distribution of HRTV and range of Amblyomma americanum ticks. A) Geographic distribution of Heartland virus, United States, 2009–2020 (1,2) with historical and expanded range of A. americanum ticks adapted from (4). B) Location of the William B. Bankhead National Forest within Lawrence and Winston Counties, Alabama, and collection site of the HRTV-positive A. americanum nymphs. All maps were created by using ArcGIS Pro 2.5 (ESRI, https://www.esri.com/en-us/home). HRTV, Heartland vir

Figure. Distribution of HRTV and range of Amblyomma americanum ticks. A) Geographic distribution of Heartland virus, United States, 2009–2020 (1,2) with historical and expanded range of A. americanum...

Heartland virus (HRTV) is an emerging pathogenic phlebovirus first identified in the United States in 2009 and now reported in 15 states (1,2). Nymphal lone star ticks (Amblyomma americanum) are considered the primary vectors of HRTV, and a variety of domestic and endemic mammalian species are potential amplification hosts of this virus (2,3). Although A. americanum ticks are well-established throughout the eastern, southeastern, and midwestern United States, their range is expanding northward and westward, most likely because of increased host availability and abundance, changes in environmental and climatic conditions, and adaptive genetic variation (Figure, panel A) (4). We tested for HRTV in A. americanum ticks collected in Alabama, USA, a state within the range of this vector where HRTV has not been documented previously from ticks.

From June 1, 2018, through August 31, 2018, we collected ticks as previously described (5) in the William B. Bankhead National Forest, Alabama (34.2270°N, 87.3461°W; Figure, panel B). In preparation for pathogen screening, we separated ticks into pools. Nymph tick pools ranged from 1 to 5 tick(s) of the same species per pool. We screened adult ticks individually (i.e., 1 adult tick per pool) (Appendix Table). We did not include larvae in pathogen screening. We used molecular methods to extract viral RNA and detect the small (S) segment of the HRTV genome using the HRTV-4 primer and probe set (6) in tick pools (Appendix Table). We sequenced HRTV-4–positive samples using the Ion Torrent Personal Genomic Machine system (Life Technologies, https://www.thermofisher.com) at the Centers for Disease Control and Prevention (CDC; Fort Collins, CO, USA) as described previously (7). We obtained sequences of the HTRV S segment of other HRTV samples and strains from the GenBank database, and aligned sequences using the MUSCLE alignment tool (https://www.ebi.ac.uk/Tools/msa/muscle) in MEGA software (8). We also included a closely related severe fever with thrombocytopenia syndrome virus isolate from the GenBank database as an outgroup for this analysis. We used a maximum-likelihood tree approach with 1,000 bootstrap replications to generate the genetic relationships between the Alabama samples and the other HRTV samples available through the GenBank database.

We collected 964 ticks, of which 921 were A. americanum (872 nymphs, 22 adult males, and 27 adult females) and 43 were Dermacentor variabilis (20 adult males and 23 adult females). We tested the ticks in 337 screened tick pools (Appendix Table). We amplified HRTV-4 from 5 pools that each contained 4 A. americanum nymphs. Therefore, the bias-corrected maximum-likelihood estimate of the infection rate (9) in questing A. americanum nymphs collected from the William B. Bankhead National Forest during 2018 was 0.58 (95% CI 0.21–1.27) and minimum infection rate (9) was 0.57 (95% CI 0.07–1.07) per 100 ticks screened on the basis of 235 nymph pools tested. To confirm results, we randomly selected homogenate from 3 of 5 HRTV-4–positive pools and submitted 3 individual RNA samples for sequencing at CDC. Sequencing RNA directly from tick homogenate confirmed HRTV in each of the 3 pools. Although we did not obtain whole-genome sequences, we identified partial coding sequences of all 3 HRTV segments in each pool. Maximum-likelihood phylogenetic inference of 730 nt of the S segment confirmed the BLAST analysis (https://blast.ncbi.nlm.nih.gov/Blast.cgi) and placed the generated HRTV S segment (submitted under GenBank accession no. MT052710) in a well-supported clade with HRTV strains previously described in Missouri and Tennessee (Appendix Figure).

Our findings of HRTV in A. americanum ticks in Alabama update knowledge of the virus’ distribution in the United States (Figure, panel A). Our findings also suggest A. americanum nymphs are the primary vectors of HRTV. As the geographic range of A. americanum continues to expand, we encourage enhanced surveillance and screening for HRTV to provide a more accurate and up-to-date understanding of where this tickborne virus probably occurs in the United States. Treatment for HRTV infection is limited to supportive care only; clinical data from the southeastern United States show that Heartland virus has a 10% death rate (10). Surveillance of HRTV in tick vector species is necessary to gain a comprehensive understanding of the environmental determinants that may put humans at risk for encountering the vector and to identify the geographic host range (both current and potential) of this emerging pathogen in the United States.

Mr. Newman is a PhD candidate in biological sciences at Tennessee State University, Nashville, Tennessee. His interests are landscape genomics, the function of biodiversity in vectorborne disease ecology, and application of One Health concepts to wildlife parasitology.

Top

Acknowledgments

We thank Allison Cochran for forest stand access and logistical support at the William B. Bankhead National Forest and Stuart Robertson and Alexander Binney for field sampling assistance. We also thank Amy Lambert for enabling collaboration and sample sequencing for this research, Javier Monzón for permission to recreate his A. americanum range map, and Suzanne Wade for help creating the maps.

This study was supported by the US Department Agriculture, National Institute of Food and Agriculture 1890 Institution Teaching, Research and Extension Capacity Building Grants Program.

Top

References

  1. Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases, Division of Vector-Borne Diseases. Heartland virus disease (Heartland): statistics & maps. 2018 Oct 22 [cited 2020 Feb 11]. https://www.cdc.gov/heartland-virus/statistics/index.html
  2. Riemersma  KK, Komar  N. Heartland virus neutralizing antibodies in vertebrate wildlife, United States, 2009–2014. Emerg Infect Dis. 2015;21:18303. DOIPubMed
  3. Bosco-Lauth  AM, Panella  NA, Root  JJ, Gidlewski  T, Lash  RR, Harmon  JR, et al. Serological investigation of heartland virus (Bunyaviridae: Phlebovirus) exposure in wild and domestic animals adjacent to human case sites in Missouri 2012-2013. Am J Trop Med Hyg. 2015;92:11637. DOIPubMed
  4. Monzón  JD, Atkinson  EG, Henn  BM, Benach  JL. Population and evolutionary genomics of Amblyomma americanum, an expanding arthropod disease vector. Genome Biol Evol. 2016;8:135160. DOIPubMed
  5. Newman  BC, Sutton  WB, Wang  Y, Schweitzer  CJ, Moncayo  AC, Miller  BT. A standardized method for the construction of a tick drag/flag sampling approach and evaluation of sampling efficacy. Exp Appl Acarol. 2019;79:43346. DOIPubMed
  6. Savage  HM, Godsey  MS Jr, Lambert  A, Panella  NA, Burkhalter  KL, Harmon  JR, et al. First detection of heartland virus (Bunyaviridae: Phlebovirus) from field collected arthropods. Am J Trop Med Hyg. 2013;89:44552. DOIPubMed
  7. Hughes  HR, Russell  BJ, Lambert  AJ. First complete genome sequences of Anopheles A virus of the genus Orthobunyavirus. Genome Announc. 2017;5:e0133117. DOIPubMed
  8. Kumar  S, Stecher  G, Li  M, Knyaz  C, Tamura  K. MEGA X: molecular evolutionary genetics analysis across computing platforms. Mol Biol Evol. 2018;35:15479. DOIPubMed
  9. Biggerstaff  BJ. PooledInfRate, version 4.0: a Microsoft Office add-in to compute prevalence estimates from pooled samples. Fort Collins (CO): Centers for Disease Control and Prevention; 2009 [cited 2020 Apr 16]. https://www.cdc.gov/westnile/resourcepages/mosqsurvsoft.html
  10. Hevey  MA, O’Halloran  JA, Jagger  BW, Staples  JE, Lambert  AJ, Panella  AJ, et al. Heartland virus infection in a heart transplant recipient from the Heartland. Transpl Infect Dis. 2019;21:e13098. DOIPubMed

Top

Figure

Top

Cite This Article

DOI: 10.3201/eid2608.200494

Original Publication Date: July 15, 2020

Table of Contents – Volume 26, Number 8—August 2020

Comments

Please use the form below to submit correspondence to the authors or contact them at the following address:

Brent C. Newman, Department of Agricultural and Environmental Sciences, 3500 John A. Merritt Blvd, Nashville, TN 37209, USA

Send To

character(s) remaining.

Comment submitted successfully, thank you for your feedback.

Top

Page created: April 28, 2020
Page updated: July 19, 2020
Page reviewed: July 19, 2020
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
file_external