Rickettsia parkeri is an obligate intracellular bacterium belonging to the spotted fever group of rickettsiae; this organism has recently been found to be pathogenic to humans (1). Infection with R. parkeri can be considered an emerging infectious disease, referred to as R. parkeri rickettsiosis, American Boutonneuse fever, and Tidewater spotted fever. Two confirmed cases of R. parkeri infections, including the index case in 2002, occurred in southeastern Virginia (1–3). Since then, 20 R. parkeri infections have been reported, mainly from the southern United States (2). In the United States, Amblyomma maculatum (familyIxodidae) ticks, commonly referred to as Gulf Coast ticks, are the only known natural vector of R. parkeri. A. maculatum ticks have been reported from 12 states: Alabama, Arkansas, Florida, Georgia, Kansas, Kentucky, Mississippi, Oklahoma, South Carolina, Tennessee, Texas (1,4,5), and Virginia (6). Sonenshine et al. reported finding individual A. maculatumticks in Virginia in 1965 but concluded that populations had not become established (7).

We found large numbers of adult and some nymph A. maculatum ticks in Virginia. This population and the different life stages of the ticks indicate that they are now established in the state. Testing by real-time PCR and sequencing indicated that a high percentage of the ticks contained R. parkeri DNA.

The Study

From May through September 2010, adult questing A. maculatum ticks were collected on flags at 3 locations in southeastern Virginia. Collection sites were selected to produce results that could be compared with those of previous surveys and to provide a comprehensive survey of southeastern Virginia (8). The first study site is 50 km inland and borders the Great Dismal Swamp in Chesapeake, Virginia. The second site, Back Bay National Wildlife Refuge, is <1 km from the Atlantic Ocean in Virginia Beach. The third site, in Portsmouth, borders the Elizabeth River.

The ticks were identified morphologically, and identity was confirmed as needed by molecular methods. DNA was extracted by using the DNeasy Blood and Tissue Kit (QIAGEN, Valencia, CA, USA) according to the manufacturer's protocol and stored at –20°C until processing.

DNA samples were tested for R. parkeri DNA by real-time PCR with a MiniOpticon Real-Time PCR System (Bio-Rad, Hercules, CA, USA). Testing for R. parkeri DNA was by amplification and detection of a fragment of the ompB gene by using Rpa129F and Rpa224R primers and Rpa188 as the probe (Table 1). Samples negative for R. parkeri DNA were tested for Rickettsia spp. by amplifying a 111-bp fragment of the 17-kDa antigen gene (Table 1).

Three representative A. maculatum samples positive for R. parkeri by real-time PCR were confirmed by sequencing of a 540-bp fragment of the ompA gene. The fragments were amplified on an iCycler (Bio-Rad) by using primers 190-FN1 and 190-RN1 (Table 1). Samples positive for Rickettsia spp. but negative for R. parkeri had their ompB gene amplified and sequenced by using primers RompB11F and RompB1902R (Table 1). All PCR products for sequencing were purified by using Wizard PCR Preps DNA Purification System (Promega, Madison, WI, USA), and sequencing reactions were performed by using the BigDye Terminator v.3.1 Cycle Sequencing Kit (Applied Biosystems, Foster City, CA, USA) as described by the manufacturer and using appropriate primers (Table 1). Sequence similarities were identified by a BLAST search (http://blast.ncbi.nlm.nih.gov).

A total of 65 adult and 6 nymph A. maculatum ticks were collected (adults in May–September, nymphs in April). A total of 54 adults were collected from the Chesapeake site, 8 from the Virginia Beach site, and 3 from the Portsmouth site. Of the 6 nymphs collected, 5 were found feeding on a cotton rat at the Chesapeake site in April, and 1 was collected on a flag at the Virginia Beach site in September. Of the 65 total adult ticks tested, 29 (44.6%) were found by real-time PCR to contain Rickettsia spp. DNA, and 28 (43.1%) of the total adults collected contained R. parkeri DNA. Of the 6 nymphs collected, 4 were infected withR. parkeri; all were from the rat at the Chesapeake site. Of the R. parkeri–positive samples sequenced, maximum identity was seen with R. parkeri sequences (GenBank accession no. FJ986616.1). The rate of R. parkeri–infected ticks started out high in May (83% infected) and then decreased to no infected ticks in August (Table 2).

Of the 3 A. maculatum ticks collected from the Portsmouth site, 1 was found by real-time PCR to be positive for Rickettsia spp. but negative for R. parkeri. Sequencing of a fragment of the ompB gene revealed this isolate to contain DNA with a 100% match to CandidatusRickettsia andeanae isolate T163 (GenBank accession no. GU395297.1), a rickettsiae initially found in Peru (9).

Conclusions

The discovery of such numbers and life stages of A. maculatum ticks in widely dispersed locations indicates that they are now established in southeastern Virginia. Finding adult A. maculatum ticks at the Portsmouth site was unexpected because this is the northernmost site at which we found these ticks and is a peninsula devoid of white-tailed deer, a major host for adult ticks (10,11).

That 43.1% of adult A. maculatum ticks collected from southeastern Virginia contained R. parkeri differs from reported rates of R. parkeri in A. maculatum ticks elsewhere in the United States. For A. maculatum ticks from Florida and Mississippi, R. parkeri infectivity rate is 28% (2); for ticks from Florida, Kentucky, Mississippi, and South Carolina, the average rate is 11.5% (12). For A. maculatum ticks collected from Georgia, an infectivity rate of 5%–11.5% has been reported (13). In Arkansas, only 3 of 207 A. maculatum ticks contained R. parkeri (14). Despite the high percentage of R. parkeri in the southeastern Virginia ticks, 27 of 28 positive samples came from 1 collection site. One explanation could be that R. parkeriis transovarially transmitted. Currently, there is no evidence that R. parkeri is transmitted transovarially by A. maculatum ticks, although transovarial transmission of R. parkeri has been shown in A. americanum ticks in the laboratory (15).

We also found an A. maculatum tick infected with Candidatus Rickettsia andeanae, which has rarely been reported in the United States (2). Whether Candidatus Rickettisa andeanae is pathogenic to humans is unknown, although it has been suspected to cause infections in persons in Peru (9).

Further research is needed to identify the vertebrate host(s) of R. parkeri. This information could be useful for controlling the transmission of R. parkeri to and from the vector, as well as predicting where R. parkeri may be present. Studies relating to transovarial transmission of R. parkeri in A. maculatum ticks would also be useful for predicting the spread of infections. Because R. parkeri is known to cause infection in humans, the presence of this pathogen in southeastern Virginia should be a health concern to persons in this region.

Acknowledgments

We thank Brandon Rowan and Ryan Wright for their help with collecting ticks. We also acknowledge the Nature Conservancy, the Back Bay Wildlife Refuge, and Elizabeth River Project for permission to use their land.

The project described was supported by grant no. K25AI067791 (to H.D.G.) from the National Institute of Allergy and Infectious Diseases. This work was supported by the US Department of Defense Global Emerging Infections Surveillance and Response System program (work unit no. 0000188M.0931.001.A0074).

Ms Wright is a PhD student in the Biological Sciences Department at Old Dominion University. Her research interests lie in microbiology, tick-borne pathogens, and infectious diseases.

References

1. Paddock CD, Sumner JW, Comer JA, Zaki SR, Goldsmith CS, Goddard J, et al.Rickettsia parkeri: a newly recognized cause of spotted fever rickettsiosis in the United States. Clin Infect Dis. 2004;38:805–11. PubMed DOI
2. Paddock CD, Fournier PE, Sumner JW, Goddard J, Elshenawy Y, Metcalfe MG, et al. Isolation of Rickettsia parkeri and identification of a novel spotted fever groupRickettsia sp. from Gulf Coast ticks (Amblyomma maculatum) in the United States. Appl Environ Microbiol. 2010;76:2689–96. PubMed DOI
3. Whitman TJ, Richards AL, Paddock CD, Tamminga CL, Sniezek PJ, Jiang J, et al.Rickettsia parkeri infection after tick bite, Virginia. Emerg Infect Dis. 2007;13:334–6.PubMed DOI
4. Merten HA, Durden LA. A state-by-state survey of ticks recorded from humans in the United States. J Vector Ecol. 2000;25:102–13.
5. Goddard J, Norment B. Notes on the geographical distribution of the Gulf Coast tick,Amblyomma maculatum (Koch) [Acari: Ixodidae]. Entomological News (USA). 1983;94:103–4.
6. Levine JF, Sonenshine DE, Nicholson WL, Turner RT. Borrelia burgdorferi in ticks (Acari: Ixodidae) from coastal Virginia. J Med Entomol. 1991;28:668–74.
7. Sonenshine D, Lamb J Jr, Anastos G. The distribution, hosts and seasonal activity of Virginia ticks. Virginia Journal of Science. 1965;16:26–91.
8. Sonenshine DE, Ratzlaff RE, Troyer J, Demmerle S, Demmerle ER, Austin WE, et al.Borrelia burgdorferi in eastern Virginia: comparison between a coastal and inland locality. Am J Trop Med Hyg. 1995;53:123–33.
9. Jiang J, Blair PJ, Felices V, Moron C, Cespedes M, Anaya E, et al. Phylogenetic analysis of a novel molecular isolate of spotted fever group Rickettsiae from northern Peru: Candidatus Rickettsia andeanae. Ann N Y Acad Sci. 2005;1063:337–42.PubMed DOI
10. Scifres C, Oldham T, Teel P, Drawe D. Gulf coast tick (Amblyomma maculatum) populations and responses to burning of coastal prairie habitats. Southwest Nat. 1988;33:55–64. DOI
11. Barker RW, Kocan AA, Ewing SA, Wettemann RP, Payton ME. Occurrence of the Gulf Coast tick (Acari: Ixodidae) on wild and domestic mammals in north-central Oklahoma. J Med Entomol. 2004;41:170–8. PubMed DOI
12. Sumner JW, Durden LA, Goddard J, Stromdahl EY, Clark KL, Reeves WK, et al. Gulf Coast ticks (Amblyomma maculatum) and Rickettsia parkeri, United States. Emerg Infect Dis. 2007;13:751–3.
13. Cohen SB, Yabsley MJ, Garrison LE, Freye JD, Dunlap BG, Dunn JR, et al. Rickettsia parkeri in Amblyomma americanum ticks, Tennessee and Georgia, USA. Emerg Infect Dis. 2009;15:1471–3. PubMed DOI
14. Trout R, Steelman CD, Szalanski AL, Williamson PC. Rickettsiae in Gulf Coast ticks, Arkansas, USA. Emerg Infect Dis. 2010;16:830–2.
15. Goddard J. Experimental infection of lone star ticks, Amblyomma americanum (L.), with Rickettsia parkeri and exposure of guinea pigs to the agent. J Med Entomol. 2003;40:686–9. PubMed DOI

Tables

Table 1. Sequences of primers and probes used to test for Rickettsia spp. DNA inAmblyomma maculatum ticks collected from southeastern Virginia, April–September 2010

Table 2. Real-time PCR results for adult Amblyomma maculatum ticks collected from southeastern Virginia, USA, 2010

Suggested Citation for this Article

Wright CL, Nadolny RM, Jiang J, Richards AL, Sonenshine DE, Gaff HD, et al. Rickettsia parkeri in Gulf Coast ticks, southeastern Virginia, USA. Emerg Infect Dis [serial on the Internet]. 2011 May [date cited]. http://www.cdc.gov/EID/content/17/5/896.htm

DOI: 10.3201/eid1705.101836

Comments to the Authors

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

Wayne L. Hynes, Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529, USA; email: whynes@odu.edu

Full article

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Vector Borne Zoonotic Dis. 2005 Winter;5(4):383-9.

Distribution of borreliae among ticks collected from eastern states.

Taft SC, Miller MK, Wright SM.

Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, Ohio, USA.

Abstract

Lyme disease is the most commonly reported vector-borne disease in the United States and is transmitted by Borrelia burgdorferi-infected Ixodes species. The disease is typically characterized by an erythema migrans (EM) rash at the site of tick feeding. EM rashes have also been associated with feeding by Amblyomma americanum ticks despite evidence suggesting that they are incompetent vectors for Lyme disease. In 1996, a Borrelia organism only recently cultivated in the laboratory was described in A. americanum ticks and designated B. lonestari. This Borrelia is believed to be the etiologic agent of a novel Lyme-like disease, southern tick associated rash illness (STARI). This study examined ticks collected from eight eastern states to evaluate the epidemiology of B. lonestari, B. burgdorferi, and their tick hosts. Three hundred individual or small pool samples were evaluated from tick genera that included Amblyomma, Ixodes, and Dermacentor. DNA was extracted following tick homogenization and the polymerase chain reaction (PCR) was performed using primers derived from the flagellin gene that amplify sequences from both B. burgdorferi and B. lonestari. Species specific digoxigenin labeled probes were designed and used to differentiate between B. burgdorferi and B. lonestari. Borrelia DNA was detected in approximately 10% of the A. americanum and I. scapularis tick samples, but none was present in any of the Dermacentor samples tested. Positive samples were detected in ticks collected from Kentucky, Maryland, Massachusetts, New Jersey, New York, and Virginia. This is the first known report of B. lonestari from Massachusetts and New York and the first detection in I. scapularis. This suggests that B. lonestari and its putative association with STARI may be more widespread than previously thought.

PMID: 16417434 [PubMed - indexed for MEDLINE]

The effects of vegetation density and habitat disturbance on the spatial distribution of ixodid ticks (Acari: Ixodidae)

Kenneth J. Stein1, Megan Waterman2, Jefferson L. Waldon1 1 Conservation Management Institute, College of Natural Resources and 2Department of Statistics, College of Science, Virginia Polytechnic Institute and State University, Blacksburg,VA 24061, USA

Abstract.Larval, nymphal, and adult Amblyomma americanum(L.), and adult Dermacentor variabilis(Say) ticks were collected using timed dragging techniques, in an attempt to examine how different habitat variables affect models that describe the distribution of ticks in Virginia, USA. Tick count data were modeled using two approaches: (i) habitat and edge, and (ii) habitat, edge, vegetation density and levels of disturbance. Nymphs and adults tended to follow a forest edge distribution when analysed by habitat and edge. Using all variables, we detected a positive relationship with forest edges and negative associations with high-density vegetation. When larvae were modeled by habitat and edge, we failed to detect associations with the edges of habitats. When all variables were included in the larval analysis, disturbed meadow edges emerged as important in the first year, and the categories of disturbed and maturing habitat in the second year. Vegetation density and levels of disturbance were marginally important towards explaining the distribution of nymphs and adults; however, levels of disturbance were potentially more important to the distribution of larvae, than habitat types. Using the habitat and edge variables, and predicted mean encounter rates for all stages of A. americanum and adult D. variabilis, we successfully cross-validated our predictions of high, moderate and low tick densities in both years. The results for nymphs and adults were combined to develop a colour-coded threat assessment map. We estimated that the majority of ticks were located on ~ 20% of the landscape. The potential uses of geographical informa-

tion system-based threat maps are discussed.

Keywords: ixodid ticks, geographical information system, habitat characterization, spatial distribution, predictive

Geospatial Health 2(2), 2008, pp. 241-252

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