Survey Shows Gulf Coast Ticks Have Become Established in Southeastern Virginia
A survey by tick and tick-borne disease specialists at Old Dominion University and the Naval Medical Research Center found that a disease-carrying species commonly called the Gulf Coast tick has become established in southeastern Virginia.
Gulf Coast ticks are found throughout the southern United States, but this is the first report of established populations as far north as Virginia. A warming trend linked to climate change could explain the presence of these ticks in Virginia, the researchers say.
Emerging Infectious Diseases, the journal of the Centers for Disease Control and Prevention, published the researchers' report in its May issue. The first author is Chelsea L. Wright, a graduate student in the Biomedical Sciences Ph.D. program at ODU. Robyn M. Nadolny, who is about to complete her master's degree in Biological Sciences at ODU, is also an author. Nadolny will be continuing her involvement on this project as a Ph.D. student in Ecological Sciences at ODU starting in fall 2011.
Three faculty members from ODU's Department of Biological Sciences are also authors: Wayne Hynes, chair of the department, Holly Gaff, an assistant professor who is also affiliated with ODU's Virginia Modeling, Analysis and Simulation Center (VMASC) and Daniel Sonenshine, an emeritus professor and a world renowned expert on ticks.
Ju Jiang and Allen Richards of the Naval Medical Research Center in Silver Spring, Md., are the other members of the research team.
The article reports the researchers' findings that Gulf Coast ticks (Amblyomma maculatum) are well established in southeastern Virginia and adds, "We found that 43.1 percent of the adult Gulf Coast ticks collected in the summer of 2010 carried Rickettsia parkeri, suggesting that persons living or visiting southeastern Virginia are at a risk for infection with this pathogen."
Rickettsia parkeri is related to the causative agent of Rocky Mountain spotted fever, but its symptoms seem to be relatively mild - such as fever and rash - and controllable by antibiotics.
This disease has been referred to as Tidewater Spotted Fever since the first two confirmed cases of Rickettsia parkeri infection in 2004 and 2006 involved Navy men who suffered bites in southeastern Virginia. Since those two cases, approximately 20 other infections have been confirmed, mostly in states to the south of Virginia. Gulf Coast ticks, which transmits Rickettsia parkeri, also are found in Alabama, Arkansas, Florida, Georgia, Kansas, Kentucky, Mississippi, Oklahoma, South Carolina, Tennessee and Texas, as well as in certain regions of Central and South America.
Between May and September of last year, the researchers collected 65 adults and six nymphs, most (54 adults and five nymphs) from a study site 30 miles from the coast in Chesapeake near the Great Dismal Swamp. Two other study sites were in the Back Bay National Wildlife Refuge, which is in Virginia Beach near the coast (8 adults and one nymph), and along the Elizabeth River in Portsmouth (three adults). The numbers and distribution suggest the tick is now established in the area. Sonenshine reported finding these ticks in Virginia in 1965, but he concluded that populations had not become established.
The Gulf Coast ticks, which are brown with gold markings and resemble the common dog tick, were identified by morphological characteristics and this was confirmed by DNA tests.
The researchers report being surprised to find Gulf Coast ticks in Portsmouth. That study site was the northernmost in the survey, and the city itself is essentially a peninsula where there are no white-tailed deer, a major host for adult ticks.
The bigger surprise, however, was the percentage of adult ticks in southeastern Virginia that were infected with Rickettsia parkeri. The 43.1 percent in this survey is much higher than for another survey in Florida and Mississippi (28 percent), for others in Florida, Kentucky, Mississippi and South Carolina (average of 11.5 percent) and for one in Arkansas (1.5 percent). But the researchers noted that 27 of 28 positive samples were from the Dismal Swamp study site, and the high concentration there could mean that Rickettsia parkeri can be transmitted from parent to offspring. Scientists currently have not confirmed this transovarial transmission of Rickettsia parkeri in the Gulf Coast tick.
On April 25, Gaff and Hynes provided expert testimony to the Virginia Lyme Disease Task Force at a hearing in Fairfax. They reported the discovery of established populations of Gulf Coast ticks in Virginia as well as other results of this ongoing project.
Gaff, with Sonenshine as a mentor, has been doing innovative research using mathematical modeling to study the spatial and temporal spread of ticks and the diseases that they carry. She said she and the other researchers who did the Gulf Coast tick study believe climate change can figure significantly in the growth and movement of tick populations.
"We aren't sure about the exact reason for Gulf Coast ticks being established here in southeastern Virginia, but I'm sure climate change is a big part," she said.
The ODU tick researchers are currently preparing a grant application seeking support for a study of how Gulf Coast ticks may have moved into Virginia and become established.