Alexis White is, by choice, spending a lot of time this summer in places where ticks abound. White is a doctoral student at Old Dominion University, and part of a multiyear “surveillance” to determine the species and abundance of ticks throughout Virginia.
Virginia, it turns out, is a mixing bowl of tick species and the pathogens they transmit, including the most famous, Borrelia burgdorferi, the bacteria associated with Lyme disease. Man-made habitat alterations and climate change are culprits in the complicated ecological equation that has ticks spreading south and west from New England and north from the Gulf States.
“Ticks are on the move in the mid-Atlantic, and Virginia is in the direct center of these waves,” said Holly D. Gaff, Smith’s professor at ODU and head of the “Tick Lab,” where tick studies have been under way for more than 30 years.
There are at least six species of ticks in the Southeast United States – and the pathogens they host number at least 15.
The one that can carry and transmit Lyme disease, the blacklegged tick (sometimes called a deer tick) has been spreading south along the Eastern Seaboard since it gained notoriety in connection with the identification of Lyme disease in the 1970s. There’s also a southern variant of this tick that’s increasingly showing up in Virginia, Maryland and West Virginia’s Piedmont and higher elevations.
The lone star tick – found throughout the mid-Atlantic and the most common biting tick in Virginia – is host to an increasing number of bacteria, including the agent of Rocky Mountain spotted fever and other maladies that cause symptoms similar to Lyme disease.
The Gulf Coast tick is showing up in southern Virginia, according to Graff, and carries “spotted fever rickettsiosis,” a disease also associated with the American dog tick — the one pet owners have been removing from pets for years.
Then there’s Powassan encephalitis, rare but increasingly noted, and carried by the blacklegged tick. Reported cases have a 10–15 percent fatality rate, with many survivors suffering long-term neurological damage.
While there is an increase in the number of reported tick bites and tick-borne illnesses being discovered and reported, the medical and public health communities are increasingly better equipped to manage cases and identify and track ticks, and many of these diseases can be treated if promptly diagnosed. But others can cause months and years of painful and debilitating symptoms.
Though there seems to be nothing good for us about the spread of tick-borne diseases, from the point of view of the tick, the explosive growth of Homo sapiens and the human drive to alter the landscape have been a bonanza.
Many ticks, including the blacklegged tick, thrive in areas that have plenty of “edges,” where two habitats meet, like field and forest, or forest and backyard.
Research conducted through the Cary Institute of Ecosystem Studies, in Millbrook, NY, found that forest patches of less than 3 acres averaged three times as many ticks and seven times more infected ticks than did larger fragments.
Fragmented landscapes disrupt ecological checks and balances that limit interaction between humans and ticks. And the life cycle of ticks — which require a “blood meal” at each of three successive life stages, takes advantage of wildlife species that thrive in edges. Each meal offers an opportunity to pick up a pathogen. The plentiful rodents like white-footed mice and shrews — many already infected by the Lyme bacteria or another pathogen — are often the first blood meal for tick larvae after they hatch in summer. When the larvae molt into nymphs in their second spring, they are already host to the pathogen and may pass it on as they feed on larger animals, including humans. The final molt into adult in the summer also coincides with a blood meal on a larger animal.
“Ticks are like perfect petri dishes for these pathogens,” said Ellen Stromdahl, from the U.S. Army Health Command at Aberdeen Proving Ground in Maryland, adding, “There’s no other group of arthropods that is host to such a wide variety of pathogens.”
While tick populations aren’t spread by deer, more deer (and rodents) increase the number of ticks possible, explained Jory Brinkerhoff, a University of Richmond researcher who studies tick vectors in the mid-Atlantic. “So if you have habitat that’s good for rodents like the mice, plus a lot of deer, that’s a recipe for lots of ticks.”
Our suburbanized landscapes are also increasingly devoid of predators. Fewer foxes, coyotes and owls mean more rodents and deer.
Also, there may be fewer opossums, which have been shown to be incredibly effective at killing ticks by eating them when they groom themselves, eliminating thousands of blacklegged ticks weekly during the summer months.
And more people living in these habitats raises the likelihood of human-tick encounters.
David Gaines, Virginia’s public health entomologist, said, “You can look at a map of the occurrences of Lyme disease over time from New England, where it was first discovered in the 1970s and see how it has spread along with the growing ‘megalopolis’ that is the Eastern Seaboard.”
Herbaceous plant species also prefer disturbed habitats, and several have been linked with higher tick populations. Japanese barberry (Berberis thunbergiii), offers the ideal habitat for ticks and their rodent hosts. The barberry can blanket the forest floor and provide shelter and protection for the rodents and life-giving moisture for the ticks. Add to this that deer don’t eat much barberry, and the ecosystem is ripe for tick explosion.
In Connecticut, a study showed that managing Japanese barberry significantly reduced the density of Lyme-infected ticks to nearly 60 percent of that of unmanaged barberry patches. Multiflora rose and Japanese honeysuckle are also tick havens.
According to the Centers for Disease Control and Prevention, there were more than 27,000 confirmed cases of Lyme disease and 9,000 probable cases in the U.S. in 2013, with the greatest risk of infection in New England, the mid-Atlantic states and upper Midwest.
Pennsylvania has reported the most cases of Lyme disease in the nation for the last five years — 4,981 confirmed and 777 probable cases in 2013. A Pennsylvania Department of Environmental Protection survey released in early 2015 found the blacklegged tick present in all 76 counties. There were 801 confirmed and 396 probable cases of Lyme disease in Maryland in 2013. In Virginia, there were 925 confirmed and 382 probable cases.
But Lyme disease isn’t the only disease spread by ticks, said the Army’s Stromdahl, warning that the intensive media coverage of Lyme disease has led to the immediate assumption that wherever there is a tick bite and a rash, Lyme disease is the culprit. But the rash and symptoms associated with the lone star tick and called STARI, or southern tick-associated rash illness, can be confused with the bull’s-eye rash of Lyme disease.
Stromdahl, who runs the Army’s Tick Test Kit program, is among those who have been keeping a wary eye on the changing patterns of tick-borne pathogens. The project, centered at Aberdeen Proving Ground, provides tick identification and testing for Department of Defense personnel and their families, and has yielded important epidemiological data for tracking ticks and tick-related diseases.
Stromdahl and Katherine A. Feldman, public health veterinarian for Maryland, have organized an annual mid-Atlantic tick summit for the last four years, bringing together public health officials and researchers to share information about ticks and tick-borne diseases in the Chesapeake region.
What is emerging from these meetings — and other discussions —is the importance of equipping health care providers with up-to-date guidance for diagnosing and treating tick-related illnesses as tick species extend to new habitat.
Climate change has already begun to impact ticks. Mid-Atlantic coastal areas are abundant with ticks, in part because of the humidity and soil moisture necessary for their survival, said ODU’s Gaff. But sea level rise may change soil moisture and ground level humidity, making the coast even more habitable for ticks. Changing weather patterns will also have an impact. “Some areas will see increased ticks, while others will see fewer, if it gets too dry with increasing temperatures,” Gaff said.
Feldman stressed the complexity. “Diseases in nature generally involve at least one animal host — and often more. With all these factors being affected by weather, the built environment and climate change, some ticks will win, and likewise some of the tick-borne diseases will flourish.”
Protect yourself – save your tick!
Save your tick! The Centers for Disease Control and Prevention recommends that you carefully remove the tick with a pair of sharp tweezers, then save the tick in a plastic bag in the freezer or a vial of alcohol, and watch for symptoms. Visit www.cdc.gov/ticks/.
If you choose to have the tick tested, make sure the lab knows what species it is — or can determine the species and advise which tests should be conducted. Ensure your medical practitioner understands that diagnosis and treatment is species-specific. See TICKBORNE DISEASES OF THE UNITED STATES A Reference Manual for Health Care Providers Third Edition, 2015.
Practice safe outdoors prevention. Apply tick repellent to clothing and shoes, wear light-colored clothing that is tucked in to more easily spot ticks, and shower and do a thorough tick check when returning indoors. Put your clothes immediately into a hot dryer for 10 minutes to kill any ticks that might be on them.
Practice safe landscaping. To reduce tick/human encounters in your backyard, visit www.tickencounter.org/tick_notes/spring_2015_ticksmart_tips.