Ticks spreading more and more serious diseases

Friday , September 14, 2012 - 11:53 AM

Kristi L. Nelson

KNOXVILLE, Tenn. — If a tick bites you, save it in a vial of alcohol or in your freezer. It might be carrying an organism that can make you sick later -- and, depending on where you are, not necessarily with the disease you’re thinking of.

That’s the conclusion of a pair of scientists who studied 25,000 ticks that had been on people, and thousands more in the wild.

Graham Hickling, director of the University of Tennessee’s Center for Wildlife Health, and Ellen Stromdahl, a Maryland-based entomologist with the Army Institute of Public Health, co-wrote the study, "Beyond Lyme: Aetiology of Tick-borne Human Diseases with Emphasis on the South-Eastern United States," published Sept. 7 in a special issue of the journal "Zoonoses and Public Health."

Hickling said the study is the first to make a state-by-state comparison of which ticks bite people. In the North, he said, it’s usually the blacklegged tick, or "deer tick," which carries the bacteria thought to cause Lyme disease.

But in the South, Hickling said, the blacklegged tick in its nymphal stage -- the life stage it’s in during summer, when more people are bitten -- tends to seek out cold-blooded hosts, such as lizards, rather than warm-blooded, such as mice, or humans.

The Lone Star tick is another story. Though it’s not thought to spread Lyme, it can infect humans with at least six other serious illnesses, including tularaemia, spotted fever rickettsiosis (formerly called Rocky Mountain Spotted Fever) and ehrlichiosis, which has been on the rise in the South for several years.

This year, for example, Tennessee has reported almost 200 percent more rickettsiosis cases than in 2011, and more than 25 percent more cases of ehrlichiosis.

Both can be serious, even fatal, especially in the very young, older people and people whose immune systems are compromised.

Hickling wonders if, with media saturation about Lyme disease, Southerners are not worried enough about the other tick-borne illnesses they’re much more likely to get.

Though avid outdoors enthusiasts may identify the adult female Lone Star tick by its white spot, males and nymphs are not as easily distinguished, he said. The Lone Star tick is aggressive in all stages, he said, and he and his team regularly collect Lone Star ticks that test positive for disease-causing pathogens.

Even medical professionals may be overlooking the obvious, he said. The study mentions a survey of 36 East Tennessee health-care providers that found 62 percent said their knowledge of ehrlichiosis was "weak" or nonexistent; two-thirds said they wouldn’t ordinarily think of testing for tick-borne illness, and a third said they wouldn’t think of identifying the type of tick to help make a diagnosis. Yet both it and rickettsiosis can be treated more easily if caught early.

Then there’s Southern Tick-Associated Rash Illness, with a rash and fever that acts like Lyme, which may be caused by the Lone Star tick’s bite. There’s disagreement on what STARI even is -- a bacteria-caused illness, or an allergic reaction -- and whether it responds to antibiotics used to treat other tick-borne illnesses.

"It’s bad enough trying to explain that there is more than one kind of tick" whose bite can make you sick, Hickling said. "Try explaining there are two disease syndromes that look the same but really aren’t."

There are also newly emerging diseases, such as "Tidewater Spotted Fever," caused by a pathogen found in 2002 in the Gulf Coast tick, which Hickling said may be a "tick on the move" to other areas.

Second-generation forests, growing in abandoned farms or previously logged areas, provide new habitats for many species of ticks, he said, as does an increasing deer population.

"My feeling is that there’s actually something out there we don’t know about yet," Hickling said. "All these vague symptoms, rashes, fevers -- I just feel like we might be missing something. Each year that goes by, there are new things popping out."

(Contact Kristi L. Nelson of The Knoxville News Sentinel in Tennessee at nelsonk@knoxnews.com)

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