UNIVERSITY PARK, Pa. -- Usually, when a species that has disappeared from Pennsylvania's landscape makes a comeback, it's a cause for celebration among people who love the outdoors. But that's not at all the case with the blacklegged tick, Ixodes scapularis.

And it's likely nobody even would have noticed or cared about the return of an organism smaller than the head of a pin, except that it carries the bacteria that causes Lyme disease. The return of the blacklegged tick almost certainly coincides with the population explosion of white-tailed deer in the past few decades, according to an entomologist in Penn State's College of Agricultural Sciences.

"There is evidence that the forests in what is now Pennsylvania were crawling with blacklegged ticks at about the time of the settlers," says Steve Jacobs, a senior extension associate. "We think that when the deer herds were greatly reduced and in some places eliminated -- and when so much of the state was deforested around the turn of the century -- the ticks more or less disappeared. They couldn't survive in the heat and dryness where trees were removed. It appears that the deer are the preferred hosts of the adult tick, and for the re-establishment of the tick population, there must be a concentration of deer in an area."

Confusion about the tick's identity, according to Jacobs, shrouded its return to the Northeast. When scientists in the 1970s began scrambling to better understand how Lyme disease is spread, they focused attention on the blacklegged tick, although they didn't realize it was that species. Instead they decided the vector for Lyme disease was a new species, and called it the deer tick, Ixodes dammini.

"The popular press, some doctors and even some epidemiologists still call them deer ticks, but actually it is the blacklegged tick that carries the bacteria that causes Lyme disease," says Jacobs. "A group from Georgia Tech published a paper in the 1970s that resolved the confusion."

A 1960s survey of ticks in Pennsylvania -- conducted by researchers looking for Rocky Mountain Spotted Fever -- identified 20 species of ticks in the state, but blacklegged ticks were found only in Philadelphia County. "Fifteen years ago, these ticks mostly were limited to the southeast corner of the state, the northcentral region around the Elk State Forest and the Presque Isle peninsula in Erie," Jacobs says. "Now they seem to be established in more areas of central, western and southeastern Pennsylvania."

That latest survey of ticks, starting in 1988 and continuing to the present, has revealed that 24 species of ticks are now present in the state. Some of those species were found on migratory birds, Jacobs notes. "Other ticks are brought to Pennsylvania on snakes and frogs from Africa," he says. "Those species are not well established here."

The expansion of the blacklegged tick's range is a concern because of its role in spreading the bacteria that causes Lyme disease, a neurological disorder that can cause a variety of symptoms, including a bullseye-like rash, fever, stiff neck, muscle aches and headaches. Left untreated, victims can suffer facial palsy, arthritis and even paralysis. The disease normally is treated with antibiotics, but if not caught early, recovery can be slow and difficult.

Even though new management policies employed by the state should result in smaller herds of deer in coming years, Jacobs believes blacklegged ticks are back to stay because forest habitat across the state is likely to endure.

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EDITORS: Contact Steve Jacobs at 814-863-3963 or sbj2@psu.edu

Jeff Mulhollem jjm29@psu.edu 814-863-2719 814-863-9877 fax #112