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The black-legged, or deer tick, is one of two kinds that carry Powassan virus.

(Centers for Disease Control and Prevention)

Five months after the death of a Warren County woman, the state Department of Health has confirmed she died of a rare tick-borne disease never before seen in New Jersey.

Her death in early May was caused by the Powassan virus, an illness so uncommon that just eight other cases have been diagnosed in the United States this year.

The unnamed 51-year-old woman had developed symptoms that included fever, headache, a rash, and encephalitis, or inflammation of the brain. She was taken and treated at an unnamed hospital and died there, a health department spokesman said.

The physician treating the woman notified the state on Nov. 11 that a tissue sample that had been sent to the Centers for Disease Control and Prevention had been confirmed for Powassan. The department declined to disclose the woman's hometown, citing privacy concerns.

The disease is spread by two kinds of ticks: the black-legged, or deer tick, which can also carry Lyme disease, and the woodchuck tick. While Lyme disease is rarely fatal, the Powassan virus is fatal in 10 percent of cases, said Tom Mather, director of University of Rhode Island's Center for Vector-Borne Disease and its Tick Encounter Resource Center.

Of the survivors, half will experience neurological complications, such as paralysis or cognitive problems.

However, very few of the ticks New Jersey residents are likely to encounter are infected with the virus, he said. While more than half of adult-stage ticks are infected with Lyme, only an estimated 1 percent have the Powassan virus.

"To put it in perspective, the tick infection rate with that virus is quite low," Mather said. It is not transmitted from person to person.

The state decided against making any kind of announcement in mid-November about the confirmed case because tick season was over, according to spokesman Daniel Emmer.

That’s an incorrect assumption, said Mather, a public health entomologist.

"To say it’s no longer tick season, it’s just irresponsible," he said. "There’s hardly a month where you couldn’t encounter a tick."

Ticks are not killed off by cold weather. They merely become so sluggish they no longer "quest," or search for food, Mather said. So-called tick season does flourish in the summer months, mostly because ticks are then in their smallest nymphal stage, so their presence goes unnoticed, he said.

Tick activity slows once the temperature drops below 20 degrees, but will bounce back after just a few days of above-freezing weather.

Nationally, about 50 cases of Powassan have been reported in the United States over the past decade. Most were in the northern woodlands of Minnesota, Wisconsin and New York.

So far this year, the CDC has confirmed eight other cases: four in Wisconsin, three in New York and one in New Hampshire. One of the New York cases killed a teenager in Poughkeepsie, according to news reports.

Symptoms may show up one week to one month after being bitten by an infected tick.

While an infected tick has to stay attached to a person for at least 24 to 48 hours to transmit Lyme disease, that timetable is thought to be shorter for the Powassan, or POW virus.

The CDC states there is no specific treatment for Powassan. Those with a severe case of the illness may need to receive respiratory support, intravenous fluids, or medications to reduce swelling in the brain.

Pronounced "Po-WASS-in," it is named for the Ontario community where it was first discovered in 1958.

Prevention advice is the same as that for avoiding Lyme disease: long-sleeved clothing and pants while walking in tall grass or woods, and insect repellent.

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