Scientist say Ticks and Lyme disease worse this season

Pittsburgh — Hunters in Pennsylvania and other northeastern states face a surge in Lyme disease this spring, according to federally-funded researchers in New York, who blame fluctuating numbers of acorns and mice – not deer – for the problem.

Bountiful mast in 2010 led to peak populations of white-footed mice in 2011, giving black-legged ticks easy access to their favorite hosts, said Richard Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies in Millbrook, N.Y., in a just-released study.

“Mice are permissive to tick feeding. They’re the worst groomers. And they’re very effective at transmitting the bacterium that causes Lyme disease.”

But the boom cycle was followed by one of the smallest acorn crops we’ve ever seen, and mouse populations are crashing, Ostfeld said.  “That means plenty of Lyme-infected ticks will be looking for a blood meal. Instead of finding mice in the woods, they’re going to find mammals like us.”

The May-July nymph season will be dangerous, he predicted, because ticks that fed as larvae last year will soon need a nymphal blood-meal. Given the mild winter, nymph activity could occur even sooner.

“Infected nymphs are the worst perpetrators,” Ostfeld said. “They’re really tiny – about as big as poppy seeds – so they’re hard to detect. You might not even know they’re crawling on you or embedding in your skin.”

And they have a high probability of being infected with Lyme disease, he said. “About 90 percent of larvae that feed on mice get infected. That’s twice as high as with many other hosts.”

Ticks feed three times in their lives – as larvae, nymphs and adults. After they consume the blood of a Lyme-infected mammal, they transmit the disease to their next host.

Various mammals are fair game for ticks, but Ostfeld contends deer get a bad rap as the main vectors of Lyme disease.

“There’s all this entrenched dogma about the quintessential role of deer in the disease, but we find in our research sites that fluctuating deer abundance has no explanatory power.”

Other factors, such as rainfall, humidity, and air temperatures, influence ticks to varying degrees of statistical importance, Ostfeld said. Fragmentation of forests also has had an impact by reducing species’ diversity and “promoting mouse populations,” he said.

“But acorns are the engine driving variability in time.”

A scenario similar to one Ostfeld is predicting for this year unfolded in 2006, when a boom in acorns, followed by a bust in 2007, caused nymphal ticks to reach a 20-year high.

Penn State University entomologist Rick Jacobs did not want to comment on the Ostfeld study, but had his own thoughts about the mushrooming presence of ticks in Pennsylvania.  

“We saw a ton of ticks this winter and all sorts of factors play in, notably deer densities, reforestation, and moisture in the environment,” said Jacobs. “Moisture is key.”

“I don’t think it’s been adequately studied, but we are seeing ticks returning to habitats they hadn’t been seen in for 20 years. The biggest area was in the southeast part of the state, and then Pike [County] had a problem, and then western Montgomery and Butler, and it picked up from there.”

Ticks get moved around principally by birds, he said. “Tick populations have been building for the past 25 or more years. As long as ecological conditions are right, they’ll explode.”

The mild winter has increased tick survivability, said Jacobs, who found himself covered with ticks during a visit last winter to a forest in Clinton County.

According to Ostfeld, cases of Lyme disease have increased over the past three decades from just a few hundred to 30,000, and 90 percent were in the northeastern United States. While there is effective treatment, if left undiagnosed, the disease can cause chronic fatigue, joint pain, and neurological problems.

If you’re heading to the woods, spray your clothes with tick repellent, such as Permanone, in advance, Jacobs said. “If you find a tick embedded in your skin, use  tweezers or a tick-removal device to pull it out.

But don’t grab the tick with your fingers, because you’ll force what’s in the tick’s gut into you, and that’s when you get infected.”

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