Local Features
3:42 pm
Wed September 5, 2012

One Square Mile: new disease gains a foothold


"So this is our tickery!"

The tickery is part of a lab Rollend manages at Yale's School of Public Health. It's stacked with what look like mini-fridges, whirring away. Inside, there are test tubes full of 100,000 ticks.

"You could go in here and pull out any tube of tick and I can tell you when it fed, what it fed on, how long it fed, when it molted, what's it infected with," she explains.

Some are infected with Lyme disease, some carry the babesia parasite. Many were collected from backyards on Block Island where babesiosis has become almost as prevalent as Lyme disease. And safe inside their test tubes, the ticks are helping Yale researchers learn why.

"Because the ticks are the real source of the problem," a problem Yale epidemiologist Durland Fish is trying to crack.

"But there are environmental components you need to understand to understand what's going on with the ticks, and then what happens when the ticks encounter people."

So Fish, who studies how diseases spread, and his colleague Peter Krause, who studies how those diseases affect people, have joined forces with an ecologist to examine the problem from a variety of angles. One question they're trying to answer is how it spreads. They don't know why it's spreading more slowly than Lyme disease, for instance. But they do know that ticks pick up babesiosis from the mice they first feed on.

"It may be something as simple as mice moving slowly from one territory to the next," says Fish. "Or it might have something to do with the interaction between Lyme disease and babesiosis in the mice or in the ticks."

Lyme disease not only spreads faster. It's spread farther. Nationally, there are about 30 cases of Lyme disease for every one case of babesiosis. But on Block Island, that ratio is 3:1.

"What we're concerned about is that babesiosis may spread to the extent that Lyme disease has spread. And it's a much more serious disease than Lyme disease."

Epidemiologist Durland Fish says they're trying to estimate how long it might take to catch up and what direction it might take first. And Block Island could be the key. The Yale researchers say Block Island is a lab like no other: an island, a closed system, where there are fewer outside influences to account for. Where residents are willing to participate in a long-term study. And the island's only medical center is willing to help. Infectious disease researcher Peter Krause has been taking blood samples and interviewing residents there for more than two decades.

"It was very helpful for islanders because they got some idea about whether they had been exposed in the past. And it was very useful for us from a research standpoint because what we could do is identify people who had developed silent disease, asymptomatic disease over the summer," says Krause.

Not everyone infected with babesiosis has symptoms. But you can detect it in a blood sample. And with that information plus the data about how many ticks are infected, the Yale team is piecing together a picture of who's at risk for babesiosis and why. Krause says they're also learning more about what brings babesiosis to a tipping point. Like on Block Island, where it got the bump it needed to expand.

"What we believe is in areas where it's been long established, the two have been present for a long time, we're going to find a ratio that's closer to the three to one ratio that we found on Block Island, that is, over time, as the babesiosis becomes established," says Krause.

What helped babesiosis get established was an explosion in the deer population on Block Island. They've gone from zero to 500-plus in the 40 years since they were reintroduced. All on an island of less than 10 square miles. Durland Fish says adult ticks feed exclusively on those deer.

"And that's why these diseases are dependent upon the presence of deer in order to maintain the tick population." Get rid of the deer, he says, and "...either the tick population will collapse or the transmission of babesiosis or Lyme disease will not occur. So we might be able to cause babesiosis, for instance, to go extinct on Block Island, which would be wonderful because there'd be no way for it get back on the island again."

That's what Block Island resident Mary Sue Record and a group of other concerned citizens would like to see. Record chairs the island's newly created Deer Task Force, which proposed eliminating the deer.

"But there was discomfort with the word 'elimination.' And so once 'drastically reduce' was added it was a unanimous vote."

While wind plucks the chimes hanging from her balcony outside, Record says the task force has helped orchestrate some of the island's first deer hunts. But so far they haven't been able to make much of a dent in the population. Part of the issue is that so much of Block Island is privately owned land. And there's just not enough room for people to roam around shooting guns wherever they want.

"It's different than hunting on the mainland," says Record. "And you need landowner permission. And there's rules about 500 feet back from any occupied building for sharp gun and 200 feet for archery. I see that to solve the problem you really have to get more involved in managed hunts, where you're dealing with large parcels of land."

The task force is slowly piecing those larger hunts together. But in the meantime, the deer, and the deer ticks, are doing just fine. So is babesiosis, which has begun to show up in the regional blood supply.

Take a listen to the rest of One Square Mile: Block Island here
