Scientists cast a wide net this week in the search for clues to why a rare disease called tularemia has a foothold on the Vineyard. They drew blood samples from landscapers, dragged for dog ticks and trapped rodents.
In quantity alone, it was a fruitful trip for the investigators. Tuesday's free blood testing attracted 109 people, most of them landscapers who are considered at the highest risk for contracting the disease. As for the ticks, Ken Gage, a zoologist and medical entomologist from the federal Centers for Disease Control and Prevention, said he collected about 700 of them.
Scientists also trapped meadow voles and white-footed mice, about 50 in all, around Katama and Chilmark, focusing on areas where many of last year's victims were likely infected, according to Mr. Gage, who is chief of the CDC's plague section in Fort Collins, Colo. Also collected were environmental samples such as rodent feces.
"We didn't target rats this time," said Mr. Gage in a telephone interview yesterday from his office in Colorado. "We wanted to look and see if we can find rodents normally associated with tularemia. But the rat question is quite interesting."
Earlier this week, Sam Telford, a parasitologist from Harvard University who has joined the CDC investigation, said the Island rat population might play an important role in the outbreak of tularemia last summer and what might be another outbreak this summer.
Already, two cases have been confirmed this year, one of them the pneumonic form of the disease. Last year's outbreak infected 15 people, killing one man from Chilmark, David Kurth. Most of the cases were pneumonic tularemia, a fact that prompted CDC investigators to come to the Island twice last summer to collect evidence.
No other place in the country has ever experienced an outbreak of pneumonic tularemia. Last summer marked the Island's second outbreak, the first one taking place back in 1978, when 15 people also came down with the disease.
Tularemia is more commonly transmitted by a tick bite from a dog tick, but pneumonic tularemia can be contracted simply by breathing in contaminated air particles. After interviewing victims, public health officials learned that 12 of the 15 people infected had been mowing a lawn within two weeks prior to becoming ill with flu-like symptoms.
It will be at least a few weeks before scientists have any new data from this week's tularemia testing and collecting of samples. Public health officials are still waiting on results from two suspect cases of pneumonia that could be tularemia. Three other cases were ruled out.
On Tuesday under the shade of trees by the state forest headquarters, scientists set up camp at two picnic tables. Nurse Donna Enos tapped people's veins for a couple tablespoons of blood, while Katherine Feldman, an epidemic intelligence officer from the CDC, and others queried landscapers with a battery of questions.
In three pages of questions, they wanted to know what kind of landscaping people did; how many hours a week; what parts of the Island; what kinds of equipment; and whether people took any preventive measures like wearing a dust mask or tucking pant legs into socks.
The researchers also asked about ticks and rodents, especially rabbits, rats, skunks and mice. How many were sick and how many dead?
"There's nothing better for us than to hear from these people," said Mr. Telford on Tuesday. "These are the people working out there, the people who live here. They're the real experts."
He encouraged landscapers who find dead rodents to freeze them and save them for his researchers, who come to the Island monthly, collecting evidence not only about tularemia but also about Lyme disease. After talking to so many Islanders, Mr. Telford said yesterday in a telephone interview, "I was surprised how [the tularemia outbreak] has taken hold of some of these people."
In one case, a friend of Mr. Kurth told Mr. Telford he has dropped some of his best lawn-mowing clients because he won't mow lawns anymore near Stonewall Beach, the area close to where officials suspect Mr. Kurth contracted tularemia.
You might expect scientists to show some frustration at not being able to crack this tularemia puzzle. On the contrary, the scientists appear to be energized by the challenge. "This is really exciting because less is known about tularemia," said Mr. Telford. "We're at a primitive place with this disease."
Mr. Telford said his team from Harvard is collecting dog ticks in the hopes of finding the source of the tularemia bacteria that killed Mr. Kurth and infected the others. One technique for doing that is to draw blood from ticks and look for the bacteria. If they inoculate a mouse with that bacteria, and the mouse dies - usually within 48 hours - they can test the bacteria again, looking for a DNA match with the bacterial strain that infected people last year.
As mysteries go, this one looks like a long-running serial with plenty of twists and turns. Scientists have different theories, but they say that what's happened on the Vineyard is extraordinary.
"The fact that pneumonic tularemia outbreak would happen twice in the same spot is like lightning striking twice in the same place. It's off-the-wall probability," said David Dennis, chief medical director for the CDC's bacterial zoonoses branch in Fort Collins.
But he added that the Vineyard's unique ecology could be a factor. "It's very moist with the winds off the seas, and the marshes have muskrats, one of the most notorious maintenance hosts of tularemia," he said. "And then there's the feral Norway rat population."
If it's true that the rat numbers are growing, Dr. Dennis said, that can create crowding and stress in the rodents, making them more susceptible to infection. And since Norway rats are big and hardy animals, they don't die from the disease.
They may be what Mr. Telford earlier this week called "inter-epidemic reservoirs" for the disease, keeping the bacteria alive and passing it on to the ticks.
Scientists are hopeful that their efforts this summer will turn up a solution to the puzzle, especially if the bacteria is as active as it was last year. Results from the two pending cases are expected next week.