Are rabbits really to blame for last summer's outbreak of tularemia and for what could be a repeat performance this year?

Sam Telford, a parasitologist from Harvard University and the newest member of a team sent here to investigate why such a rare disease has taken hold on the Vineyard, doesn't think so. What's more, Mr. Telford is just as skeptical about the prevailing theory that most victims breathed in air particles contaminated with the tularemia bacteria.

His own hypothesis? An increased population of rats, not rabbits, could be a big factor. "The dogma out there is that it's rabbits," Mr. Telford said Friday in a telephone interview. "But [at Harvard] we're focusing on rats as the so-called inter-epidemic reservoir. Rabbits are poor reservoirs because they die from tularemia. If rabbits are the reservoir, then how does tularemia keep going from year to year?"

Bucking another assumption about the disease which killed a Chilmark man last summer and infected 14 others, Mr. Telford argued that it's possible to get pneumonic tularemia from a tick bite and not from inhaling bacteria-laden air particles.

"That reflects a controversy in the tularemia medical literature itself," he said. "Not every instance of primary pneumonic tularemia is a result of exposure by aerosol. That's what I have an issue with. You have to have an alternative hypothesis. There may be a combination of factors. Some may have gotten it by tick bites and some may be inhaling it."

According to Mr. Telford, it is entirely possible to contract the pneumonic form of the disease from a dog tick bite. And, he added, since not all tick bites result in swollen glands, the absence of that one symptom in a person with pneumonia should not be used to rule out a tick bite.

Mr. Telford, who is a lecturer at the Harvard School of Public Health, has been studying Lyme disease on the Vineyard for the last seven years and on Nantucket for most of the last 15 years. And while his theories run right against the grain of what state and federal public health officials have assumed for the last year, he doesn't see himself butting heads with the team he has just joined - the Centers for Disease Control and Prevention (CDC).

"We disagree over the source [of the tularemia outbreak]," he said. "But we've forged an alliance with the CDC, and everyone will benefit."

When the CDC heard that Mr. Telford's team from Harvard was adding tularemia to its list of tick-borne illnesses, he was invited to join the latest investigation, prompted by last week's confirmation of the first case of pneumonic tularemia so far this year. Five other cases are still being evaluated.

Today, landscapers across the Island have been called to stop by the state forest headquarters to help in the study. They will give blood samples and receive free, confidential testing for tularemia. They will also answer a short questionnaire.

Landscapers are considered to be at the highest risk for contracting tularemia. Last year's CDC investigation found that 11 of the 15 people infected had been mowing a lawn or cutting brush within two weeks of experiencing the first flu-like symptoms of the disease. That fact led scientists from both the state and the CDC to speculate that victims had inhaled dust or grass clippings that contained the bacteria, present either in rodent feces, urine or the rodent carcass itself.

Public health officials began warning people to wear dust maks when they engaged in any outdoor work that would kick up such dirt and dust.

But Mr. Telford pointed out that scientific knowledge about inhaling tularemia bacteria is based on one single study done in the 1950s. "People have been making a major assumption about inhalation, but much of that understanding comes from one experiment that the Army did with human volunteers," he said.

The Army experiment exposed the volunteers to 25 different organisms through a gas mask, Mr. Telford said. "That's very different from being on a lawn with a breeze blowing in your face," he added. "This study has just never been critically questioned."

But tularemia is a virulent bacterium, so potent that it is considered one of the top agents in biological warfare or terrorism. Last year, the CDC dispatched experts in bio-terrorism to the Island to investigate the outbreak and to road-test new equipment designed to deal with biological attacks.

And Mr. Telford said that while no one believes the Island is the object of a bio-terrorist assault, the CDC can't help but understand the implications of what has happened here and may be happening again in light of bio-terrorist threats.

"This is a very rare opportunity to have something in our own backyard like this and with all the emphasis on bio-terrorism," he said. "If we can't understand how people are getting it in a relatively small community, how on earth are we ever going to respond to a bio-terrorist attack of tularemia?"

The Vineyard is the only place in the country ever to experience an outbreak of pneumonic tularemia. And last summer's outbreak marked the second time it's happened. Back in 1978, another outbreak also infected 15 people.

"In the ecology of vector-borne disease, we know that the bacteria is always around at a low level," said Mr. Telford. "But for some reason, the transmission has increased over the last couple years."

The problem is that scientists know very little about how the bacteria exist in that "constant, low-level state." All kinds of theories have cropped up to explain the Island's two outbreaks. One has blamed wet weather in both those years. Another has tried to point the finger at rabbits, the most prevalent carriers for the disease commonly known as rabbit fever.

But Mr. Telford has now focused on rats. On anecdotal evidence alone, their numbers have risen. The county last week reinstated the rodent control program, hiring a new officer and charging him with mounting a campaign not only to cut down the numbers but also to educate Islanders about keeping rats and rodents at bay. Officials have blamed the closing of Island landfills for the increased rat sightings.

And Mr. Telford said the rats could be spreading the tularemia bacteria, playing host to dog ticks before they bite humans and infect them. In last year's CDC study, the only animals to test positive for tularemia were a Chilmark skunk and a Katama rat. Still, the CDC had trapped a total of 11 Norway rats.

Whatever the source for the tularemia, Mr. Telford is enthusiastic about getting to the bottom of this mystery. That rare opportunity he spoke of is also a scientific challenge. But it carries economic implications, too. "There are rumors that tourist numbers are down because they hear there's something you can breathe in that can kill you," he said. "One has to be careful when making recommendations. The Island depends on the tourist economy."

The fact is, Mr. Telford said, that tularemia is a very treatable disease if caught early. And like all tick-borne illnesses, he added, in most cases, it can be prevented by dilgent tick checks.