State public health officials yesterday confirmed this year's third case of pneumonic tularemia, the rare and potentially fatal disease that killed a Chilmark man two years ago and has baffled scientists for the last three summers.
The latest victim, like the first two cases of the year, is a landscaper. According to the state Department of Public Health (DPH), the man is in his thirties and a resident of Holliston who commuted to the Vineyard to do landscaping. He was diagnosed and treated at a Framingham hospital.
The latest confirmation brings the total tularemia count on the Island to 22 cases since 2000. All but five cases have been the pneumonic form of the disease, which is supposed to be the rarer form of the disease also known as rabbit fever.
No one disputes that the Island remains in the midst of an outbreak that first hit in the summer of 2000. In most years the disease infects only one or two people statewide.
No place else in the country has ever experienced such an outbreak. Epidemic intelligence teams from the federal Centers for Disease Control have come to the Vineyard three times already, looking for clues to explain why pneumonic tularemia seems to thrive here.
Scientists investigating the outbreak have pinpointed potential hot spots for the disease around Katama and the Squibnocket area. But state health officials could not say where on the Island the most recent landscaper to get sick may have contracted the bacterial infection.
"He worked all over the Island," said Dr. Bela Matyas, epidemiologist for DPH.
The one common thread Dr. Matyas could identify between all three cases this year is that none of the landscapers was wearing a dust mask while working.
Public health officials have urged landscapers to wear dust masks as a possible preventive measure against the disease in its pneumonic form, which scientists believe is contracted by inhaling airborne particles contaminated with the virulent bacteria.
Landscapers are at the highest risk because they are constantly creating airborne particles by mowing lawns and cutting brush. Of the 22 cases, 18 of them have been landscapers or people who worked outdoors on a regular basis.
"It is helpful to note that they didn't wear masks," said Dr. Matyas. "That's still consistent with the way we think they're getting sick."
But not all landscapers are taking the precaution. "It's not always easy to follow that recommendation," said Dr. Matyas. "In 90-degree weather, wearing a mask while doing that kind of work is very hard to do."
It remains unclear whether the third confirmed case of tularemia will trigger a fourth visit to the Island by the CDC.
David Dennis, medical epidemiologist and coordinator of the tularemia program at the CDC's division of vector-borne infectious diseases in Fort Collins, Colo., said yesterday that his team is poised to come back if necessary.
Tularemia bacteria is at the top of the list of bioterrorist agents. Last month, Dr. Dennis said the CDC may be interested in coming back to the Island with some of its high-tech "sniffing" devices which may be able to detect airborne tularemia. But it's not likely that the CDC will want to make such a visit public, he added.
Dr. Matyas also said he probably would not invite the CDC back to the Vineyard. He pointed to the fact that a team from the Harvard School of Public Health led by parasitologist Sam Telford is already coming to the Vineyard each month to trap animals and collect dog ticks for any evidence of tularemia.
The goal of Mr. Telford's investigation, Dr. Matyas said, is "to identify pockets of risk so we can be more focused in prevention efforts."
But Mr. Telford has also told the Gazette that this is no easy task to unlock the riddle of tularemia's strange foothold on the Vineyard.
He stressed the fact that scientists know surprisingly little about the disease. The disease is more commonly passed to humans when they are bitten by a dog tick that carries the bacteria.
Rabbits are well-known carriers, but they die from the disease. What fascinates Mr. Telford is how the disease can persist when the bacteria is so deadly.
"It's a very strange parasite because it kills most of its hosts," he said. "The clever parasite doesn't."
The pneumonic form of the disease can have a mortality rate as high as 60 per cent if left untreated.
Tularemia bacteria is also hardy. According to the CDC study published last November in the New England Journal of Medicine, the bacteria "can survive in water, soil and decaying animal carcasses. The organism persists in water and mud for as long as 14 weeks, in straw for six months and in oats for four months."
Last year, Mr. Telford joined up with the CDC investigation and quickly pinpointed rats as a potential culprit in keeping tularemia going on the Island. Of the 40 animals trapped by the CDC in the summer of 2000, only two tested positive for tularemia - a Chilmark skunk and a rat from Katama. But the CDC tested 11 rats, and Mr. Telford has tested 15. All were negative. Of the more than 500 dog ticks collected from the Island, only one tested positive.
Public health advisories have urged landscapers to dispose of animal carcasses in double plastic bags. They also warn people to seek immediate medical attention if they "develop fever or respiratory symptoms within seven days of potential exposure to aerosols of dust, soil or grasses, or after direct contact with a wild animal."
Skin sores or swollen lymph glands after a tick bite are considered telling symptoms of the more common form of tularemia. For more public health information on tularemia, people may call DPH at 617-983-6800.