State health advisories warning people to wear dust masks when mowing the lawn or cutting brush may have put a dent in this summer's total for cases of tularemia, the rare disease that has an unexplained foothold on the Vineyard.
A bacterial infection that killed a Chilmark man and infected 14 others on the Island last year, tularemia has struck just four people so far this year. Still, even four victims is considered by public health officials to be a high number since the disease is very uncommon with only one or two cases a year statewide, sometimes none.
"Whatever is happening is still happening. Fortunately, it's at a lower rate," said Dr. Alfred DeMaria, director of communicable disease control at the state department of public health. "That may be because of all the precautions. We still need to have a heightened awareness. The problem didn't go away."
Island landscapers appear to have gotten the message. At Western Auto, a lawnmower sales and service outlet in Oak Bluffs, co-owner Amy Billings said, "People aren't so much talking about it, but they are buying the masks. Landscapers buy them by the box, and everyday people just add in a mask with the mower."
Tularemia is typically spread to humans through a bite from an infected dog tick, but it can also be transmitted by breathing in air particles laced with the bacteria, resulting in a pneumonic form of the disease.
Most of the Island cases in the last two years have been pneumonic, and most of the people infected worked outdoors on a daily basis. Of the 15 people infected last year, 12 had been mowing a lawn within two weeks prior to becoming ill with flu-like symptoms.
This year, three of the four cases were pneumonic. Two were landscapers, and one was a farmer. The first case of the year involved a four-year-old boy from Newton who was bitten by a tick while visiting the Island in April and came down with the more common form of the disease. One pneumonic case was also confirmed on Nantucket, a landscaper falling ill after mowing over an infected rabbit.
But it's the Vineyard that holds an unenviable spot in the medical record books. No place else in the country has ever experienced an outbreak of pneumonic tularemia, much less two outbreaks. Back in 1978, 15 people also came down with the pneumonic form of the disease.
Last June, for the third time in a year's span, investigators from the federal Centers for Disease Control arrived on the Island to try their luck at unlocking this riddle. This time, they joined forces with a team of Lyme disease researchers from Harvard University led by Sam Telford, a parasitologist and Lyme expert who has done field testing on the Island since 1994.
Inviting landscapers to a free blood screening, they set up camp at the state forest headquarters, drawing samples from 123 people. Mr. Telford tested an additional 42 landscapers over at Walter Ashey's repair shop by the airport. Of the 165 people screened, only 10 tested positive for tularemia antibodies, a rate of six per cent among the population considered at highest risk.
But what surprised Mr. Telford from the blood results is that two people had high levels of antibodies, suggesting a recent exposure, but they reported no symptoms.
"That means that opposed to what we read in the textbooks, tularemia can range from asymptomatic to death," he said. "There may be a lot more mild infections than we realize."
Mr. Telford also said he was surprised to compare incidence rates of tularemia to Lyme disease and find that based on his tests, tularemia is one-fourth as common as Lyme on the Island. "It's astounding to me," he said.
Both Mr. Telford and the epidemic intelligence officers from the CDC believe the answers lie somewhere in the Island ecology, possibly emanating from some peculiar mix of climate and mammal population. Both have trapped dozens of animals and dragged fields for hundreds of ticks in pursuit of clues. They have concentrated their efforts around the Katama section of Edgartown and the Squibnocket region of Chilmark, two areas where experts believe many of the victims were infected.
Already, 12 rabbits caught in Chilmark by the Harvard team have tested positive. Mr. Telford also harbors strong suspicions that the Island's abundant rat and skunk population could play a role, but he has yet to trap and test them in significant numbers. The county's new rodent control officer, T.J. Hegarty, is storing any rats he catches in a freezer for Mr. Telford.
Results from the CDC's animal trapping are still pending. Dr. Ned Hayes, medical epidemiologist at CDC's division of vector borne infectious diseases in Fort Collins, Colo., blamed delays at the federal agency on the fact that the same CDC experts called to the Vineyard are frequently dispatched to hot spots around the globe.
Last year, investigators were pulled off the tularemia case to help British health officials cope with foot and mouth disease. Now, both Katherine Feldman and Ken Gage from the CDC's Colorado office are in Mongolia, dealing with a plague outbreak.
So, it will be weeks before the CDC lab can begin testing some 50 mice and voles and over 700 dog ticks trapped on the Island last June. But Dr. Hayes said the CDC is committed to understanding the unusual situation on the Vineyard.
"We didn't have an outbreak like we did the year before, but we know there seems to be the potential for transmission," he said. "The fact that we had other cases associated with lawn mowing indicates that it's not just a one-shot deal. There's still some of that risk out there."
Until scientists can solve this puzzle, prevention is what public health officials are pushing. Even Tristan Israel, 52, a landscaper and Tisbury selectman who was one of this summer's tularemia victims, is not taking any chances. "I hope I have an immunity, but I still wear a mask sometimes," he said. "I don't want to have it again."
Mr. Israel became ill back in June with symptoms of pneumonia and spent 10 days in the hospital on intravenous antibiotics. Full recovery has been slow. "This week is really the first week I felt 90 per cent plus," he said.
But his recollection of how bad he felt remains painfully clear. "It just came on, bang-o. I was sick with headaches that wouldn't quit," he said. "If I had gotten in [to the hospital] a few days later and taken no antibiotics, I'd be dead."