Vineyard outpaces Nantucket in Lyme cases
By Nelson Sigelman - June 14, 2007
The islands of Martha's Vineyard and Nantucket regularly meet on the sports field, where victories are savored. But one category in which the Vineyard surpassed Nantucket provides no reason to cheer.
The Vineyard recorded more than double the confirmed cases of Lyme disease on Nantucket in 2005, the most recent year for which statistics are available, according to the Massachusetts Department of Public Health (DPH).
There were 89 confirmed cases of Lyme in Dukes County, which includes the Elizabeth Islands, compared with 32 recorded in Nantucket County.
The tiny deer tick causes Lyme disease. An increase in the number of deer has led to an increase in incidences of tick-borne diseases, according to Sam Telford, associate professor of infectious diseases at the Tufts University School of Veterinary Medicine and a well-known islands' tick researcher.
On Thursday, June 21, the Martha's Vineyard Hospital in association with the DPH will host a tick-borne illness forum from 6 to 8 pm in the Oak Bluffs School community room designed to educate people and answer questions.
Speakers will include DPH researcher Susan Soliva and hospital infection control nurse Donna Enos.
The tick most people are likely to pull off their pant legs is the adult dog tick, which can carry Rocky Mountain spotted fever, a rare occurrence on the Vineyard. Also known as wood ticks, they can also spread tularemia, sometimes called rabbit fever, a potentially fatal disease caused by the Francisella tularensis bacterium.
The Island has one of the highest rates of the virulent form of pneumonic tularemia infection in the world. From 2000 through 2006, there were 59 cases associated with the Vineyard, more than in the previous 50 years. Of those, 38 were tularemia of the lung, according to DPH officials.
The smaller deer tick, which is responsible for infecting humans with Lyme disease, is also capable of transmitting a malaria-like disease called babesiosis, and ehrlichiosis (HGE), a disease related to Rocky Mountain spotted fever.
Deer ticks cling to plants near the ground in brushy, wooded, or grassy places. The ticks climb onto animals and people who brush against the plants. Very young ticks, called larvae, which are no bigger than the period at the end of a sentence, pick up the bacteria that cause Lyme disease by biting infected animals, such as field mice. Slightly older ticks, called nymphs, which are the size of a poppy seed, are the stage most likely to bite and infect humans, according to information on the DPH web site (www.mass.gov/dph). Adult deer ticks can also transmit the disease, but they are not as great a risk as nymphs because the adults are less likely to bite humans and they are easier to see and remove.
In a recent e-mail to The Times, Mr. Telford, who has studied ticks extensively on the islands, provided some insights as to what Vineyarders could expect this season. He said he does not think the number of ticks will vary greatly from previous years, and that much depends on the weather.
Hot dry conditions do not favor deer ticks in either the nymph or adult stage. "As for dog (wood) ticks, there may be fewer due to fewer skunks and raccoons in the last year or so, but because even in poor years there are lots of dog ticks and they are very visible, people will still get the impression that there are hordes of them," he said.
Mr. Telford said he has no good reason why the Vineyard is continuing to see high incidences of tularemia. He found tularemia infected dog ticks on the Vineyard when he visited in April and May. "We should have seen it disappear from ticks and animals after a couple of years," he said. "Why it sticks around when it should disappear is what we are trying to understand."
Asked what homeowners and visitors can do to protect themselves beyond the well-reported precautions, Mr. Telford said it is useful to remember that only a small fraction of ticks are infected. "Finding one on you is not a cause for a visit to the emergency room," he said. "By no means should someone not enjoy their time on the Vineyard because they are worried about ticks."
He recommends people always check for ticks while showering. "Remove any promptly by just pulling them out," he said. "Save by taping it on an index card with the date. Take this to a doctor if there is a rash or fever within two weeks of having removed the tick."
Mr. Telford also recommends people spray shoes, socks and legs with insect repellant. When gardening it is important to spray the sleeves of a shirt because ticks can crawl up when hands are in the garden.
Mr. Telford said that when ticks walk across clothing sprayed with a repellant that contains duranone or permethrin they die within a few hours, long before they could transmit anything.
As an added note he said, "Always see a physician for any unexplained fever of greater than two days duration."
No easy predictions
Mr. Telford said that despite years of study he has found no way to predict tick numbers. "One of the reasons I continue to crawl around the bushes hunting ticks, 20 years now, is to try to come up with a predictive model," he said. "I am humbled and chagrined that I still cannot do so. One of the reasons for this is because weather is an important variable, but weather itself is poorly predictable and therefore long-term trends in tick numbers are not predictable."
One area of research is what aspects of weather are most influential. These factors include direct and indirect effects. For example, a direct effect is hot and dry weather in June and July. Deer ticks need very high relative humidity to survive.
An indirect effect might be a severe winter with no snow but hard freezes. Because mice provide a link in the deer tick's infection chain, any mortality reduces the possibility of ticks feeding in the summer, which means fewer infected ticks the subsequent summer.
The dog tick is far hardier. "You can bury them in hot sand on the beach and come back and dig them up a few hours later, unharmed," Mr. Telford said. "I am not sure anything really regulates them except for the numbers of skunks and raccoons, which are to dog ticks what deer are to deer ticks, namely, the blood meal source needed for laying eggs. But, the relationship is more difficult to track because dog tick adults can live for at least two years whereas deer tick adults die within seven months. And, dog tick females lay 6,000 eggs each, compared with the relatively paltry 2,000 by deer tick females so it doesn't take many skunks and raccoons to keep dog tick populations high."
Global warming, more accurately referred to as global climate variability, might push the Vineyard's tick problem north, said Mr. Telford. "If we have more hot and dry summers with a trend to overall warming, it is good news for New England based on the state of our knowledge, admittedly rudimentary, about the effects of weather on deer ticks. There is no Lyme disease to speak of in the South; it is too warm. Deer ticks hate hot weather, and the various pathogens (Lyme, babesia, ehrlichia) do too. So Canada will inherit the Lyme problem and we will become more like the South (pest ticks, fire ants, chiggers etc.)."
