Bug-borne diseases still worrisome
Recent findings indicate there's reason for continued caution about mosquito-borne West Nile virus and Eastern equine encephalitis, while state statistics indicate the tick-borne Lyme disease continues to spread into new areas.
On the mosquito front, there have been no human cases of either West Nile or EEE reported in the state this year. There have been 50 findings in birds and 116 in mosquito pools for West Nile, and four EEE findings in mosquitoes, according to the state Department of Public Health. Those numbers eclipse the 108 findings in birds and mosquitoes in 2007, when there also were six human cases reported.
"It's a little too early to say we're out of the woods," said Dr. Bela Matyas, medical director of the health department's epidemiology program, who cautioned there's often a lag between the time a person contracts West Nile and when it's diagnosed and reported.
"There is an inherent randomness to where sporadic cases occur," Matyas said, noting that many infected people experience no or only mild symptoms and those cases are rarely diagnosed or reported. "The one thing we can say for certain is that with good mosquito- control efforts, and with people taking prevention behaviors to heart, the chance of cases occurring goes way down."
After very few West Nile findings earlier this summer by the Northeast Massachusetts Mosquito & Wetlands Management District - which includes Essex County plus Winthrop and Revere - September testing produced findings in Lynn, Merrimac, North Andover, Winthrop, and Revere. Testing was increased after discoveries of the virus in dead birds in Saugus, North Andover, Salem, Haverhill, and Lynn, according to Walter Montgomery, director of the district.
The heavy rainfall this summer helped control the population of the Culex species of mosquitoes identified as prime West Nile carriers. "From our perspective, we feel confident that we get higher numbers of Culex and higher numbers of West Nile in drought conditions, not wet conditions," Montgomery said.
While the quiet summer was unusual, the early-September increase was not, said Montgomery, who noted that the virus typically becomes more widespread at that time. The district responded by spraying school and athletic fields in North Andover, and with truck spraying in Winthrop, Revere, Lynn, and Merrimac.
The small number of West Nile positives in Essex County does not take health officials off the alert. The six human cases serious enough to be reported in 2007 were logged from Aug. 11 to Sept. 27. None were in Essex County.
In Danvers, where mosquitoes tested positive in late August, follow-up tests found no other West Nile samples.
"Some might go a couple of miles, but most mosquitoes are going to travel around in a few hundreds yards. So to really know the picture you'd have to have so many traps that it's just not possible to do it," Matyas said.
"It's out there," he added, referring to West Nile.
The first human cases of West Nile in Massachusetts were reported in 2001, when there were three. There were 25 in 2002, 19 in 2003, none in 2004, and single-digit cases the following years.
"Our expectation is that it will eventually find a pattern," Matyas said. "What we don't know is how long that will take."
Meanwhile, partly because of a change in reporting methods for human cases of Lyme disease, the Department of Public Health's state total for 2007 was 3,350, a steep increase from the 2,402 in 2006 and 2,450 in 2005. The number for Essex County was 351 in 2007, compared with 278 in 2006 and 271 in 2005.
Public health officials also have observed the spread of the disease into areas where there hasn't been a history.
"If we go back 15 years ago, the risk of Lyme disease was clearly highest in the Cape and Islands, parts of Southeastern Massachusetts, Cape Ann - particularly in the Ipswich area - and the Connecticut River Valley," Matyas said.
The deer population has increased, and with more development there's less habitat, moving the deer to forage for food in communities such as Peabody, Danvers, and Salem. The Lyme-carrying deer tick has migrated with them.
"We're seeing measurable increases," Matyas said.
Peter Mirandi, director of public health for Danvers, said the increase is reflected in his annual compilation of communicable diseases. In a four-year span from fiscal year 2001 through fiscal year 2005, there were 27 cases reported in the town.
But Danvers had 26 cases in fiscal year 2006, followed by 28 in 2007, and 36 in 2008.
Mirandi thinks that change is in part the result of improved diagnostic tools used by doctors, along with the increased deer population.
Mirandi said the disease hasn't clustered in any one area, and that people may have come in contact with the ticks somewhere other than their own neighborhood.
"Maybe they were hiking somewhere else," he said. "This doesn't necessarily mean people are getting it in Danvers."
Horses, dogs, and other animals are also at risk for Lyme disease. Veterinarian George Myers, who runs Danvers Animal Hospital, said dogs are often a sentinel for the disease, and he's seen a steady increase over 20 years.
The number of cases in Danvers or abutting towns is still not as high as in Ipswich, he noted, where approximately half of the dogs he treats have Lyme disease. 