NORTHEAST METRO — Does a greater number of deer add up to a greater incidence of Lyme disease?
The question remains debated among Lyme disease prevention advocates, scientists and other experts, but there’s no denying the tick-borne disease is on the rise in Minnesota. According to the Minnesota Department of Health, over 900 Lyme disease cases were reported each year since 2004, and a record 1,293 cases were confirmed in 2010.
Public health experts attribute the increase partially to increased awareness by doctors, rising tick infection rates and an expanding presence of ticks.
Heavily wooded North Oaks provides habitat conducive to the survival of ticks and potential for Lyme disease transmission to humans. Host animals are plentiful, and the mossy forest floor provides insulation for cold winter months. Resident Shaila Cunningham called Lyme disease the “biggest problem facing North Oaks” in a letter to the editor of the North Oaks News last month, and places the blame on a large deer population, which she estimated at 25-30 per square mile.
“It’s a public health menace we continue to ignore,” Cunningham wrote. “Fewer than 10 deer per square mile is widely agreed to be the maximum number for safety.”
Tufts University professor Sam Telford called deer “the root of the Lyme disease evil” in an email last week.
Telford, who specializes in infectious diseases at Tufts’ Department of Biomedical Sciences, wrote a 2002 academic article incriminating deer as the culprit for the spreading of Lyme disease to humans.
He pointed to a study conducted near Hyannis, Mass. in the 1980s that reduced deer population on a 300-hectare tombolo from between 30 to 50 down to six or so over a three-year period. Before the deer population intervention, 16 percent of residents in the area experienced infection from a tick-borne disease; after, only three such diseases were recorded from 1986 to 2002.
“(There) is strong evidence that deer are the definitive hosts for the deer tick and that risk of acquiring infection is related to deer density,” Telford wrote.
Yet other experts maintain that the relationship between deer and the disease is far too complex to form a causal relationship. According to Minnesota Department of Health epidemiologist Dave Neitzel, deer produce antibodies which protect them from the Lyme infection.
“It’s too simple to say that by reducing deer populations, you will reduce disease risk,” Neitzel said.
This time of the year, adult female ticks are at their final life stage and are fairly easy to spot by humans. It’s the smaller nymph stage of the tick, in late spring and early summer, that presents a greater potential health risk to humans.
According to Neitzel, ticks pick up the bacteria that causes Lyme disease from small mammals like mice and chipmunks. While deer don’t carry the actual disease, they do provide a means for ticks to mate and a blood meal for the female.
“Generally, with whitetail deer population resurgence, there’s been a resurgence in their parasites,” he said.
Yet Neitzel said controlling deer would mean upping the ante on what he called “already aggressive measures.”
“It’s impossible to eliminate all of the deer, and in many of the studies (with deer thinning) you just see the other deer with a lot more ticks on them,” he said. “If parasites don’t have deer to feed on they will be on other mammals, including people.”
And not all regions in Minnesota with deer populations play host to blacklegged tick populations, for example, in the prairie lands of western Minnesota. That’s because ticks need wooded habitats and warm ground to survive, Neitzel said.
If anything, the health department scientist recommends a “multi-pronged” approach on Lyme disease prevention action. He said controlling ticks by treating small animals could help, but such pesticide products can cost hundreds of dollars per square acre.
According to the Department of Health, most of the northeast metro is included in a tick-borne disease risk zone that includes most of the east-central and north-central part of the state.
The Department of Health recommends using repellent and wearing protective clothing among measures to help prevent exposure to tick-borne diseases.
For more stories on Lyme disease and Lyme disease prevention in the northeast metro, visit www.pressspubs.com.