Study shows deer aren't sole cause of Lyme disease
Recent research shows that deer aren't the only ones to blame for carrying ticks infected with Lyme disease.
Senior Scientist at the Cary Institute Richard Ostfeld released a book detailing his study of white-footed mice and the impact they have on tick populations. His research has found that deer herds are not the sole culprits in carrying potentially infected ticks.
"What happens is when new babies are hatched, they are free of Lyme," Ostefeld said. "They have to get the infection from whoever they get their first blood meal from."
According to his research, Ostfeld found that the white-footed mouse makes an excellent host for ticks.
"Ticks are much more likely to get infected from a mouse because mice are less fastidious groomers," Ostfeld said. "For that reason, ticks are more likely to survive on a mouse because they won't be groomed off."
Ostfeld explained that the reason most ticks die is because they are groomed off by the animal host. His research found that mice are more permissive of the ticks and seem less conscious that the ticks are on them. "Where most animals might notice the ticks because of swelling or irritation, mice don't seem as bothered by their presence," Ostfeld said.
However, even though Ostefeld said deer aren't the only suitable host for ticks, he did explain that adult ticks won't feed on mice.
"The deer are an important host but it is assumed that they are the only host," Ostfeld said. "There's this 30-year-old dogma that says deer are responsible for ticks and that just isn't the case."
Ostefeld said he had read studies that showed a correlation between deer populations and the number of ticks, but that the studies had taken place on a island where the deer were the only available host animals.
"There are good reasons for reducing the number of deer, but reducing deer to eliminate Lyme disease is not as effective," Ostfeld said.
The Fairfield County Municipal Deer Management Alliance Public Education Chairman Kent Haydock explained that one of the issues Connecticut faces in regards to deer populations is that for 75 years, it was against the law to hunt after the deer population was nearly wiped out.
"The idea is to keep the number of deer in check, not to eliminate them," Haydock said.
The Centers for Disease Control reports that there were 2,751 confirmed cases of Lyme disease in Connecticut in 2009, the latest data available.
An economic study conducted in Fairfield County found that deer overpopulation results in an annual cost of about $1,037 to Darien households, the study says. The study also quotes State Entomologist Kirby Stafford as saying that Lyme disease is less prevalent in areas where the deer population density is below 10 to 12 per square mile because the ticks require their last blood meal from a large mammal.
The Connecticut Department of Environmental Protection website states that 11,774 total deer were harvested in 2009.
However, even though deer are not the sole contributor to Lyme disease infected ticks, they can still have a negative impact on local ecosystems because of overabundance, according to a guide to managing deer populations released by the Connecticut DEP. "Because deer can eat five to 10 pounds of forage per day, overabundant deer herds can eliminate native plant species and change the structure and diversity of plant communities," the guide stated.
The Connecticut Agricultural Experiment Station found similar evidence which was released in a fact sheet by Stafford. The sheet says that tick larvae and nymphs "typically become infected with Lyme disease bacteria when they feed on infected white-footed mice, chipmunks or certain species of birds. However, the fact sheet does say that white-tailed deer are the principal hosts for adult ticks and large numbers of ticks are associated with larger deer populations, but notes that deer are not reservoirs for Lyme disease.
Ostfeld explained that controlling the deer population wouldn't necessarily reduce the number of ticks because the ticks don't die when the deer dies.
"The ticks are forced to crowd onto the remaining animals such as raccoons," Ostfeld said.
Steps can be taken to control the number of ticks in an area, but as Ostfeld explained, "there is no silver bullet."
Four-poster systems are found to be reasonably effective at treating deer with ticks because the deer treats itself after walking through paint rollers with pesticides on them to reach a food source, Ostfeld said. Other systems include building boxes for mice that have the same ingredients that Frontline uses to treat ticks on cats and dogs. Ostfeld also said the other option for limiting the number of ticks in an area is to have more natural predators that hunt mice.
"Areas that maintain predator species, like owls, hawks and foxes, have lower populations of mice," Ostfeld said.
No matter what options are pursued for combating infected ticks, Ostfeld said nothing is 100 percent effective.