Experts say mice are primary cause of Lyme disease, not deer

Tick and Lyme disease experts pointed to mice, not deer, for the rising number of tick-borne illnesses in New York this year.

Last year’s mild winter and growing mice populations could have caused an increase in tick-borne illnesses, including Lyme disease, New York Upstate reported.

Phillip Baker, executive director at the American Lyme Disease Foundation, said there is a misconception of deer being the main transmitters of tick-borne illnesses. Baker said mice and other small rodents are the main organisms that keep the diseases percolating in the area where they are introduced.

Mice act as a reservoir for Lyme disease bacteria, said Brian Leydet, assistant professor of epidemiology and disease ecology and State University of New York College of Environmental Science and Forestry in an email.

Leydet noted ticks are not born infected. They pick up the bacteria from a host in their environment — most often mice.

A lot of tick activity is influenced by the amount of food animals have to feed on, Baker said. Increasing amounts of acorns in the fall translates to more mice, more ticks and therefore more Lyme disease.

Mature female ticks attach to deer that can travel miles. The ticks drop off the deer and then feed off field mice in that particular area, Baker said.

Joseph Domachowske, professor of pediatrics at Upstate Golisano Children’s Hospital, said in an email Lyme disease was not common in central New York 15 years ago. The number of cases began to increase as Lyme-infected ticks became more widespread.

Felicia Keesing, an ecologist and educator at Bard College in Annandale, New York, has spent the past 20 years studying ticks and risk variations for people contracting tick-borne diseases.

Keesing said rodents are most efficient in passing the bacteria for Lyme disease.

“If a tick feeds on a mouse, it will almost certainly pick up the pathogen that causes Lyme disease,” Keesing said.

However, Keesing said if a tick feeds on something other than a mouse, such as a fox or a squirrel, the tick is much less likely to pick up the bacteria that causes the disease.

Keesing studies the relationship between mice and Lyme disease through The Tick Project. The project focuses on reducing the amount of ticks in high-risk areas. She said her goals are to implement chemical treatments in neighborhoods and to educate towns and villages about options for tick prevention.

Most cases of Lyme are contracted in the spring and summer, Keesing said. When it comes to temperature, she said there are beginnings of some evidence that hot and very dry temperatures can be bad for tick survival in newly-hatched and teenage ticks.

“Ticks are actually remarkably resistant to temperature changes,” she said. “They are very good at finding places in the forest or wherever they are living that are within their temperature range, their preferred temperature range, which is already quite broad.”

Leydet said areas that couldn’t sustain tick growth in the past are now beginning to see tick populations increase.

It is difficult to predict tick populations on a year-to-year basis.

“Every year is a ‘bad’ tick year, and the public should always remain vigilant with personal protective practices, such as wearing Acaricides and doing tick checks,” Leydet said.