Mice and squirrels love acorns.. What is its relationship to Lyme disease in humans?

Ticks cause an increase in the number of visits to emergency departments during the month of October each year. A 35-year study in New York City reveals how climate, and some acorns, can help predict the risk of Lyme disease in an area.

Dr. Richard Ostfeld and his team at the Cary Institute for Ecosystem Studies have been studying Lyme disease for 35 years. This is one of the longest studies of its kind, and the acorns are key to one of their surprising findings. “The acorns are an early indicator of how bad a year we're going to have in terms of our exposure to tick-borne diseases,” Ostfeld said.

The bacteria that cause Lyme disease are mainly carried by small organisms such as mice and squirrels, and they love to eat acorns. Ostfeld explained that if rodents store "a large number of acorns for them to eat, they will not have to move as much during the winter, they will not be as vulnerable to predators, and they will begin to reproduce earlier the following spring, and have large numbers of young."

The presence of large numbers of young rodents means more opportunities for blood-sucking ticks, which feed on rodents, to pick up the bacteria that cause Lyme disease. It became clear in Dr. Ostfeld's study that “the number of mice in summer is a decisive factor for blacklegged ticks, because if the number of mice is large, the newly hatched tick larvae, which are active in August and September, find their favorite food available in large quantities.

“And when they feed on a mouse, they are very likely to survive, get a blood meal, and turn into a nymph.” Then if those tick nymphs bite us and stay attached to us long enough, they can transmit the bacteria to us and give us Lyme disease.

So, more acorns means more mice the following summer, and more mice means more infected tick nymphs two summers later. So, on your next walk in the woods, remember that what you see at your feet may be a glimpse of the future. “If you have a very abundant year for acorns, write it down in your electronic calendar so that it will remind you two summers later that this is going to be a very bad year for acorns,” Ostfeld said.