They look so cute, grazing quietly in your backyard. But the overpopulation of white-tailed deer across the Northeastern United States could help spread Lyme disease and another tick-borne illness, anaplasmosis, especially in suburban areas, a new study suggests.
The research points out that these deer, which carry ticks that transmit the two diseases, are no longer confined to wooded areas, but often live within yards of suburban homes, increasing the risk of transmission.
"Your yard is their home, and if you're concerned about ticks or tick management, or potentially damage done, then you need to recognize that this is where they actually choose to live and either work with them or manage against them," said lead researcher Jennifer Mullinax. She's an assistant professor of wildlife ecology and management at the University of Maryland.
The deer themselves are not a threat to health. But the black-legged (deer ticks) and lone star ticks they carry spread Lyme and other diseases, Mullinax explained.
Lyme disease is a bacterial infection caused by the bite of an infected tick. It causes symptoms such as a rash, fever, headache and fatigue. If left untreated it can spread to the heart, joints and nervous system. Anaplasmosis causes similar symptoms and can lead to hemorrhages and kidney failure.
The ticks that cause these illnesses lodge and breed on your lawn.
As development encroaches on their habitats, deer are living closer to humans, and landscapes offer easy grazing on grasses, shrubs and flowers, Mullinax said. Your lawn is "warm, it's safe, there's fewer predators, and it's just convenient," she said.
This five-year study found that suburban deer often spend the night within 55 yards of human homes.
For the study, Mullinax's team tracked 51 deer that were outfitted with GPS tracking devices.
The trackers revealed that deer avoided residential areas during the day, but gravitated to them at night, especially during winter. The animals often slept near the edges of lawns and within yards of houses and apartment buildings.
So many deer in residential areas increase the risk of human exposure to tick-borne illnesses, Mullinax said. Reducing tick populations by removing deer or treating areas where deer bed down can help limit the spread of disease, she said.
Managed deer hunting can help keep the tick population in check, but culling the herd can be hard to accomplish, the study pointed out. People don't want hunters in suburban areas, and chemically reducing the fertility of deer hasn't worked, it added.
Mullinax said it's possible to limit access to your yard by installing deer fencing or mulch barriers, but a better way to prevent disease may be to control the tick population.
"Most people get Lyme disease from the ticks in their yard. There are a lot of different methods to control ticks," she said. "For the county agencies and state agencies, it's really pointing them to make some adjustments in managing the deer population."
Dr. Marc Siegel is a clinical professor of medicine at NYU Langone Medical Center in New York City who reviewed the findings.
He offered several strategies to reduce the tick population in your yard: Cut your grass short. Have your yard sprayed for ticks. Use tick repellent. And check your body and clothing for ticks after you've spent time outdoors.
"I tell them to look for bumps on their scalp and in their pubic area," Siegel said. "I tell them that if you feel fatigued, it may not be COVID -- it may be Lyme."
Because Lyme disease can be hard to diagnose, Siegel said he's not afraid to prescribe antibiotics if he suspects Lyme disease by symptoms alone.
"I'm in the category of over-treaters," he said. "But this study makes me not look bad, because it's basically saying these things are going out of control. We expect to see a lot more disease."
The research was published online Sept. 17 in the journal Urban Ecosystems.