Black-legged ticks are making a home in New York City, representing a heightened risk of infections like Lyme disease for their human neighbors in the Big Apple and in urban areas beyond, a new study shows.
The study, published Wednesday by the Centers for Disease Control and Prevention’s Emerging Infectious Diseases journal, “challenges the perspective that tickborne disease risk is restricted to suburban and natural settings,” its authors said.
And amid efforts to create and preserve urban green space like parks and community gardens, its results show that “landscape composition and configuration have direct implications on urban Lyme disease risk,” presenting a potential public health problem in the making.
“The connectivity of these park systems in urban environments is really important for the dispersal of ticks, as well as the dispersal of the pathogen causing Lyme disease,” says Meredith VanAcker, the study’s lead author. “And so, when we think about how we’re developing cities, the connectivity of the green spaces that are being designed for urban populations (and) the connectivity of those parks may be important to consider when we’re thinking about the movement of infectious disease.”
VanAcker, a doctoral student at Columbia University, and fellow researchers conducted tick surveys in 24 parks throughout New York City’s five boroughs in 2017 to assess how factors like tree canopy, bodies of water and the distance between parks may impact the spread and density of black-legged ticks – also known as deer ticks.
Their study says the distance between urban parks “best explained” whether black-legged ticks were present, while the flow centrality of parks – “an indicator of the connectivity of parks for deer and other hosts” of ticks – positively impacted tick density and the prevalence of ticks carrying the bacteria that causes Lyme disease.
Overall, black-legged ticks were found in 17 of the parks surveyed, with 10 determined to have established populations – nine of which were on Staten Island and one in the Bronx. Using data specific to Staten Island, the researchers determined that more tree canopy around a park correlated with a higher density of tick nymphs, while soil and water buffers appeared to negatively affect tick density.
“On Staten Island, we see the same infection prevalence in ticks as we do in highly endemic regions like Connecticut,” VanAcker says, with an average of about 1 in 4 black-legged ticks across the 10 sites in Staten Island and the Bronx carrying the bacteria that causes Lyme disease.
VanAcker notes that the study only looked at one tick species, and the dispersion of these deer ticks largely depends on the travels of their main hosts – white-tailed deer – through various corridors.
“It’s important to realize that not every park in New York City has the same level of risk. … These are areas like Pelham Bay up in the Bronx and then Staten Island,” VanAcker says. “If parks are buffered by, you know, grassy areas or shrubs where deer might be foraging, then those parks may be better at drawing deer.”
“Having a better idea of what corridors may be most important for deer populations to either invade into new urban parks or introduce tick populations into parks where ticks aren’t from previously – identifying those corridors first can help park managers and public health departments potentially control the spread of the ticks,” she says.
VanAcker says she hopes her study’s results also help inform the general public about parks where they may want to take extra precautions to prevent tick bites, such as wearing long pants and long sleeves, or tucking pants into their socks.
“Staying just on the trail path can reduce your risk quite significantly,” she says.