With an estimate of 300,000 cases reported yearly, the proliferation of Lyme disease has led researchers to investigate the population and dietary patterns of the regional wildlife most commonly associated with the disease. The majority of these cases, according to a 2013 analysis of the latest information by the US Centers for Disease Control and Prevention (CDC), are attributed to the northeast.
The white-footed mouse, a rodent native to North America, is identified by the National Science Foundation (NSF) as the key reservoir for Lyme disease. With an immune system too weak to fight off the B. burgdorferi bacteria once infected, the mouse transmits the infection to the tick larvae that feed on its blood. Ultimately, the disease is then spread to the surrounding human population through a tick bite.
And the mice, like any other species, are specific to areas that offer them the highest chance of survival.
According to a 2013 study published in PLOS ONE on New York City urbanization in relation to the white-footed mice population, the small mammals are a “common resident” of forest fragments such as those of central New York and the mid-Hudson valley region.
Forest fragments, small and isolated woodland patches due to urbanization, attract less predators and allow for the white-footed mice to thrive without a threat. These regions are then at high risk for a Lyme outbreak among the interacting human population.
“The white-footed mice population is influenced by predation,” said wildlife ecologist Dr. Taal Levi of the Cary Institute of Ecosystem Studies in a 2012 study. Levi says this factor is a key component in the rise of Lyme disease in humans as the deer ticks, which transmit the disease between mouse and human, are dependent on an environment rich with small mammals. With a growing mouse population, the ticks have their source of infection.
Lyme disease in the New York region, however, is not only dependent on the predator population. It can also be traced to the dietary needs of white-footed mice and the recent fluctuation in the acorn supply.
The most notable acorn drought was reported by the New York Times in 2011, a record low in the 20 years of monitoring by the Cary Institute. Dr. Richard S. Ostfeld, a disease ecologist at the Cary Institute, acknowledged this record in a 2012 report.
“We had a boom in acorns, followed by a boom in mice,” Ostfeld said. “Now, on the heels of one of the smallest acorn crops we’ve ever seen, the mouse population is crashing.”
In 2012 there were 2,044 cases reported in the state of New York, categorizing it in the top 13 states with Lyme.
Without a consistent source of white-footed mice for food, Lyme-carrying ticks will resort to seeking humans as their primary source.