Ticks, and the Lyme disease they carry, have become a daily reality in much of North America and beyond. Repellent and detailed checks of every limb have become routine, even in suburbia.
This year is expected to herald a bumper crop of blood-sucking arachnids to wooded areas of the Northeast U.S., according to some experts. Such predictions are based off a count of mice – another host species of ticks.
But a complex new model incorporating a variety of other climate factors and life cycle phases of ticks can offer a new forecasting model for the regional spread of Lyme, for each season, as proposed by mathematicians at the Memorial University of Newfoundland.
“Climate impacts tick survival mostly during nonparasitic periods of the life cycle,” said Xiunan Wang, one of the authors of the study in the Society for Industrial and Applied Mathematics Journal on Applied Dynamical Systems. “Seasonal variations in temperature, humidity, and resource availability have a strong effect on tick population dynamics.”
The deer tick’s two-year life cycle is accounted for, over four stages: from egg, larva, nymph, to adult.
The model incorporates mice and deer populations and their mortality rate, as well as the climate factors. It also incorporates the frequency of infection among the bloodsuckers, and even the bite rates of individual ticks.
An eight-dimensional non-autonomous model with three different time delay results, said Wang, and his colleague, Xiao-Qiang Zhao, also at Newfoundland.
Their model was tested at Long Point, a town in Ontario where the disease has taken off since 1980. The Canadian settlement was subject to the pandemic because of songbird transmission of ticks over long distances, they add.
Their prediction: Lyme will continue to thrive in Long Point, due to climate predictions.
But they offer solutions: clearing out ticks’ egg locations may help curb the spread in the Canadian hamlet. Destroying nests in attractive locations near human habitation could turn the tide, they added.
“It may be helpful to regularly search for the spots where adult ticks usually lay eggs, like in sheds, in woodpiles, under rocks and in the crevices of walls,” said Wang. “Since tick eggs are static, it is more feasibly to focus on the clearance of eggs than to think about killing ticks of the other three life stages.”
The prevailing prediction for this season, put forth by a husband-and-wife team, was covered widely by NPR and other media outlets last month. The New York-based pair based their forecast off mice counts from the year before. The theory is based off the fact that mice are the most efficient transmitter of the Borrelia burgdorferi bacteria – and a population explosion from one year will result in a bumper crop of ticks the following year.