Then there’s what humans do — whether we wear personal protection, put on repellent, spray our lawns, treat our pets, check our bodies for ticks. And while we can control our own behavior, we can’t control the whole ecosystem, especially the weather and food supply for rodents.
Finally, we can’t just count the number of ticks at the end of a study because what we really care about is the number of human infections. Some studies show impressive reductions in the numbers of ticks, but don’t show much impact on the number of infections.
In the face of this complexity, scientists have to do high-quality studies to give more certainty to the results. But that means large studies that span years and large areas to be more sure the results aren’t just due to weather changes or other things outside our control. All of that costs a lot of money.
Take, for example, a recent high-quality study led by Alison Hinckley, a CDC scientist. The researchers sprayed yards once a year with tick-killing chemicals and looked for the effect on tick bites and infections.
It was a two-year, randomized, double-blind, placebo-controlled study. It’s tough to get higher quality than that. It looked at over 2,700 households in three states. And it went further than most studies by looking not just at the numbers of ticks but also the number of tick-borne infections.
All of this cost about $3 million, a huge sum in the world of entomology and ecology.
And it didn’t work. That is, tick numbers dropped by 63 percent but tick sightings and infections didn’t change. Maybe people got ticks from the areas of their yards that weren’t sprayed, like gardens. Or maybe they got infected while on hikes. And, since it was only a two-year study, maybe rainy spring weather made spraying less effective.
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