Patti Casey and Eliza Doncaster are part of the Vermont Agency of Agriculture’s tick surveillance team. …Over the last 20 years, ticks and the diseases they carry, like Lyme disease, have spread rapidly in Northeastern states, including in Vermont. Scientists say human-caused climate change is one piece of the puzzle, but it’s not the only thing driving their growth here. Blacklegged ticks, also called deer ticks, carry the bacteria that causes Lyme disease. But they also carry a suite of other bacteria, viruses and parasites that cause other illnesses. Natalie Kwit, the state public health veterinarian for the Vermont Department of Health, said people are now contracting these infections in Vermont year-round. …Climate change is one major driving factor of the upward trend in tick-borne diseases, said Rick Ostfeld, with the Cary Institute of Ecosystem Studies. Decrease in the winter freeze period increases egg laying. Suburban sprawl is also to blame.