Now, the entire state of Connecticut is considered high risk, and Massachusetts and New Hampshire are close behind. The disease also expanded from its base in northern Wisconsin to Michigan, Minnesota and Iowa.
The CDC reports somewhere around 300,000 cases of the disease each year, and the infection rate has been on the rise for the past few decades. But scientists say the disease is widely unreported and inconsistently diagnosed, so the real infection rate could be as much as 10 times what we think it is.
Why is it a growing problem? Well, there's a number of theories.
Some say that a big part of the problem is that bloodsuckers have more to eat. Deer populations have exploded over the past century, thanks to reduced predators and hunting. Some states are even encouraging more deer hunting specifically to curb the disease. It's also been suggested that mice populations have also play a big part for similar reasons.
But deer counts have actually declined during the Lyme disease expansion, and mice numbers aren't very convincing, either, said Richard Ostfeld, an ecologist at the Cary Institute of Ecosystem Studies in Millbrook, N.Y., who has done a lot of research on Lyme disease. He says a more sound theory is rising temperatures.
"Climate change is responsible for opening up areas that were just too harsh for ticks," Ostfeld said.
Tick larvae are basically vampires — they hatch in midsummer and have to find a good blood meal before going to sleep in the winter. If they don't, they die. Warmer weather gives them more time to find their victims.
Still, that doesn't explain why the disease is moving south, to places like Virginia, West Virginia and the Carolinas. It could be the case that some of the rise is actually a good thing — more people are aware of the disease and are reporting it.
"We know some of the answer, but not all of it," Ostfeld said.
There are methods available that could reduce the tick population, but Ostfeld said the funding to pull together an all-out assault against the insect is limited.
"This is something the government and philanthropy could help with if they pony up," he said.
The prevalence of the disease is important to keep on the radar, because the infection can be pretty nasty. Immediate symptoms include fever, headache, fatigue and possibly a bulls-eye skin rash, but that can extend to the joints, heart and nervous system if left untreated.
Most cases can be addressed within a few weeks with the help of antibiotics, but it's not the easiest disease to treat. Experts say about 10 to 20 percent of people treated will experience ongoing symptoms.
The CDC recommends that people use insect repellents, apply pesticides and remove any ticks from skin as quickly as possible with a pair of fine-tipped tweezers. After the bug is removed, people should thoroughly wash the area with soap and water, and monitor the area for rashes.
This post has been corrected to show that the Cary Institute of Ecosystem Studies is in Millbrook, N.Y.