Research on Lyme disease conducted at Mayo Clinic shows there are two types of bacteria that can cause it.
Scientists had long known of only one bacterium that spread the disease, which is transmitted to humans by deer ticks.
First spotted in 2013, the newly discovered bacterium has appeared in only six patients out of 9,000 Lyme disease cases since then. All six lived in Minnesota, Wisconsin, or North Dakota, Mayo says.
As National Public Radio reports, scientists say both of the bacteria are carried by the deer tick (also known as the black legged tick). Patients infected with the newer bacterium (Borrelia mayonii) have symptoms only slightly different than those with the original one (Borrelia burgdorferi).
Rashes develop, but they are not in the bulls-eye pattern associated with the more common bacterium. Also, the symptoms include nausea and vomiting as well as fever, headache, neck pain, and arthritis.
The newer version is rare: researchers say only three percent of the deer ticks they tested had that bacterium, whereas the more familiar one was present in 30 to 40 percent of deer ticks. Both can be treated with anitbiotics.
Mayo's lead researcher on the study (published in The Lancet) was Dr. Bobbi Pritt. She tells NPR "It just seems like every time you turn around there's a new tick-borne disease. So, when people go outside, I think they have to think about protecting themselves from ticks."
That's best done by avoiding tick-infested areas, by using repellent, and by removing ticks as soon as possible, the CDC says.