Scientists have discovered a new species of bacteria that can cause Lyme disease.
This one, named Borrelia mayonii, is closely related to the Borrelia burgdorferi bacteria already known to cause Lyme disease, the team at the Mayo Clinic in Rochester, Minnesota, and the Centers for Disease Control and Prevention found.
But the second bacteria causes slightly different symptoms and seems to be found only in Minnesota and Wisconsin, the researchers report in Lancet Infectious Diseases.
"Scientists at the Mayo Clinic in Rochester, Minnesota, first suspected the possibility of new bacteria after lab tests from six people with suspected Lyme disease produced unusual results," the CDC said in a statement.
"Additional genetic testing at the Mayo Clinic and CDC found that the bacteria, provisionally named Borrelia mayonii, is closely related to B. burgdorferi."
Current tests will pick up both infections, and the same antibiotics can treat both types, the CDC said.
CDC estimates that about 300,000 people are infected with Lyme disease every year. The infection is gradually spreading from the Northeast, where it was first identified in 1975, and becoming more common farther south and east. Lyme is now found in four times as many counties now as it was in 1993.
There was a vaccine, but it was taken off the market because of low demand.
Borrelia bacteria are carried by blacklegged ticks. People catch the infection from tick bites.
"This discovery adds another important piece of information to the complex picture of tickborne diseases in the United States," said the CDC's Dr. Jeannine Petersen.
B. mayonii and B. burgdorferi both cause fever, headache, rash, and neck pain soon after infection, and arthritis some weeks later. "Unlike B. burgdorferi, however, B. mayonii is associated with nausea and vomiting, diffuse rashes (rather than a single so-called 'bull's-eye' rash), and a higher concentration of bacteria in the blood," the CDC said.
"The newly recognized species was discovered when six of approximately 9,000 samples drawn from residents of Minnesota, Wisconsin, and North Dakota with suspected Lyme disease between 2012 and 2014 were found to contain bacteria that were genetically distinct from B. burgdorferi."
More tests showed it was a ralted species of bacteria causing the infection.
"To date, the evidence suggests that the distribution of B. mayonii is limited to the upper midwestern United States. The new species was not identified in any of the approximately 25,000 blood samples from residents of 43 other states with suspected tickborne disease taken during the same period, including states in the Northeast and Mid-Atlantic region where Lyme disease is common," CDC added.