Scientists now know that there are at least 2 different types of bacteria that cause Lyme disease after lab tests on 6 people produced unexpected results.
The scientists suspected there was another culprit after conducting tests on 6 patients with Lyme disease. They found that B. mayonii – so far only found in the Midwest – is closely related to B. burgdorferi in that it also initially causes fever, headache, rash, and neck pain, and eventually arthritis.
“We detected this result which was positive, but it was clearly different from what we would have expected for Borrelia burgdorferi, which at that time was the only known cause of Lyme disease in the U.S.” says Dr. Bobbi Pritt, a microbiologist at the Mayo Clinic. 
But B. mayonii also causes nausea, vomiting, widespread rash, and a higher concentration of bacteria in the blood. The patients who tested positive for B. mayonii also lacked the telltale bull’s-eye pattern associated with B. burgdorferi. Instead, they had diffuse or spotty rashes.
Some of the rather unusual symptoms were quite terrifying, with one child being unable to wake up from sleep, and an adult suffering with double-vision.
“This organism doesn’t behave completely like the Lyme disease that we all know,” said Pritt.
Dr. Jeannine Petersen, microbiologist at the CDC, said:
“This discovery adds another important piece of information to the complex picture of tickborne diseases in the United States.”
Each year, an estimated 300,000 people are diagnosed with Lyme disease. There is currently no way to say whether B. mayonii is more or less dangerous than B. burgdorferi, which is rarely fatal and typically-treated with antibiotics. The patients infected with the recently-discovered bacteria were treated successfully with the same antibiotics used to treat B. burgdorferi. 
“We have fairly limited information in that our study described six patients,” Petersen told Reuters. “We need more patients in order to capture the full spectrum of those who might have less severe symptoms and those who might have more severe ones.”
She added that B. mayonii must have recently emerged, as it never showed up in earlier, extensive testing of blood samples taken from patients suspected of having Lyme disease.
“Maybe it infected woodchucks and no one ever tested them,” explained Pritt. “But what we can say is, it’s a species that no one has ever described before and it’s clearly infecting patients.”
Fortunately, it appears that B. mayonii is rare. Entomologists found that of 600 ticks collected across Wisconsin, just 3% tested positive for B. mayonii. The older type is normally found in 30-40% of blacklegged deer ticks.
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