It’s long been known that Lyme disease is caused by bacteria transmitted through the bite of an infected black-legged tick (otherwise known as the deer tick). The understanding for many years was that one species of bacteria was the main culprit behind Lyme disease in the United States: Borrelia burgdorferi.

But in 2016, researchers at Mayo Clinic discovered a new species of bacteria that causes Lyme disease. They named it Borrelia mayonii, after Mayo Clinic’s founders, Drs. William and Charles Mayo.

The bacterium was revealed through Mayo Clinic Laboratories’ polymerase chain reaction (PCR) blood test for Lyme disease (Test ID: PBORR). That PCR testing is the preferred method for differentiating between the two bacteria. People who have B. mayonii infection also may test positive with the Lyme disease serology test (Test ID: LYME), but the test will not distinguish a B. mayonii infection from a B. burgdorferi infection.

A key difference that has been noted between B. mayonii and B. burgdorferi is that B. mayonii spirochetes are found at high levels in peripheral blood, whereas B. burgdorferi spirochetes are not. Researchers surmised that meant the B. mayonii spirochetes potentially could be found on routine peripheral blood smears.

That proved to be true earlier this year when staff in Mayo Clinic’s Division of Clinical Microbiology observed several spirochaetes on thin blood films from a specimen that had tested PCR positive for B. mayonii. The bacteria were confirmed to be B. mayonii through genome sequencing. The findings were published in July in the journal Clinical Microbiology and Infection.