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This article waslast modified on July 10, 2017.

Scientists have recently reported finding a second species of bacteria that can cause Lyme disease. The species was discovered after lab tests from six patients in Minnesota suspected of having Lyme disease showed results that were different from what would be expected for Borrelia burgdorferi, the known cause of Lyme disease.

Genetic testing confirmed enough differences from Borrelia burgdorferi for the second bacteria to be considered a new species, which has been given the name Borrelia mayonii after the Mayo Clinic, where it was found. In a two-year period, six patients out of 9,000 people tested for Lyme disease had B. mayonii. The findings about the new bacteria were recently published in The Lancet Infectious Diseases.

B. mayonii is closely related to B. burgdorferi. Like B. burgdorferi, B. mayonii is spread by the bite of a deer tick, also called the blacklegged tick. It causes signs and symptoms similar to B. burgdorferi, including fever, headache, rash, and neck pain within a few days of infection, with joint pain and arthritis developing weeks after the tick bite.

However, B. mayonii seems to produce other symptoms, including nausea and vomiting. Most notably, instead of the signature Lyme disease "bull's eye" rash that may be found at the site of the tick bite with B. burgdorferi infections, B. mayonii may cause a rash that is more spread out (diffuse) and lacks the bull’s eye target appearance. Some of these differences may lead to missed cases of Lyme disease.

The blood tests currently used for Lyme disease should be able to diagnose the infection if it is caused by the new bacteria, according to the Centers for Disease Control and Prevention (CDC). And the good news is that patients can be treated with the same antibiotics typically prescribed for Lyme disease caused by B. burgdorferi. The six infected patients from the Mayo report who were confirmed with the new bacteria were successfully treated in this manner.

For now, cases of B. mayonii seem to be confined to the upper Midwest of the U.S. Scientists did not detect the new species in 25,000 blood samples of people in 43 states suspected of having tick-borne disease at about the same time that the new bacteria species was identified. How or when this new species appeared remains a mystery.

The CDC, along with state health departments in Minnesota, Wisconsin and North Dakota, will continue to investigate the new bacterial species and the illness it causes, and will monitor ticks carrying the new species to other parts of the country. To definitively find out if the new bacteria has caused an infection, researchers can use the polymerase chain reaction (PCR) method of testing to identify the bacteria's DNA.

To avoid tick bites and prevent Lyme disease, follow the CDC's suggested precautions:

  • Avoid wooded areas, especially where grass has grown high and leaves have accumulated.
  • Walk in the center of trails.
  • Use insect repellent containing DEET whenever outdoors and use products that contain permethrin on clothing.
  • Bathe after returning indoors from areas that could harbor ticks; check for and remove ticks as soon as possible.
  • Remember to check both gear and pets for ticks when returning indoors.

(February 5, 2016) Identification of a novel pathogenic Borrelia species causing Lyme borreliosis with unusually high spirochaetaemia: a descriptive study. The Lancet Infectious Diseases. Available online at Accessed February 24, 2016.

Centers for Disease Control and Prevention. Press Release: New Lyme-disease-causing bacteria species discovered. February 8, 2015. Available online at Accessed February 24, 2016.

Weintraub, Karen. A New Culprit in Lyme Disease. The New York Times. February 15, 2016. Available online at Accessed February 24, 2016.