New light shed on Lyme disease-causing bacteria

The duration of attachment of a single nymphal blacklegged tick (Ixodes scapularis) needed for the tick to be likely to transmit the bacterial species Borrelia mayonii, identified in 2016, is 48 hours or more, according to the study. By 72 hours, however, likelihood of transmission has risen significantly. This timeframe aligns with existing research on Borrelia burgdorferi, previously the sole bacteria species known to cause Lyme disease in the United States. The research is published in the Entomological Society of America's Journal of Medical Entomology.

"Our findings show that recommendations for regular tick checks and prompt tick removal as a way to prevent transmission of Lyme disease spirochetes to humans via the bites of infected ticks applies to the newly recognized B. mayonii as well as B. burgdorferi, for which these recommendations originally were developed," says Lars Eisen, Ph.D., CDC research entomologist and senior author of the study.

The study authors tested transmission rates of B. mayonii from ticks to mice at four time intervals: 24, 48, and 72 hours after attachment and after the tick's full feed. Their experiment focused on nymphal-stage ticks (the more common source of pathogen transmission, compared to larval or adult ticks) and exposed the mice to a single infected tick each. They found no evidence of transmission by single nymphs infected with B. mayonii in the first 24 or 48 hours, but 31 percent of mice examined after 72 hours were found to be infected. In mice examined after a tick's complete feed (4-5 days), the infection rate was 57 percent.

"Our findings underscore the importance of finding and removing ticks as soon as possible after they bite," says Eisen.

Lyme disease is the most commonly reported vector-borne illness in the United States, with around 300,000 people estimated to be diagnosed each year, mostly in the Northeast and upper Midwest regions. The blacklegged tick is the primary vector of Lyme disease as well as at least a dozen other illnesses.

To reduce the risk of tick bites and tickborne diseases, CDC recommendations include:

• Avoid wooded and brushy areas with high grass and leaf litter.
• Use insect repellent when outdoors.
• Use products that contain permethrin on clothing.
• Bathe or shower as soon as possible after coming indoors to wash off and more easily find ticks.
• Conduct a full-body tick check after spending time outdoors.
• Examine gear and pets, as ticks can come into the home on these and later attach to people.

The bacterial species B. mayonii was discovered when six patients exhibiting symptoms of Lyme disease at the Mayo Clinic in Rochester, Minnesota, in 2013 showed unusual blood-test results. The discovery of the new species was confirmed in 2016.

"There is much still to discover about B. mayonii, including to clarify the geographic range of this emerging human pathogen in the U.S., to determine how commonly different life stages of the blacklegged tick are infected with B. mayonii, and to find out whether the same vertebrate animals that serve as natural reservoirs for B. burgdorferi play the same role also for B. mayonii," says Eisen.