CDC Study Sheds Light on New Lyme Disease-Causing Bacteria
A new species of bacteria that causes Lyme disease needs the same amount of time for transmission after a tick bite compared to previously implicated bacteria, according to new research by the Centers for Disease Control and Prevention (CDC). Existing guidelines for frequent tick checks and prompt removal of attached ticks remain the same.
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 today in the 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.
Also of note in the study was an increased rate of infection among mice that were exposed to two ticks infected with B. mayonii—25 percent after 48 hours, 71 percent after 72 hours, and 83 percent after a complete feed. Additionally, the researchers found that no mice were infected in 72 hours by ticks with B. mayonii detected in their bodies but not their salivary glands, whereas transmission did occur in several cases in which the bacteria was detected in ticks’ salivary glands.
Tick saliva is known to play a role in facilitating infection of B. burgdorferi in mice, and the study on B. mayonii indicates a similar dynamic. The researchers speculate that multiple ticks feeding on a host at once result in higher transmission rates either through a greater volume of passage of the bacteria into the host or through an increased presence of the ticks’ saliva, or both. “If the amount of injected tick saliva is a major factor facilitating establishment of viable spirochetal infection in the host, then transmission by a single infected nymph could … be facilitated by simultaneous cofeeding of noninfected ticks,” the researchers note in their report. “This would seem a fruitful line of follow-up research.”
Journal of Medical Entomology