Research
How Ticks Transmit Lyme Disease to Humans
By
Nov 17, 2009 - 12:13:24 PM

Live Imaging Technique Reveals Two Phase Mode of Dissemination


(HealthNewsDigest.com) - FARMINGTON, CONN. – Using a powerful microscopic live imaging technique, a research team led by Dr. Justin Radolf, professor in the Departments of Medicine and Genetics and Developmental Biology at the University of Connecticut Health Center, has discovered the way ticks transmit Lyme disease to humans is different than previously thought. Better understanding of how the transmission process works is essential if new methods of preventing human infection with the Lyme disease-causing microbe are to be developed. The research is published online in the Journal of Clinical Investigation.

Lyme disease is caused by transmission of the spirochete bacterium Borrelia burgdorferi from ticks to humans but for a number of technical reasons, the transmission process has been difficult to study. Radolf and his team tried a novel approach to better visualize the microbe moving through the feeding tick. They genetically modified a virulent strain of B. burgdorferi to express green fluorescent protein (GFP). “This bacterium glows and can be followed in the living state as it migrates through the tick to the mouse during feeding,” explains Radolf. “Then using a powerful microscopic technique called confocal microscopy, we discovered that the transmission process unfolds quite differently than previously believed.”

The conventional viewpoint is that the Lyme disease-causing microbes are always moving within ticks and that this drives their dissemination. But Radolf and his team found that during much of the feeding period, the spirochetes do not move. They actually divide and adhere to the cells lining the tick midgut. “We also found that the reason they don’t move is that the tick midgut secretes molecules that actually inhibit the motility of the spirochetes,” explains Radolf.

In the second phase of dissemination, the spirochetes become motile, detach, and completely penetrate the midgut, although in very small numbers. These few bacteria then swim to the salivary glands, which they penetrate en route to the mouse. “So rather than being entirely motility-driven, dissemination of spirochetes within ticks actually happens in two phases,” says Radolf, “which is something we didn’t know before.”

Lyme disease is the most prevalent vector-borne infection in the United States with more than 25,000 new cases reported annually. A substantial percentage of these cases occur in Connecticut. “The improved understanding of the transmission process revealed by our study could lead to novel strategies for controlling the spread of Lyme disease,” says Radolf.

The University of Connecticut Health Center includes the schools of medicine and dental medicine, the UConn Medical Group, University Dentists, and John Dempsey Hospital. Founded in 1961, the Health Center pursues a mission of providing outstanding health care education in an environment of exemplary patient care, research and public service. More information about the UConn Health Center is available at www.uchc.edu.

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