This is Borrelia burgdorferi, the bacterium that cause
Lyme disease. It is a spiral-shaped bacterium that is frequently
carried by deer ticks of the genus Ixodes. When the deer tick bites a
human being, the bacteria are transmitted to the human bloodstream,
where it travels throughout the body. The symptoms of Lyme disease
are kind of like the flu, but the disease sticks around for a long
time unless treated right away. This is a whole bacterium as seen
with the TEM. It is about 20 micrometers (0.02 millimeters or
0.0008 inch) long and about 200 nanometers (0.2 micrometers or
0.0002 millimeters or 0.000008 inch) wide. This is one of the
smallest things on this web site.
Original image courtesy of Rocky Mountain Laboratories, NIAID, NIH.