The story of the western fence lizard

One of the most interesting differences between the Lyme disease systems in the eastern and western US is the presence of the western fence lizard (pictured below) in the western US as an important host for the ticks that transmit Lyme disease.

Image obtained from wikimedia commons

The immune system's of these lizards have been found to clear feeding ticks of the bacteria that causes Lyme disease. Essentially this means that when infected ticks feed on a western fence lizard, they are cleared of infection resulting in one fewer ticks capable of infecting humans and one fewer infected hosts capable of passing the infection along to a new tick.
 
However, in work conducted by Andrea Swei and colleagues, removal of western fence lizards was found to decrease Lyme disease risk. This is likely because the effect of removal of lizards, one of the most important hosts for ticks in the system, was to cause tick densities to decline, outweighing the effect of tick "cleansing". This finding is important because it suggests there are other factors at play that are contributing to the low Lyme disease prevalence on the west coast.