Lyme disease is a very serious illness caused by the spirochete Borrelia burgdorferi. It is most commonly spread by deer ticks, although other ticks can also carry and spread the disease.
The most common symptom of Lyme disease in dogs is lameness and joint pain. This lameness may shift from one leg to another.
Full article: Lyme Disease in Pets: What do You Need to Really Know?
Further reading: Lyme Is Lame (Pun Intended)