Lyme disease, or borreliosis, is caused by the bacterium Borrelia burgdorferi, which is transmitted by the bite of infected black-legged or deer ticks. Lyme disease affects animals differently, and many display no clinical signs at all. In dogs, many cases exhibit lameness on more than one leg, lack of appetite, lethargy and/or fever. Dogs typically don't show signs for two to five months after infection. The lyme vaccine is recommended only for dogs with a known high risk of exposure due to high prevalence of infected deer ticks or where the disease is endemic.