Final answer:
The classical sign of Lyme disease caused by Borrelia burgdorferi is a bulls eye rash. Known as erythema migrans, it is an indicator of the disease and can be used alongside other symptoms for a diagnosis.
Step-by-step explanation:
The classical sign of Lyme disease caused by Borrelia burgdorferi is a bulls eye rash, also known as erythema migrans. This rash is typically a clear sign of Lyme disease and appears at the site of the tick bite 3 to 30 days after being bitten, with an average of 7 days. It is important to note, however, that up to 30% of infected individuals may never develop this rash. Other symptoms include flu-like symptoms such as fever and muscle stiffness, and if left untreated, Lyme disease can lead to more severe problems such as facial paralysis, arthritis, and even potentially fatal conditions like carditis and chronic neurological disorders.