What is the first stage symptom of Lyme disease?

The first stage symptom of Lyme disease is erythema migrans, which is a characteristic skin rash that typically appears several days to weeks after being bitten by an infected tick. This rash often has a distinctive "bull's-eye" appearance, with a red outer ring surrounding a central area that is either clear or slightly raised. Erythema migrans is a key diagnostic feature of early Lyme disease and is a result of the immune response to the bacteria Borrelia burgdorferi, which is transmitted through tick bites.

While flu-like illness and myalgia can occur during the early stages of Lyme disease, they are more general symptoms and not as specific to Lyme disease as erythema migrans. These symptoms may present as part of the body's reaction to the infection but are not unique indicators of Lyme disease. Carditis, on the other hand, typically occurs in the second stage of the disease, where the infection can affect the heart, leading to conditions such as atrioventricular block. Thus, erythema migrans is the most prominent and earliest symptom that differentiates Lyme disease from other conditions.