What are bad signs after a tick bite?

Bad signs after a tick bite that indicate possible tick-borne illness and require prompt medical attention include expanding rash, flu-like symptoms, and other systemic symptoms appearing within days to weeks after bite. Key bad signs include bull's eye or expanding circular rash called erythema migrans that appears 3 to 30 days after bite, often at bite site but can appear elsewhere, that expands over days and may have central clearing, which is classic sign of Lyme disease, though not all Lyme rashes have bull's eye. Other bad signs include fever, chills, headache, fatigue, muscle and joint aches, swollen lymph nodes within days to weeks after bite, which can indicate Lyme disease, anaplasmosis, or other tick-borne illnesses. Joint pain and swelling, especially in knees, that appears weeks to months later can indicate late Lyme arthritis. Neurological signs like facial palsy with drooping on one side, numbness, tingling, severe headache, and neck stiffness are bad signs of early disseminated Lyme. Heart palpitations or chest pain can indicate Lyme carditis. If bite area becomes very red, swollen, warm, with pus, it may indicate secondary bacterial infection. If you develop rash, fever, or persistent symptoms within 30 days after tick bite, see doctor promptly, mention tick bite, bring saved tick for identification if possible, and early antibiotic treatment is effective. Monitor for 30 days after bite.