While a rash from a tick bite is normal, individuals should see a doctor if the rash expands to form a bull's eye pattern a few days following the bite, as this indicates Lyme disease, states Mayo Clinic. Left untreated, Lyme disease can lead to neurological and joint complications.
Untreated Lyme disease can remain latent for months or even years after infection from a tick bite, explains Mayo Clinic. In the meantime, it can spread to various parts of the body, leading to ailments such as chronic arthritis of the joints, facial palsy, neuropathy and heart arrhythmia. In addition to Lyme disease, bites can also transmit other illnesses, including Rocky Mountain spotted fever, a dangerous bacterial infection that can lead to shock and kidney failure, according to WebMD.