Two black-legged ticks (Ixodes scapularis) on a person?™s left index finger. On the left is an adult female, and on the right is a nymph (juvenile). This species carries several disease, notably Lyme disease, for which it is the primary vector in North America. Lyme disease causes a rash and flu-like symptoms and, if left untreated, neurological issues, cardiac abnormalities, and arthritis can develop. Treatments include antibiotics and corticosteroid drugs.