Prevent Lyme disease. Antibiotics are sometimes taken after at tick bite if there is a high risk that the tick was the species of tick that is known to carry lyme disease. The antibiotics provide an early treatment of the potential lyme disease carried by the tick bite, since lyme disease in its early, most treatable stages can often be difficult to detect.
It depends. A variety of infectious diseases can be transmitted after a tick bite. The most common in the U.S. Is lyme disease. 200mg of Doxycycline taken within 3 days after a deer tick bite can help prevent lyme but this does not prevent other tick borne infections. If you experience illness after any tick bite it is best to be evaluated for other infections including: babesiosis, ehrlichiosis & rmsf.
Not much to the bite. Certain tick-borne infection such as lyme borreliosis, southern tick related rash illness (stari), tularemia and meditarrean and african tick fever can have a specific rash or ulcer or eschar at the bite site itself but others such as rocky mountain fever, babesiosis, ehrlichiosis, anaplasmosis and relapsing fever do not. Not all tick bites call for antimicrobials preventatively.