Ticks can transmit diseases. This happens when ticks themselves are infected by pathogens and transmit them by a tick bite on humans.
Borrelia in the intestine
Tick-borne encephalitis virus in the salivary glands
This is exactly why it is important to remove ticks gently without squeezing them.
The most well-known tick-borne diseases include Lyme disease caused by Borrelia and the tick-borne encephalitis (TBE) caused by tick-borne encepahlitis virus.
Less well known diseases which can be transmitted through tick bite include Q-Fever, which is caused by the Coxiella burnetii bacteria, Ehrlichiosis, Babesiosis and Tularemia.
Your sent in tick can be screened for many pathogens using the PCR-method. This can be used to determine whether the tick poses a risk of infection.
Take every tick bite seriously. Avoid squeezing the tick when removing it.