Fleas and ticks are not just minor nuisances; they can transmit serious and sometimes life-threatening diseases, some of which can be passed to people. Even indoor-only pets are at risk because fleas and ticks can hitch a ride inside on your clothing, shoes, or other pets. It only takes one flea to start an infestation or one tick to transmit disease. Keeping your pet on a monthly preventive is your best bet for protecting your pet—and your family—against these parasites.