Ticks transmit devastating illnesses like Lyme disease and Rocky Mountain Spotted Fever, and fleas carry tapeworms. Cat scratch fever, which affects humans, is caused by a bacterium called Bartonella henselae, which is also spread by flea bites. Intestinal parasites, including hookworms, tapeworms, and roundworms, cause several health problems and can be transmitted to people and other animals. Heartworms, which spread through bites from infected mosquitoes, damage the heart and lungs and can lead to premature death.

Parasites can cause everything from hair loss and itchy skin to diarrhea and coughing. And sometimes, they don’t cause any symptoms at all until irreparable damage has already been done. That’s why keeping your pet on a parasite preventative is crucial.